Petrological investigation of UHT-rocks from the Blumau ...

Christian Schwaiger, BSc

Petrological investigation of UHT-rocks from

the Blumau granulite body,

Lower Austria

Master’s Thesis

Thesis prepared for the degree of

Master of Science

submitted at

UNIVERSITY OF GRAZ

Supervisor

Ao.Univ.-Prof. Mag. Dr.rer.nat., Christoph Hauzenberger

NAWI Graz Geozentrum

Petrology & Geochemistry

Graz, March 2017

...for my family

and friends...

Danksagung

Hiermit möchte ich mich bei all jenen bedanken, die mich durch das Studium begleitet und

mich bei meiner Masterarbeit unterstützt haben.

Zuallererst möchte ich mich bei meinem Betreuer Prof. Christoph Hauzenberger bedanken,

der mich bei jeglichen analytischen sowie petrologischen Fragestellungen unterstützte und

mir ein tieferes Verständnis für granulitfazielle Prozesse ermöglicht hat. Des Weiteren möchte

ich mich bei Dr. Karl Ettinger und Herrn Jürgen Neubauer für Ihre Unterstützung an der

Mikrosonde und am Rasterelektronenmikroskop bedanken. Die Naturwissenschaftliche

Fakultät sei ebenfalls an dieser Stelle erwähnt, die mir durch ein Förderstipendium

Ausrüstung und eine detaillierte Feldarbeit ermöglichte.

Einen besonderen Dank möchte ich auch an meine Studienkollegen, Freunde und

Mitbewohner aussprechen, insbesondere an Philip, Dominik, Ruth, Silvia, Fede, Sebastian,

Dragan, Max, Sara, Marlene, Isa und Anna für die gegenseitige Unterstützung und eine

schöne Studienzeit.

Zu guter Letzt möchte ich mich auch noch ganz besonders bei meiner Familie bedanken,

die mich während meiner gesamten Studienzeit immer unterstützten und in jeder Lebenslage

hinter mir gestanden sind.

Abstract

The Moldanubian Zone, part of the Boemian Massif, represents the eastern end of the

Variscan belt in Europe and reflects the crystalline high-grade core of the Variscides (Matte et

al. 1990). A comprehensive investigation of mesocratic and leucocratic rocks from the

Blumau granulite body is presented in this study. Conventional geothermobarometry

combined with zirconium-in-rutile thermometry, major and trace elements analysis of whole

rock chemistry and computation of equilibrium phase diagrams including isopleths was

conducted to reconstruct the evolution of these rocks. Evaluation of whole rock chemistry

reveals a magmatic origin and a calc-alkaline trend of the protholites. Leucocratic granulites

preserved a HP-UHT event with conditions of ~16.5 kbar and 1060 °C. In mesocratic

granulites and to a lesser extent in felsic granulites with new sillimanite and biotite growth a

retrogressive MP-HT overprint at ~8 kbar and 800 °C can be observed. Reaction textures like

symplectitic orthopyroxene-plagioclase coronas and compositionally zoned plagioclase

coronas around garnet indicate a fast decompression. Compositional profiles of garnet cores,

reflecting possibly a pre-HP-UHT event are influenced by diffusion, which is extremely fast

at estimated 1000°C, but are still preserved to some extent. This leads to the conclusion that

the residence time of rocks under HP-UHT conditions had to be of short duration.

Crystallographic oriented rutile needles in garnet cores propose a pressure dominated pre-HP-

UHT event. First findings of UHP phases like coesite in northwestern parts of the

Moldanubian Zone in the Czech Republic was documented by Perraki and Faryad (2014).

Additionally, the occurrence of ultrabasite and eclogite in the Gföhl Unit supports a former

UHP metamorphic event of the Moldanubian granulites.

Kurzfassung

Das Moldanubikum repräsentiert den östlichen Teil des variszischen Gebirges in Europa,

ist Teil der Böhmischen Masse und stellt den kristallinen, hochgradigen Kern der Varisziden

dar (Matte et al. 1990). Die vorliegende Arbeit präsentiert Untersuchungen von mesokraten

und leukokraten Gesteinen des Blumauer Granulitkörpers. Um die Entwicklung der Gesteine

zu rekonstruieren, wurde eine Kombination aus konventioneller Geothermobarometrie und

Zirkonium-in-Rutil Thermometrie, Haupt- und Spurenelementanalysen vom

Gesamtgesteinschemismus, sowie thermodynamische Modellierungen angewendet. Die

Auswertung der Gesamtgesteinsanalyse ergab einen magmatischen Ursprung mit

kalkalkaliner Entwicklung des Protolith. In leukokraten Granuliten kann ein HP-UHT Event

mit Bedingungen von ~16.5 kbar und 1060 °C beobachtet werden. In mesokraten, sowie in

manchen leukokraten Granuliten mit retrogradem Sillimanit und Biotit Wachstum kann eine

retrograde Überprägung bei ~8 kbar und 800 °C festgestellt werden. Reaktionstexturen wie

bspw. symplektitische Orthopyroxen-Plagioklas Koronen und chemisch zonierte Plagioklas-

Koronen um Granat deuten auf eine rasche Dekompression bzw. Hebung hin. Profile von

Granatkernen, die ein mögliches prä-HP-UHT Ereignis widerspiegeln sind diffusiv

beeinflusst (Diffusion läuft bei geschätzten 1000 °C sehr schnell ab), aber noch immer noch

zu einem bestimmten Ausmaß erhalten. Dies führt zu der Schlussfolgerung, dass die

Aufenthaltsdauer der Gesteine unter HP-UHT Bedingungen nur von kurzer Dauer gewesen

sein kann. Zusätzlich könnten kristallographisch orientierte Rutilnadeln in Granatkernen auf

ein druck-dominierendes prä-HP-UHT Ereignis hindeuten. Funde von UHP-Phasen wie

Coesit im nordwestlichen Teil des Moldanubikums (Tschechischen Republik) wurden von

Perraki and Faryad (2014) dokumentiert. Zusätzliches Auftreten von Ultrabasiten und

Eklogiten in der Gföhler Einheit unterstützen die Annahme eines früheren UHP Events der

Moldanubischen Granulite.

6

Table of content

Introduction ................................................................................................................................. 7

Geological background ................................................................................................................ 9

Methods ..................................................................................................................................... 16

Petrography and mineral chemistry ........................................................................................... 18

Geothermobarometry ................................................................................................................. 51

Thermodynamic Modelling ....................................................................................................... 56

Interpretation and discussion ..................................................................................................... 63

Conclusion ................................................................................................................................. 68

References ................................................................................................................................. 69

Digital Appendix ....................................................................................................................... 75

7

Introduction

Remnants of the Variscan orogen are distributed over several thousand of kilometers from

parts of North America to Europe. Many structural, petrological and geochronological

investigations have been undertaken for a better understanding of the geodynamic evolution

of the Variscan orogeny during the formation of the supercontinent Pangea. Nevertheless,

different models of geotectonical formation of the eastern part of the Variscan belt are still

subject of discussion. Matte et al. (1990) suggested a continent-continent collision model with

subsequent exhumation of crust material, whereas studies after Schulmann et al. (2009)

propose an Andean type convergence. The Bohemian Massif, as part of the eastern

Variscides, reveals one of the most spectacular areas for extreme conditions of metamorphism

(O'Brien 2008). Within the Bohemian Massif, the Moldanubian Zone represents the

crystalline high-grade core of the Variscides (Matte et al. 1990). Meanwhile it is accepted that

the evolution of the Moldanubian Zone was polyphase and discontinuous (Finger et al. 2007).

For a long time it was assumed that the origin of granulites is limited to shield areas in

Archaean and Proterozoic time. Nowadays it is widely accepted that granulite metamorphism

is associated with the formation of major continental crust and reworking episodes, not related

to a specific part in history of Earth. Most granulite terranes record PT conditions of 7.5 kbar

and 800 °C (Harley 1989).

ITD (near-isothermal decompression) granulites are assumed to develop under thickened

crust with magmatic intrusions as an additional heat source. Exhumation is based on

extensional thinning rather than erosion. IBC (near-isobaric cooling) granulites evolve under

various tectonic settings. Those which emerged under anti-clockwise PT history are formed in

and beneath magmatic accretion. IBC granulites at shallow levels (<5 kbar) originate under

extension of normal crust. Deeper-level IBC granulites arise under thickened crust with rapid

extensional thinning (Harley 1989).

With PT conditions of more than 1000 °C and 1.5 GPa, the peak metamorphism of

Moldanubian granulites is higher than the majority found somewhere else on this planet. This

indicates metamorphism at mantle depths with higher temperature conditions than in a typical

subduction zone environment (O'Brien 2008). Additionally, two retrogressive overprints

could be observed. The first overprint revealed values of more than 7 kbar and 800 °C. The

second overprint was estimated at more than 4 kbar and 500 °C (Cooke and O'Brien 2001).

8

However, recent findings of coesite and microdiamonds in the Moldanubian Zone in the

Czech Republic indicates to former UHP conditions (Perraki and Faryad 2014). Therefore,

detailed investigation of the complex metamorphic evolution of Moldanubian granulites could

provide a better comprehension of the development of the eastern Variscides.

This work presents petrological and geochemical results of the Blumau granulite body, as

part of the Moldanubian Zone in Lower Austria. Conventional geothermobarometry was

combined with computation of equilibrium phase diagrams and isopleths. Furthermore, whole

rock chemistry and trace element analysis was applied for a better understanding of evolution

of granulite facies rocks.

9

Geological background

The collision of Laurussia and Gondwana in the Carboniferous led to the formation of the

supercontinent Pangea, accompanied with the Variscan orogeny. The Bohemian Massif

(Figure 1A) represents the eastern end of the Variscan belt in Europe. The Moldanubian Zone

(Moldanubian s.s.) (Figure 1B), is part of the Bohemian Massif and represents exhumed lower

and middle crustal levels within the internal part of the Variscan orogen. It is distributed in

parts of Germany, Czech Republic and Austria, restricted from the Teplá-Barrandian Unit

(north-west) and Moravian Zone (east) (Schulmann 2005; Zeitlhofer et al. 2014).

The evolution of the Moldanubian sector can be differentiated in at least two different

tectonometamorphic events, termed Moravo-Moldanubian (345-330 Ma) and Bavarian phase

(330-315 Ma). The Moravo-Moldanubian phase involves the main tectonometamorphic

overprint of the Moldanubian Zone. This includes the subduction of the Rheic Ocean and the

thrusting of the Moldanubian onto the Moravian Zone. Furthermore, the subduction of crustal

rocks to partly mantle depths and fast exhumation to middle and upper crustal levels (Gföhl

Unit). A subsequent late stage LP-HT metamorphic overprint can be identified in wide areas

of the Moldanubian zone. The Bavarian phase is associated with delamination of mantle

lithosphere and slab break-off. It represents a reheating of crust with LP-HT metamorphism

and granitic plutonism (South Bohemian Batholith) (Petrakakis 1997; O’Brien 2000; Finger et

al. 2007; Schulmann 2005).

The Moldanubian Zone can be subdivided into three units: The basal Ostrong Unit, the

overlying Drosendorf Unit and the uppermost Gföhl Unit (Petrakakis, 1986; O’Brien, 2000;

Schnabel & Fuchs, 2002). The Ostrong Unit (Monotonous Series) is composed of stromatitic

to nebulitic cordierite-bearing gneiss, cordierite-free gneiss, orthogneiss and subordinate

eclogitic and calc-silicate rocks and represents the deepest unit in the western part of the

Moldanubian Zone in Austria. A thin layer of amphibolite and blastomylonitic gneiss

represents the boundary to the overlying Drosendorf Unit (Petrakakis 1997, 1986a).

Geochronological investigations of Friedl (1997) reveal an age of 339-334 Ma. The Ostrong

Unit is intruded in the west by the granitic Southern Bohemian pluton with an age of 330-300

Ma (Finger et al. 1997; Gerdes et al. 2003; Klötzli 2001)

The Drosendorf Unit (Variegated/Bunte Series) is made up of granodioritic orthogneiss

(Dobragneiss) at the base with amphibolite intercalations and calcsilicate rock, marble,

quartzite, schist and graphite-bearing paragneiss above. Compared to the Gföhl Unit, the

10

Drosendorf Unit has experienced a relatively low degree of metamorphism (Petrakakis 1997,

1997; Zeitlhofer et al. 2014; Schulmann 2005). Metamorphic overprints yields an age of ca.

600 Ma and ca. 333 Ma (Gebauer and Friedl 1994).

The Gföhl Unit comprises high grade metamorphic rocks consisting of amphibolite at the

bottom with intercalations of serpentinite, augen-gneiss and graphite-quartzite, often defined

as Raabs Unit. The overlaying Gföhler Gneiss consists of granitic gneiss, migmatite,

amphibolite and lenses of peridotite (Petrakakis 1986b; Schnabel and Fuchs 2002; Zeitlhofer

et al. 2014; O’Brien 2000; Petrakakis 1997). The top of the Gföhl Unit is marked by several

granulite bodies (Dunkelsteiner Wald, Sankt Leonhard, Blumau, Pöchlarn Wieselburg,

Zöbing). These heterogeneous bodies represent high pressure rocks of the crust and the upper

mantle. The mainly felsic granulites consists of quartz, ternary feldspar (now mesoperthite)

and minor garnet, kyanite and rutile (Kröner et al. 2000). Protoliths of these rocks have been

interpreted as magmatic (Janoušek et al. 2004; Fiala, et al. 1987). Minor granulites of mafic to

intermediate composition are composed of plagioclase, garnet and pyroxene, descending from

calc-alkaline magmatic differentiates (Fiala, et al. 1987, 1987; Carswell 1991).

Cooke and O'Brien (2001) estimated a HP-UHT granulite facies event at 14-16 kbar and

950-1050 °C. This was followed by a MP-HT event at 7-8 kbar and 800-870 °C. A retrograde

overprint at >4 kbar and 500-700 °C could be observed. Other authors as Krenn and Finger

(2010), Carswell and O'Brien (1993) and Kryza et al. (1996) came to similar results.

Geochronological investigations of Friedl et al. (2011) yield an age of 460-430 Ma of the

granitic protolith formation and ca. 340 Ma for the metamorphic peak (Friedl et al. 2011;

Lange et al. 2005).

This study focuses on the Blumau granulite body as can be seen in Figure 2. Table 1 shows

a list of all taken samples.

11

Figure 1 A Simplified geological map of the Bohemian Massif (modified after Franke, 2000; Schantl, 2016). Upper right inset

shows the subdivision of the Variscan belt in central Europe (Friedl et al., 2011; Schantl, 2016). B Geological map of the main

tectono-stratigraphic units of the Moldanubian Zone (modified after Schnabel & Fuchs, 2002; Schantl, 2016) . Black box

corresponds to the area investigation in this work as it can be seen in Figure 2. CBP: Central Bohemian Pluton; SBP: South

Bohemian Pluton; CO: Cornwall; AM: Armorican Massif; MC: Massif Central; RS: Rheinisches Schiefergebirge; V: Vosges;

SW: Schwarzwald; H: Harz; MGCH: Mid German Crystalline Highe; H: Harz; BM: Bohemian Massif; MOR: Moravian Zone

12

Figure 2 Geological map of the Blumau granulite body. Position of selected samples are marked as red points. Modified map after (Schnabel et al., 2002)

13

Table 1 List of samples with GPS data, outcrops, locations and the lithology

Latitude Longitude Outcrop Location Sample Lithology

48.77564 15.42668 OC1 Ellends GR1 grt-sil-granulite

48.77564 15.42668 OC1 Ellends GR2 grt-sil-granulite

48.76361 15.44704 OC2 Blumau GR3 grt-bt-granulite


48.76340 15.44515 OC3 Blumau GR5 grt-ky-granulite


48.76332 15.44490 OC5 Blumau GR7 grt-opx-bt-granulite

48.78455 15.56571 OC6 Wenjapons GR8 bt-granulite

48.78459 15.56618 OC7 Wenjapons GR9 ky-sil-grt-bt-granulite

48.78536 15.57013 OC8 Japons GR10 bt-grt-granulite

48.78651 15.56961 OC9 Japons GR11 grt-sil-granulite

48.78659 15.57165 OC10 Japons GR12 bt-granulite

48.78837 15.57343 OC11 Japons GR13 migm. grt-bt-gneiss

48.78837 15.57343 OC11 Japons GR14 migm. grt-bt-gneiss

48.78963 15.56913 OC12 Japons GR15 grt-bt-granulite

48.76394 15.44871 OC13 Blumau GR16 bt-grt-granulite

48.76394 15.44871 OC13 Blumau GR17 opx-bt-grt-granulite

48.76337 15.44955 OC14 Blumau GR18 grt-granulite



48.77021 15.47474 OC18 Seebs GR21 grt-granulite

48.77021 15.47474 OC18 Seebs GR22 opx-bt-grt-granulite

48.77504 15.47546 OC19 Seebs GR23 sil-bt-grt-granulite

48.77466 15.47591 OC20 Seebs GR24 sil-bt-grt-granulite

48.77466 15.47591 OC20 Kirchberg a.d.W. GR25 opx-grt-granulite

48.75515 15.40524 OC21 Kirchberg a.d.W. GR26 bt-grt-granulite


48.75335 15.40256 OC22 Kirchberg a.d.W. GR28 grt-bt-granulite

48.75251 15.40358 OC23 Kirchberg a.d.W. GR29 grt-granulite


48.75251 15.40358 OC23 Kirchberg a.d.W. GR31 opx-bt-grt-granulite

48.75811 15.40475 OC24 Kirchberg a.d.W. GR32 pyroxenite

48.62641 15.56116 OC25 Steinegg GR33 grt-granulite



48.62831 15.55548 OC27 Steinegg GR36 mylonite

48.62831 15.55548 OC27 Steinegg GR37 bt-granulite

48.63169 15.54918 OC28 Steinegg GR38 bt-grt-granulite

48.63169 15.54918 OC28 Steinegg GR39 grt-bt-granulite

48.63262 15.54754 OC29 Steinegg GR40 ky-grt-granulite

48.63292 15.54715 OC30 Steinegg GR41 vulcanite


48.64141 15.50476 OC31 Krug GR43 orthogneiss

48.64141 15.50476 OC31 Krug GR44 mylonitic bt-grt-ky-granulite

48.64141 15.50476 OC31 Krug GR45 mylonitic bt-grt-ky-granulite

48.64036 15.50949 OC32 Krug GR46 ultramylonite

48.64036 15.50949 OC32 Krug GR47 mylonite

14





48.64036 15.50949 OC32 Krug GR52 carbonate

48.64093 15.51891 OC33 Krug GR53 grt-ky-granulite

48.64093 15.51891 OC33 Krug GR54 opx-grt-granulite

48.63392 15.55518 OC34 Krug GR55 bt-grt-ky-granulite

48.63392 15.55518 OC34 Krug GR56 bt-grt-ky-granulite


48.61596 15.52676 OC36 Amtwiesen GR58 bt-grt-granulite

48.61596 15.52676 OC36 Amtwiesen GR59 bt-grt-granulite

48.60151 15.53113 OC37 St. Leonhard a. H. GR60 bt-grt-granulite

48.59772 15.55288 OC38 St. Leonhard a. H. GR61 bt-grt-granulite

48.58272 15.54408 OC39 St. Leonhard a. H. GR62 bt-grt-ky-granulite

48.76259 15.41576 OC40 Schönfeld GR63 bt-grt-granulite

48.76016 15.42855 OC41 Schönfeld GR64 bt-grt-granulite

48.78202 15.47583 OC42 Seebs GR65 grt-bt-granulite



48.80168 15.48378 OC43 Diemschlag GR68 bt-grt-granulite



48.73648 15.48908 OC45 Rothweinsdorf GR71 granluite

48.72819 15.39368 OC46 Göpfritz GR72 bt-grt-granulite

48.73617 15.41261 OC47 Göpfritz GR73 metagabbro

48.73915 15.35624 OC48 Scheideldorf GR74 opx-granulite

48.73915 15.35624 OC48 Scheideldorf GR75 opx-granulite

48.80228 15.50037 OC49 Tröbings GR76 gneiss

48.79848 15.48933 OC50 Tröbings GR77 gneiss

48.79747 15.49195 OC51 Tröbings GR78 bt-grt-granulite

48.79747 15.49195 OC51 Tröbings GR79 bt-grt-granulite

48.77347 15.54020 OC52 Klein-Ulrichschlag GR80 granluite




48.83645 15.39243 OC54 Loibes GR84 grt-granulite

48.81009 15.39777 OC55 Wienings GR85 bt-grt-granulite

48.81009 15.39777 OC55 Wienings GR86 bt-grt-granulite

48.78679 15.39107 OC56 Gross-Sieghards GR87 mylonite

48.78558 15.39260 OC57 Gross-Sieghards GR88 mylonite

48.88032 15.71623 OC58 Šafov GR89 amphibolite




48.87872 15.72033 OC61 Šafov GR93 grt-bt-granulite

48.87872 15.72033 OC61 Šafov GR94 grt-bt-granulite

48.95148 15.71400 OC62 Zblovice GR95 granulite

48.95070 15.71579 OC63 Zblovice GR96 opx-grt-granulite

15

48.96521 15.70772 OC64 Zblovice GR97 marmor




48.98219 15.64695 OC65 Kdousov GR101 granulite

48.98219 15.64695 OC65 Kdousov GR102 granulite

48.75730 15.48825 AS5 Oedt a.d.W GG11 grt-bt-px-granulite

48.77577 15.42647 AS6 Ellends GG12 grt-amph-cpx-granulite

48.77577 15.42647 AS7 Ellends GG13 granulite

48.77577 15.42647 AS8 Ellends GG14 grt-sil-granulite

48.77577 15.42647 AS9 Ellends GG15 grt-sil-granulite

48.77577 15.42647 AS10 Ellends GG16 granulite

48.77770 15.47827 AS7 Seebs GG18 grt-granulite

48.77770 15.47827 AS8 Seebs GG19 grt-px-granulite

48.82588 15.53565 AS13 Kolmnitzgraben GG34 grt-granulite

48.82588 15.53565 AS13 Kolmnitzgraben GG35 grt-sil-granulite

48.82562 15.53845 AS14 Kolmnitzgraben GG36 grt-px-amp-granulite

48.82562 15.53845 AS14 Kolmnitzgraben GG37 px-amp-granulite

48.82562 15.53845 AS14 Kolmnitzgraben GG38 grt-px-amp-granulite

48.87998 15.41502 AS19 Karlstein GG47 opx-grt-granulite





48.87998 15.41502 AS19 Karlstein GG53 grt-bt-gneiss

48.52805 15.57380 AS24 Gföhl GG62 grt-sil-granulite

48.52805 15.57380 AS24 Gföhl GG63 grt-granulite

48.52805 15.57380 AS24 Gföhl GG64 bt-grt-granulite

48.93548 15.56490 AS25 Waldhers GG65 serpentinite

48.93548 15.56490 AS25 Waldhers GG66 grt-granulite

48.93548 15.56490 AS25 Waldhers GG68 grt-granulite

16

Methods

Fieldwork was carried out in autumn 2015. In total, 127 samples were collected for further

petrological analysis. Polished thin sections were prepared and investigated by transmitted

light microscopy.

Quantitative mineral chemical analyses were performed at the NAWI Graz Geocenter,

Petrology and Geochemistry, University of Graz (Austria) using a JEOL-JSM-6310 scanning

electron microscope equipped with a MICROSPEC wavelength dispersive system (WDS) and

a LINK-ISIS energy dispersive system (EDS). Measurement time for WDS was 20 sec on

peak position and 10 sec/10 sec on background, 1 µm beam diameter, 15 kV acceleration

voltage and 6 nA beam current on PCD. Standards used were Adularia (K, Si, Al), Titanite

(Ca, Ti), Rhodonite (M), Garnet (Fe, Mg, Si, Al), Chromite (Cr), Albite (Na, Al, Si),

Atacamite (Cl), Baryte (Ba) and synthetic F-Phlogopite (F). Furthermore, quantitative

analysis and chemical mappings were done, using a JEOL JXA-8200 electron microprobe at

the UZAG (University of Graz, Graz University of Technology, Mining University Leoben)

EUGEN F. STUMPFL Electron Microprobe Laboratory, located at the Mining University

Leoben (Austria). Measurement time was 20 sec on peak position and 10 sec/ 10 sec on

background, 1 µm beam diameter by 15 kV acceleration voltage and 12 nA beam current.

Standards used were Albite (Na, Al, Si), Atacamite (Cl), Chromite (Cr), Garnet (Mg, Fe, Si,

Al), Diopside (Si, Ca, Mg), synthetic F-Phlogopite (F, K, Mg), Rhodonite (Mn), Almandine

(Fe, Al, Mg, Si), Sanidine (K, Ba), Rutile (Ti), Cubic Zirconia (Zr), F-Topaz (F), Plagioclase

(Ca) and Jadeite (Na).

The Raman spectra for differentiation between polymorphic phases and mineral phases

were obtained with a HORIBA JOBIN YVON LABRAM-HR 800 Raman micro-

spectrometer at the NAWI Graz Geocenter, Petrology and Geochemistry, University of Graz

(Austria). Phases were excited at room temperature with a 532 nm line of a He-Ne laser

through an OLUMPUS 100x objective with a numerical aperture of 0.9. Dispersion of light

was performed by a holographic grating with 1800 grooves/mm.

Quantitative chemical analyses for whole rock compositions were determined with a

BRUKER PIONIEER S4 wave length dispersive fluorescence spectrometer (WDXRF) at the

NAWI Graz Geocenter, Petrology and Geochemistry, University of Graz (Austria).

Approximately 100 g of 14 samples were crushed and ground in a RETSCH RS 200 vibratory

disc mill with tungsten carbide grinding rings. The production of glass disks were realized by

17

a VULCAN VAA 2M semi-automatic fusion machine with 1.0 g sample + 7.0 g di-

Lithiumtetraborate.

Mineral formulas and conventional geothermobarometric calculations were computed with

the petrological elementary tools (PET 7) for Wolfram Mathematica (Dachs 1998). In

addition, winTWQ (version 2.3) was used with internally consistent dataset from Berman

(1991), database version 2.32 (DEC06.DAT for mineral data and DEC06.SLN for mineral

solution data). Thermodynamic modelling of equilibrium phase assemblage diagrams and

calculations of chemical solid solution isopleths were computed with Theriak Domino

(Version 03.01.2012) by Capitani and Petrakakis (2010) using the internally consistent

thermodynamic mineral dataset from Holland and Powell (1998) and updates. Uncertainties

due to extrapolated activity models might affect calculations at high pressures.

Mineral abbreviations were used after Whitney and Evans (2010).

18

Petrography and mineral chemistry

Leucocratic granulites

Samples (Figure 3A) taken from the Blumau granulite body exhibit usually strong

foliation. The mineral assemblage consists of garnet + plagioclase + perthitic potassium

feldspar ± biotite and minor amounts of kyanite/sillimanite. Accessory phases are rutile,

spinel, ilmenite, titanite and apatite. The granoblastic matrix is made up of fine grained quartz

and recrystallized mosaics of K-feldspar and plagioclase representing former mesoperthite

(Figure 3B).

Kyanite appears in different textural features and reaches up to 700 µm in size. One type is

the appearance as subhedral porphyroblasts, adjacent to quartz and feldspar ± biotite (Figure

5A). In some cases, kyanite is partially replaced by retrograde fibrous sillimanite (Figure 5B).

Another type of kyanite is within a rim of garnet and spinel, surrounded by a corona of zoned

plagioclase (Figure 5C).

Rutile is common in matrix as well as inclusions in garnet (Figure 5D). Zr content reveals

a wide variation of 918 up to 4338 ppm.

Figure 3 A Representative hand specimen of leucocratic granulite type. B Photomicrograph with XPL. Garnet in the matrix

of quartz, recrystallized K-feldspar and plagioclase (2x magnification).

19

Matrix plagioclase is mostly fine grained and subhedral in habitus. Infrequent

porphyroblasts extend in size up to 700 µm. Typical twinning in crossed polarized light is

rarely present. The chemical composition (Table 2) is rich in albite (Xab=0.75-0.84).

Inclusions in garnet are rich in albite with a wider variability (Xab=0.55-0.93)

Subhedral matrix K-feldspar is fine grained whereby sparse grains are medium grained.

The chemical composition is in the range of Ab10-19An3-16Or78-94

Table 2 Representive analysis of feldspar. Mx=matrix, inc=inclusion, ic=inner corona, oc=outer corona

Analysis GR9p150 GR28p63 GR9p608 GR5p137 GR28p64 GR28p69 GR28p73 GR28p74 Location mx mx mx mx inc inc ic oc Mineral plag plag kf kf plag plag plag plag SiO2 63.79 63.32 64.46 64.93 58.00 67.00 59.84 62.00 Al2O3 22.99 22.80 19.66 17.94 26.18 20.28 24.67 23.36 Fe2O3 <0.10 <0.10 <0.10 <0.10 <0.10 0.25 0.14 <0.10 CaO 4.34 4.43 0.18 <0.10 8.35 1.38 6.49 5.01 BaO <0.10 <0.10 0.34 0.30 <0.10 <0.10 <0.10 <0.10 Na2O 9.03 9.07 1.93 1.29 6.82 11.05 7.67 8.81 K2O 0.31 0.34 13.90 14.71 0.31 <0.10 0.34 0.29

Total 100.49 99.97 100.46 99.30 99.75 100.02 99.15 99.47 Si 2.806 2.803 2.951 3.011 2.605 2.939 2.689 2.765 Al 1.192 1.189 1.061 0.981 1.386 1.049 1.306 1.228 Fe3 0.001 0.001 0.000 0.002 0.003 0.008 0.005 0.000 Ca 0.205 0.210 0.006 0.005 0.402 0.065 0.668 0.761 Ba 0.000 0.000 0.009 0.004 0.402 0.065 0.312 0.239 Na 0.770 0.779 0.171 0.116 0.594 0.940 0.668 0.761 K 0.017 0.019 0.812 0.870 0.018 0.003 0.019 0.016

Sum 4.991 5.001 5.010 4.989 5.008 5.004 4.999 5.009 Xab 0.776 0.773 0.171 0.874 0.586 0.933 0.669 0.749 Xan 0.207 0.208 0.009 0.117 0.396 0.064 0.312 0.235 Xor 0.017 0.019 0.814 0.004 0.018 0.003 0.019 0.016

Xcel 0.000 0.000 0.006 0.005 0.000 0.000 0.000 0.000

20

Subhedral to anhedral mesoperthitic K-

feldspar (Figure 5 E-F) is mostly fine grained

and infrequent porphyroblasts extend in size up

to 1100 µm. K-felspar host varies from 0.72-

0.96 in Xor. Xab is between 0.04 and 0.27 (Table

3). Xcel shows values between 0.003 and 0.008.

Distribution and size of plagioclase exsolution

lamellae are very unregularly. The albite

component shows values between 0.75 and 0.82.

For obtaining original chemical composition of

former ternary feldspar, the reintegration technique after Raase (1998) was used, resulting in a

chemical composition of Xab=0.18-0.29, Xan=0.05-0.10, Xor=0.61-0.76.

Table 3 Representative analysis of feldspar. Pert=perthitic K-feldspar

Analysis GR5p53 GR5p52 GR9p37 GR9p64 GR11p165 GR11p159 Mineral pl kfs pl kfs pl kfs Location pert pert pert pert pert pert

SiO2 64.47 64.50 62.01 64.40 64.54 66.02 Al2O3 22.29 18.46 24.04 19.32 22.20 18.63 Fe2O3 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10 CaO 3.59 0.00 4.80 0.26 3.54 0.16 BaO <0.10 0.31 <0.10 0.50 <0.10 0.12 Na2O 9.89 0.99 8.93 2.58 9.51 2.99 K2O 0.18 14.92 0.22 13.10 0.16 12.39

Total 100.42 99.18 99.99 100.15 100.02 100.31 Si 2.835 2.996 2.749 2.956 2.845 3.001 Al 1.156 1.010 1.256 1.045 1.153 0.998 Fe3 0.000 0.000 0.000 0.000 0.001 0.000

Ba 0.000 0.006 0.000 0.009 0.001 0.002 Ca 0.169 0.000 0.228 0.013 0.167 0.008 Na 0.843 0.090 0.767 0.229 0.813 0.264 K 0.010 0.884 0.012 0.767 0.009 0.718

Sum 5.013 4.986 5.012 5.019 4.989 4.991 Xab 0.825 0.092 0.762 0.225 0.821 0.266 Xan 0.165 0.000 0.226 0.013 0.169 0.008 Xor 0.010 0.902 0.012 0.753 0.009 0.724 Xcel 0.000 0.006 0.000 0.009 0.001 0.002

Figure 4 Ternary plot of feldspar. Black symbols:

matrix; red symbols: perthites

21

Figure 5 Photomicrograph and BSE images of leucocratic granulite samples. A Kyanite interbedded in a matrix of

plagioclase, quartz and biotite. B The core of kyanite as replaced by fibrous sillimanite in a matrix of quartz and plagioclase. C

Kyanite is replaced by a spinel-plagioclase symplectite and garnet within a zoned plagioclase corona. D Garnet with

exsolution of rutile needles restricted to the core. E K-feldspar host with exsolution lamellae of plagioclase. F Garnet with

inclusion of mesoperthitic K-feldspar, plagioclase and quartz.

22

Figure 6 Photomicrograph and BSE images of leucocratic granulite samples. A Poikiloblastic allanite surrounded by

plagioclase. B, C Garnet with monazite inclusion, encompassed in a matrix of perthitic K-feldspar, plagioclase and quartz. D

Two types of plagioclase exsolution in k-feldspar. Type 1(T1) consist of fine regular lamellae. Type 2(T2) is an irregular

patchy exsolution pattern with different orientation to type1. E Garnet with melt inclusions. F Melt inclusion.

23

Spinel appears either with plagioclase as spinel-plagioclase symplectite or as inclusion in

garnet. Two types of spinel can be observed (Table 4). Type 1 is rich in hercynite with minor

contents of Mg-spinel (Xhc=0.66-.074, Xsp=0.23-0.30). Type 2 is almost balanced in

hercynite and Mg-spinel (Xhc=0.44-.046, Xsp=0.44-.046). The gahnite component is

negligible in both types (Xgh=0.02-0.08).

Table 4 Representative composition of spinel. Two different types of spinel. Type1 is dominant in

spinel and type2 in hercynite. Grt adj=garnet adjacent to garnet, pl sym=plagioclase symplectite, pl

cor=plagioclase corona, grt inc=garnet inclusion

Analysis GR28p602 GR28p603 GR28p604 GR5p508 GR5p511 GR5p514

Mineral spl spl spl spl spl spl Location grt adj pl sym grt adj pl cor pl cor grt inc SiO2 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10 TiO2 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10 Al2O3 61.49 61.79 61.94 58.69 58.68 57.30 Cr2O3 0.14 0.11 <0.10 <0.10 <0.10 <0.10 FeO 22.97 22.75 22.47 33.06 32.74 36.15 MgO 12.55 12.33 12.84 6.85 6.68 5.42 ZnO 2.52 2.49 2.63 2.09 2.07 1.54 MnO <0.10 <0.10 <0.10 <0.10 <0.10 <0.10

Total 99.74 99.54 99.95 100.80 100.27 100.58 Si 0.001 0.001 0.000 0.000 0.000 0.001 Ti 0.001 0.001 0.000 0.001 0.001 0.001 Al 1.934 1.947 1.939 1.910 1.919 1.891 Cr 0.003 0.002 0.001 0.000 0.000 0.001 Fe2 0.452 0.461 0.440 0.676 0.681 0.744 Fe3 0.060 0.048 0.059 0.087 0.079 0.103 Mg 0.499 0.491 0.508 0.282 0.276 0.226 Zn 0.050 0.049 0.052 0.043 0.042 0.032 Mn 0.000 0.000 0.000 0.001 0.001 0.001

Sum 3.000 3.000 2.999 3.000 2.999 3.000 Xspl 0.50 0.49 0.51 0.28 0.28 0.23 Xhc 0.45 0.46 0.44 0.67 0.68 0.74 Xghn 0.05 0.05 0.05 0.04 0.04 0.03 Xglx 0.00 0.00 0.00 0.00 0.00 0.00

24

Subhedral garnet porphyroblasts are fractured and up to 1300 µm in size. Inclusions of

quartz, potassium feldspar, plagioclase, monazite and apatite are common. Latter two are

restricted to garnet inclusions. Garnet cores show exsolution of rutile needles (Figure 5D).

Two distinct chemical zoning patterns are recognizable (Figure 7, Figure 8, Figure 9A-D).

Garnet profile type 1 occurs in SiO2-rich rocks with the mineral assemblage of quartz +

plagioclase + K-feldspar and the absence of biotite. Typical is a high grossular plateau with

strongly zoned rims (Table 5). Xprp and Xalm are increasing, whereas Xgrs is increasing

towards the rims. Xsps is constantly low throughout the profile. A typical core composition of

type 1 is ca. Xalm61Xprp18Xgrs20Xsps1.The rim composition of this type is ca.

Xalm72Xprp22Xgrs4Xsps2.

Garnet profile type 2 is common in leucocratic granulites with the peak-mineral

assemblage of quartz + plagioclase + K-feldspar and the presence of significant amounts of

retrogressive developed biotite and sillimanite. Type 2 is characterized by significant lower

Xgrs and a weaker zoning, compared to type 1. The typical core composition of type 2 is ca.

Xalm53Xprp35Xgrs11Xsps1. The rim composition of type 2 shows values of ca.

Xalm64Xprp32Xgrs3Xsps1.

As shown in Figure 6E, some garnets reveal melt inclusions with mineral phases as quartz,

plagioclase and K-feldspar. A compositional profile of the former displays a totally

homogenized composition of Xalm70Xprp25Xgrs4Xsps1.

An exceptional garnet profile can be seen in sample GR28 (Figure 10A,B). This sample

with the peak mineral assemblage of quartz + plagioclase + K-feldspar, contains frequently

the accessory phase rutile. The core is characterized by a high grossular plateau with

Xgrs=0.19. Xalm and Xprp are constant throughout the core with values of 0.45 and 0.35,

respectively. At the rims, Xgrs is strongly decreasing to a value of 0.02, whereas Xalm and

Xprp are increasing to values of 0.51 and 0.46, respectively. Xsps is constant with a value of

0.01.

25

Table 5 Representative composition of garnet. Spl pl = adjacent to spinel-plagioclase symplectite, pl cor=adjacent to

plagioclase corona, adj bt=adjacent to biotite.

Analysis gr5a7l79 gr5a7l39 gr9a12l1 gr9a12l31 gr5p49 gr5p48 gr9p23 Location rim core rim core spl pl pl cor adj bt Mineral grt grt grt grt grt grt grt SiO2 37.97 38.16 38.25 39.03 37.69 37.28 38.95 TiO2 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10 Al2O3 21.81 21.45 21.43 22.13 21.37 21.17 22.20 FeO 32.61 27.36 29.92 25.36 33.36 32.33 27.76 MgO 5.80 4.16 8.40 8.69 5.66 5.94 10.28 CaO 1.32 8.07 1.00 4.25 0.96 1.24 0.90

MnO 0.59 0.46 0.48 0.48 0.59 0.61 0.27

Total 100.19 99.75 99.50 99.94 99.63 98.57 100.42 Si 2.988 3.003 2.984 2.995 2.993 2.983 2.971 Ti 0.005 0.005 0.001 0.000 0.000 0.000 0.003 Al 2.023 1.989 1.970 2.002 2.000 1.997 1.996 Fe2 2.146 1.801 1.892 1.621 2.201 2.127 1.712 Fe3 0.000 0.000 0.060 0.008 0.015 0.037 0.058 Mg 0.681 0.488 0.977 0.994 0.670 0.709 1.169 Ca 0.111 0.680 0.084 0.350 0.082 0.106 0.074 Mn 0.039 0.030 0.032 0.031 0.040 0.041 0.018

Sum 7.993 7.996 8.000 8.001 8.001 8.000 8.001 Xfe 0.76 0.79 0.66 0.62 0.77 0.75 0.59 Xalm 0.72 0.60 0.63 0.54 0.74 0.71 0.58 Xprp 0.23 0.16 0.01 0.00 0.00 0.00 0.01 Xgrs 0.04 0.23 0.11 0.11 0.08 0.08 0.13 Xsps 0.01 0.01 0.01 0.04 0.01 0.01 0.01

26

Flaky biotite is up to 400 µm in length and Xmg varies from 0.71-0.73. A high TiO2

content of up to 5.92 wt% is noticeable. Small amounts of Na2O could be detected (up to 0.17

wt%). Fluorine ranges from 0.26 to 0.41 wt%. Chlorine content is below 0.1 wt% (Table 6).

Table 6 Representative analysis of biotite. Adj grt=adjacent to

garnet, mx=matrix

Analysis GR9p82 GR9p84 GR9p86 GR9p87 Location adj grt mx adj grt mx Mineral bt bt bt bt SiO2 37.00 37.11 37.13 37.14

TiO2 5.92 5.49 5.37 5.27 Al2O3 17.80 17.39 17.76 17.68 FeO 10.18 10.75 10.03 10.65 MgO 15.45 15.41 15.24 14.78 Na2O <0.10 0.15 0.14 0.13 CaO <0.10 <0.10 0.12 0.17 MnO <0.10 <0.10 <0.10 <0.10 BaO 0.17 <0.10 <0.10 0.12 K2O 9.36 9.41 8.91 8.83 F 0.26 0.31 0.41 0.31 Cl <0.10 <0.10 <0.10 <0.10

Total 96.33 96.14 95.23 95.10 Si 2.676 2.697 2.708 2.717 Ti 0.322 0.300 0.294 0.290 Al 1.517 1.489 1.527 1.524 Fe2 0.616 0.653 0.612 0.652 Mg 1.666 1.669 1.657 1.612 Na 0.012 0.022 0.020 0.018

Ca 0.004 0.002 0.009 0.013 Mn 0.000 0.000 0.000 0.000 Ba 0.005 0.002 0.003 0.003 K 0.864 0.872 0.829 0.824

F 0.060 0.070 0.094 0.071 Cl 0.004 0.004 0.004 0.005

Sum 7.746 7.780 7.757 7.729 Xmg 0.730 0.719 0.730 0.712

27

Figure 7 A-B BSE image and compositional garnet profile of sample GR5, representing typical garnet profiles of leucocratic

granulite type from the Blumau granulite body. Xalm and Xprp increases in the rims, whereas Xgrs shows a significant drop.

Xgrs is constant throughout the profile. Position of the profile was selected, due to the chemically influence of the inclusion in

the garnet center. C-F Element distribution maps of C calcium D iron E magnesium and F manganese.

28

Figure 8 BSE image and compositional garnet profiles of leucocratic sample GR5. A-D Xalm and Xprp increases in the rims,

wheareas Xgrs shows a significant drop. Xgrs is constant throughout the profile. Profile B shows a content variation of the

core region due to the adjacent plagioclase inclusion in the garnet core. E-F Homogenous garnet profile, reflecting rim

composition of A and D.

29

Figure 9 A-F BSE image and compositional garnet profile of sample GR9, representing typical garnet profiles of leucocratic

granulite type from the Blumau granulite body.

30

Figure 10 BSE image and compositional garnet profile of leucocratic sample GR28. A,B Compositional profile. Xgrs

exhibits a high grossular plateau and sharply decreases at the rims. Xalm and Xprp are constant throughout the core and

increase at the rims. Xsps shows a homogenous distribution. C-F Element distribution map of C calcium, D magnesium, E

manganese and F titanium.

31

Figure 11 Mesocratic granulite type. A Outcrop situation with multiple joining. B Hand specimen of representative

mesocratic granulite sample. C Microphotograph of typical mineral assemblage under plane-polarized light and D under

cross-polarized light.

Mesocratic granulite

Mesocratic samples were taken from the Blumau granulite body and exhibits weak

schistosity (Figure 11A-B). The investigated samples contain the mineral assemblage garnet +

plagioclase + biotite + orthopyroxene ± clinopyroxene ± K-feldspar ± amphibole (Figure

11C-D, Figure 13A-F). Accessory phases are rutile, spinel, ilmenite, pyrite, zircon and apatite.

32

Matrix plagioclase is subhedral in habitus and

mostly fine grained. Rare porphyroblasts can

reach up to 600 µm. Albite component is

dominant (Xab=0.51-0.74, Xan=0.29-0.47).

Plagioclase inclusions in garnet show albite

values between 0.20 to 0.60 and anorthite values

of 0.39-0.80 (Table 7).

Plagioclase in spinel-plagioclase symplectite

(Figure 13D) is rich in anorthite (Xan=0.85-0.89,

Xab=0.11-0.15).

Subhedral K-feldspar is fine grained and does not occur in all samples as matrix phase, but

rather as inclusion. The orthoclase component is 0.89-0.95, albite content is low with 0.03 and

0.09. The anorthite and celsian component shows values of up to 0.02.

Table 7 Representative composition of feldspar; Cor=corona, mx=matrix, inc=inclusion, sp pl=spinel-plagioclase

symplectite, rea cor=inclusion in reaction corona

Analysis GG19p91 GR7p2 GR17p60 GR31p80 GR19p58 GR7p68 Gr17p97 Gr31p100 Location cor mx inc cor sp pl mx inc rea cor Mineral plag plag plag plag plag kf kf kf SiO2 59.07 61.07 55.93 51.18 45.18 63.82 64.42 64.97 Al2O3 26.13 24.42 27.58 31.43 35.24 19.16 18.73 18.66 Fe2O3 0.24 <0.10 0.13 0.19 0.28 0.07 0.31 0.28 CaO 7.46 6.50 9.89 13.97 17.94 0.08 0.11 <0.10

BaO <0.10 <0.10 <0.10 <0.10 <0.10 0.72 0.41 <0.10 Na2O 7.43 8.15 5.72 3.49 1.22 0.95 0.60 0.90 K2O 0.13 0.25 0.45 0.18 <0.10 15.35 15.90 15.36

Total 100.53 100.39 99.72 100.53 99.92 100.15 100.48 100.32 Si 2.626 2.709 2.524 2.316 2.084 2.957 2.973 2.986 Al 1.369 1.277 1.467 1.677 1.916 1.046 1.019 1.011 Fe3 0.008 0.000 0.005 0.006 0.010 0.003 0.011 0.010 Ca 0.355 0.309 0.478 0.678 0.887 0.004 0.005 0.005 Ba 0.000 0.000 0.000 0.000 0.000 0.013 0.007 0.001 Na 0.640 0.701 0.501 0.306 0.109 0.086 0.054 0.080 K 0.007 0.014 0.026 0.010 0.004 0.907 0.936 0.901

Sum 5.005 5.010 5.001 4.993 5.010 5.016 5.005 4.994 Xab 0.639 0.685 0.499 0.308 0.109 0.085 0.054 0.081 Xan 0.354 0.302 0.476 0.682 0.887 0.004 0.005 0.005 Xor 0.007 0.014 0.026 0.010 0.004 0.898 0.934 0.913

Xcel 0.000 0.000 0.000 0.000 0.000 0.013 0.007 0.001

Figure 12 Ternary feldspar diagram of mesocratic

samples

33

Anhedral to subhedral brownish

amphibole (Figure 13B) is rare and up to

200 µm in size. After Leake et al. (2004),

all amphiboles are classified as

ferropargasite and magnesiohastingsite.

Xmg values are between 0.48 and 0.53.

TiO2 is restricted to values between 2.40

and 2.86 wt%. CaO ranges from 10.46 to

10.59 wt%. Small amounts of fluorine

(0.19-0.34 wt%) and chlorine (0.08-0.35

wt%) could be quantified. Na2O values

are up to 2.84 wt% (Table 8).

Table 8 Representative analysis of amphibole. Cor inc=corona

inclusion, mx=matrix

Analysis GG19p15 GG19p18 GG19p21 GG19p23 Location cor inc mx cor inc cor inc Mineral amph amph amph amph SiO2 40.97 41.04 40.91 41.04 TiO2 2.86 2.80 2.40 2.70 Al2O3 12.16 11.50 12.24 12.39 Cr2O3 <0.10 <0.10 <0.10 <0.10 FeO 17.58 17.65 17.94 17.48

MgO 8.52 9.74 9.14 9.48 CaO 10.46 10.54 10.46 10.59 MnO 0.20 0.10 0.16 0.17 ZnO 0.13 <0.10 0.10 0.10 Na2O 2.84 2.57 2.55 2.54 K2O 0.66 0.72 0.82 0.78 F 0.34 0.31 0.27 0.19 Cl 0.35 0.08 0.13 0.21

Total 97.10 97.08 97.14 97.72 Si 6.273 6.239 6.226 6.195 Ti 0.329 0.320 0.274 0.306

Al 2.194 2.061 2.196 2.204 Cr 0.005 0.001 0.004 0.009 Fe2 2.127 1.932 1.979 1.908 Fe3 0.124 0.312 0.304 0.298 Mg 1.944 2.208 2.074 2.133 Ca 1.715 1.716 1.706 1.713 Mn 0.026 0.013 0.020 0.022

Zn 0.014 0.003 0.011 0.011 Na 0.844 0.757 0.752 0.743 K 0.130 0.140 0.159 0.149

F 0.166 0.151 0.129 0.090 Cl 0.091 0.020 0.035 0.053

Sum 15.982 15.873 15.869 15.834 Xmg 0.478 0.533 0.512 0.528

34

Subhedral clinopyroxene is up to 200 µm in length. All clinopyroxenes could be identified

as diopside after Morimoto (1988). Xmg value varies between 0.58 and 0.75. TiO2 is up to

0.88 wt% and small amounts of Al2O3 (up to 3.99 wt%) and Na2O (up to 0.72 wt%) can be

observed (Table 9).

Table 9 Representative composition of clinopyroxene. Mx=matrix, inc=inclusion

Analysis GG19p51 GG19p52 GG19p53 GG19p56 GG19p57 GR31p44 GR31p45 GR31p46 Location mx mx mx mx inc mx mx mx Mineral cpx cpx cpx cpx cpx cpx cpx cpx SiO2 51.69 51.86 52.27 51.48 50.46 51.95 52.31 53.67

TiO2 0.46 0.29 0.16 0.23 0.88 0.38 0.25 0.16 Al2O3 2.87 2.39 1.33 1.48 3.99 2.63 1.75 0.85 FeO 12.79 13.26 12.11 12.17 9.80 8.67 8.63 8.01 MgO 9.86 10.13 10.90 10.85 11.06 12.53 12.94 13.45 CaO 22.26 21.88 22.90 22.66 22.21 23.17 22.92 23.54

MnO 0.16 0.21 0.17 0.18 <0.10 0.16 0.19 0.20 Na2O 0.72 0.58 0.43 0.45 0.65 0.42 0.39 0.29

Total 100.80 100.59 100.26 99.50 99.11 99.92 99.38 100.18 Si 1.947 1.960 1.975 1.959 1.910 1.941 1.964 1.994 Ti 0.013 0.008 0.004 0.007 0.025 0.011 0.007 0.004

Al 0.127 0.106 0.059 0.066 0.178 0.116 0.077 0.037 Fe2 0.397 0.419 0.369 0.351 0.309 0.260 0.262 0.249 Fe3 0.005 0.000 0.013 0.037 0.001 0.011 0.009 0.000 Mg 0.554 0.571 0.614 0.616 0.624 0.698 0.724 0.745 Ca 0.898 0.886 0.927 0.924 0.901 0.927 0.922 0.937 Mn 0.005 0.007 0.005 0.006 0.002 0.005 0.006 0.006 Na 0.053 0.043 0.032 0.033 0.048 0.030 0.028 0.021

Sum 3.999 4.000 3.998 3.999 3.998 3.999 3.999 3.993 Xmg 0.583 0.577 0.625 0.637 0.669 0.729 0.734 0.749

35

Subhedral orthopyroxene has a size up to 400 µm. All orthopryoxene could be classified as

enstatite after MMorimoto 11988with Xmg ranging from 0.57 to 0.66 wt%. CaO varies

between 0.19 and 0.59 wt%. Al2O3 shows values from 0.45 to 1.78 wt%. MnO values up to

0.46 wt% can be observed (Table 10).

Table 10 Representative analysis of orthopyroxene. Mx=matrix, cor inc=corona inclusion, inc=inclusion

Analysis GR7p172 GR7p14 GR17p29 GR17p31 GR31p36 GR31p42 GR19p102 GR19p106 Location mx mx cor inc inc cor mx cor inc Mineral opx opx opx opx opx opx opx opx SiO2 52.10 52.37 52.26 53.75 53.36 52.81 51.54 52.54

TiO2 <0.10 <0.10 <0.10 <0.10 0.11 0.18 0.04 0.17 Al2O3 2.67 2.33 1.58 1.24 1.05 1.05 1.22 1.45 FeO 23.02 23.41 24.95 21.57 24.78 23.60 25.70 23.04 MgO 22.68 22.28 20.38 22.76 20.28 20.59 20.58 21.62 CaO 0.15 0.20 0.30 0.53 0.65 0.70 0.38 0.19

MnO 0.21 0.12 0.22 0.17 0.43 0.43 0.33 0.19 Na2O <0.10 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10

Total 100.96 100.77 99.80 100.11 100.68 99.37 99.79 99.26 Si 1.915 1.934 1.969 1.985 1.991 1.989 1.947 1.972 Ti 0.002 0.001 0.003 0.002 0.003 0.005 0.001 0.005

Al 0.116 0.102 0.070 0.054 0.046 0.047 0.054 0.064 Fe2 0.656 0.694 0.786 0.666 0.773 0.743 0.763 0.724 Fe3 0.052 0.029 0.000 0.000 0.000 0.000 0.049 0.000 Mg 1.243 1.227 1.145 1.253 1.128 1.156 1.159 1.210 Ca 0.006 0.008 0.012 0.021 0.026 0.028 0.015 0.008 Mn 0.007 0.004 0.007 0.005 0.014 0.014 0.010 0.006 Na 0.003 0.001 0.002 0.001 0.000 0.000 0.000 0.003

Sum 4.000 4.000 3.994 3.987 3.981 3.982 3.998 3.992 Xmg 0.655 0.639 0.593 0.653 0.593 0.609 0.603 0.626

36

Anhedral to subhedral flaky biotite is up to 1200 µm in size. Xmg of matrix biotite is

between 0.57 and 0.67, whereas inclusions show slightly higher values (0.64 to 0.68). In

contact to garnet Xmg can reach up to 0.77. Very high concentration of TiO2 (up to 7.44

wt%) can be observed. Highest fluorine and chlorine values are 1.04 and 0.08 wt%,

respectively. Barium shows concentrations up to 0.64 wt% and chromium 0.15 wt% (Table

11).

Table 11 Representative analysis of biotite. Mx=matrix, adj grt=adjacent to garnet, inc=inclusion, cor inc=corona

inclusion.

Analysis GR7p79 GR7p80 GR17p110 GR17p111 GR31p116 GR31p118 GR19p88 GR19p93 Location mx adj grt cor inc adj grt adj grt mx inc mx Mineral bt bt bt bt bt bt bt bt SiO2 36.63 37.37 36.98 37.05 38.79 37.02 36.33 36.22 TiO2 6.17 6.12 5.92 5.68 3.28 5.99 7.44 7.29 Al2O3 16.02 16.27 15.22 15.55 15.52 14.26 15.50 15.14 Cr2O3 <0.10 <0.10 <0.10 0.15 0.12 0.47 <0.10 0<0.10 MgO 13.80 14.82 12.81 13.93 18.33 13.83 13.41 11.89 FeO 13.24 11.85 15.63 13.93 9.85 13.42 13.35 15.81 CaO <0.10 <0.10 <0.10 <0.10 0.12 <0.10 <0.10 <0.10 MnO <0.10 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10

BaO 0.11 0.23 0.41 0.51 <0.10 0.28 0.42 0.36 Na2O <0.10 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10 K2O 10.12 9.92 9.61 9.38 9.47 9.92 9.98 10.01 F <0.10 <0.10 0.12 0.18 0.57 0.36 <0.10 <0.10 Cl <0.10 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10

Total 96.17 96.77 96.90 96.55 96.21 95.66 96.50 96.89 Si 2.703 2.717 2.741 2.734 2.809 2.767 2.682 2.697 Ti 0.343 0.335 0.330 0.315 0.178 0.337 0.413 0.408 Al 1.393 1.395 1.329 1.352 1.324 1.256 1.349 1.328 Cr 0.000 0.000 0.003 0.009 0.007 0.028 0.000 0.000 Mg 1.518 1.606 1.415 1.533 1.978 1.541 1.476 1.319

Fe2 0.817 0.721 0.969 0.860 0.596 0.839 0.824 0.984 Ca 0.000 0.004 0.004 0.007 0.009 0.002 0.000 0.000 Mn 0.000 0.002 0.000 0.001 0.002 0.003 0.000 0.003 Ba 0.003 0.007 0.012 0.015 0.002 0.008 0.012 0.010 Na 0.009 0.010 0.011 0.005 0.010 0.002 0.009 0.014 K 0.952 0.920 0.909 0.883 0.875 0.945 0.940 0.950 F 0.000 0.000 0.028 0.043 0.130 0.084 0.000 0.000 Cl 0.002 0.004 0.002 0.005 0.000 0.003 0.002 0.005

Sum 7.740 7.721 7.753 7.762 7.920 7.815 7.707 7.718 Xmg 0.650 0.690 0.594 0.641 0.768 0.647 0.642 0.573

37

Subhedral garnet porphyroblasts are fractured and up to 2750 µm in size. Inclusions are

quartz, plagioclase, K-feldspar, spinel, pyrite, apatite, clinopyroxene, orthopyroxene, biotite,

ilmenite and rutile. Exsolution of rutile needles can be observed. A distinct chemical zoning

can be noticed. Grossular content exhibits a plateau in the core and strongly decreases at the

rims. Almandine content is almost constant in the core and increases at the rims. Pyrope is

mostly constant at the core region and sharply increases at the outermost rim. Spessartine

content is homogenous in the core region and slightly increasing at the rims. Garnet cores are

rich in iron (Xalm=0.26-0.55), magnesium (Xprp=0.18-0.35) and calcium (Xgrs=0.22-0.36).

Manganese content is low (Xsps < 0.01). Garnet rims show the highest iron and pyrope values

of Xalm=0.56-0.62 and Xprp=0.16-0.32, respectively. Spessartine is significant higher at the

rim (Xsps=0.013-0.030). Garnet surrounding spinel-plagioclase symplectite (Figure 13D) is

chemically homogenous and shows a typical composition of Alm56 Pyp33Grs10 Sps1 (Table

12).

Table 12 Representative analysis of garnet. Cor grt=corona garnet.

Analysis GR31A4l1 GR31A4l19 GR7A4l159 GR17A2l58 GG19A6l61 GG19A6l29 GR19A3p29 Location rim core rim core rim core cor grt Mineral grt grt grt grt grt grt grt SiO2 38.86 40.03 38.79 39.08 37.92 38.37 38.37 TiO2 0.01 0.15 0.03 0.25 0.17 0.16 0.03 Al2O3 21.25 21.60 22.19 21.92 21.33 21.41 21.69 FeO 26.07 20.41 27.56 18.44 25.95 24.09 26.76 CaO 4.39 8.60 2.56 12.36 8.44 9.25 3.55 MgO 7.39 9.36 8.36 7.06 4.54 5.43 8.44 MnO 1.17 0.33 0.59 0.41 1.24 0.71 0.51 Total 99.14 100.52 100.08 99.51 99.59 99.43 99.34 Si 3.032 3.016 2.990 2.984 2.982 2.995 2.976 Ti 0.001 0.008 0.002 0.014 0.010 0.010 0.002 Al 1.954 1.918 2.016 1.973 1.976 1.970 1.983 Fe2 1.701 1.245 1.777 1.133 1.666 1.553 1.674 Fe3 0.000 0.041 0.000 0.044 0.040 0.020 0.062 Ca 0.367 0.694 0.212 1.011 0.711 0.774 0.295 Mg 0.859 1.051 0.961 0.803 0.532 0.631 0.975 Mn 0.077 0.021 0.039 0.026 0.083 0.047 0.034 Sum 7.991 7.994 7.997 7.988 8.000 8.000 8.001 Xmg 0.336 0.458 0.351 0.415 0.299 0.333 0.368 Xalm 0.566 0.413 0.595 0.381 0.557 0.517 0.562 Xprp 0.286 0.349 0.322 0.270 0.238 0.258 0.327 Xgrs 0.122 0.230 0.071 0.340 0.178 0.210 0.099 Xsps 0.026 0.007 0.013 0.009 0.028 0.016 0.011

38

Spinel is restricted to garnet inclusions as shown in Figure 13E (type 1) and spinel-

plagioclase symplectites (type 2). Type 1-spinel shows higher values in the spinel endmember

component and lower values in the hercynite component (Xspl=0.44-0.46, Xhc=0.46-0.48)

than type 2 (Xspl=0.39-040, Xhc=0.58-0.59). The gahnite component is also significant

higher in type 1 (Xghn=0.08-0.09) than in type 2 (Xghn=0.02-0.03) (Table 13).

Table 13 Representative analysis of spinel. Grt inc=garnet inclusion, sp pl=spinel-plagioclase symplectite.

Analysis GR7p506 GR7p507 GR7p517 GR19p505 GR19p518 GR19p519 GR19p521 GR19p522 Location grt inc grt inc grt inc sp pl sp pl sp pl sp pl sp pl

Mineral spin spin spin spin spin spin spin spin SiO2 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10 TiO2 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10 Al2O3 59.64 60.43 60.31 58.22 58.40 58.41 58.44 58.67 Cr2O3 0.26 0.27 0.30 <0.10 <0.10 <0.10 <0.10 <0.10 FeO 24.16 23.69 23.86 30.03 30.25 30.35 30.18 29.95

MgO 11.19 11.35 10.93 9.81 9.65 9.52 9.45 9.61 ZnO 4.25 4.40 4.12 1.13 1.22 1.03 1.01 1.25 MnO <0.10 <0.10 <0.10 <0.10 <0.10 0.13 0.10 <0.10

Total 99.64 100.29 99.64 99.36 99.68 99.59 99.32 99.58 Si 0.000 0.001 0.002 0.001 0.000 0.001 0.001 0.002

Ti 0.002 0.001 0.000 0.002 0.001 0.002 0.001 0.000 Al 1.906 1.915 1.926 1.883 1.885 1.888 1.893 1.894 Cr 0.006 0.006 0.006 0.001 0.001 0.001 0.001 0.000 Fe2 0.463 0.457 0.477 0.578 0.580 0.590 0.592 0.583 Fe3 0.085 0.076 0.064 0.112 0.113 0.107 0.102 0.103 Mg 0.452 0.455 0.442 0.401 0.394 0.389 0.387 0.392 Zn 0.085 0.087 0.082 0.023 0.025 0.021 0.020 0.025 Mn 0.001 0.002 0.001 0.001 0.002 0.003 0.002 0.001

Sum 3.000 3.000 3.000 3.002 3.001 3.002 2.999 3.000 Xspl 0.452 0.455 0.441 0.400 0.394 0.388 0.387 0.392 Xhc 0.463 0.457 0.476 0.576 0.579 0.588 0.591 0.582

Xghn 0.085 0.087 0.082 0.023 0.025 0.021 0.020 0.025

Xglx 0.001 0.002 0.001 0.001 0.002 0.003 0.002 0.001

39

Figure 13 Photomicrograph and BSE images of mesocratic samples. A,C Garnet in orthopyroxene-plagioclase corona. B

Sample of basic mesocratic granulite facies rock type. Garnet with plagioclase corona, surrounded by amphibole,

clinopyroxene and ilmenite. D Spinel-plagioclase symplectite with garnet corona. E Spinel inclusions in garnet. F Garnet

with biotite-orthopyroxene-plagioclase corona.

40

Figure 14 BSE images and compositional garnet profiles of representative mesocratic samples. A,B BSE image and

compositional garnet profile of sample GR7, where corona textures are lacking. Xalm and Xprp increase at the rims, whereas

Xgrs is strongly declining. Xsps remains almost constant. C-F Element distributon map of C calcium, D iron, E magnesium

and F manganese

41

Figure 15 BSE images and compositional garnet profiles of representative mesocratic samples with corona structure. In

contrast to garnets with no corona structure, Xsps is significant increasing at the rims. A-B Sample GR17, C-D Sample

GR31, E-F Sample GG19.

42

Corona structures


In rocks of the Blumau granulite body, development of corona structures is common. In

leucocratic granulites, plagioclase coronas around kyanite, spinel-plagioclase symplectites

and spinel-bearing garnet can be observed. Compositional profiles of leucocratic samples can

be seen in Figure 16. Compositional profile P1 from matrix to spinel show an increase from

0.16 to 0.25 Xan, whereas a second profile P2 from matrix to garnet comprises a more

attenuated trend in calcium (0.17 to 0.22 Xan) (Figure 13A,C,D). Figure 16E-F exhibits

highest Xan values of 0.25 in the spinel-bearing core region and a decrease towards matrix of

perthitic K-feldspar to 0.17 Xan.

Mesocratic granulites

In mesocratic granulites, inclusion-poor textures containing only plagioclase in the corona

reveal an increase in Xan from matrix to core. Mesocratic sample GR19, as can be seen in

Figure 17 reveals a complex corona structure. The core consists of spinel-plagioclase

symplectite 0.84 to 0.92 Xan. Inner corona is composed of garnet with homogenous

composition of Alm56Prp33Grs10Sps1. A second corona is constituted of plagioclase. In

contact to garnet, profile P1 (Figure 17A,E) starts with Xan of 0.48, drops to 0.33 and slightly

increases to 0.35 in vicinity to K-feldspar. Profile P2 (Figure 17A,F) starts at the spinel-

plagioclase symplectite with Xan=0.91 cross an area with incomplete garnet corona where

Xan sharply decline to 0.50. Subsequently Xan is decreasing to 0.30 with a slight increase of

0.34 in vicinity to K-feldspar. Plagioclase coronas around garnet or spinel-bearing garnet are

often heterogeneous and additionally include biotite and orthopyroxene, whereby no distinct

trend in Xan and a patchy distribution of calcium (Figure 18) can be observed.

43

Figure 16 BSE images and plagioclase profiles of leucocratic sample GR5. A Incomplete garnet pseudomorph after kyanite

with spinel inclusions. P1 and P2 are plagioclase profiles towards the core. B High contrast element distribution map of

calcium. C Plagioclase profile of P1. Xan increases from matrix towards spinel, from 0.16 to 0.25. D plagioclase profile of

P2. Xan increases from matrix towards garnet from 0.17 to 0.22. E,F Profile across spinel-bearing plagioclase corona. Xan is

decreasing towards matrix consisting of perthitic K-feldspar.

44

Figure 17 BSE image, element distribution maps and profiles of mesocratic sample GR19. A Spinel-plagioclase symplectite

with complex corona structure. Inner corona composed of garnet, surrounded by a plagioclase corona and K-feldspar as outer

corona. B element distribution map of calcium, C sodium and D potassium. E Plagioclase profile P1 from garnet towards K-

feldspar. F Plagioclase profile P2 from spinel-plagioclase symplectite towards K-feldspar.

45

Figure 18 A BSE image of mesocratic sample GR31. B Patchy element distribution calcium in a corona built up of

plagioclase, biotite and orthopyroxene

46

Major and trace element whole rock chemistry

A whole rock data set of 14 samples was prepared for geochemical research (Table 14).

Attention was paid to process fresh and unaltered specimens. The data set contains major and

trace element information of mesocratic and leucocratic samples of the Blumau granulite

body.

Leucocratic granulites display SiO2 contents between 67.38 and 76.60 wt%. TiO2 is

between 0.10 and 2.45 wt%. Al2O3 contents are 12.26 to 16.84 wt%. Fe2O3tot (total iron

expressed as Fe2O3) ranges between 1.44 and 4.75 wt%. MgO and CaO show values up to

1.72 and 2.06 wt%, respectively. Barium is in between 316 and 932 ppm. Rubidium varies

from 46.5 to 217 ppm. Strontium ranges from 56.8 to 158 ppm.

Mesocratic granulites show a wider range in SiO2 content compared to leucocratic rocks

with values between 46.80 to 67.86 wt%. TiO2 ranges from 0.57 to 2.45 wt%. Al2O3 is

between 13.94 and 16.84 wt%. Fe2O3tot show values from 4.65 to 14.98 wt%. MgO and CaO

content are up to 7.72 and 11.26 wt%, respectively. Barium is in between 102 and 995 ppm.

Rubidium ranges from 28.5 to 96 ppm and strontium varies from 57 to 154 ppm.

In the discrimination diagram between magmatic and sedimentary protoliths after Werner

(1987), the majority of samples show distinct magmatic origin (Figure 19A). An exception is

sample GR9. With a Mgo/CaO ratio of 1.22 it would indicate sedimentary origin.

Nevertheless, due to the geographic position and the ambient former magmatic rocks with

equal texture and mineralogy, a magmatic origin is suggested. Loss on ignition (LOI) is

between 0.06 and 0.57 wt%. In the TAS diagram after Cox et al. (1979) in Figure 19B , all

samples are subalkaline, whereby leucocratic rocks are granitic to granodioritic and

mesocratic granulites are granodioritic to gabbroic. A calc-alkaline trend can be observed in

the ternary AFM diagram after Irvine and Baragar (1971) (Figure 19C). In the B-A diagram

after Villaseca et al. (1998), leucocratic samples plot in the f-P (felsic peraluminous), m-P

(moderately peraluminous) and h-P (highly peraluinous) area (Figure 19D). Mesocratic

samples plot in the m-P to strongly metaluminous area. In Harker diagrams of SiO2 vs. major

elemets ( ), Al2O3, MgO, CaO and Fe2O3tot reveal a negative correlation. K2O shows a

positive correlation. In mesocratic samples, A/CNK show positive correlation. With 46.80%

SiO2, one outlier could be observed. This sample was taken from a lens of ultramafic rocks. In

Figure 21, Harker Diagrams of SiO2 vs. trace elements are plotted. Vanadium and zinc show a

negative correlation. In mesocratic samples, barium reveals a positive trend. Rubidium values

47

in mesocratic rocks are significant lower than in leucocratic with values of 48 and 149 ppm,

respectively. Average Rb/Sr values in mesocratic samples are 0.50 and in leucocratic samples

1.55.

Table 14 Whole rock composition of leucocratic and mesocratic samples. Major elements are given in wt%. Trace elements

are given in ppm. LOI=loss of ignition

Sample GG18 GG19 GR5 GR7 GR9 GR11 GR17 GR19 GR28 GR31 GR32 GR46 GR54 GR55

SiO2 67.86 46.80 76.60 65.82 69.32 76.18 60.24 64.68 68.64 56.79 52.38 74.41 72.01 73.79

TiO2 0.57 2.45 0.10 0.67 0.62 0.13 0.81 0.65 0.53 0.91 1.02 0.25 0.43 0.25

Al2O3 14.89 13.94 12.35 16.11 14.61 12.47 16.84 15.69 15.13 16.48 16.22 13.33 13.64 13.68

Fe2O3 4.65 14.98 1.49 5.74 4.53 1.47 7.92 6.46 4.81 8.17 8.94 2.17 2.81 2.17

MnO 0.06 0.25 0.02 0.08 0.06 0.03 0.11 0.09 0.06 0.10 0.14 0.03 0.03 0.03

MgO 1.66 6.09 0.24 2.30 1.72 0.27 3.67 2.63 1.66 6.00 7.72 0.58 0.65 0.43

CaO 2.78 11.26 0.91 3.66 1.41 0.62 5.96 4.77 2.08 6.92 10.59 1.13 1.30 0.96

Na2O 3.04 2.77 2.79 3.41 2.60 2.40 2.58 3.13 3.30 2.53 1.56 2.76 2.35 2.68

K2O 3.13 0.26 4.64 1.72 3.51 5.06 1.23 1.10 2.66 1.25 0.89 4.32 5.40 5.10

P2O5 0.14 0.32 0.03 0.10 0.09 0.10 0.18 0.11 0.16 0.16 0.13 0.15 0.15 0.22

LOI 0.44 0.57 0.15 0.37 0.52 0.32 0.14 0.22 0.25 0.23 0.06 0.28 0.29 0.33

Sum 99.21 99.68 99.31 99.95 99.00 99.05 99.67 99.51 97.64 99.54 99.64 99.41 99.06 99.63

Ba 995 102 655 507 932 316 402 328 603 342 205 409 636 444

Ce 68 51 58 34 71 32 39 29 38 78 71 36 94 47

Cr 46 99 <20 63 64 <20 84 65 49 295 306 <20 <20 <20

Cu <20 72 <20 20 <20 <20 <20 <20 26 34 <20 <20 <20 <20

Ga 18 18 15 17 17 14 18 18 19 23 21 16 16 19

Nb <20 <20 <20 <20 <20 <20 <20 <20 <20 <20 <20 <20 <20 <20

Nd <20 33 33 26 31 <20 25 25 24 31 53 27 29 <20

Ni <20 22 <20 30 <20 <20 <20 <20 25 37 55 <20 <20 <20

Pb <20 <20 <20 <20 <20 <20 <20 <20 <20 <20 <20 <20 20 <20

Rb 96 <20 139 43 107 217 32 29 47 53 36 150 171 215

Sc <20 36 <20 <20 <20 <20 <20 22 <20 26 33 <20 <20 <20

Sr 154 110 97 113 158 107 105 81 107 58 57 72 78 57

Th <20 <20 <20 <20 <20 <20 <20 <20 <20 <20 <20 <20 <20 <20

U <20 <20 <20 <20 <20 <20 <20 <20 <20 <20 <20 <20 <20 <20

V 75 356 <20 93 75 <20 128 96 65 208 202 26 25 <20

Y 36 41 40 27 25 22 29 24 27 25 25 39 51 45

Zn 64 122 <20 95 45 15 91 72 64 116 102 21 26 35

Zr 142 149 48 121 184 21 116 187 157 138 90 65 184 96

48

Figure 19 A Discrimination diagram after Werner (1987) between magmatic and sedimentary origin. B TAS diagram after Cox et

al. (1979). C AFM diagram after Irvine, Baragar (1971). D B-A diagram after Villaseca et al. (1998). Red symbols: mesocratic

granulites, black symbols: leucocratic granulites.

49

Figure 20 Harker diagrams of SiO2 versus major element oxides (wt%). Red symbols: mesocratic granulites, black symbols:

leucocratic granulites.

50

Figure 21 Harker diagrams of SiO2 versus trace elements (ppm). Red symbols: mesocratic granulites, black symbols: leucocratic

granulites.

51

Geothermobarometry

Conventional geothermobarometric calculations were applied to constrain PT conditions

for inherent metamorphic events. Furthermore, the trace element zirconium in rutile was

analyzed for calculating temperatures.

Attention should be paid to the limitations of conventional thermobarometry in granulites.

The duration of HT/UHT conditions has a significant impact on the degree of diffusive

resetting. This affects in particular former evidences of prograde metamorphism as well as

apparent PT conditions caused by retrogressive resetting (O'Brien and Rotzler 2003). Most

geothermometers are based on cation exchange between coexisting phases. During cooling,

re-equilibration of certain cations can result in significantly lower peak temperatures. For

determining high temperature peak metamorphism, net transfer reactions are better suited than

ion exchange reactions and therefore better suitable. Furthermore, the application of relict

mineral assemblages and reintegration of exsolution lamellae are appropriate methods to

obtain peak temperatures in granulite facies rocks (Frost and Chacko 1989).

HP-UHT granulite facies event

An essential problem for PT determination in UHT-granulites from the Blumau area is the

process of mylonisation, where anti(pertithic) feldspar recrystallizes to single potassium

feldspar and plagioclase crystals (O'Brien and Rotzler 2003). Due to the presence of rare relict

pertithic potassium feldspar and plagioclase, the ternary feldspar-mixing model after Benisek

et al. (2010) is a suitable method for the calculation of metamorphic peak temperature under

UHT conditions. While K and Na may be freely interchanged between the (Na,Ca)- and

(K,Ca)-feldspar binaries, intercrystalline (K,Na) + Si ↔ Ca + Al diffusion is inert. At constant

anorthite values and the mathematical reversion of the K-Na exchange, the temperature at

which the hypothetical former ternary feldspar existed, can be calculated (Benisek et al.

2004). Endmembers calculation of the former ternary feldspar results from reintegration of the

pertithic potassium feldspar and plagioclase exsolution lamellae. All temperature estimations

and standard deviations, based on the two-feldspar thermometry, were determined after

Benisek et al. (2010). Calculated temperatures are given in Table 15.

52

Table 15: Two-feldspar thermometry and inherent quantitative chemical analysis of pertithic potassium feldspar.

Temperatures are mean values ± standard deviation, calculated with a pressure of 1.5 GPa and a presumed error of ±0.2 GPa.

Ho= potassium feldspar host; ex=plagioclase exsolution lamella; mx = plagioclase in matrix.

Sample/Area

GR5/6 GR5/10 GR9/8 GR9/14

Temperature ± σ (°C)

1063 ± 19 1028 ± 13 1001 ± 16 963 ± 25

Analysis p132 p140 p144 p532 p526 p529 p155 p152 p150 p617 p621 p623

Location ho ex mx ho ex mx ho ex mx ho ex mx

Mineral kfs pl pl kfs pl pl kfs pl pl kfs pl pl

SiO2 65.66 64.83 64.54 63.96 62.73 62.73 65.70 63.73 63.87 64.34 62.00 61.47

Al2O3 18.19 22.11 22.28 18.90 22.68 23.04 18.52 23.26 23.39 19.36 24.21 24.12

Fe2O3 0.00 0.06 0.00 0.01 0.01 0.00 0.06 0.03 0.01 0.00 0.01 0.00

CaO 0.26 3.73 3.70 0.21 4.07 4.13 0.18 4.89 4.68 0.10 5.21 5.13

BaO 0.03 0.00 0.02 0.07 0.00 0.03 0.39 0.01 0.05 0.29 0.01 0.06

Na2O 0.98 9.27 9.20 1.62 9.92 9.88 2.47 8.76 8.89 1.89 9.74 9.23

K2O 14.94 0.20 0.23 14.64 0.12 0.18 12.98 0.17 0.22 14.30 0.23 0.19

Total 100.06 100.21 99.97 99.40 99.53 100.00 100.29 100.86 101.12 100.28 101.42 100.19

Si 3.017 2.851 2.845 2.968 2.794 2.783 2.999 2.794 2.794 2.957 2.725 2.729

Al 0.985 1.146 1.157 1.034 1.191 1.205 0.997 1.202 1.206 1.048 1.254 1.262

Fe3 0.000 0.002 0.000 0.000 0.000 0.000 0.002 0.001 0.000 0.000 0.000 0.000

Ca 0.005 0.176 0.175 0.004 0.194 0.197 0.009 0.230 0.220 0.005 0.245 0.244

Ba 0.002 0.000 0.000 0.004 0.000 0.001 0.007 0.000 0.001 0.005 0.000 0.001

Na 0.087 0.791 0.786 0.146 0.856 0.850 0.218 0.745 0.754 0.168 0.830 0.794

K 0.876 0.011 0.013 0.867 0.007 0.010 0.756 0.010 0.012 0.839 0.013 0.011

Sum 4.972 4.977 4.976 5.023 5.042 5.046 4.988 4.982 4.987 5.022 5.067 5.041

Xab 0.090 0.809 0.807 0.143 0.810 0.803 0.220 0.756 0.764 0.165 0.763 0.756

Xan 0.002 0.180 0.180 0.004 0.184 0.186 0.009 0.234 0.223 0.005 0.225 0.232

Xor 0.903 0.011 0.013 0.849 0.007 0.009 0.764 0.010 0.012 0.825 0.012 0.010

Xcel 0.005 0.000 0.000 0.004 0.000 0.001 0.007 0.000 0.001 0.005 0.000 0.001

Reintegrated ternary feldspar

Xab 0.288

0.208

0.217

0.216

Xan 0.101

0.056

0.054

0.070

Xor 0.611

0.737

0.729

0.714

For result validation of the two-feldspar thermometry, zirconium-in-rutile thermometry

was applied following Tomkins et al. (2007) and Zack et al. (2004a). In contrast to the

equation of Zack et al. (2004a):

𝑇(°𝐶) = 127.8 ∗ 𝑙𝑛Ø − 10

calculations of Tomkins et al. (2007) suggest also a slight pressure dependency of zirconium

incorporation in rutile:

53

𝑇(°𝐶) =83.9 + 0.410 ∗ 𝑃

0.1453 − 𝑅𝑙𝑛Ø− 273

in which P is in kbar, Ø is ppm Zr and 𝑅 is the gas constant, 0.0083144 kJK-1

.

Measurements of five samples with 45 rutile analysis were performed by microprobe.

Average temperature calculations after Tomkins et al. (2007) yields 94 – 105 °C lower

temperatures than after Zack et al. (2004a) shown in Table 16 below:

Table 16: Temperature estimation with zirconium-in-rutile thermometry. Analysis were carried out at matrix

rutiles. Number of rutile analysis per sample: GR5=5; GR7=5;GR9=12;GR19=1;GR28=23.

Tomkins et al. (2007) Zack et al. (2004)

Sample Average T ± 1σ [°C]

GR5 952 ± 31 1054 ± 29

GR7 918 ± 21 1012 ± 21

GR9 818 ± 37 915 ± 42

GR19 896 ± 0 1001 ± 0

GR28 878 ± 32 983 ± 34

Estimation of pressure in the UHT granulite facies event was realized by using the GASP-

barometer with winTWQ, version 2.4 (Berman 1991). Detailed settings can be seen in chapter

“Methods”. Values of anorthite compositions have been derived from reintegrated ternary

feldspars Table 15. For garnet composition, analyses of the outermost rim were used. The

combination of two-feldspar thermometry combined with GASP barometry is shown in a.

Pressure varies from 1.12-1.75 GPa and temperature ranges between 1006-1060 °C. These

results are consistent with the values of zirconium-in-rutile thermometry (983-1054 °C) after

Zack et al. (2004a). One outlier (GR9 with 915 °C) could be observed.

54

MP-HT granulite facies overprint

Estimation of pressure and temperature conditions of the MP-HT granulite facies event

was applied in mesocratic granulites. For thermometry, amphibole-plagioclase, garnet-

amphibole, garnet-orthopyroxene and garnet-biotite thermometer were used. For barometry,

garnet-amphibole-plagioclase-quartz, garnet-orthopyroxene-plagioclase-quartz and garnet-

plagioclase-biotite-quartz barometer were used (Table 17).

Table 17 Thermometers and barometers for MP-HT granulite facies estimation

Thermometer Author

Amphibole-plagioclase Holland and Blundy (1994)

Garnet-amphibole Dale et al. (2000)

Garnet-orthopyroxene Harley (1984)

Garnet-biotite Holdaway (2000)

Barometer

Garnet-amphibole-plagioclase Dale et al. (2000)

Garnet-orthopyroxene-plagioclase Newton and Perkins (1982)

Garnet-plagioclase-biotite-quartz Newton and Perkins (1982)

Garnet-orthopyroxene-plagioclase thermobarometry of sample GR7, GR17 and GR31

shows a range in temperature between 758 and 902 °C and 0.67 to 0.79 GPa in pressure (b).

Garnet-amphibole-plagioclase thermometer of GG19 with 773 to 799 °C is in good

agreement with the results of garnet-orthopyroxene-plagioclase thermometry (c). Whereas

pressure shows higher values-between 0.80 to 1.02 GPa.

Garnet-biotite-plagioclase thermobarometry with samples GR7, GR17 and GR31 shows a

larger range of temperature and pressure with 685 to 857 °C and 0.64 to 0.98 GPa (d).

55

Figure 22 A: PT estimation of the HP-UHT granulite facies event. Temperature estimation by ternary feldspar-mixing model

after Benisek et al. (2010) in gray area. Zirconium-in-rutile thermometry after Zack et al. (2004a) is represented by dashed lines.

GASP barometry is shown in solid lines. B Garnet-orthopyroxene-plagioclase thermobarometry of samples GR7, GR17 and

GR31. C Garnet-amphibole-plagioclase thermobarometry of sample GG19. D Garnet-biotite-plagioclase thermobarometry of

samples GR7, GR17 and GR31. B,C,D represents MP-HT granulite facies overprint. Horizontal axis are given in °C, vertical axis

are given in bar.

56

Thermodynamic Modelling

Thermodynamic modelling was used for a better understanding of the PT evolution and

metamorphic history. Computation of equilibrium assemblage diagrams and chemical solid

solution isopleths were performed with Theriak Domino (Version 03.01.2012) by Capitani

and Petrakakis (2010). This software is based on Gibbs free energy minimization.

Calculations were performed in the chemical system Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-

H2O-TiO2-MnO (NCKFMASHTMn). The following solid-solution models were used:

feldspar (Benisek et al. 2010), biotite (Tajčmanová et al. 2009), garnet (Connolly 2005),

clinopyroxene (Green et al. 2007), orthopyroxene (Powell and Holland 1999), spinel (White

et al. 2007), amphibole (Diener et al. 2007) , white mica (Coggon and Holland 2002) and melt

phase (White et al. 2007).

During the growth of garnet certain elements (Ca, Mg, Fe, Mn) fractionate into the cores

and the effective bulk composition is changed (Stüwe 1997). Therefore, a core-corrected

whole rock chemistry was used for calculating pseudosections and corresponding isopleths for

rim compositions. Due to the observed mineralogy and the lack of hydrous phases in

sufficient amounts, a water content of 1 wt% was assumed.


Leucocratic sample GR5 and GR11 was chosen for thermodynamic modelling of the UHT

granulite facies event. EBC of sample GR5 yields a chemical composition of Si=73.12 mol%,

Ti=0.07 mol%, Al=13.81 mol%, Ca=0.85 mol%, Mg=0.31 mol%, Fe=0.96 mol%, K=5.67

mol%, Na=5.18 mol%, Mn=0.014 mol%, H=6.29 mol. Isopleth intersections of garnet

endmembers (Xalm=0.72, Xprp=0.22, Xgrs=0.04) results in a PT window of 15.6–17.5 kbar

and 1040–1070 °C which is in good agreement with results of conventional

geothermobarometry (Figure 23). The computed mineral assemblage of field 5 consists of

feldspar, garnet, kyanite, quartz, rutile and melt. This field has a range of 910–1180 °C and

12.3–30 kbar.

57

Figure 23 Calculated pseudosection of leucocratic sample GR5 in the NCKFMASHTMn system. Isopleths of Xgrs, Xprp and

Xalm yields a PT window of 15.6 – 17.5 kbar and 1040 – 1070 °C. Computed equilibrium mineral assemblage consists of ternary

feldspar, garnet, kyanite, quartz, rutile and melt. 1:fsp grt wm omp melt ky qz rt; 2:fsp grt wm melt qz rt; 3:(2)fsp grt wm omp

melt ky qz rt; 4:(2)fsp grt wm melt ky qz rt; 5:fsp grt melt ky qz rt; 6:fsp grt (2)melt ky qz rt; 7:fsp grt (2)melt qz rt; 8:fsp grt melt

qz rt; 9:fsp grt sil melt qz rt; 10:(2)fsp grt melt ky qz rt; 11:(2)fsp grt bt melt ky qz rt; 12:(2)fsp grt melt qz rt; 13:(2)fsp grt melt sil

qz rt; 14:(2)fsp ilm grt melt qz rt; 15:fsp ilm grt melt qz rt; 16:fsp ilm grt melt q; 17:grt melt qz rt; 18:ilm grt melt qz rt;

58

EBC of sample GR11 yields a chemical composition of Si=73.14 mol%, Ti=0.09 mol%,

Al=14.07 mol%, Ca=0.62 mol%, Mg=0.37 mol%, Fe=1.02 mol%, K=6.20 mol%, Na=4.47

mol%, Mn=0.023 mol%, H=6.40 mol%. Due to the presence of kyanite in this sample, the

intersection of Xalm with ky can be considered as minimum PT. A further intersection of

Xprp and Xgrs results in a PT window of 15.0–18.0 kbar and 1030–1130 °C which is in good

agreement with results of conventional geothermobarometry. The computed mineral

assemblage of field 4 consists of feldspar, garnet, kyanite, quartz, rutile and melt.

Figure 24 Calculated pseudosection of leucocratic sample GR11 in the NCKFMASHTMn system. Isopleths of Xalm, Xprp

and an average ternary feldspar composition of Xan yields a PT window of 15.0 – 18.0 kbar and 1030 – 1130 °C. Computed

equilibrium mineral assemblage consists of ternary feldspar, garnet, kyanite, quartz, rutile and melt. 1:(2)fsp2 grt wm omp

melt q rt;2:(2)fsp2 grt wm melt q rt;3:fsp2 grt wm melt q rt;4:fsp2 grt melt ky q rt;5:fsp2 grt (2)melt ky q rt;6:(2)fsp2 grt wm

bt melt q rt;7:(2)fsp2 grt melt ky q rt;8:(2)fsp2 grt bt melt ky q rt;9:(2)fsp2 grt bt melt sill q rt;10:(2)fsp2 grt melt sill q

rt;11:fsp2 grt melt sill q rt;12:fsp2 grt melt q rt;13:grt melt q rt;

59

Figure 25 Calculated pseudosection of mesocratic sample GR9 in the NCKFMASHTMn system. Isopleths of Xgrs, Xalm, Xprp,

yields a PT window of 9.4 – 9.6 kbar and 870 – 880 °C. 1:fsp2 grt wm bt q;2:fsp2 grt wm bt melt q;3:(2)fsp2 grt wm bt

q;4:(2)fsp2 grt wm bt melt q;5:(2)fsp2 grt bt melt ky q;6:(2)fsp2 grt bt melt ky q rt;7:(2)fsp2 grt bt melt sil q rt;8:(2)fsp2 grt bt

melt sil q;9:(2)fsp2 wm bt melt q;10:(2)fsp2 bt melt sil q;11:(2)fsp2 grt bt cord melt sil q;12:(2)fsp2 grt bt cord melt q;13:(2)fsp2

ilm grt bt cord melt q;14:(2)fsp2 ilm grt bt melt sil q;15:(2)fsp2 ilm grt cord melt q;16:(2)fsp2 ilm grt opx cord melt q;17:(2)fsp2

grt melt ky q rt;18:fsp2 grt melt ky q rt;19:fsp2 grt melt sil q rt;20:(2)fsp2 grt melt sil q rt;21:fsp2 grt melt q rt;22:fsp2 ilm grt melt

q rt;23:fsp2 ilm grt cord melt q;24:fsp2 ilm grt melt q;25:fsp2 ilm grt opx melt q;26:fsp2 ilm grt opx cord melt q;

Leucocratic sample GR9 (Figure 25) was chosen for thermodynamic modelling of the HT

granulite facies event. EBC of sample GR9 yields a chemical composition of Si=68.88 mol%,

Ti=0.45 mol%, Al=16.53 mol%, Ca=1.43 mol%, Mg=2.49 mol%, Fe=3.24 mol%, K=4.31

mol%, Na=4.86 mol%, Mn=0.047 mol%, H=6.41 mol. Isopleth intersections of garnet

endmembers (Xalm=0.64, Xprp=0.32, Xgrs=0.04) results in a PT window of 9.4 – 9.6 kbar

and 870 – 880 °C.

60

Figure 26 Calculated pseudosection of mesocratic sample GR7 in the NCKFMASHTMn system. Isopleths of Xgrs, Xalm,

Xprp, Xal yields a PT window of 7.5 – 8.5 kbar and 865 – 875 °C. Intersections of grt end member isopleths and aluminum in

orthopyroxene isopleths plot in area 5. 1:fsp grt wm bt melt qz rt;2:fsp grt bt melt qz rt;3:fsp ilm grt bt melt qz rt;4:fsp ilm grt bt

melt q;5:fsp ilm grt bt opx melt q;6:fsp ilm grt bt opx crd melt q;7:fsp ilm grt opx crd melt q;8:fsp ilm grt opx melt q;9:fsp ilm

grt opx melt qz rt;10:fsp grt opx melt qz rt;11:fsp grt bt opx melt qz rt;12:fsp ilm grt bt opx melt qz rt;13:fsp grt bt cpx opx melt

qz rt;14:fsp grt bt cpx melt qz rt;15:fsp grt omp opx melt qz rt;16:fsp grt omp melt qz rt;17:fsp ilm grt bt amp melt q;18:fsp ilm

grt bt amp melt qz H2O;19:fsp ilm grt bt amp qz H2O;20:fsp ilm grt bt qz H2O;21:fsp ilm grt bt melt qz H2O;22:fsp ilm grt bt qz

H2O;23:fsp grt bt melt qz rt H2O;

Mesocratic granulites

Mesocratic sample GR7 was chosen for thermodynamic modelling of the HT granulite facies

event (Figure 26). EBC consists of Si=62.27 mol%, Ti=0.48 mol%, Al=17.97 mol%, Ca=3.57

mol%, Mg=3.23 mol%, Fe=4.06 mol%, K=2.08 mol%, Na=6.28 mol%, Mn=0.063 mol%,

H=6.23 mol%. PT window of isopleths intersections from garnet endmembers (Xalm=0.61,

Xgrs=0.07, Xprp=0.31) and aluminum in orthopyroxene (Xal=0.10) varies between 7.5–8.5

kbar and 865–875 °C which confirms the results of conventional geothermobarometry.

61

Figure 27 Calculated pseudosection of mesocratic sample GG19 in the NCKFMASHTMn system. Isopleths of Xgrs, Xalm, Xprp,

Xdi and Xan yields a PT window of 7.1 – 8.3 kbar and 767 – 792 °C. 1:fsp grt bt omp amp q rt H2O;2:fsp grt bt omp amp rt

H2O;3:fsp grt bt omp amp melt rt H2O;4:fsp grt bt omp amp melt rt;5:fsp ilm grt bt omp amp rt H2O;6:fsp ilm grt bt omp amp

melt rt H2O;7:fsp ilm grt bt omp amp melt rt;8:fsp ilm grt bt omp melt rt;9:fps2 ilm grt bt omp melt;10:fsp ilm grt omp

melt;11:fsp ilm grt bt omp amp H2O;12:fsp ilm grt bt omp amp melt H2O;13:fsp ilm grt bt omp amp melt;14:fsp ilm grt bt omp

amp;15:fsp ilm grt bt omp opx amp H2O;16:fsp ilm grt bt omp opx amp melt H2O;17:fsp ilm garne bt omp opx amp melt;18:fsp

ilm grt bt omp opx melt;

Mesocratic sample GG19 was chosen for thermodynamic modelling of the HT granulite

facies rocks with corona structure (Figure 27). EBC consists of Si=45.26 mol%, Ti=1.78

mol%, Al=15.89 mol%, Ca=11.26 mol%, Mg=8.78 mol%, Fe=10.90 mol%, K=0.32 mol%,

Na=5.20 mol%, Mn=0.21 mol%, H=6.45 mol%. PT window of isopleths intersections from

garnet endmembers (Xalm=0.72, Xgrs=0.04, Xprp=0.22), anorthite (Xan=0.05. inner corona)

and diopside (Xdi=0.55, average clinopyroxene composition) varies between 7.1–8.3 kbar and

767–792 °C which confirm the results of conventional geothermobarometry.

62

Figure 28 Calculated pseudosection of mesocratic sample GR19 in the NCKFMASHTMn system. Isopleths of Xgrs, Xalm, Xprp,

yields a PT window of 7.4 – 9.4 kbar and 835 – 935 °C. 1:fsp grt bt omp melt q rt;2:fsp grt omp melt q rt;3:fsp grt omp opx melt q

rt;4:fsp ilm grt omp opx melt q rt;5:fsp grt bt omp opx melt q rt;6:fsp ilm grt bt omp opx melt q rt;7:fsp ilm grt bt omp melt q

rt;8:fsp ilm grt bt omp melt q;9:fsp ilm grt bt omp opx melt q;10:fsp ilm grt omp opx melt q;11:fsp ilm grt opx melt q;12:fsp ilm

grt bt opx LIQc q;13:fsp grt bt omp amp melt q rt;14: fsp grt bt omp amp melt q rt;15:fsp ilm grt bt omp amp melt q;16:fsp grt bt

amp melt q rt;17:fsp ilm grt bt amp melt q;18:fsp ilm grt bt (2)amp melt q;19:fsp ilm grt bt amp melt q;20:fsp ilm grt bt opx amp

melt q;21:fsp grt bt amp q rt h2o;22:fsp ilm grt bt amp q h2o;23:fsp ilm grt bt (2)amp q h2o;24:fsp ilm grt bt amp q h2o;

Mesocratic sample GR19 was chosen for thermodynamic modelling of the HT granulite

facies rocks with corona structure (Figure 28). EBC consists of Si=61.60 mol%, Ti=0.47

mol%, Al=17.58 mol%, Ca=4.85 mol%, Mg=3.72 mol%, Fe=4.60 mol%, K=1.34 mol%,

Na=5.79 mol%, Mn=0.069 mol%, H=6.35 mol%. PT window of isopleths intersections from

garnet endmembers (Xalm=0.57, Xgrs=0.12, Xprp=0.28) varies between 7.4–9.4 kbar and

835–935 °C.

63

Interpretation and discussion

Petrography

The presence of perthitic K-feldspar represents former hypersolvus ternary feldspar.

Additionally, a granoblastic matrix of fine grained quartz and recrystallized mosaics of K-

feldspar and plagioclase, derived from former mesoperthite, are good indicators for a

metamorphic HT/UHT event. Sillimanite replacing kyanite and the presence of amphibole

instead of pyroxene in mesocratic granulites is attributed to a retrogressive post-UHT event.

In leucocratic granulites, the development of plagioclase coronas around metastable kyanite

representing a micro domain which is isolated from the

surrounding matrix. These micro domains with silica

undersaturated bulk chemistry allows the crystallization of

spinel (Figure 5C) along the kyanite-plagioclase interface

(Tajčmanová et al. 2006).

In mesocratic orthopyroxene-bearing samples, the

formation of double coronas around garnet is common. The

inner corona consists of plagioclase-orthopyroxene

symplectite with minor amounts of garnet, whereby the

elongated orthopyroxene exhibits a radial arrangement

around garnet. The discontinuous outer corona comprises

larger orthopyroxene crystals. Single biotite flakes also

occur in both coronas. The evolution of such textures

indicates a multilevel process after the following

endmember reaction: Grs + Kfs + Py + H2O = Qz + Phl +

An, Qz + Py + Grs = An + En and Bt + Sil + Pl + Qz =

Melt + Grt + Kfs as it can be seen in Figure 29.

Under HP conditions, a garnet porphyroblast is

encompassed by a quartzo-feldspathic matrix (Figure 29A).

During decompression, large orthopyroxene crystals and

plagioclase are constituted at the expense of garnet and

quartz (Figure 29B). At the final stage, a texture of radial arranged and elongated

orthopyroxene is developed (Figure 29C).

Figure 29 Multistage evolution of radial

orthopyroxene-plagioclase coronas around

garnet. A Garnet in quartzo-feldspathic

matrix. B Development of larger

orthopyroxene crystals and plagioclase

corona consuming garnet. C Establishment

of smaller, mostly elongated and radial

arranged orthopyroxene.

64

In felsic granulites plagioclase coronas around garnet are frequently developed. These

coronas show a strong zonation in anorthite component where Xan decreases from the garnet

– plagioclase interface outwards. This feature suggests a fast decompression with insufficient

time for equilibration which was also described for other granulites from the Moldanubian

zone by Štípská et al. (2010), Tajčmanová et al. (2006) and Vrána et al. (2013).

Garnet profiles

In leucocratic samples, two characteristic types of compositional garnet profiles could be

observed. Type 1 reveals a high grossular plateau with strongly chemically zoned rims where

Xgrs is greatly decreasing and Xprp, respectively, Xalm is increasing. It is assumed that the

core developed in a pre-HP-UHT event and the chemically zoned rims are reflecting the HP-

UHT metamorphic event. Garnet profile type 2 is characterized by significantly lower Xgrs

and a weaker zoning compared to type 1, which is interpreted to have developed by the HP-

UHT event. The high Xgrs content has been erased by diffusional processes. However most

samples with garnet profile type 2 contain significant amounts of retrogressive evolved biotite

and sillimanite which are considered to be in equilibrium with garnet rims and display the

later MP-HT granulite facies event.

In leucocratic and mesocratic samples garnet cores are chemically homogenous. This can

be caused by growth within a narrow PT window or re-equilibration of the garnet core at

elevated temperatures by diffusional processes. Furthermore, the fact that zoning is preserved

at the rims implies a short duration of the HP-UHT event. Nonetheless, garnets are still

affected by chemical diffusion processes and are therefore not applicable for estimation of PT

values of the pre-HP-UHT event. Crystallographic oriented rutile needles in garnet cores

could indicate a pressure dominated pre-HP-UHT event. Ti solubility with increasing pressure

could be verified by Zhang et al. (2003), carrying out high pressure multianvil experiments.

During decompression, Ti solubility decreases and rutile needles start to exsolve.

Additionally, high grossular contents of garnet profile type 1 support a former UHP event.

In retrogressive developed plagioclase corona around garnet, spessartine content increases

towards the rims. This feature is attributed to garnet resorption because manganese is not

incorporated in significant amounts in any other phase.

65

Geothermobarometry

For PT calculation of the HP-UHT granulite facies event, the combination of GASP-

barometer with reintegrated feldspar and two-feldspar thermometer results in a PT window of

11.2-17.5 kbar and 1005-1060 °C. Zirconium-in-rutile thermometry after Zack et al. (2004a)

reveals slightly higher temperatures of 1020-1095 °C. The calibration after Tomkins et al.

(2007) results in lower temperatures of 825-895 °C.

In mesocratic granulites, we assume that the outermost rim of garnet is in equilibrium with

the reactant products plagioclase, orthopyroxene, biotite and amphibole and can be therefore

used to constrain the PT conditions of the garnet breakdown. PT-conditions of 6.7-10.0 kbar

and 760-900°C could be calculated. Biotite-garnet thermometry is limited applicable in

granulite facies rocks due to retrogressive re-equilibration of iron-magnesium contents.

Nevertheless, high temperatures of garnet-biotite thermometry (Figure 22D) indicate a fast

decompression and cooling.

Thermodynamic modelling

Thermodynamic modelling from garnet isopleths (rim) of leucocratic granulites with

garnet type 1 resulted in a PT-window of 15.0-18.0 kbar and 1030-1130 °C. These values are

in slightly higher compared to geothermobarometry. The higher values might also be the

consequence of uncertainties due to extrapolated activity models such as the used melt model,

which might not be accurate at high pressures. Garnet isopleths (rim) with garnet type 2 from

sillimanite and biotite rich domains reveal a PT-window of 9.4-9.6 kbar and 870-880 °C and

underline outcomes of the conventional geothermobarometry. Thermodynamic modelling of

garnet isopleths (rim) of mesocratic granulites shows similar values with 7.1-8.5 kbar and

767-875 °C. Similar PT conditions have been suggested other authors as Cooke and O'Brien

(2001) and Krenn and Finger (2010).

Geochemistry of major and trace elements

The discrimination diagram of Werner (1987) as shown in Figure 19A clearly identifies the

protholites as magmatic. In the AFM Diagram (Figure 19B), a calc-alkaline trend can be

observed. Harker diagrams of major- and trace elements confirm magmatic origin of the

protolithes.

66

Geotectonical implications

Quantitative PT estimation and phase equilibrium modelling of the HP-UHT event

suggests a subduction to a depth of ca 55 km (Figure 30). Residence time at this PT

conditions had to be of short duration due to a non-re-equilibrated garnet core found in some

samples. Furthermore, reaction textures and strongly zoned plagioclase coronas around

kyanite and garnet indicating fast decompression following the metamorphic peak. A

retrogressive granulite facies overprint at ca. 30 km depth could be observed. Geodynamic

evolution of the pre-HP-UHT stage of Moldanubian granulites in Austria is still under

discussion. Findings of UHP phases like coesite and microdiamonds in felsic granulites of the

Kutná Hora Complex in the Czech Republic by Perraki and Faryad (2014) is evidence for

subduction of rocks to mantle depths. Besides these findings, eclogites and meta-peridotites

which can be found in all granulite bodies indirectly indicate such UHP conditions. Based on

the similar appearance of all granulites as well as similar mineral chemistry and garnet zoning

pattern, Perraki and Faryad (2014) proposes the subduction to mantle depths for the whole

Moldanubian granulites. Since the occurrence of ultrabasite, eclogite in the Gföhl Unit and

exsolved crystallographic rutile needles in garnet cores, indicate a pressure-dominated pre-

HT-UHP metamorphic event, it is suggested to support the argument of Perraki and Faryad

(2014), regarding a former UHP metamorphic event of the Moldanubian granulites.

67

Figure 30 Final interpretation of PT evolution of the Blumau granulite body. (1) Suggested pre-HP-UHT event of Perraki

& Faryad (2014) with material subduction to mantle depths. (2) HP-UHT event with suggested prograde evolution, due to

the lack of UHP phases. (3) Retrogressive MP-HT granulite facies overprint.

68

Conclusion

Based on petrological investigations conducted in the present study of leucocratic and

mesocratic rocks from the Blumau granulite body and comparison with the literature,

following conclusions can be summarized:

(1) Geochemistry of major and trace elements indicates magmatic origin and a

calc-alkaline trend of protholites.

(2) Crystallographic oriented rutile needles in garnet cores suggest a pressure

dominated pre-HP-UHT event. The high grossular content of garnets with zoning type

1 indicates an UHP event. However, due to chemical diffusion processes, garnet cores

are not applicable for PT estimation of the pre-HP-UHT event.

(3) Leucocratic granulites with garnet profile type 1 reveal a strongly decline of

the grossular content towards the rims, reflecting a HP-UHT metamorphic event with

conditions of ~16.5 kbar and 1060 °C.

(4) Residence time of rocks under HP-UHT conditions is assumed to be short due

to the fact that garnet cores would re-equilibrate to garnet rim composition. Reaction

textures like symplectitic orthopyroxene-plagioclase coronas and compositionally

zoned plagioclase coronas around garnet indicate fast decompression.

(5) In mesocratic as well as in leucocratic granulites with garnet profile type 2

reveal a retrogressive MP-HT granulite facies overprint at ~8 kbar and 800 °C.

(6) Findings of UHP phases in the Kutná Hora Complex, the presence of

ultrabasite, eclogite in the Gföhl Unit and exsolved rutile needles in garnet cores

support the argument of Perraki and Faryad (2014) for former UHP conditions of the

Moldanubian granulites.

69

References

Benisek A, Dachs E, Kroll H (2010) A ternary feldspar-mixing model based on calorimetric

data: Development and application. Contrib Mineral Petrol 160(3):327–337. doi:

10.1007/s00410-009-0480-8

Benisek A, Kroll H, Cemic L (2004) New developments in two-feldspar thermometry.

American Mineralogist(89):1496–1504

Berman RG (1991) Thermobarometry using multi-equilibrium calculation: A new technique,

with petrological application. Canadian Mineralogist(29):833–855

Capitani C de, Petrakakis K (2010) The computation of equilibrium assemblage diagrams

with Theriak/Domino software. American Mineralogist 95(7):1006–1016. doi:

10.2138/am.2010.3354

Carswell D (1991) Variscan high P-T metamorphism and uplift history in the Moldanubian

Zone of the Bohemian Massif in Lower Austria. ejm 3(2):323–342. doi:

10.1127/ejm/3/2/0323

Carswell DA, O'Brien PJ (1993) Thermobarometry and Geotectonic Significance of High-

Pressure Granulites: Examples from the Moldanubian Zone of the Bohemian Massif in

Lower Austria. Journal of Petrology 34(3):427–459

Coggon R, Holland TJB (2002) Mixing properties of phengitic micas and revised garnet-

phengite thermobarometers. J Metamorph Geol 20(7):683–696. doi: 10.1046/j.1525-

1314.2002.00395.x

Connolly J (2005) Computation of phase equilibria by linear programming: A tool for

geodynamic modeling and its application to subduction zone decarbonation. Earth and

Planetary Science Letters 236(1-2):524–541. doi: 10.1016/j.epsl.2005.04.033

Cooke R, O'Brien P (2001) Resolving the relationship between high P–T rocks and gneisses

in collisional terranes: An example from the Gföhl gneiss–granulite association in the

Moldanubian Zone, Austria. Lithos 58(1-2):33–54. doi: 10.1016/S0024-4937(01)00049-4

Cox KG, Bell JD, Pankhurst RJ (eds) (1979) The Interpretation of Igneous Rocks. Springer

Netherlands, Dordrecht

Dachs E (1998) PET: Petrological elementary tools for mathematica. Computers &

Geosciences 24(3):219–235. doi: 10.1016/S0098-3004(97)00141-6

Dale J, Holland T, Powell R (2000) Hornblende–garnet–plagioclase thermobarometry: A

natural assemblage calibration of the thermodynamics of hornblende. Contrib Mineral

Petrol 140(3):353–362. doi: 10.1007/s004100000187

70

Diener JFA, Powell R, White RW, Holland TJB (2007) A new thermodynamic model for

clino- and orthoamphiboles in the system Na2O-CaO-FeO-MgO-Al2O3-SiO2-H2O-O. J

Metamorph Geol 25(6):631–656. doi: 10.1111/j.1525-1314.2007.00720.x

Fiala, J, Matějovská O, Vaňkovă V (1987) Moldanubian granulites: source material and

petrogenetic considerations. Neues Jahrbuch für Mineralogie Abhandlungen 157:133–165

Finger F, Gerdes A, Janoušek V, René M, Riegler G (2007) Resolving the Variscan evolution

of the Moldanubian sector of the Bohemian Massif: The significance of the Bavarian and

the Moravo-Moldanubian tectonometamorphic phases. Jour. Geosci.:9–28. doi:

10.3190/jgeosci.005

Finger F, Roberts MP, Haunschmid B, Schermaier A, Steyrer HP (1997) Variscan granitoids

of central Europe: Their typology, potential sources and tectonothermal relations.

Mineralogy and Petrology 61(1-4):67–96. doi: 10.1007/BF01172478

Friedl G (1997) U-Pb Datierungen an Zirkonen und Monaziten aus Gesteinen vom

österreichischen Anteil der Böhmischen Masse. Unpublished Ph.D thesis, University of

Salzburg

Friedl G, Cooke RA, Finger F, McNaughton NJ, Fletcher IR (2011) Timing of Variscan HP-

HT metamorphism in the Moldanubian Zone of the Bohemian Massif: U-Pb SHRIMP

dating on multiply zoned zircons from a granulite from the Dunkelsteiner Wald Massif,

Lower Austria. Miner Petrol 102(1-4):63–75. doi: 10.1007/s00710-011-0162-x

Frost RB, Chacko T (1989) The Granulite Uncertainty Principle: Limitations on

Thermobarometry in Granulites. The Journal of Geology 97(4):435–450

Gebauer D, Friedl G (1994) A 1.38 Ga protolith age for the Dobra orthogneiss (Moldanubian

Zone of the Southern Bohemian Massif, NE-Austria): Evidence from ion-microprobe

(SHRIMP) dating of zircon. Journal of the Czech Geological Society(39/1)

Gerdes A, Friedl G, Parrish RR, Finger F (2003) High-resolution geochronology of Variscan

granite emplacement – the South Bohemian Batholith.

JournaloftheCzechGeologicalSociety4(48/1-2)

Green E, Holland T, Powell R (2007) An order-disorder model for omphacitic pyroxenes in

the system jadeite-diopside-hedenbergite-acmite, with applications to eclogitic rocks.

American Mineralogist 92(7):1181–1189. doi: 10.2138/am.2007.2401

Harley SL (1984) An experimental study of the partitioning of Fe and Mg between garnet and

orthopyroxene. Contr. Mineral. and Petrol. 86(4):359–373. doi: 10.1007/BF01187140

Harley SL (1989) The origins of granulites: A metamorphic perspective. Geol. Mag.

126(03):215. doi: 10.1017/S0016756800022330

71

Holdaway MJ (2000) Application of new experimental and garnet Margules data to the

garnet-biotite geothermometer. American Mineralogist 85(7-8):881–892. doi:

10.2138/am-2000-0701

Holland T, Blundy J (1994) Non-ideal interactions in calcic amphiboles and their bearing on

amphibole-plagioclase thermometry. Contr. Mineral. and Petrol. 116(4):433–447. doi:

10.1007/BF00310910

Holland TJB, Powell R (1998) An internally consistent thermodynamic data set for phases of

petrological interest. Journal of Metamorphic Geology 16(3):309–343. doi:

10.1111/j.1525-1314.1998.00140.x

Irvine TN, Baragar WRA (1971) A Guide to the Chemical Classification of the Common

Volcanic Rocks. Can. J. Earth Sci. 8(5):523–548. doi: 10.1139/e71-055

Janoušek V, Finger F, Roberts M, Frýda J, Pin C, Dolejš D (2004) Deciphering the

petrogenesis of deeply buried granites: whole-rock geochemical constraints on the origin

of largely undepleted felsic granulites from the Moldanubian Zone of the Bohemian

Massif. In: Special Paper 389: The Fifth Hutton Symposium on the Origin of Granites and

Related Rocks, vol 389. Geological Society of America, pp 141–159

Klötzli US (2001) Cadomian Lower-Crustal Contributions to Variscan Granite Petrogenesis

(South Bohemian Pluton, Austria): Constraints from Zircon Typology and

Geochronology, Whole-Rock, and Feldspar Pb-Sr Isotope Systematics. Journal of

Petrology 42(9):1621–1642. doi: 10.1093/petrology/42.9.1621

Krenn E, Finger F (2010) Unusually Y-rich monazite-(Ce) with 6–14 wt.% Y2O3 in a

granulite from the Bohemian Massif: Implications for high temperature monazite growth

from the monazite-xenotime miscibility gap thermometry. Mineral. Mag. 74(2):217–225.

doi: 10.1180/minmag.2010.074.2.217

Kröner A, O'Brien PJ, Nemchin AA, Pidgeon RT (2000) Zircon ages for high pressure

granulites from South Bohemia, Czech Republic, and their connection to Carboniferous

high temperature processes. Contributions to Mineralogy and Petrology 138(2):127–142.

doi: 10.1007/s004100050013

Kryza R, Pin C, Vielzeuf D (1996) High-pressure granulites from the Sudetes (south-west

Poland): Evidence of crustal subduction and collisional thickening in the Variscan Belt. J


Lange U, Brocker M, Armstrong R, Trapp E, Mezger K (2005) Sm-Nd and U-Pb dating of

high-pressure granulites from the Zlote and Rychleby Mts (Bohemian Massif, Poland and

Czech Republic). J Metamorph Geol 23(3):133–145

72

Leake BE, Woolley AR, Birch WD (2004) Nomenclature of amphiboles: Additions and

revisions to the International Mineralogical Associationʼs amphibole nomenclature.

American Mineralogist 89:883–887

Matte P, Maluski H, Rajlich P, Franke W (1990) Terrane boundaries in the Bohemian Massif:

Result of large-scale Variscan shearing. Tectonophysics 177(1-3):151–170. doi:

10.1016/0040-1951(90)90279-H

Morimoto N (1988) Nomenclature of Pyroxenes. Mineralogy and Petrology 39(1):55–76. doi:

10.1007/BF01226262

Newton RC, Perkins D (1982) Thermodynamic calibration of geobarometers based on the

assemblages garnet-plagioclase-orthopyroxene (clinopyroxene)-quar. American

Mineralogist(67):203–2022

O’Brien PJ (2000) The fundamental Variscan problem: High-temperature metamorphism at

different depths and high-pressure metamorphism at different temperatures. Geological

Society, London, Special Publications 179(1):369–386. doi:

10.1144/GSL.SP.2000.179.01.22

O'Brien PJ (2008) Challenges in high-pressure granulite metamorphism in the era of

pseudosections: Reaction textures, compositional zoning and tectonic interpretation with

examples from the Bohemian Massif. J Metamorph Geol 26(2):235–251. doi:

10.1111/j.1525-1314.2007.00758.x

O'Brien PJ, Rotzler J (2003) High-pressure granulites: Formation, recovery of peak conditions

and implications for tectonics. J Metamorph Geol 21(1):3–20. doi: 10.1046/j.1525-

1314.2003.00420.x

Perraki M, Faryad SW (2014) First finding of microdiamond, coesite and other UHP phases

in felsic granulites in the Moldanubian Zone: Implications for deep subduction and a

revised geodynamic model for Variscan Orogeny in the Bohemian Massif. Lithos 202-

203:157–166. doi: 10.1016/j.lithos.2014.05.025

Petrakakis K (1986a) Metamorphism of high-grade gneisses from the Moldanubian zone,

Austria, with particular reference to the garnets. J Metamorph Geol 4:323–344

Petrakakis K (1986b) Metamorphism of high-grade gneisses from the Moldanubian zone,

Austria, with particular reference to the garnets. J Metamorph Geol 4(3):323–344. doi:

10.1111/j.1525-1314.1986.tb00354.x

Petrakakis K (1997) Evolution of Moldanubian rocks in Austria: Review and synthesis. J


73

Powell R, Holland T (1999) Relating formulations of the thermodynamics of mineral solid

solutions; activity modeling of pyroxenes, amphiboles, and micas. American Mineralogist

84(1-2):1–14. doi: 10.2138/am-1999-1-201

Raase P (1998) Feldspar thermometry: A valuable tool for deciphering the thermal history of

granulite-facies rocks, as illustrated with metapelites from Sri Lanka. Canadian

Mineralogist 36:67–86

Schnabel W, Fuchs G (eds) (2002) Geologische Karte von Niederösterreich. Geologische

Karte 1. Geologische Bundesanstalt, Wien

Schnabel W, Fuchs G, Matura A, roetzel R, Scharbert S, Krenmayr H, Egger H, Bryda G,

Mandl G, Nowotny A, Wessely G Geologische Karte von Niederösterreich 1:200 000.

Geologische Bundesanstalt, Wien

Schulmann K (2005) Chronological constraints on the pre-orogenic history, burial and

exhumation of deep-seated rocks along the eastern margin of the Variscan Orogen,

Bohemian Massif, Czech Republic. American Journal of Science 305(5):407–448. doi:

10.2475/ajs.305.5.407

Schulmann K, Konopásek J, Janoušek V, Lexa O, Lardeaux J, Edel J, Štípská P, Ulrich S

(2009) An Andean type Palaeozoic convergence in the Bohemian Massif. Comptes

Rendus Geoscience 341(2-3):266–286. doi: 10.1016/j.crte.2008.12.006

Štípská P, Powell R, White RW, Baldwin JA (2010) Using calculated chemical potential

relationships to account for coronas around kyanite: An example from the Bohemian

Massif. Journal of Metamorphic Geology 28(1):97–116. doi: 10.1111/j.1525-

1314.2009.00857.x

Stüwe K (1997) Effective bulk composition changes due to cooling: A model predicting

complexities in retrograde reaction textures. Contributions to Mineralogy and Petrology

129(1):43–52. doi: 10.1007/s004100050322

Tajčmanová L, Connolly JAD, Cesare B (2009) A thermodynamic model for titanium and

ferric iron solution in biotite. Journal of Metamorphic Geology 27(2):153–165. doi:

10.1111/j.1525-1314.2009.00812.x

Tajčmanová L, Konopásek J, Connolly JAD (2006) Diffusion-controlled development of

silica-undersaturated domains in felsic granulites of the Bohemian Massif (Variscan belt

of Central Europe). Contrib Mineral Petrol 153(2):237–250. doi: 10.1007/s00410-006-

0143-y

Tomkins HS, Powell R, Ellis DJ (2007) The pressure dependence of the zirconium-in-rutile

thermometer. J Metamorph Geol 25(6):703–713. doi: 10.1111/j.1525-1314.2007.00724.x

74

Villaseca C, Barbero L, Herreros V (1998) A re-examination of the typology of peraluminous

granite types in intracontinental orogenic belts. Transactions of the Royal Society of

Edinburgh: Earth Sciences 89(02):113–119. doi: 10.1017/S0263593300007045

Vrána S, Janoušek V, Franěk J (2013) Contrasting mafic to felsic HP-HT granulites of the

Blanský les Massif (Moldanubian Zone of southern Bohemia): Complexity of mineral

assemblages and metamorphic reactions. Jour. Geosci.:347–378. doi: 10.3190/jgeosci.157

Werner C (1987) Saxonian Granulites – Igneous or Lithogenous. A contribution to the

geochemical diagnosis of the original rocks in high-metamorphic complexes.

ZfIMittelungen 133:221–250

White RW, Powell R, Holland TJB (2007) Progress relating to calculation of partial melting

equilibria for metapelites. J Metamorph Geol 25(5):511–527. doi: 10.1111/j.1525-

1314.2007.00711.x

Whitney DL, Evans BW (2010) Abbreviations for names of rock-forming minerals. American

Mineralogist 95(1):185–187. doi: 10.2138/am.2010.3371

Zack T, Moraes R, Kronz A (2004a) Temperature dependence of Zr in rutile: Empirical

calibration of a rutile thermometer. Contrib Mineral Petrol 148(4):471–488. doi:

10.1007/s00410-004-0617-8

Zeitlhofer H, Schneider D, Grasemann B, Petrakakis K, Thöni M (2014) Polyphase tectonics

and late Variscan extension in Austria (Moldanubian Zone, Strudengau area). Int J Earth

Sci (Geol Rundsch) 103(1):83–102. doi: 10.1007/s00531-013-0952-y

Zhang RY, Zhai SM, Fei YW, Liou JG (2003) Titanium solubility in coexisting garnet and

clinopyroxene at very high pressure: The significance of exsolved rutile in garnet. Earth

and Planetary Science Letters 216(4):591–601. doi: 10.1016/S0012-821X(03)00551-X

75

Digital Appendix

Petrological investigation of UHT-rocks from the Blumau ...

Documents

Transcript of Petrological investigation of UHT-rocks from the Blumau ...