www.elsevier.com/locate/lithos

Lithos 70 (2003) 141–161

Conditions and timing of high-pressure Variscan metamorphism in

the South Carpathians, Romania

Gordon Medaris Jr.a,*, Mihai Duceab, Ed Ghentc, Viorica Iancud

aDepartment of Geology and Geophysics, University of Wisconsin-Madison, Madison, WI 53706, USAbDepartment of Geosciences, University of Arizona, Tucson, AZ 85719, USA

cDepartment of Geology and Geophysics, University of Calgary, Calgary, Alberta, Canada T2N 1N4dGeological Institute of Romania, RO-78344 Bucharest 32, Romania

Abstract

High-pressure (HP) metamorphic rocks, including garnet peridotite, eclogite, HP granulite, and HP amphibolite, are

important constituents of several tectonostratigraphic units in the pre-Alpine nappe stack of the Getic–Supragetic (GS)

basement in the South Carpathians. AVariscan age for HP metamorphism is firmly established by Sm–Nd mineral–whole-rock

isochrons for garnet amphibolite, 358F 10 Ma, two samples of eclogite, 341F 8 and 344F 7 Ma, and garnet peridotite,

316F 4 Ma.

A prograde history for many HP metamorphic rocks is documented by the presence of lower pressure mineral inclusions

and compositional zoning in garnet. Application of commonly accepted thermobarometers to eclogite (grt + cpxF kyFphnF pgF zo) yields a range in ‘‘peak’’ pressures and temperatures of 10.8–22.3 kbar and 545–745 jC, depending on

tectonostratigraphic unit and locality. Zoisite equilibria indicate that activity of H2O in some samples was substantially

reduced, ca. 0.1–0.4. HP granulite (grt + cpx + hb + pl) and HP amphibolite (grt + hbl + pl) may have formed by retrogression

of eclogites during high-temperature decompression. Two types of garnet peridotite have been recognized, one forming from

spinel peridotite at ca. 1150–1300 jC, 25.8–29.0 kbar, and another from plagioclase peridotite at 560 jC, 16.1 kbar.

The Variscan evolution of the pre-Mesozoic basement in the South Carpathians is similar to that in other segments of the

European Variscides, including widespread HP metamorphism, in which P–T– t characteristics are specific to individual

tectonostratigraphic units, the presence of diverse types of garnet peridotite, diachronous subduction and accretion, nappe

assembly in pre-Westphalian time due to collision of Laurussia, Gondwana, and amalgamated terranes, and finally, rapid

exhumation, cooling, and deposition of eroded debris in Westphalian to Permian sedimentary basins.

D 2003 Elsevier B.V. All rights reserved.

Keywords: Eclogite; Garnet peridotite; Sm–Nd geochronology; Variscan; South Carpathians

1. Introduction

Eclogite facies metamorphism is a well-docu-

mented feature of European Variscan massifs and

0024-4937/$ - see front matter D 2003 Elsevier B.V. All rights reserved.

doi:10.1016/S0024-4937(03)00096-3

* Corresponding author.

E-mail address: medaris@geology.wisc.edu (G. Medaris).

Variscan basement incorporated in the Alpine belt,

providing evidence for the important role played by

subduction and continental collision in development

of the Variscan orogen (O’Brien et al., 1990). In

Romania, eclogite occurs in the pre-Alpine nappe

stack of the Getic–Supragetic basement in the South

Carpathians, where it was first recognized by Mrazec

G. Medaris Jr. et al. / Lithos 70 (2003) 141–161142

(1897) and subsequently described on a regional basis

by Iancu et al. (1988). Geological mapping at a scale

of 1:50,000 and accompanying petrological investiga-

tions have established the details of eclogite occur-

rence in several topographic subdivisions of the South

Carpathians, including the Fagaras-Leaota Mountains

(Gherasi et al., 1971; Dimitrescu and Murariu, 1984;

Balaban, 1986; Gheuca and Dinica, 1986; Kasper,

1993; Sabau et al., 1986; Maruntiu et al., 1997), the

Mehedinti-Capatana Mountains (Hann, 1983; Iancu et

al., 1987; Iancu, 1995), the Sebes-Cindrel Mountains

(Maruntiu, 1988), and the Lotru Mountains (Iancu and

Maruntiu, 1994).

Geological relations constrain high-pressure (HP)

metamorphism in the South Carpathian basement

units to be pre-Westphalian in age. Hornblende and

muscovite 40Ar/39Ar cooling ages between ca. 320

and 295 Ma for basement units (Dallmeyer et al.,

1998) indicate that high-pressure metamorphism was

pre-Alpine and most likely Variscan, although the

time of HP metamorphism has not yet been deter-

mined precisely. Despite several recent petrological

investigations (Maruntiu et al., 1997; Iancu et al.,

1998; Sabau, 2000), data on high-pressure metamor-

phism in the South Carpathians remain relatively

sparse, compared to that in central Europe.

The present investigation was undertaken to estab-

lish the conditions and age(s) of high-pressure meta-

morphism in the various eclogite-bearing basement

units in the South Carpathians. Such information is

essential for deciphering the pre-Alpine evolution of

the South Carpathians and for documenting the extent

of the Variscan orogen in southeastern Europe.

2. Regional geology

The Carpathian Mountains constitute a convex-

eastward loop of the Alpine belt, extending from the

Austrian Alps through Slovakia, Hungary, and

Romania, and rejoining the Dinaric Alps in Serbia.

The Carpathians are characterized by thrust and

nappe tectonics of Alpine age, with vergence in the

South Carpathians being to the south and east. Three

main structural units have been recognized in the

South Carpathians: a lower Danubian nappe system,

consisting of Proterozoic metamorphic rocks and

low-grade Paleozoic sedimentary formations, over-

lain in turn by Westphalian to Permian and Mesozoic

sedimentary rocks; a middle Severin–Arjana nappe

system, composed of Jurassic ophiolite, flysch, and

bimodal alkaline igneous rocks; and an upper Getic–

Supragetic nappe system, containing several pre-

Alpine basement gneissic units which are overlain

by Late Carboniferous to Permian sedimentary rocks

and a transgressive Mesozoic cover. The Supragetic

unit was thrust over the Getic unit in Lower Creta-

ceous (pre-Vraconian) time; the Getic–Supragetic

nappe system was thrust over the Severin nappe in

post-Aptian to Turonian time, and the amalgamated

Getic–Supragetic/Severin system was thrust over the

Danubian unit in Upper Cretaceous (Senonian) time

(Balintoni et al., 1986; Codarcea, 1940; Iancu, 1986;

Sandulescu, 1984). Miocene thrusts juxtapose the

South Carpathian nappe system against the Moesian

platform on the east, while westward thrust faults of

the orogen are covered by Neogene sediments of the

Pannonian basin.

Eclogite, garnet peridotite, HP granulite, and HP

amphibolite in the South Carpathians occur in the

pre-Alpine Getic–Supragetic (GS) basement and in a

tectonic melange, the Bughea complex, at the eastern

end of the range, as shown in the simplified geo-

logical map of Fig. 1 (modified from Iancu et al., in

press). Among the many tectonostratigraphic units in

the GS basement, high-pressure rocks are restricted

to the Sebes, Lotru, and Cumpana terranes (listed in

descending structural position). The reader is re-

ferred to Iancu et al. (1998) for a complete descrip-

tion of pre-Alpine basement units in the South

Carpathians and a discussion of stratigraphic and

structural relations.

The Sebes unit has been divided on the basis of

lithology into three subunits, these being 3, 2, and 1 in

descending structural sequence. Sebes 3 is composed

of a monotonous sequence of aluminous schist and

paragneiss, with a few distinctive manganese-rich

horizons marked by tephroite- and spessartine-bearing

paragneiss. Sebes 2 is characterized by a bimodal

suite of quartzofeldspathic gneiss and amphibolite that

closely resembles the classic leptynite–amphibolite

association in the Massif Central and Bohemian

Massif (Matte, 1986; Franke, 1989). Sebes 1 consists

predominantly of terrigenous metasedimentary rocks,

including mica gneiss, quartzofeldspathic gneiss, and

subordinate quartzite, marble, and amphibolite.

Fig. 1. Simplified geological map of the South Carpathians, emphasizing tectonostratigraphic units in the pre-Alpine Getic–Supragetic basement (Sebes, Lotru, and Cumpana), where

most high-pressure metamorphic rocks are located. Sample designations: S1, S2, S3, Sebes 1, 2, and 3, respectively; L, Lotru; C, Cumpana; B, Bughea complex.

G.Medaris

Jr.et

al./Lith

os70(2003)141–161

143

G. Medaris Jr. et al. / Lithos 70 (2003) 141–161144

The Lotru unit is a volcano-sedimentary terrane

with oceanic affinities, consisting largely of amphib-

olite and biotite–plagioclase gneiss. Scattered through

the Lotru unit are dismembered layered metabasic–

ultrabasic complexes, derived from lherzolite, dunite,

plagioclase wehrlite, and gabbro.

Augen orthogneiss is predominant in the Cumpana

unit, but subordinate mica schist, biotite paragneiss,

and quartzofeldspathic gneiss also occur. Locally,

layered metagabbro complexes and felsic gneiss–

amphibolite (leptynite–amphibolite) associations are

important.

The Bughea complex is a tectonic melange located

between a lower, polymetamorphic basement of Cum-

pana type (Voinesti Formation) and an overlying

sequence of low-grade Paleozoic metabasic com-

plexes (Calusu and Leresti Formations). Within the

melange, boudins of eclogite, coronitic metagranite,

and garnet amphibolite are enclosed by a mylonitic

matrix composed of various types of amphibolite,

mica schist, and garnet gneiss, which equilibrated

under conditions of the epidote amphibolite facies.

Protolith ages of the gneiss units and associated HP

rocks in the Getic–Supragetic basement are unknown,

although Paleozoic and Proterozoic ages are presumed

on the basis of regional geological relations and a few

isotopic determinations (Pavelescu et al., 1983; Dra-

gusanu and Tanaka, 1999).

3. South Carpathian high-pressure rocks

As elsewhere in the European Variscides, eclogite,

garnet peridotite, HP granulite, and HP amphibolite in

the South Carpathians occur as meter- to decameter-

sized boudins and larger dismembered bodies, sur-

rounded by various types of gneissic rocks. Eclogite is

the medium-temperature type (Carswell, 1990) and

commonly contains evidence of a prograde history,

such as local preservation of preexisting igneous

textures, inclusions of pre-eclogite stage minerals in

garnet, and prograde compositional zoning in garnet.

Retrograde effects are pervasive, including decompo-

sition of omphacite to symplectite, development of

kelyphite and coronas around garnet and kyanite, and

extensive recrystallization to amphibolite.

The emphasis of the present study is to determine

the conditions and timing of high-pressure metamor-

phism in the South Carpathians, and toward this end,

26 samples have been investigated. Their most impor-

tant characteristics are summarized in Table 1, and

representative textures and mineralogical features are

illustrated on a microscopic scale in Figs. 2 and 3. A

detailed evaluation of pre- and post-eclogite stage

mineral reactions, although a worthy subject, is beyond

the scope of the present reconnaissance investigation.

Eclogite varies in outcrop from massive to layered

and texturally from isotropic (L3, Fig. 3) to foliated

(S1-1, Fig. 2) and lineated. Eclogite samples from the

Danis and Bughita localities in the Bughea complex

are notable for having high-pressure phases (ompha-

cite, phengite, kyanite, zoisite) oriented along an S–C

type, mylonitic foliation. Garnet, omphacite, and rutile

are essential minerals in eclogite, but additional

phases, such as quartz, kyanite, zoisite, phengite, or

paragonite are stable in some samples (Table 1, Figs. 2

and 3), depending largely on rock chemical composi-

tion and equilibration conditions. Pre-eclogite stage

minerals, including plagioclase, amphibole, epidote or

zoisite, and low-Na clinopyroxene, occur as inclusions

in garnet in many eclogites (Table 1). Eclogite is

relatively abundant in the Sebes 1, Lotru, Cumpana,

and Bughea units, but is rare in Sebes 2 and 3, where

high-pressure granulite and amphibolite, perhaps rep-

resenting overprinted eclogite, are found instead. In

this respect, the Sebes 2 and 3 units resemble the Gfohl

nappe in the Bohemian Massif, in which eclogite is

rarely preserved, having been extensively recrystal-

lized to granulite and amphibolite during a later high-

temperature overprint (Medaris et al., 1998).

The single sample of garnet granulite analyzed in

this study is located in the Sebes Valley in the Sebes 2

unit. Although the granulite yields a relatively high

pressure of 11.7 kbar, the presence of plagioclase

(Ab78-83) coronas around garnet and intergrowths

of Na-poor clinopyroxene, amphibole, and plagioclase

(Ab75-81), which resemble coarse-grained symplec-

tite (S2-1, Fig. 2), suggest that the granulite has

recrystallized from a higher pressure precursor that

contained sodic pyroxene.

Garnet amphibolite (C3, Fig. 2) is commonly

associated with eclogite, and textural and field rela-

tions indicate that some amphibolites formed by

retrograde recrystallization of preexisting eclogites.

However, other amphibolite samples, some of which

contain rutile, are devoid of textures indicating a prior

Table 1

Analyzed South Carpathian high-pressure rocks: summary of characteristics

Unit and locality Sample Lithology HP assemblage Garnet zoning (core to rim) Inclusions in garneta

Sebes 3

Foltea S3-1 grt peridotite ol–opx–cpx–grt slight retrograde spl, phl

Foltea S3-2 grt peridotite ol–opx–cpx–grt slight retrograde spl

Sebes 2

Sebes Valley S2-1 grt granulite grt –cpx–am–pl–q– ttn–op slight #sps zgrs pl, am, ttn, q

Sebes Valley S2-2 grt amphibolite grt –am–pl–ep–q–op– ttn slightzprp #grs pl, am, ep, q

Sebes 1

Mehedinti S1-1 ky eclogite grt –omp–ky– rt –op slightzprp #grs am, zo, kyb, omp

Mehedinti S1-2 ky–phn eclogite grt –omp–ky–phn–rt –op negligible zo, kyb, omp

Mehedinti S1-3 zo–ky eclogite grt – sympl–ky–zo–q– rt –op slight #alm, prpzgrs pl, am, zo, omp, q

Capatana S1-4 zo eclogite grt –omp–zo–q–rt –op irregular in alm, grs omp, rt, q

Capatana S1-5 zo eclogite grt –omp–zo–q–rt –op irregular in alm, grs omp, rt, q

Capatana S1-6 czo eclogite grt –omp–czo–q– rt–op irregular in alm, grs omp, rt, czo, q

Lotru

Paltinis L1 eclogite grt –omp–rt– ilm slightzgrs pl, am, ep, cpx

Paltinis L2 eclogite grt –omp–rt– ilm negligible am, cpx

Paltinis L3 eclogite grt –omp–rt– ilm slightzgrs am, cpx, rt, ilm

Paltinis L4 grt amphibolite grt –am–pl– rt –op negligible zo, am

Paltinis L5 grt peridotite ol–opx–grt intergrain variation spl, crn

Deluselu V. L7 eclogite grt –omp–rt–op slight intergrain var. omp, rt

Deluselu V. L8 czo eclogite grt –omp–czo–rt –op irregular zo, am, omp, rt

Cumpana

Topolog C1 ky eclogite grt –omp–ky–q– rt negligible am, kyb, omp, q

Topolog C2 zo eclogite grt –omp–zo–q–rt – ilm sector omp, rt, q

Cugir Valley C3 bt grt amphibolite grt –am–pl–bt–q–rt – ilm negligible chl, am, rt, q

Bughea

Danis B1 zo–phn eclogite grt –omp–zo–phn–q– rt prograde am, pg, zo, omp, phn

Bughita B2 ky–phn–pg eclogite grt –omp–ky–phn–pg–q– rt prograde am, phn, rt, q

Bughita B3 ky–phn–pg eclogite grt –omp–ky–phn–pg–q– rt prograde am, kyb, omp, rt, q

Bughita B4 metagranite

Bughita B5 metagranite

Tirgului B6 zo–phn eclogite grt –omp–zo–phn–q– rt sector am, rt, q

Abbreviations: alm, almandine; am, amphibole; bt, biotite; cpx, low-Na clinopyroxene; crn, corundum; ep, epidote; grs, grossular; grt, garnet;

ilm, ilmenite; ky, kyanite; omp, omphacite; op, opaque mineral; pg, paragonite; phl, phlogopite; phn, phengite; pl, plagioclase; prp, pyrope; q,

quartz; rt, rutile; spl, spinel; sps, spessartine; sympl, symplectite after omphacite; ttn, titanite; zo, zoisite. z, increase; #, decrease.a Pre-HP stage inclusions in garnet designated by italics.b Abundant fine needles of kyanite in garnet.

G. Medaris Jr. et al. / Lithos 70 (2003) 141–161 145

eclogite stage and may represent metabasic rocks that

recrystallized at relatively high pressures, but less than

those of eclogite facies conditions.

Two different types of garnet peridotite are present

in the South Carpathians, one at Foltea Peak in the

Sebes 3 unit and another at Paltinis in the Lotru unit.

The Foltea garnet peridotite is a large, lens-like body

f 250 m in length, surrounded by garnet–kyanite

mica schist and plagioclase-rich paragneiss. Coarse-

grained garnet porphyroblasts, which are typically

surrounded by pyroxene–spinel kelyphite, are set in

a granoblastic matrix consisting of olivine, orthopyr-

oxene, and clinopyroxene (S3-1, Fig. 2). Although Al-

rich spinel inclusions in garnet have been reported

(Maruntiu, 1988), they were not observed in the

samples examined here. The petrological and miner-

Fig. 2. Photomicrographs (plane polarized light) of representative high-pressure rocks from the Sebes and Cumpana units. S3-1, garnet

peridotite, Foltea, Sebes 1: garnet (g) porphyroblast with clinopyroxene (cpx) and olivine (ol) inclusions, surrounded by pyroxene–spinel

kelyphite (k), in a matrix of olivine, orthopyroxene, and clinopyroxene. S2-1, garnet granulite, Sebes Valley, Sebes 2: note plagioclase (pl)

corona around garnet (g), intergrowth of clinopyroxene (cpx), amphibole (a), and plagioclase with a texture resembling coarse symplectite, and

the presence of titanite (t). S1-1, kyanite eclogite, Mehedinti, Sebes 1: coarse-grained garnet (g) containing abundant tiny kyanite inclusions (ki),

in a foliated matrix of omphacite (o) and kyanite (ky). C3, biotite garnet amphibolite, Cugir Valley, Cumpana: coarse-grained garnet (g)

associated with amphibole (a), plagioclase (pl), rutile (r), and ilmenite (i).

G. Medaris Jr. et al. / Lithos 70 (2003) 141–161146

alogical features of the Foltea garnet peridotite are

identical to those of high-temperature Mg–Cr garnet

peridotites in Eurasian HP/UHP terranes elsewhere

(Medaris, 1999). In contrast, garnet peridotite at

Paltinis has formed from plagioclase peridotite that

constitutes part of a layered metabasic–ultrabasic

igneous complex (Maruntiu et al., 1998). Concomitant

with transformation of gabbro to eclogite was the

growth in peridotite of thin garnet and orthopyroxene

reaction rims at the contacts between olivine and

preexisting plagioclase (L5, Fig. 3), clearly establish-

ing an early, low-pressure stage in the P–T– t evolu-

tion of this particular garnet peridotite. Lenses of

peridotite, which are scattered through the Sebes 1

unit, are also thought to have contained garnet, based

on the presence of amphibole or chlorite pseudo-

morphs, but these peridotites are so extensively retro-

graded that they have not been investigated here.

Decameter-sized boudins of massive metagranite

(sensu lato) occur in the Bughea complex, and the

Fig. 3. Photomicrographs (plane polarized light) of representative high-pressure rocks from the Lotru unit and Bughea complex. L3, eclogite,

Paltinis, Lotru: peak assemblage of garnet (g), omphacite (o), and rutile (r), with retrograde amphibole (a) and clinopyroxene–plagioclase

symplectite (s) after omphacite. L5, garnet peridotite, Paltinis, Lotru: orthopyroxene (opx) and garnet (g) reaction products at the boundary of

olivine (ol), partly serpentinized (srp), and former plagioclase, now consisting of amphibole, zoisite, and chlorite (a + z + chl); orthopyroxene

and garnet are separated by an intergrowth of amphibole and spinel (a + spl). B6, zoisite–phengite eclogite, Tirgului, Bughea complex: fine-

grained assemblage of garnet (g), omphacite (o), zoisite (z), phengite (phn), and sodic–calcic amphibole (a). B4, metagranite, Bughita, Bughea

complex: garnet (g) growth at the boundary of relict biotite (b) and opaques with former feldspar (f), now replaced by extremely fine-grained

zoisite and kyanite; note phengite (phn) grains within biotite.

G. Medaris Jr. et al. / Lithos 70 (2003) 141–161 147

analyzed samples were collected from the Bughita

Albestilor Valley. Although the igneous texture of the

metagranite is preserved on a hand specimen scale,

microscopic examination reveals the growth of garnet

at the boundaries of relict igneous biotite and opaques,

the presence of phengite in biotite, and the replace-

ment of feldspar by extremely fine-grained zoisite and

kyanite (B4, Fig. 3).

4. Rock chemistry

4.1. Major elements

Major element compositions for 30 samples of

peridotite, eclogite, granulite, amphibolite, and meta-

granite were determined by standard X-ray fluores-

cence techniques at the XRAL Laboratory, Ontario

Fig. 4. Selected Harker diagrams for South Carpathian high-

pressure metamorphic basic and intermediate rocks, illustrating

some of their important geochemical characteristics (peridotite and

metagranite are not included because of scale considerations). All

data are plotted on an anhydrous basis, normalized to 100%;

symbols as in Fig. 5. Alkaline and subalkaline fields from Irvine and

Baragar (1971); tholeiitic and calc-alkaline fields from Miyashiro

(1975); basic and intermediate fields by convention.

G. Medaris Jr. et al. / Lithos 70 (2003) 141–161148

(complete analyses are available from the first author

upon request). The analyzed samples were collected

from different tectonostratigraphic units at widely

separated localities and clearly are not comagmatic,

so a rigorous evaluation of petrogenetic processes is

precluded. Although general geochemical affinities

can be inferred, they may not necessarily represent

protolith affinities, because of the possibility of major

element modification, especially of Na2O and K2O,

during metamorphism.

Samples of eclogite, granulite, and amphibolite are

all subalkaline, except for two phengite-bearing sam-

ples from the Bughea complex and one from the Sebes

1 (Capatana) unit (Fig. 4A). Seven samples of basic

rocks are ne-normative (Sebes 1, Capatana; Lotru,

Deluselu; Cumpana, Topolog; Bughea, Bughita); all

four intermediate rocks and one basic rock (granulite

from the Sebes Valley, Sebes 2) are q-normative, and

the remainder of the basic rocks are olivine tholeiites

(Fig. 4A). With respect to tholeiitic and calc-alkaline

assignment (Figs. 4B and 5), samples from the Sebes 1

unit (Mehedinti) and Cumpana unit (Topolog) are calc-

alkaline, samples from the Bughea complex range

from tholeiitic to calc-alkaline, and the remainder are

tholeiitic (recognizing the slight difference in the field

boundaries defined by Miyashiro, 1975, Fig. 4B and

Irvine and Baragar, 1971, Fig. 5). The calc-alkaline

samples also tend to have lower TiO2 contents than do

the tholeiitic ones (Fig. 4C). Eclogites from the Paltinis

body and the Deluselu Valley in the Lotru unit have the

lowest SiO2 contents among the analyzed samples and

exhibit the strongest tholeiitic trend (Figs. 4 and 5).

The effect of rock chemistry on eclogite mineral

assemblage is best illustrated in a plot of wt.% CaO

vs. molar MgO/(MgO+FeO) (Fig. 6). In these terms,

18 samples fall into three distinct fields for eclogite,

zoisite eclogite, and kyanite eclogite, the single ex-

ception being sample S1-3 (Sebes 1, Mehedinti),

which contains stable zoisite and kyanite.

Chemical differences between the Foltea (Sebes 1)

and Paltinis (Lotru) garnet peridotites (Fig. 5) are

consistent with their petrological differences. Mg-

and Cr-numbers of 87.6–87.8 and 5.7–5.9 for the

Foltea peridotite are typical for Mg–Cr garnet peri-

dotites in Eurasian HP/UHP terranes, and lower Mg-

and Cr-numbers of 80.0–80.6 and 3.9–4.0 for the

Paltinis peridotite reflect its origin as part of a layered

mafic–ultramafic complex.

The two metagranites, samples B4 and B5 from

the Bughea complex, are peraluminous adamellites,

containing 4.7% and 8.6% normative c, and norma-

Fig. 5. AFM diagram for South Carpathian high-pressure rocks. All

Fe is taken as FeO; tholeiitic and calc-alkaline fields from Irvine and

Baragar (1971).

Fig. 6. Correlation of eclogite mineral assemblage and major

element chemical composition, in terms of wt.% CaO and molar

MgO/(MgO+FeO). Sample S1-3 is a zoisite–kyanite eclogite.

Duplicate sample numbers in upright and italicized type indicate

analyses of samples from the same outcrop.

G. Medaris Jr. et al. / Lithos 70 (2003) 141–161 149

tive q:or:(ab + an) proportions of 44:22:34 and

32:44:24.

4.2. Nd isotopes and geochronology

4.2.1. Methods

Four high-pressure rocks from the South Carpathi-

ans, including two eclogites, one garnet amphibolite,

and one garnet peridotite, were analyzed for Sm–Nd

mineral–whole-rock geochronology. Fresh whole-

rock samples (typically 100–500 g) were crushed in

a jaw crusher to about 1/3 of their average grain size.

Sample segments with visible alteration products were

discarded. The samples were then homogenized and

split, roughly two-thirds for mineral separation, and a

third for whole-rock analysis. Both splits were initially

washed in deionized water and then acid leached for

25–30 min in warm 1 N distilled HCl, while in an

ultrasonic bath. The whole-rock samples were then

ground to a fine powder using a shatterbox prior to

their dissolution. The split for mineral analyses

remained relatively coarse throughout the separation

procedure, although for some samples rich in compos-

ite grains, a few additional grinding steps were neces-

sary. Separation of minerals was accomplished by a

Franz magnetic separator and handpicking in alcohol

under a binocular microscope. The mineral separation

procedure resulted in two fractions for each mineral:

(1) ultrapure mineral separates, containing translucent

grains with no stains or visible inclusions and (2) lower

purity separates, which contained occasional kely-

phitic rims or common inclusions of other minerals.

The second fraction was not used further in analyses.

To eliminate any grain-boundary alteration effects, the

handpicked mineral separates were leached again in

2.5 N distilled HCl. The samples were then ultrason-

ically cleaned, rinsed multiple times with ultrapure

water and dried in methanol.

The samples were spiked with mixed 147Sm–150Nd

tracers. Dissolution of the spiked samples for isotopic

analyses was performed in screw-cap Teflon beakers

using HF–HNO3 (on hot plates) and HF–HClO3

mixtures (in open beakers at room temperature). A

few garnet separates were subjected to several, up to

three dissolution steps, before becoming residue-free.

The samples were taken in 1 N HCl and any undis-

solved residue was attacked in the same way. Separa-

tion of the bulk of the REE was achieved via HCl

elution in cation columns. Separation of Sm and Nd

was carried out using an LNSpecR resin. The highest

procedural blanks measured during the course of this

study were: 5 pg Sm and 18 pg Nd.

Isotopic analyses for Nd, as well as isotope dilution

analyses of Sm, and Nd were performed at the

University of Arizona using a VG 354 multiple col-

Table 2

Sm–Nd concentrations, 143Nd/144Nd isotope compositions, and Sm–Nd ages for South Carpathian high-pressure rocks

Sample Lithology Sm Nd 147Sm/144Nd 143Nd/144Nd Age (Ma) MSWD eNd (340)

S3-2 grt peridotite grt 0.405 0.330 0.7428 0.514261 (28) 7.98

cpx 1.169 3.581 0.1973 0.513133 (15) 9.63

wr 0.284 0.773 0.2217 0.513189 (23) 315.5F 4.2 0.640 9.66

L1 eclogite grt 0.479 0.721 0.4022 0.513438 (18) 6.69

wr 0.842 2.636 0.2161 0.513022 (24) 341.4F 8.2 6.65

L3 eclogite grt 0.314 0.422 0.4506 0.513533 (16) 6.45

cpx 0.649 1.458 0.2689 0.513122 (32) 6.31

am 0.520 1.033 0.3044 0.513201 (12) 6.31

wr 0.892 2.312 0.2333 0.513044 (09) 343.6F 6.6 0.324 6.33

C3 bt grt amphibolite grt 1.769 4.197 0.2548 0.512477 (14) � 5.66

wr 2.940 12.065 0.1473 0.512225 (15) 358F 10 � 5.91

Standard errors (in parentheses) for 143Nd/144Nd are 2r from internal statistics; Ludwig (1991) ISOPLOT.

G. Medaris Jr. et al. / Lithos 70 (2003) 141–161150

lector mass spectrometer. The filament loading and

mass spectrometric analysis procedures were similar

to the ones previously described by Patchett and Ruiz

(1987). The Nd isotopic ratios were normalized to146Nd/144Nd = 0.7219. Estimated analytical F 2runcertainties are: 147Sm/144Nd = 0.8%, and 143Nd/144Nd = 0.002%. External reproducibility, based on

the range of multiple runs of standard La Jolla Nd is

estimated to be F 0.00001. Replicate analyses of two

samples analyzed in this study (garnet and clinopyr-

oxene from samples L3 and L1) indicate similar

reproducibility. The grand means of isotopic ratios

Fig. 7. Sm–Nd mineral–whole-rock isochron diagram for samples S3-

Paltinis), and C3 (garnet amphibolite, Cugir Valley). Isochron ages were

were corrected by an off-line manipulation program,

which adjusts for the spike contributions to both the

fractionation correction and each ratio, and performs

isotope dilution calculations.

4.2.2. Results

Four mineral and whole rock Sm–Nd isochron

ages were determined (Table 2, Fig. 7), one on a

garnet peridotite, two on eclogites and one on a

biotite–garnet amphibolite. Eclogite L1 of the Lotru

unit near Paltinis yielded a garnet–whole-rock age of

341.4F 8.2 (2r) Ma. Eclogite L3 from the same unit

2 (garnet peridotite, Foltea), L1 (eclogite, Paltinis), L3 (eclogite,

calculated using the ISOPLOT program of Ludwig (1991).

G. Medaris Jr. et al. / Lithos 70 (2003) 141–161 151

yielded a four-point isochron age of 343.6F 6.6 Ma,

identical within errors with L1. The whole-rock Sm/

Nd is lower than that of each of the individual

analyzed phases in eclogite L3, probably because of

the presence of apatite which contributes significantly

to the REE budget of this sample. Amphibolite C3

from Cugir Valley (Cumpana unit) yielded a garnet–

whole-rock age of 358F 10 Ma, within error of

eclogites L1 and L3. These Sm–Nd ages for eclogite

and garnet amphibolite are believed to represent the

high-pressure metamorphic age within 3–8 My, based

on the observed grain sizes in these rocks and

assuming a cooling rate of 10 jC/My (following

Ganguly et al., 1998). Compared to the previous

rocks, the Foltea garnet peridotite (Sebes unit) has a

younger garnet–clinopyroxene–whole-rock age of

315.5F 4.2 Ma.

Fig. 8. Garnet compositions in high-pressure metamorphic rocks

(specified by sample number and rock type) from the Sebes, Lotru,

and Cumpana units and the Bughea complex. Arrows indicate core

to rim compositional trends in samples where such zoning occurs.

Note that garnet is sector zoned in two samples.

5. Mineral chemistry

Mineral compositions were determined by means

of a Cameca SX50 electron microprobe, using an

accelerating voltage of 15 kV, a beam current of 20

nA, a suite of analyzed natural minerals as standards,

and the B(Uz) data reduction program (Armstrong,

1988). Based on replicate analyses, major element

abundances are estimated to be precise within F 3%

and minor element abundances within F 10%. Anal-

yses used in thermobarometric calculations are avail-

able from the first author upon request. Ferric/ferrous

ratios for garnet and clinopyroxene were calculated

from the means of numerous spot analyses by stoi-

chiometry, following the method of Ryburn et al.

(1976), and for amphibole, by the method of Robin-

son et al. (1982), taking total cations to be 13,

exclusive of K, Na, and Ca.

5.1. Garnet

Garnet compositions for all samples are plotted in

Fig. 8, arranged by tectonostratigraphic unit and

locality. Garnet exhibits a wide range in composition

among the analyzed samples and encompasses the

entire spectrum of garnet compositions from type A,

B, and C eclogites, as defined by Coleman et al.

(1965). Such a wide range in garnet composition

reflects in large part the predominant influence of

rock chemistry on garnet composition in the investi-

gated eclogites, which typically contain low variance

mineral assemblages. For example, the most pyrope-

rich garnet among the analyzed samples occurs in the

Foltea Mg–Cr peridotite (S3-1), and garnet in eclo-

gite, amphibolite, and peridotite from the Lotru Palti-

nis suite (L1-5) spans a wide range in composition.

Garnet consists essentially of almandine–pyrope–

grossular solid solutions, with spessartine component

always being less than 4 mol% and generally, less

than 1 mol%. Except where destroyed by growth of

kelyphite, retrograde compositional zoning commonly

occurs within ~50 Am of garnet margins, due to

arrested Fe–Mg exchange during cooling. Although

G. Medaris Jr. et al. / Lithos 70 (2003) 141–161152

the interiors of some garnet grains are compositionally

homogeneous, other grains show a variety of compo-

sitional zoning patterns, including irregular, prograde,

and sector types (summarized in Table 1). Prograde

compositional zoning, which is best preserved in

garnet grains in the Bughea complex (sample B3,

Fig. 9), exhibits a core to rim decrease in Mn and

increase in Mg, little change in Fe, and decrease in Ca

at the rim. Sector zoned garnet has been found in two

eclogite samples (sample C2, zoisite eclogite, Topolog

locality, Cumpana unit, and sample B6, zoisite–

phengite eclogite, Raul Tirgului locality, Bughea

complex). The sector zoning, which is developed in

an intermediate domain between an indistinct core and

outer rim, is due to heterogeneous distribution of Mg

and Fe on the {110} faces of garnet (sample B6, Fig.

9). Mn shows less pronounced sector variation, and

Ca is uniform in the intermediate domain. The rim of

the grain is characterized by an increase in Mg, slight

increase in Mn, and decreases in Fe and Ca. Such

Fig. 9. X-ray maps of garnet in eclogite from the Bughea complex; light

lower concentrations. B3, kyanite–phengite–paragonite eclogite, Bughita:

grains (diameter of garnet is 2 mm); B6, zoisite–phengite eclogite, Tirgulu

concentric zoning in Ca (diameter of garnet is 1 mm).

sector zoning, although rare in metamorphic garnet,

has been described by Shirahata and Hirajima (1995)

for garnet at several localities in the Sanbagawa schist.

5.2. Clinopyroxene

The interiors of clinopyroxene grains in eclogite

are relatively homogeneous, but Al and Na decrease

and Mg, Fe, and Ca increase at grain boundaries and

in the vicinity of symplectite, in response to partial re-

equilibration during decompression. Clinopyroxene

compositions, in terms of jadeite, diopside + heden-

bergite + Ca-tschermakite, and acmite, are plotted in

Fig. 10 according to tectonostratigraphic unit and

locality. The maximum jadeite content of pyroxene

in eclogite is largely determined by rock chemistry,

stable plagioclase being absent from the high-pressure

assemblage, and although omphacite occurs in most

of the analyzed samples, sodic augite is the stable

pyroxene in less sodic eclogites, such as S1-1, S1-2,

shades represent higher elemental concentrations and dark shades,

prograde compositional zoning patterns in two amalgamated garnet

i: strong sector zoning in Mg and Fe, faint sector zoning in Mn, and

Fig. 10. Clinopyroxene compositions in high-pressure rocks

(specified by sample number and rock type) from the Sebes, Lotru,

and Cumpana units and the Bughea complex. Circles indicate

matrix pyroxene, inverted triangles, pyroxene inclusions in garnet,

and upright triangles, symplectite pyroxene.

G. Medaris Jr. et al. / Lithos 70 (2003) 141–161 153

L7, and L8. Sodic augite occurs in Mg-rich and Na-

poor eclogites elsewhere, e.g. the Silberbach eclogite

in the Munchberg Massif, which is thought to be

cumulate in origin (Stosch and Lugmair, 1990).

Mineralogical evidence for a prograde history is

provided by clinopyroxene in the Lotru Paltinis eclo-

gite (Fig. 10, L1,2,3), in which sodic augite occurs as

inclusions in garnet, and omphacite, in the matrix.

Clinopyroxene in symplectite, which occurs to some

degree in all eclogite samples, ranges in composition

from sodic augite to almost Na-free clinopyroxene.

Clinopyroxene in garnet granulite S2-1 occurs with

plagioclase and contains almost no jadeite component

(Fig. 10), despite a calculated pressure of 11.7 kbar

(see below). Clinopyroxene in the Foltea garnet peri-

dotite (samples S3-1 and S3-2, not figured), is Cr-

diopside, containing 0.78–0.92 wt.% Cr2O3 and 10

mol% jadeite.

5.3. Amphibole

Amphibole is a widespread and abundant mineral

in high-pressure metabasic rocks in the South Carpa-

thians, deserving of a detailed treatment that is beyond

the scope of the present investigation. Amphibole is

an essential constituent in amphibolite and granulite

(Fig. 2), and it occurs in eclogite as inclusions in

garnet, matrix grains in some samples, and a retro-

grade product, commonly in poikilitic or kelyphitic

textures. The compositions of predominant amphibole

in the analyzed samples are shown in Fig. 11 (mod-

ified after Leake., 1997), in which Na occupancy in

the B-site is plotted against Si per formula unit, and

level of Na +K occupancy in the A-site is indicated by

open ( < 0.5) and closed (>0.5) symbols.

Amphibole in granulite, amphibolite, and most

eclogite is calcic, but sodic–calcic amphibole is char-

acteristic of eclogite samples S1-5 (Sebes 1, Capa-

tana), C1 (Cumpana, Topolog), and B1, B2, and B3

(Bughea complex). Calcic amphibole in most eclogite

samples appears to be retrograde, based on its intersti-

tial occurrence and kelyphitic growth around garnet. In

contrast, sodic–calcic amphibole is in apparent textur-

al equilibrium with garnet and omphacite. Most am-

phibole contains more than six atoms of Si per formula

unit, but amphibole inclusions in garnet in samples S1-

3, S2-2, L2, and L3 are unusually aluminous, contain-

ing less than six atoms of Si. Within several samples,

an increase in Si appears to be correlated with a

decrease in level of Na +K in the A-site (Fig. 11).

6. Thermobarometry

6.1. Methods

In calculating temperatures and pressures for poly-

metamorphic rocks that commonly contain zoned

minerals, the problem arises as to what parts of

mineral grains, if any, are in equilibrium and suitable

for P–T evaluation. For eclogite that contains pro-

grade-zoned garnet, maximum P–T conditions were

Fig. 11. Summary of amphibole compositions in South Carpathian high-pressure rocks. Plot based on the IMA classification scheme (Leake,

1997); filled circles indicate (Na +K)A-sitez 0.5, open circles, (Na +K)A-siteV 0.5. Abbreviations: rich, richterite; kat, kataphorite; tar,

taramite; ed, edenite; parg, pargasite; win, winchite; bar, barroisite; tr, tremolite; hb, hornblende; tsch, tschermakite.

G. Medaris Jr. et al. / Lithos 70 (2003) 141–161154

obtained from the most pyrope-rich part of the zoned

garnet, combined with the most jadeite-rich core of

adjacent clinopyroxene, following the suggestion of

Spear (1991). An analogous approach was taken for

other analyzed high-pressure lithologies, utilizing the

most pyrope-rich part of garnet, combined with

domains of pertinent coexisting minerals that were

judged to be in equilibrium, based on petrographic

observation, backscattered electron imaging, numer-

ous spot analyses of several grains in each sample,

and selected line traverses and X-ray mapping. An

additional problem in Fe–Mg exchange thermometry

is estimation of the oxidation state of iron in ferro-

magnesian phases. As described in the section on

mineral chemistry, ferric/ferrous ratios were calculated

from charge-balance considerations for garnet, clino-

pyroxene, and amphibole. Although such estimates of

ferric/ferrous ratios have inherent difficulties (Sobolev

et al., 1999), the relative differences in values among

samples are thought to be significant, because the

same set of standards and operating conditions were

used throughout the collection of mineral composi-

tional data.

For eclogite, metamorphic conditions were calcu-

lated from calibrations of the following equilibria:

Prpþ 3Di ¼ Almþ 3Hd ð1Þ

(Powell, 1985)

Jdþ Qtz ¼ Ab ð2Þ

(Gasparik, 1985; Brown et al., 1989; Holland, 1990)

Prpþ 2Grs ¼ 6Diþ 3Phn ð3Þ

(Waters and Martin, 1993; Searle et al., 1994)

Pg ¼ Jdþ Kyþ H2O ð4Þ

(Brown et al., 1989; Holland, 1990)

12Zoþ 15Di ¼ 13Grsþ 5Prpþ 12Qtzþ 6H2O ð5Þ

(Brown et al., 1989)

Solutions to combinations of the various equilibria

were obtained by iteration or application of the GEO-

CALC program (Berman, 1988; Brown et al., 1989).

Regardless of whether the Gasparik (1985) or Holland

(1990) calibration was used for equilibrium (2), com-

Table 3

Temperature–pressure conditions for South Carpathian high-

pressure rocks

Unit and

locality

Sample Lithology T (jC),P (kbar)

a(H2O)

Sebes 3

Foltea S3-1 grt peridotite 12971, 29.02 –

Foltea S3-2 grt peridotite 11491, 25.82 –

Sebes 2

Sebes

Valley

S2-1 grt granulite 7033, 11.74;

7145, 11.46–

Sebes

Valley

S2-2 grt amphibolite 9095, 14.56 –

Sebes 1

Mehedinti S1-1 ky eclogite z 5463, 11.67 –

Mehedinti S1-2 ky–phn

eclogite

6043, 11.28;

z 6033, 10.87–

Mehedinti S1-3 zo–ky

eclogite

z 5693, 13.87 z 0.1510

Capatana S1-4 zo eclogite z 6653, 15.27 –

Capatana S1-5 zo eclogite z 6473, 14.97 –

Capatana S1-6 czo eclogite z 6213, 14.17 –

Lotru

Paltinis L1 eclogite z 6623, 12.37 –

Paltinis L2 eclogite z 6853, 13.47 –

Paltinis L3 eclogite z 6713, 13.17 –

Paltinis L4 grt amphibolite 7105, 11.46 –

Paltinis L5 grt peridotite 5591, 16.12;

6199, 19.12–

Deluselu V. L7 eclogite z 6523, 12.57 –

Deluselu V. L8 czo eclogite z 6943, 12.47 –

Cumpana

Topolog C1 ky eclogite z 6163, 14.57 –

Topolog C2 zo eclogite z 6193, 14.37 z 0.310

5 6

G. Medaris Jr. et al. / Lithos 70 (2003) 141–161 155

parable results were obtained. Because stable plagio-

clase is absent from the eclogite assemblages, the

resulting pressures and, to a lesser degree, temperatures

are minimum values, although the presence of stable

phengite or paragonite in some samples of eclogite

allows a definitive P–T value to be established. For

samples containing stable paragonite or zoisite, esti-

mates for H2O activity may be obtained from some

combination of equilibria (4) and (5) with equilibria

(1)–(3), depending on the specific mineral assemblage.

Conditions for garnet granulite were determined

from Fe–Mg exchange between clinopyroxene and

garnet, equilibrium (1), and the following:

3Fe� Prgþ 4Prp ¼ 3Prgþ 4Alm ð6Þ

(Graham and Powell, 1984)

3Diþ 3An ¼ 2Grsþ Prpþ 3Qtz ð7Þ

(Brown et al., 1989)

2Ttnþ An ¼ Grsþ 2Rtþ Qtz ð8Þ

(Brown et al., 1989)

The combination of results from equilibria (1) and (6)

with equilibrium (7) yields a specific temperature and

pressure, and application of equilibrium (8), in the

absence of rutile, provides a maximum pressure.

Equilibration conditions for garnet amphibolite

were obtained from Fe–Mg exchange between am-

phibole and garnet, equilibrium (6), and two end-

member equilibria (Mg and Fe) for the assemblage,

plagioclase–amphibole–garnet–quartz:

6Anþ 3Tr ¼ 2Grsþ Prpþ 3Tschþ 6Qtz ð9Þ

(Kohn and Spear, 1990)

6Anþ 3Act ¼ 2Grsþ Almþ 3Fe� Tschþ 6Qtz

ð10Þ(Kohn and Spear, 1990)

Notes to Table 3:

Equilibria used in thermobarometric calculations: 1Fe–Mg ex-

change, ol–grt (O’Neill and Wood, 1979; O’Neill, 1980); 2Al-in-

opx (Brey and Kohler, 1990); 3Fe–Mg exchange, cpx–grt (Powell,

1985); 4di + an = grs + prp + q (Brown et al., 1989); 5Fe–Mg ex-

change, hb–grt (Graham and Powell, 1984); 6an + tr = grs + prp +

tsch + q (Kohn and Spear, 1990); 7a(Jd) in cpx (Gasparik, 1985);8prp + grs =di + phn (Waters and Martin, 1993); 9Fe–Mg exchange,

opx–grt (Brey and Kohler, 1990); 10zo + di = grs + prp + q +V

(Brown et al., 1989); 11pg = jd + ky +V (Brown et al., 1989).

The preferred method of approximating maximum

temperatures for garnet peridotite is based on the

compositions of coexisting garnet, which is a slowly

diffusing phase, and matrix olivine, which consti-

Cugir

Valley

C3 bt grt

amphibolite

710 , 10.5 –

Bughea

Danis B1 zo–phn

eclogite

z 6863, 15.57 f 1.010

Bughita B2 ky–phn–pg

eclogite

6083, 22.311 1.0

Bughita B3 ky–phn–pg

eclogite

7463, 19.011 1.0

Tirgului B6 zo–phn

eclogite

5773, 16.48;

z 5723, 13.97f 0.3510

G. Medaris Jr. et al. / Litho156

tutes the bulk of the rock and whose composition is

little changed by intergranular diffusion during cool-

ing (Brenker and Brey, 1997), according to the

equilibrium:

1=2Faþ 1=3Prp ¼ 1=2Foþ 1=3Alm ð11Þ

(O’Neill and Wood, 1979; O’Neill, 1980)

Pressure is then determined from the Al-in-orthopyr-

oxene barometer:

Prp ¼ Enþ TschðopxÞ ð12Þ

(Brey and Kohler, 1990)

An additional Fe–Mg exchange equilibrium:

1=2Fsþ 1=3Prp ¼ 1=2Enþ 1=3Alm ð13Þ

(Brey and Kohler, 1990)

was utilized for the Lotru Paltinis garnet peridotite,

in which grains of garnet are never in direct contact

with olivine and orthopyroxene.

Fig. 12. Details of pressure– temperature estimates for 21 South Carpa

calculation methods and results). Note that the P–T value for sample B2 is

order to be included on the scale of the figure.

6.2. Results

South Carpathian eclogite belongs to the medium-

temperature group (Carswell, 1990), and samples

range in temperature from f 545 to 745 jC and in

pressure from f 11.2 to 22.3 kbar (Table 3, Fig. 12),

remembering, however, the caveat that the P–T deter-

minations derived from the jadeite content of ompha-

cite are only minima (note that the temperatures cited

here are generally lower than those reported by

Maruntiu et al., 1997, and Iancu et al., 1998, because

their determinations apparently did not include a

correction for ferric iron). Pressure estimates from

equilibrium (4) for paragonite-bearing samples, B2

and B3, are significantly higher than those predicted

by their omphacite compositions, 22.3 vs. 13.6 kbar

and 19.0 vs. 16.2 kbar, respectively. Pressure esti-

mates based on phengite composition are comparable

to that based on jadeite content of pyroxene in sample

S1-2 (11.2 vs. 10.8 kbar), higher in sample B6 (16.4

vs. 13.9 kbar), and appreciably lower in samples B2

s 70 (2003) 141–161

thian high-pressure metamorphic rocks (see text for discussion of

608 jC, 22.3 kbar at a(H2O) = 1.0, but is plotted at a(H2O) = 0.50 in

G. Medaris Jr. et al. / Lithos 70 (2003) 141–161 157

and B3, possibly due to retrograde re-equilibration of

phengite in these two samples. Application of equi-

librium (5) to three samples of zoisite eclogite (S1-3,

C2, and B6) suggests that H2O activity was substan-

tially reduced at the eclogite stage, on the order of

0.15–0.35, although a fourth sample (B1) indicates an

activity of f 1.0.

Despite the small number of analyzed samples, it

appears that P–T fields are relatively restricted at each

specific locality, except for the Bughea complex

(tectonic melange), and differ among the tectonostrati-

graphic units, as well as within some units, such as the

Mehedinti and Capatana localities in Sebes 1 (Figs. 12

and 13). However, additional analyses are required to

evaluate the possibility of regional trends in P and T.

Pyroxene and amphibole equilibria applied to

garnet granulite (S2-1) yield consistent results of

703 jC, 11.7 kbar and 714 jC, 11.4 kbar (Table 3,

Fig. 12), and demonstrate the high-pressure nature of

Sebes 2 granulite. The three analyzed samples of

garnet amphibolite (S2-2, L4, and C3), each from a

different tectonostratigraphic unit, also equilibrated

at high pressure, from 10.5 to 14.5 kbar (Table 3,

Fig. 12).

Fig. 13. Summary P–T– t diagram for South Carpathian high-pressure roc

pre-HP prograde path is shown schematically. Note that the Sebes 3 peridot

its retrograde path is shown schematically. 40Ar/39Ar cooling ages from D

Extreme P–T conditions (f 1150–1300 jC,25.8–29.0 kbar) are preserved in the Foltea garnet

peridotite, Sebes 3 unit, but much lower P–T con-

ditions (f 560– 620 jC, 16.1 – 19.1 kbar) are

recorded in the Paltinis garnet peridotite, Lotru unit.

Such disparate conditions reflect the contrasting tec-

tonothermal regimes for the two types of peridotite,

the Foltea body originating by the introduction of hot

mantle into the Sebes 3 crustal sequence, and the

Paltinis body representing part of a mafic–ultramafic

complex that shared a prograde metamorphic history

with associated Lotru crust.

7. Discussion

The Sm–Nd ages reported here for Sebes 3 garnet

peridotite (316F 4 Ma), Lotru eclogite (341F 8 and

344F 7 Ma), and Cumpana garnet amphibolite

(358F 10 Ma) firmly establish a Variscan age for

high-pressure metamorphism of the pre-Alpine Ge-

tic–Supragetic basement in the South Carpathians.

Although the eclogite and amphibolite ages are indis-

tinguishable within error, the peridotite age is signif-

ks. Symbols: E, eclogite; G, granulite; A, amphibolite. An inferred

ite plots outside the diagram at 1150–1300 jC, 25.8–32.2 kbar, andallmeyer et al. (1998).

G. Medaris Jr. et al. / Lithos 70 (2003) 141–161158

icantly younger, raising the possibility that high-pres-

sure metamorphism (or exhumation) was diachronous

in different tectonostratigraphic units in the South

Carpathians, as elsewhere in the European Variscides

(Brueckner et al., 1991; Beard et al., 1995). Our newly

determined Variscan metamorphic ages are consistent

with three types of previously acquired geochrono-

logical data: (1) several 207Pb/206Pb analyses of zircon

from synkinematic pegmatites in Getic basement

yielded ages of 338–333 Ma, with no errors reported

(Ledru et al., 1997), (2) Sm–Nd mineral ages of 358–

323 Ma were determined for Cumpana amphibolites

and gneisses (Dragusanu and Tanaka, 1999), and (3)

f 320–295 Ma 40Ar–39Ar cooling ages for horn-

blende and muscovite were determined on samples

from throughout the Getic and Supragetic basement

nappes (Dallmeyer et al., 1998). The Sm–Nd data

presented here and in Dragusanu and Tanaka (1999),

when compared to the limited U–Pb zircon geochro-

nology of Getic basement pegmatites (Ledru et al.,

1997), suggest that partial melting and production of

pervasive pegmatites and migmatites within the Getic

basement (Balintoni, 1975) took place synchronously

with, or shortly following, the Variscan peak meta-

morphism. The Sm–Nd results combined with pub-

lished 40Ar–39Ar ages suggest initial (i.e. high

temperature) cooling rates of about 10F 5j/My,

based on estimated closure temperatures of f 650

jC for Sm–Nd in garnet (following Ganguly et al.,

1998) and 500 jC for Ar diffusion in hornblende

(Dallmeyer et al., 1998). It has been suggested that the

cooling/unroofing of the basement rocks and deposi-

tion of unmetamorphosed Carboniferous–Permian

sediments took place during an episode of continental

extension between 320 and 300 Ma (Dallmeyer et al.,

1998). Such a scenario is consistent with the hypoth-

esis that the Variscan orogen of Europe has collapsed

in its late stages, leading to the formation of numerous

continental extensional basins (Menard and Molnar,

1988).

We interpret the Sm–Nd age of the high-temper-

ature Foltea garnet peridotite to represent the time of

its tectonic emplacement into the crust, when it cooled

through an estimated garnet Sm–Nd closure temper-

ature of f 850 jC, assuming a cooling rate of 100

jC/My (Ganguly et al., 1998). Interestingly, emplace-

ment of the hot, asthenosphere-derived Foltea garnet

peridotite in the Getic basement took place during

extension towards the end of the orogeny, subsequent

to the peak of Variscan high-pressure metamorphism

and migmatization. The emplacement of the Foltea

peridotite could possibly be a result of late orogenic

delamination of mantle lithosphere in the area, as

postulated for similar high-temperature garnet perido-

tites in the Bohemian Massif (Medaris et al., 1990;

1998).

Further detailed investigation is needed to verify

the apparent differences in ‘‘peak’’ eclogite facies

conditions among different tectonostratigraphic units

(Fig. 13) and to establish P–T– t paths for high-

pressure lithologic associations at individual locali-

ties. The Paltinis metabasic–ultrabasic complex raises

the intriguing possibility that garnet peridotite (L5),

eclogite (L1-3), and garnet amphibolite (L4) have

captured P–T conditions experienced by the complex

at various times along a clockwise metamorphic path

(Fig. 12), although the differences in P–T estimates

among the three rock types might also be due to

disequilibrium in the garnet peridotite (note the dis-

tribution of orthopyroxene and garnet illustrated in

Fig. 3) or to inherent differences in P–T estimates

derived from different equilibria. Another interesting

result from our P–T estimates is that samples of

garnet amphibolite in the Lotru (L4) and Cumpana

(C3) units yield higher temperatures than do eclogites

in the same units, and garnet amphibolite and garnet

granulite in the Sebes 2 unit give elevated temper-

atures of f 910 and 710 jC, respectively (Fig. 13).

Such a temperature distribution might signify post-

eclogite stage heating, perhaps due to thermal relax-

ation of crustal rocks that were thickened by nappe

stacking, or the apparent temperature pattern may

again be due to differences among different geother-

mometers. High temperatures in the Sebes 2 and 3

units may originate from the introduction of high-

temperature peridotite masses, whose emplacement

may be related to Late Carboniferous extension.

The existence of relatively low H2O activity in

some samples of eclogite, for which there is limited

evidence from several zoisite eclogites, is consistent

with the apparent absence of amphibole and para-

gonite, whose stability fields are restricted at reduced

H2O activity, from the peak mineral assemblages in

most eclogite samples.

The Sebes 2 and 3 units are noteworthy for the

presence of high-temperature garnet peridotite, the

G. Medaris Jr. et al. / Lithos 70 (2003) 141–161 159

occurrence of leptynite–amphibolite, the development

of elevated temperatures in granulite and amphibolite,

and the rarity of eclogite, although textures in gran-

ulite and amphibolite suggest that they formed from

preexisting eclogite. Such features closely resemble

those of the Gfohl Nappe in the Bohemian Massif, in

which post-eclogite, high-temperature recrystalliza-

tion has largely obliterated evidence for the prior

existence of eclogite (Medaris et al., 1998). The Sebes

2 and 3 units are the uppermost tectonic units in the

South Carpathians, as is the Gfohl Nappe in the

Bohemian Massif, and the likely correlation of these

similar tectonostratigraphic entities provides a plausi-

ble link between the Variscan basement of the South

Carpathians and that of central Europe.

8. Conclusions

High-pressure metamorphic rocks, including gar-

net peridotite, eclogite, garnet granulite, and garnet

amphibolite are important constituents in the Sebes,

Lotru, and Cumpana units and in the Bughea complex

(tectonic melange) of the pre-Alpine nappe stack of

the Getic–Supragetic basement in the South Carpa-

thians. Sm–Nd mineral–whole-rock isochrons for

garnet peridotite (316F 4 Ma), eclogite (341F 8

and 344F 7 Ma), and garnet amphibolite (358F 10

Ma) demonstrate a Variscan age for high-pressure

metamorphism, which is consistent with deposition

of detritus from the high-pressure terranes in West-

phalian to Permian sedimentary basins.

P–T conditions for eclogite are in the range, 545–

745 jC and 11.2–22.3 kbar, which may be attributed

to subduction and continental collision in Carbonifer-

ous (pre-Westphalian) time. A widespread, post-eclo-

gite recrystallization at possibly higher temperatures

and the emplacement of high-temperature peridotite in

Sebes 2 and 3, the uppermost structural units in the

South Carpathians, may be related to late Variscan

extensional processes.

In summary, the Variscan evolution of the pre-

Mesozoic Getic–Supragetic basement in the South

Carpathians is similar to that in other segments of the

European Variscides, including widespread high-pres-

sure metamorphism, whose P–T– t signatures are

specific to individual tectonostratigraphic units, the

presence of diverse types of garnet peridotite, dia-

chronous subduction and accretion, nappe assembly in

pre-Westphalian time due to collision of Laurussia,

Gondwana, and amalgamated terranes, and finally,

rapid exhumation, cooling, and deposition of eroded

debris in Westphalian to Permian sedimentary basins.

Acknowledgements

This investigation was supported by grants from

the National Research Council Twinning Program for

Romania, 1999 –2001 (Medaris), the NSERC

(Ghent), and the Romanian Education and Research

Ministry, ANSTI 5078/1999–2001 (Iancu). We are

grateful to Jonathan Patchett for his advice and

direction in performing isotope analyses at the

University of Arizona mass spectrometer laboratory,

and to John Fournelle for his expertise in electron

probe microanalysis and imaging at the University of

Wisconsin. Constructive reviews were provided by

Esther Schmadicke and Anthi Liati, although the

interpretations given here are solely the views of the

authors.

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