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ORIGINAL PAPER
Redox state of subcontinental lithospheric mantleand relationships with metasomatism: insights from spinelperidotites from northern Victoria Land (Antarctica)
Cristina Perinelli • Giovanni B. Andreozzi •
Aida M. Conte • Roberta Oberti • Pietro Armienti
Received: 8 January 2012 / Accepted: 28 July 2012 / Published online: 28 August 2012
� Springer-Verlag 2012
Abstract Rift-related Cenozoic alkaline mafic lavas
from northern Victoria Land (Antarctica) carry abundant
mantle xenoliths whose oxygen fugacities (fO2) were
determined to assess how the metasomatism, related to
Cenozoic magmatism, affected the state of oxidation of
the lithospheric mantle. The xenoliths used for this study
are anhydrous spinel peridotites sampled in two localities,
Greene Point and Baker Rocks, that show different
extents of metasomatism: these are limited to incompati-
ble element enrichments in Greene Point and to enrich-
ments in major, minor and trace elements at Baker Rocks.
The data set includes a composite xenolith from Baker
Rocks, formed by a depleted lherzolite crosscut by an
amphibole-bearing vein. Mossbauer spectroscopy was
used to accurately determine the Fe3?/Fetot ratios in spinel
and amphibole minerals. Amphiboles were also charac-
terized by Single-Crystal X-ray Diffraction, and the
crystallographic data were used to calculate the dehy-
drogenation. The oxidation state recorded by the xenoliths
ranges from 0.2 to 1.5 log-bar units below the fayalite–
magnetite–quartz (FMQ) buffer (DlogfO2) with the high-
est values observed in the metasomatized samples from
Greene Point. For the vein of composite Baker Rocks
xenolith, Dlog fO2 was estimated on the basis of the
amphibole in -1.7 log-bar units, a value close to those
calculated for all Baker Rocks xenoliths (DlogfO2 = -1.5
to -1.1 log-bar units). These results indicate a similar
oxidation state for lithospheric mantle prior to the meta-
somatic event at Greene Point and Baker Rocks
(DlogfO2 * -1.3 log-bar units). Metasomatism produced
different effects in the shallow mantle at the two sites. At
Greene Point, an oxidizing metasomatic melt caused the
rise of fO2 in peridotite portions close to melt conduits up
to FMQ. In contrast, at Baker Rocks, a metasomatizing
melt with fO2 similar to that of the peridotite matrix
produced chemical changes in the surrounding mantle
rocks and amphibole crystallization without significantly
modifying the local oxidation state. The origin of such
different metasomatic melts, as well as the variety of
primary magmas produced during the magmatic phase of
Cenozoic rifting, is linked to the geodynamic evolution
of the rift and probably involved the melting of a heter-
ogeneous mantle source composed of a peridotite veined
by pyroxene-bearing veins formed from an earlier
amagmatic phase of the rift.
Keywords Upper mantle oxygen fugacity � Mantle
metasomatism � Rift evolution � Northern Victoria Land �Antarctica
Communicated by C. Ballhaus.
C. Perinelli (&) � P. Armienti
Dipartimento di Scienze della Terra, Universita degli Studi di
Pisa, Via S. Maria 53, 56126 Pisa, Italy
e-mail: cperinelli@dst.unipi.it
P. Armienti
e-mail: armienti@dst.unipi.it
G. B. Andreozzi
Dipartimento di Scienze della Terra, Sapienza Universita di
Roma, P.le A. Moro 5, 00185 Rome, Italy
e-mail: gianni.andreozzi@uniroma1.it
A. M. Conte
Istituto di Geoscienze e Georisorse (IGG-CNR) UOS Roma,
P.le A. Moro 5, 00185 Rome, Italy
e-mail: aidamaria.conte@uniroma1.it
R. Oberti
Istituto di Geoscienze e Georisorse (IGG-CNR) UOS Pavia,
via Ferrata 1, 27100 Pavia, Italy
e-mail: oberti@crystal.unipv.it
123
Contrib Mineral Petrol (2012) 164:1053–1067
DOI 10.1007/s00410-012-0788-7
Introduction
Oxygen fugacity (fO2) is a key factor in controlling magma
genesis and metasomatism in the mantle. In fact, mantle
fO2 constrains mineral assemblages and the speciation of
C–O–H fluids (CO, CO2, CH4, H2 and H2O), which in turn
play a primary role in determining the pressure (P) and
temperature (T) conditions for the onset of partial melting.
Many studies that focused on upper mantle fO2 have shown
the presence of vertical and lateral heterogeneities, which
were ascribed to partial melting (Bryndzia and Wood 1990;
Woodland et al. 2006), tectonic setting (Wood 1990;
Ballhaus 1993; Parkinson and Arculus 1999) and metaso-
matism (McGuire et al. 1991; Ballhaus 1993; McCammon
et al. 2001).
Spinel peridotite xenoliths included in Cenozoic volca-
nic rocks of northern Victoria Land (NVL), Antarctica, are
used to assess the redox state and its possible evolution
during Cenozoic magmatism, in this part of lithospheric
mantle.
Cenozoic magmatism in the NVL is linked to the West
Antarctic Rift System in a region of consistent crustal
thinning (the Moho in the coastal area is at *20–25 km of
depth; Trehu et al. 1989) as revealed by a topographical
trough running from the Antarctic Peninsula to the Ross
Embayment–northern Victoria Land (Fig. 1) (LeMasurier
and Thomson 1990; Tessensohn and Worner 1991; Beh-
rendt et al. 1991). Many lines of evidences point to the
origin of Cenozoic igneous activity in NVL consistent with
a passive rifting frame related to a transtensive tectonic
regime; this is also in agreement with the geothermobaro-
metric estimates on xenoliths from lower crust and upper
mantle (Worner 1999; Armienti and Perinelli 2010).
NVL mantle xenoliths revealed heterogeneities in the
mantle composition, which were interpreted in terms of
partial melting episodes and metasomatism (Coltorti et al.
2004, Perinelli et al. 2006; Melchiorre et al. 2011). In
particular, samples hosted by magmas from two localities
only 80 km apart show distinct metasomatic features. In
Baker Rocks samples (BR: Mt. Melbourne Volcanic
Province), metasomatism is evident by the occurrence of
amphibole (both disperse and in vein) as well as by the
enrichment in major, minor (Fe and Ti, respectively) and
incompatible trace elements. On the contrary, in Greene
Point (GP) samples, the metasomatism is cryptic and is
only recorded by clinopyroxene through selective
Meander Intrusives McMurdo Volcanics Ultramafic Xenoliths
This work
Other outcrops
Weddell Sea
Transantarctic M
ountains
Ross Sea
90 W90 E
Inferred boundary of the West Antarctic Rift System
60S
0
Cenozoic dike swarms
Fig. 1 Sketch map of northern
Victoria Land and sampling
localities. McMurdo Volcanics
enclose the Cenozoic volcanic
products (Kyle 1990), while
Meander Intrusives enclose the
intrusive-subvolcanic varieties
(Tonarini et al. 1997)
1054 Contrib Mineral Petrol (2012) 164:1053–1067
123
enrichment in incompatible elements. Metasomatic chan-
ges on BR and GP lithospheric mantle have been inter-
preted as results of ‘‘wall-rock’’ metasomatism and/or
‘‘diffuse’’ metasomatism: the first is linked to the transport
of melt in fractures (veins and dykes); the latter is related to
percolation of small melt fractions along grain boundaries
in the peridotite matrix. The shift from ‘‘wall-rock’’ to
‘‘diffuse’’ metasomatism is controlled by the different
ratios of melt/rock interaction volume involved during the
metasomatism (Xu and Bodinier 2004 and reference
therein). Mineralogical and chemical modifications of BR
xenoliths were indeed induced by both ‘‘wall-rock’’
(presence of amphibole and/or Fe–Ti enrichments) and
‘‘diffuse’’ metasomatism (variable enrichments in incom-
patible trace elements in clinopyroxene), while only dif-
fusive processes acted at Greene Point.
Perinelli et al. (2006) related the metasomatic event to
Cenozoic magmatism and documented a similar metaso-
matic agent for both suites, even if its oxidation state was
not evaluated. Our working hypothesis is that mineralogi-
cal and geochemical differences observed in BR and GP
spinel peridotites contain information on the oxidation state
of the metasomatic melts. To verify this hypothesis,
information on fO2 conditions was retrieved from a selec-
tion of variably metasomatized BR and GP peridotite
xenoliths and used to decipher the complex evolution of
lithospheric mantle in northern Victoria Land.
Materials and methods
Petrographic and mineralogical features of spinel
peridotites
Mantle xenoliths selected for this study (Table 1) occur in
a melanephelinite (Greene Point) and in an alkali basalt
(Baker Rocks) belonging to the McMurdo Volcanic Group,
the Unit that collects the volcanic products of Cenozoic
igneous activity related to the rift of Ross Sea (Kyle 1990).
Details on petrography and mineral chemistry of GP and
BR samples are reported in Perinelli et al. (2006) and
Armienti and Perinelli (2010). The main textural and
compositional features of GP and BR samples are briefly
described here. Xenoliths from both localities consist of
coarse-textured spinel lherzolites (12–6 % of clinopyrox-
ene) and spinel harzburgites (5–3 % of clinopyroxene).
Table 1 Spinel peridotite xenoliths from lithospheric mantle of northern Victoria Land (NVL) selected for the present study
Sample Rock
type
T (�C) P (GPa) Cr# in
Spinel
F % Sp-based
(Hellebrand
et al. 2001)
F % Cpx-based
(Hellebrand
et al. 2002)
Shape of Cpx
REE pattern
(La/Yb)N
in CpxcType of
metasomatism
GP6 Hz 1032 1.74 0.39 15 15b Spoon LREE-
enriched
1.6 Cryptic
GP22 Hz 1048 1.1 0.47 17 15 Convex-upward
LREE-enriched
22.4 Cryptic
GP31 Hz 1109 1.45 0.24 10 7b Flat LREE-
enriched
0.7 Cryptic
GP40 Lh 985 1.53 0.20 8 9b Normal LREE-
depleted
0.01 Unmetasomatized
GP42 Lh 1113 1.64 0.11 2 3 Normal LREE-
depleted
0.04 Unmetasomatized
BR213 Lh 907 1.1 0.27 11 – Convex-upward
LREE-enriched
2.8 Cryptic
BR218 Lh 911 0.9 0.19 8 10b Spoon LREE-
enriched
4.2 Cryptic
BR218* Lh 927a 0.9 0.22 9 – Convex-upward
LREE-enriched
4.6 Fe–Ti
BR219 Hz 933 1.21 0.16 6 9b Spoon LREE-
enriched
2.8 Cryptic
Temperatures are estimated by the geothermometer of Ballhaus et al. (1991). Pressure data are from Armienti and Perinelli (2010)
GP greene point, BR baker rocks, Hz harzburgite, Lh lherzolite, Cr# Cr number expressed as Cr/(Cr ? Al) atom, F % estimated degree of partial
melting, Sp spinel, Cpx clinopyroxene
* Lherzolite portion adjacent to amphibole-bearing vein (see text)a Temperature estimated using the composition of olivine-spinel pair adjacent to amphibole-bearing veinb Partial melting occurred partly in the garnet field stability (Perinelli et al. 2006)c (La/Yb)N ratio in clinopyroxene is normalized with respect to C1-Chondrite (McDonough and Sun 1995). REE data are from Perinelli et al.
(2006)
Contrib Mineral Petrol (2012) 164:1053–1067 1055
123
They are generally homogeneous, with the only exception
of a sample from Baker Rocks (BR 218, Fig. 2), where
the lherzolite is crosscut by an amphibole-bearing vein
*2-mm wide. Minerals forming the peridotite xenoliths
exhibit in general uniform composition: the forsterite (Fo)
component of olivine ranges from 89 (lherzolite) to 92
(harzburgite); orthopyroxenes and clinopyroxenes can be
referred to as enstatite (En88–91, Wo2, Fs7–10) and
Cr-diopside (Wo44–48, En46–52, Fs4–6), respectively, and
their compositional range is consistent with the degree of
partial melting suffered by the source (e.g., the Al2O3
content in clinopyroxene decreases from 6.88 to 3.19 wt %
in GP42 lherzolite and in GP22 harzburgite, respectively).
Both ortho- and clinopyroxenes show selective enrichment
in incompatible trace elements, which have been related to
a metasomatic event (Perinelli et al. 2006). The chromium
number (Cr# = Cr/(Cr ? Al) ratio) of Cr-rich spinels
increases from 0.11 in lherzolites to 0.47 in harzburgites, as
expected in a mantle affected by variable degrees of partial
melting. In the sample BR218, all phases have higher Fe
contents than in the xenoliths with similar lithology. In
particular, mineral phases of the peridotite portion closest
to the amphibole-bearing vein (hereafter named BR218*,
see Table 1) are enriched in iron; spinel is depleted in
Al2O3 and enriched in Cr2O3, and clinopyroxene and spinel
are also enriched in titanium (Table 2).
In the vein, amphibole occurs as follows: (1) small
euhedral grains (B0.1 mm in diameter), in direct contact
with the peridotite matrix, classified as Ti–rich pargasite
according to Hawthorne and Oberti (2007) (average
#mg = 87, TiO2 = 3.70 wt % and Al2O3 = 14.65 wt %);
(2) larger crystals (up to *0.3 mm in diameter) of kaer-
sutitic composition (#mg = 85, TiO2 = 4.87 wt % and
Al2O3 = 13.51 wt % on average) occasionally surrounded
by a pale yellow glass with microcrystals of
clinopyroxene ? olivine ± plagioclase. At a distance of
2.5 cm far from the vein, only clinopyroxene still reveals
metasomatic features such as the selective enrichment of
incompatible trace elements. The gradual chemical evolu-
tion detected in this sample reflects the action of a me-
tasomatizing chromatographic process which occurred at
the scale of a mantle xenolith (Perinelli et al. 2006).
Mossbauer spectroscopy for Fe3?/Fetot determination
in spinel and amphibole
Eight mantle xenoliths (5 from Greene Point and 3 from
Baker Rocks) representative of unmetasomatized (GP40
and GP42) and differently metasomatized samples were
selected on the basis of texture (coarse type; Table 1) and
size, in order to provide enough material for mineral sep-
arates with minimal contamination by the host basalt. All
samples were crushed, and fresh spinels were picked up by
hand under a binocular microscope.
Since the amphibole-bearing vein that crosscuts the
BR218 peridotite can be reasonably considered as the
metasomatizing agent of this portion of upper mantle,
Mossbauer spectroscopy (MS) was also carried out on
amphibole itself in order to measure its Fe3?/Fetot ratio,
and hence allow calculation of fH2, and fO2 conditions in
the vein. The limited amount of available sample allowed
only Mossbauer analysis of the kaersutite-type amphibole
(hereafter named BR218Amph).
Mossbauer absorbers were prepared by pressing finely
ground samples, mixed with powdered acrylic resin to self-
supporting discs. The amount used corresponded to about
2 mg Fe/cm2, to avoid thickness effects. Spectra were
collected at Sapienza University of Rome, using a con-
ventional spectrometer system operating at room temper-
ature (298 K) in constant acceleration mode with a 57Co
source in rhodium matrix. Spectral data for the velocity
range -4 to ?4 mm/s were recorded in a multichannel
analyzer using 512 channels. After velocity calibration
against a high-purity a-iron foil spectrum, the raw data
were folded in 256 channels. The spectra are made of
doublets and were fitted using a five-doublet model by the
Recoil 1.04 (Lagarec and Rancourt 1998) fitting program
and assuming symmetrical Lorentzian peak shapes (Fig. 3).
The best fits were evaluated by reduced v2, and uncer-
tainties were calculated using the covariance matrix. Errors
were estimated to be close to ±0.02 mm/s for isomer shift
(d), quadrupole splitting (DEQ) and peak width (C). In the
present study, spectral areas for Fe2? and Fe3? were cor-
rected for the temperature effect with f factors calculated
by De Grave and Van Alboom (1991) for room tempera-
ture conditions (f2 = 0.687 and f3 = 0.887). Errors asso-
ciated with doublet areas are estimated to be less than
±3 % (Table 3).
Fig. 2 Plane-polarized light image of composite peridotite xenolith
BR218. Enlarged image shows the large kaersutitic amphiboles
crystallized in the vein that crosscuts the BR218 lherzolite
1056 Contrib Mineral Petrol (2012) 164:1053–1067
123
Table 2 Representative analyses of minerals of Greene Point and Baker Rocks spinel peridotite xenoliths
GP6 GP22 GP31
Ol Opx Cpx Sp Ol Opx Cpx Sp Ol Opx Cpx Sp
SiO2 40.68 56.32 53.45 0.04 40.57 56.33 53.02 0.02 41.02 54.74 52.67 0.04
TiO2 0.04 b.d.l. b.d.l. 0.03 0.04 0.01 0.05 0.10 b.d.l. 0.07 0.16 0.08
Al2O3 0.01 3.16 3.33 36.14 0.34 2.77 3.19 30.63 0.02 4.19 5.57 47.70
Cr2O3 n.a. 0.70 1.07 35.09 n.a. 0.73 1.39 41.12 n.a. 0.68 1.40 22.00
FeOtot 8.35 4.61 2.14 11.13 7.80 5.04 2.14 11.98 8.96 5.33 2.40 9.94
MnO 0.10 0.14 0.10 b.d.l. 0.05 0.14 0.05 b.d.l. 0.12 0.06 0.05 b.d.l.
NiO 0.25 n.a. n.a. 0.20 0.32 n.a. n.a. 0.16 0.34 n.a. n.a. 0.30
MgO 49.69 34.82 18.44 17.88 50.02 34.75 17.69 16.67 49.40 32.91 16.22 19.11
CaO 0.08 1.06 21.88 n.a. 0.10 1.01 20.77 n.a. 0.07 0.93 20.47 n.a.
Na2O n.a. b.d.l. 0.43 n.a. n.a. 0.09 0.99 n.a. n.a. 0.09 1.32 n.a.
K2O n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a.
Total 99.20 100.79 100.83 100.52 99.24 100.86 99.28 100.67 99.93 99.00 100.24 99.18
Fo 91.4 92.0 90.9
Mg# 0.93 0.94 0.74 0.92 0.94 0.71 0.92 0.92 0.77
Cr# 0.39 0.47 0.24
GP40 GP42 BR213
Ol Opx Cpx Sp Ol Opx Cpx Sp Ol Opx Cpxa Sp
SiO2 40.75 54.86 52.75 0.22 40.86 54.75 51.75 0.04 40.54 55.36 52.51 0.04
TiO2 0.01 0.02 0.18 0.09 0.02 0.08 0.41 0.14 b.d.l. 0.11 0.16 0.11
Al2O3 b.d.l. 4.04 4.89 50.04 0.02 4.08 6.88 57.92 b.d.l. 3.41 5.21 44.01
Cr2O3 n.a. 0.46 0.93 18.26 n.a. 0.53 1.01 10.46 n.a. 0.50 1.30 24.24
FeOtot 9.53 6.02 2.49 10.82 10.66 6.11 2.97 10.46 9.34 5.66 2.55 12.14
MnO 0.17 0.10 0.05 b.d.l. b.d.l. 0.17 0.02 b.d.l. 0.12 0.08 b.d.l. b.d.l.
NiO 0.42 n.a. n.a. 0.36 0.34 n.a. n.a. 0.35 0.38 n.a. n.a. 0.23
MgO 49.08 32.99 16.15 19.65 48.42 33.19 15.50 20.75 48.65 32.66 16.24 18.25
CaO 0.07 0.66 22.17 n.a. 0.09 0.74 20.20 n.a. 0.07 0.88 20.24 n.a.
Na2O n.a. 0.09 0.86 n.a. n.a. 0.06 1.42 n.a. n.a. 0.37 1.66 n.a.
K2O n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a.
Total 100.02 99.25 100.46 99.43 100.42 99.71 100.14 100.10 99.10 99.03 99.87 99.00
Fo 90.2 89.3 90.3
Mg# 0.91 0.92 0.76 0.91 0.90 0.78 0.91 0.92 0.73
Cr# 0.20 0.11 0.27
BR218 BR218* BR219
Ola Opxa Cpxa Sp Ol Opx Cpx Sp Pargasitic Ampha Kaersutitic Amph Ol Opx Cpx Sp
SiO2 40.24 55.38 52.39 0.03 39.84 55.05 51.33 0.03 42.72 42.27 40.69 54.35 52.48 0.04
TiO2 b.d.l. b.d.l. 0.49 0.13 0.00 0.12 0.87 0.51 3.66 4.87 b.d.l. 0.03 0.17 0.20
Al2O3 b.d.l. 4.00 5.19 50.27 0.01 4.55 6.07 46.91 14.82 13.51 0.01 4.23 5.09 52.22
Cr2O3 n.a. 0.50 0.88 17.93 n.a. 0.46 0.90 19.69 0.82 0.90 n.a. 0.54 0.94 15.28
FeOtot 11.97 6.70 2.84 14.28 14.53 8.22 3.74 15.53 4.62 5.15 9.39 6.75 2.64 11.42
MnO 0.02 b.d.l. 0.18 b.d.l. 0.23 0.19 0.11 b.d.l. b.d.l. 0.05 0.18 0.11 0.05 b.d.l.
NiO 0.35 n.a. n.a. 0.29 0.30 n.a. n.a. 0.29 n.a. n.a. 0.38 n.a. n.a. 0.35
MgO 47.31 33.10 15.54 17.35 45.25 31.38 15.68 16.68 16.38 15.87 48.87 32.77 16.11 19.44
CaO 0.07 0.76 21.46 n.a. 0.07 0.90 21.16 n.a. 11.68 11.51 0.08 0.83 22.23 n.a.
Na2O n.a. b.d.l. 1.31 n.a. n.a. 0.09 0.94 n.a. 2.98 2.81 n.a. 0.06 0.78 n.a.
K2O n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. 0.81 0.91 n.a. n.a. n.a. n.a.
Total 99.96 100.44 100.28 100.28 100.22 100.97 100.80 99.64 98.49 97.84 99.59 99.68 100.49 98.93
Fo 87.6 84.7 90.3
Mg# 0.90 0.91 0.68 0.87 0.88 0.66 0.86 0.85 0.90 0.92 0.75
Cr# 0.19 0.22 0.16
Fo forsterite component in olivine; Mg# [MgO/(MgO ? FeOtot) molar]; Cr# [Cr3?/(Cr3??Al3?) atomic]; n.a. not analyzed; b.d.l. below detection limit
* Minerals close to amphibole-bearing veina Data from Perinelli et al. (2006)
Contrib Mineral Petrol (2012) 164:1053–1067 1057
123
Crystallographic and crystal-chemical analysis
of BR218Amph.
Single-crystal structure refinement (SREF) and crystal-
chemical analyses were done in order to understand in
detail the crystal-chemical mechanisms ruling dehydroge-
nation and to evaluate the O2- component in BR218
amphibole. The data collection was done with a Philips
PW1100 single-crystal 4-circle diffractometer equipped
with graphite monochromated Mo-Ka X radiation. The
unit-cell parameters were calculated from least-squares
refinement of the d* values obtained for 60 rows of the
reciprocal lattice by measuring the center of gravity of each
reflection and of its antireflection in the 2h range -70 to
70�. Two monoclinic equivalents were collected in the 2h
range 4–70�, and corrections were applied for absorption
and Lorentz polarization. Reflections with Io [ 3 r(I) were
considered as observed during unweighted full-matrix
least-squares refinement on F done using a program spe-
cifically written at CNR-IGG Pavia to deal with complex
solid-solutions. Scattering curves for fully ionized scatter-
ing species were used at sites where chemical substitutions
occur; neutral versus ionized scattering curves were used at
the T and anion sites. Atom coordinates, equivalent iso-
tropic displacement parameters and their anisotropic
components are reported in Table 4.
Site populations were calculated from the unit formula
and validated based on the structure refinement and the
methods developed for amphiboles at CNR-IGG Pavia
(Oberti et al. 2007). In particular, the populations of the
M(1), M(2) and M(3) sites were derived from refined site-
scattering values and mean bond lengths, and those of the
T(1) and T(2) sites based on the mean bond lengths and
selected compositional parameters. The O2- component
was estimated based on its relation with the M(1)–M(2)
distance, which had been calibrated by SIMS analysis of a
suite of partially dehydrogenated pargasite–hastingsite–
kaersutite (R2 = 0.99). The crystal was then mounted in
epoxy, polished and analyzed by electron microprobe
(same procedures as for the thin section). The crystal-
chemical formula, obtained combining electron microprobe
analyses (EMPA), structure refinement and Mossbauer
results, is discussed in a section below.
Analytical results
Quantification of Fe3?/Fetot ratios in spinel
and amphibole
Fe3?/Fetot ratios measured by Mossbauer analyses (Fe3þMS)
in spinel grains are reported in Table 3. The same table
also reports Fe3þ=Fetot ratios calculated from EMP analy-
ses on basis of charge balance by assuming a perfect
stoichiometry for the mineral (Fe3þEMPA). Fe3þ=Fetot ratios
determined by MS on GP spinels range from 0.17 to 0.35;
in contrast, those determined on BR spinels are lower and
more homogeneous, ranging from 0.13 to 0.15. Notably,
for GP spinels, Fe3þ=Fetot ratios show a rough correlation
with metasomatism, whereas for BR spinels, there is no
significant difference between cryptically and modally
metasomatized samples (Tables 1, 3).
Indeed, for all samples, Fe3?/Fetot ratios derived by
Mossbauer analysis are systematically higher than those
calculated from EMPA assuming spinel stoichiometry, the
largest differences being observed for metasomatized GP
xenoliths (Table 3; Fig. 4). It is well known that the
expcalc.
Fe3+
Fe2+
velocity (mm/s)
tran
smit
tanc
e (%
)
-4 0-1-2-3 1 2 3 4
99.2
99.4
99.6
99.8
100.0
99.0
Fig. 3 Typical 57Fe Mossbauer spectrum of spinels from NVL
mantle xenoliths, collected at room temperature
Table 3 Fe3?/Fetot ratios and oxidation degree in spinels of NVL
mantle xenoliths
Sample Fe3?/Fetot from
Mossbauer
Fe3?/Fetot from
EMPA
z (%)
GP6 0.35 0.06 26
GP22 0.25 0.04 19
GP31 0.31 0.01 27
GP40 0.17 0.13 5
GP42 0.22 0.11 9
BR213 0.15 0.12 1
BR218 0.14 0.06 6
BR218* 0.13 0.10 2
BR219 0.14 0.12 1
BR218Amph 0.24
* Close to amphibole vein; BR218Amph: kaersutite-type amphibole
within amphibole-bearing vein in BR218; errors on Fe3?/Fetot ratios
estimated at maximum ±0.03; z %: oxidation degree of spinels cal-
culated after Quintiliani et al. (2006)
1058 Contrib Mineral Petrol (2012) 164:1053–1067
123
assumption of spinel stoichiometry may produce large
uncertainties on Fe3?/Fetot ratios quantification due to the
following: (1) systematic errors associated with the very
low amounts of magnetite component in mantle spinels
(commonly \ 10 mol %; Canil et al. 1990); (2) underes-
timation of Fe3? content in the spinel arising from possible
non-stoichiometry linked to Fe3? excess and cation
vacancies (Andreozzi and Lucchesi 2002; Bosi et al. 2004;
Lenaz et al. 2004; Quintiliani et al. 2006).
As pointed out by Bosi et al. (2004), the Fe3? excess
(the difference between Fe3þMS and Fe3þ
EMPA) can reflect
secondary oxidation processes. In particular, Fe3? of pri-
mary mineral formation (Fe3þP ) must be distinguished from
Fe3? excess derived by secondary oxidation. In this pro-
cess, the oxidation of primary Fe2þ Fe2þP
� �is matched by
the formation of cation vacancies (h). Menegazzo et al.
(1997) and Quintiliani et al. (2006) used crystal-chemical
data of spinel samples to calculate their degree of oxidation
z ¼ 8h= 3�hð ÞFe2þP . The parameter z may be used to
reconstruct the oxidation history of spinel samples: absence
of secondary oxidation corresponds to z = 0 %, full oxi-
dation corresponds to z = 100 %. Moreover, at z = 0 %,
the spinel composition is perfectly stoichiometric, and
therefore, Fe2þP and Fe3þ
P contents may be effectively rep-
resented by Fe2? and Fe3? calculated from EMPA data.
Values of z obtained for GP and BR spinels range from 5
to 27 % and from 0 to 6 %, respectively (Table 3; Fig. 5).
On conservative basis, only z values higher than 10 %
should be used to infer oxidation event(s). Therefore, GP
metasomatized spinels are characterized by minor to
medium oxidation, whereas BR spinels do not show any
clear evidence of oxidation. It is important to point out that
none of the crystals shows any evidence of alteration by
Table 4 Atom coordinates and atomic-displacement parameters (Beq, A2; bii 9 104) for the refined amphibole from amphibole-bearing vein in
BR218 xenolith (no. 1215 in the CNR-IGG-Pv database)
Atom x/a y/b z/c Beq b11 b22 b33 b12 b13 b 23
O(1) 0.10745 0.08658 0.21882 0.94 0.00226 0.00081 0.00866 -0.00017 0.00089 -0.00007
O(2) 0.11878 0.17171 0.72855 0.90 0.00218 0.00078 0.00826 -0.00004 0.00069 0.00026
O(3) 0.10793 0.00000 0.71446 1.09 0.00247 0.00094 0.01023 0.00000 0.00066 0.00000
O(4) 0.36580 0.25019 0.78686 1.19 0.00392 0.00078 0.01073 -0.00040 0.00146 0.00023
O(5) 0.35004 0.13961 0.10891 1.21 0.00270 0.00116 0.01010 -0.00007 0.00067 0.00115
O(6) 0.34610 0.11676 0.60813 1.25 0.00278 0.00113 0.01188 0.00007 0.00131 -0.00104
O(7) 0.34291 0.00000 0.27861 1.46 0.00312 0.00102 0.01716 0.00000 0.00099 0.00000
T(1) 0.28253 0.08523 0.30243 0.68 0.00188 0.00052 0.00632 -0.00008 0.00067 -0.00004
T(2) 0.29070 0.17271 0.81009 0.66 0.00175 0.00056 0.00580 -0.00011 0.00082 0.00005
M(1) 0.00000 0.08501 0.50000 1.16 0.00245 0.00147 0.00674 0.00000 0.00143 0.00000
M(2) 0.00000 0.17683 0.00000 0.69 0.00195 0.00057 0.00611 0.00000 0.00095 0.00000
M(3) 0.00000 0.00000 0.00000 0.81 0.00247 0.00057 0.00658 0.00000 0.00022 0.00000
M(4) 0.00000 0.27845 0.50000 1.00 0.00317 0.00074 0.01020 0.00000 0.00305 0.00000
A 0.00000 0.50000 0.00000 2.71 0.01071 0.00110 0.04164 0.00000 0.01957 0.00000
A(m) 0.05518 0.50000 0.10767 2.75 0.00941 0.00183 0.02934 0.00000 0.01000 0.00000
A(2) 0.00000 0.46926 0.00000 2.86 0.01034 0.00085 0.04949 0.00000 0.01934 0.00000
M(40) 0.00000 0.25438 0.50000 1.10
oxidation
0.0
0.1
0.2
0.3
0.4
0.0 0.1 0.2 0.3 0.4
Fe3+/Fetot EMPA
Fe3+
/Fe to
t Mss
baue
r
GP
BR
BR218*
1:1 lin
e
Fig. 4 Fe3?/Fetot ratios calculated from EMPA by assuming a perfect
stoichiometry for the spinels compared with Fe3?/Fetot ratios based
on Mossbauer Fe3? determination. The gray field about the 1:1 line
represents the confidence band for which spinels may be considered
not have been affected by secondary oxidation (z \ 10 %, see text).
GP Greene Point, BR Baker Rocks, BR218* portion of the lherzolite
adjacent to amphibole-bearing vein
Contrib Mineral Petrol (2012) 164:1053–1067 1059
123
weathering (atmospheric or superficial alteration); hence,
the observed oxidation must have occurred in the mantle.
The Fe3?/Fetot ratio measured on the amphibole
BR218Amph is 0.24 (Table 3). This value falls within the
range 0.2–0.5 typical for Ti–rich amphiboles in the upper
mantle (Popp and Bryndzia 1992; Canil and O’Neill 1996).
Cation distribution of the amphibole BR218Amph
and dehydrogenation
Crystal data and structure refinement results of relevance
are summarized in Table 5; the unit formula based on all
the available information (EMP, SREF and MS) is reported
in atoms per formula unit (apfu) in Table 6. Note the close
agreement between SREF and EMP analyses (126.25 vs.
126.45 electrons per formula unit, epfu, for all the cation
sites). Site populations for the T and M sites were calcu-
lated based on refined site-scattering values (ss, epfu) and
mean bond lengths (mbl, A). Tetrahedral mbl confirm that
all TAl is ordered at the T(1) site; the absence of TAl dis-
order usually indicates temperature of crystallization
B850 �C. For the M(1, 3) sites, the crystal-chemical
information to be taken into account is as follows: (1) a
M(1) - M(2) distance corresponding to 0.94 O2- apfu at
O(3) (Oberti et al. 2007); (2) the presence of significant Ti
(because the Beq value at M(1) is much higher than those at
the M(2) and M(3) sites) and of very low Fe3? content
(because the value of DM(1) is very low) at the M(1) site.
Taking into account these constraints and the refined ss and
mbl values, the best cation distribution we have obtained
(in apfu) is as follows:
M 1ð Þ : Mg1:33Fe2þ0:18Fe3þ
0:05Ti0:44 ssobs¼ 31:52;sscal¼ 31:62½ �;M 2ð Þ : Mg1:19Fe2þ
0:03Al0:48Fe3þ0:10Cr0:11Ti0:09
ssobs¼ 28:22;sscal¼ 28:45½ �;M 3ð Þ : Mg0:78Fe2þ
0:22 ssobs¼ 15:10;sscal¼ 15:08½ �:
Hence, the BR218Amph is kaersutite according to the
nomenclature of Leake et al. (1997), but will become
partially dehydrogenated Ti-rich pargasite in the new
nomenclature scheme for amphiboles recently approved
by IMA. What is more relevant to the present study,
the oxo component in BR218Amph is balanced almost
uniquely by the occurrence of Ti at the M(1) site
[Mð1ÞTi1Oð3ÞO2�
2Mð1Þ Fe2þ;Mg� �
�1Oð3ÞOH��2], a feature
that testifies crystallization in a low aH2O environment. In
contrast, the presence of M(1)Fe3? in BR218 kaersutite,
which would have testified post-crystallization dehydro-
genation according to the reaction Mð1;3ÞFe3þ1
Oð3ÞO2�1
Mð1;3ÞFe2þ�1
Oð3ÞOH��1, is very low (max 0.05 apfu) and
implies that the H loss in kaersutite during the xenolith
ascent, if any, is negligible. It follows that the oxo
-1.8
-1.6
-1.4
-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0 5 10 15 20 25 30
GP 31 F ~ 10%
GP 6 F ~ 15%
degree of oxidation z (%)
Δlog
fO2
GP 22 F ~ 15%
metasomatic oxidationno oxidation
BR218*close to amphibole-bearing vein
Δ log fO2 error bar
GP 42 F ~ 2%
GP 40 F ~ 8%
BR218 F ~ 8%
BR219F ~ 6%
BR213F ~ 11%
GP cryptically metasomatized
GPunmetasomatized
BR cryptically metasomatized
Fig. 5 DlogfO2 (fO2 relative to FMQ) for GP and BR mantle
xenoliths plotted against the oxidation degree parameter z. F is the
degree of partial melting for the two indicated xenoliths estimated by
the Hellebrand et al. (2001) method
Table 5 Crystal data and miscellaneous refinement information for kaersutite from amphibole-bearing vein in BR218 xenolith (no. 1215 in the
CNR-IGG-Pv database)
a (A) 9.8543(4) Crystal size (lm) 200 9 220 9 350 ss M(1) 31.57 T(1)–O (A) 1.672(1)
b (A) 18.0431(8) Radiation/monochromator MoKa/Graphite ss M(2) 28.22 T(2)–O (A) 1.638(1)
c (A) 5.3037(2) No. unique reflections 1380 ss M(3) 15.10 M(1)–O (A) 2.070(1)
b (�) 105.201(1) No. observed reflections (I C 3rI) 1270 ss M(4) 37.20 M(2)–O (A) 2.064(1)
V (A3) 910.02 Rmerge % 1.80 ss M(40) 1.94 M(3)–O (A) 2.065(1)
Sp. Gr. C2/m Robs % 2.26 ss A 3.34 M(1)–M(2) (A) 3.127(1)
Z 2 Rall % 2.44 ss A(m) 5.65 DM(1) 4.41
Dcalc (g cm-3) 3.17 Largest diff. peak (eA-3) 0.88 ss A(2) 3.48
ss refined site-scattering values (electrons per formula unit), DM(1) calculated according to Brown and Shannon (1973)
1060 Contrib Mineral Petrol (2012) 164:1053–1067
123
component (O2-*1 apfu) can be entirely ascribed to
crystallization conditions.
Redox conditions estimates
Oxygen fugacity calculations from spinel
One of the approaches most used to quantify the oxidation
state of shallow spinel-facies peridotite mantle is based on
the equilibrium reaction:
6Fe2SiO4 olivineð Þ þ O2 ¼ 3Fe2Si2O6 orthopyroxeneð Þþ 2Fe3O4 spinelð Þ ð1Þ
where Fe2SiO4, Fe2Si2O6 and Fe3O4 are the fayalite, fer-
rosilite and magnetite component in olivine (ol), orthopy-
roxene (opx) and spinel (sp), respectively.
Oxygen fugacity of BR and GP spinel peridotites was
estimated by two of the most accepted formulations, those
proposed by Wood (1990) and by Ballhaus et al. (1991).
The computed fO2 are expressed in log-bar unit relative to
the fayalite–magnetite–quartz (FMQ) buffer and are called
Dlog fO2 (Table 7). To calculate oxygen fugacity, we used
the Fe3?/Fetot value determined in spinel by Mossbauer
analyses, along with the equilibrium T and P values
reported in Table 1, with the exception for BR218*, for
which the equilibrium temperature was fixed at 900 �C
instead of 927 �C (Table 1) to take into account the
information obtained from SREF on amphiboles
(T B 850 �C) and on spinel (T = 909 �C, Perinelli et al., in
preparation). The use of T = 900 �C for calculation pro-
duces an uncertainty on Dlog fO2 (\0.1 log-bar units) well
below to that associated with the two methods used to
calculate fO2 (Dlog fO2 ± 0.5 log-bar units, Wood 1990;
Canil et al. 1990; Ballhaus et al. 1991).
Finally, the T–P uncertainties associated with each
investigated sample provide a maximum error on Dlog fO2
of ± 0.12 log-bar units.
The methods of Wood (1990) and Ballhaus et al. (1991)
yielded similar estimations for all samples at the level of
the calibration (differences are Dlog fO2 B 0.5 log-bar
units). Since both the Ballhaus et al. (1991) and Wood
(1990) models yield similar fO2 estimates and identify
similar variations of the local oxidation state, in the fol-
lowing discussion we chose to adopt the values calculated
following the first model.
Oxygen fugacity calculations from amphibole
The hydrogen fugacity, (fH2), and hence the oxidative
conditions, fO2, at which kaersutite BR218Amph crystal-
lized can be evaluated by the method proposed by Popp
et al. (1995; 2006). The Popp et al. (1995) approach is
Table 6 Chemical composition and unit formula (based on 24
anions) for kaersutite from amphibole-bearing vein in BR218 xenolith
wt % apfu
SiO2 42.27 Si 6.162
TiO2 4.87 Al 1.838
Al2O3 13.51 Sum T 8.000
Cr2O3 0.90 Ti4? 0.534
FeO* 3.92 Al 0.484
Fe2O3* 1.36 Fe3? 0.149
MnO 0.05 Fe2? 0.428
MgO 15.87 Mg 3.301
CaO 11.51 Cr 0.104
Na2O 2.81 Sum C 5.000
K2O 0.91 Ca 1.798
H2O** 1.00 Mg 0.145
F 0.19 Fe2? 0.050
Cl 0.03 Mn2? 0.007
–O=F -0.08 Sum B 2.000
–O=Cl -0.01 K 0.169
Total 99.12 Na 0.793
Sum A 0.962
ssEMPA 126.25 OH 0.972
ssSREF 126.45 O 0.933
F 0.088
Cl 0.007
Sum W 2.000
* FeO:Fe2O3 ratio calculated from SREF and Mossbauer results
** Calculated based on 24 (O, OH, F, Cl) with (OH ? F?Cl) = 2
apfu
Table 7 Oxygen fugacities for NVL mantle xenoliths
Sample DlogfO2
(Ballhaus
et al. 1991)
DlogfO2
(Wood
1990)
DlogfO2
from
BR218Amph
GP6 -0.23 -0.47
GP22 -0.54 -0.68
GP31 -0.65 -0.14
GP40 -1.35 -1.04
GP42 -1.20 -0.95
BR213 -1.21 -0.88
BR218 -1.14 -1.21
BR218* -1.52 -1.48 -1.71
BR219 -1.27 -0.89
DlogfO2: oxygen fugacity relative to FMQ buffer. In the first and
second columns, fO2 is based on spinel-bearing inter-crystalline
equilibrium (log-bar units, estimated error ±0.5); in the third column,
fO2 is based on amphibole intra-crystalline equilibrium (log-bar units,
estimated error ±1)
* Close to amphibole-bearing vein
Contrib Mineral Petrol (2012) 164:1053–1067 1061
123
based on the reaction expressed in terms of amphibole Ca,
Fe end-member:
Ca2Fe2þ5 Si8O22 OHð Þ2¼ Ca2Fe2þ
3 Fe3þ2 Si8O24 þ H2 ð2Þ
For this reaction, the equilibrium constant (K) is
expressed as
K ¼ f H2ð28:94Þ XFe3þð Þ2 Xvð Þ2
XFe2þð Þ2 XOHð Þ2U ¼ KXU ð3Þ
where v is the oxo component (i.e., the amount of O2-
instead of OH- at the O(3) site), U is the activity
coefficient term and KX is the thermodynamic mole
fraction term (i.e., the K expressed as mole fractions
rather than as activities). Popp et al. (2006) also expressed
the variation of KX as a function of T, P and amphibole
composition, with the equation:
log KX ¼ 4:23� 4380
T Kð Þ þ 2:61 Ti apfuð Þ � 0:42½ �f g
þ 88
T Kð Þ P kbarð Þ � 1½ �� �
ð4Þ
which takes into account also the Ti content. The method is
calibrated experimentally, and its uncertainty is ±0.4 log-
bar units (Popp et al. 2006). In the case of BR218Amph,
using the crystal-chemical data, the measured Fe3?/Fetot
ratio by Mossbauer analyses and the P and T of 0.9 GPa
and 900 �C, respectively, the method provided estimates of
log fH2 = ?1.62 log-bar units.
As stated previously, the approach used by Popp et al.
provides the fH2 conditions of amphibole crystallization;
thus, the corresponding fO2 is to be determined using the
following equilibrium reaction:
H2O ¼ 1
2O2 þ H2 ð5Þ
for which the equilibrium constant (KH2O) is as follows:
KH2O ¼f H2 f O2ð Þ1=2
f H2Oð6Þ
In the environment in which mantle amphiboles formed,
the pressure of fluid is likely less than of the total pressure
(Pfluid \ Ptotal), and hence, the fH2O is a function of water
activity, aH2O:
f H2O ¼ f �H2O � aH2O ð7Þ
where f*H2O is the fugacity of pure H2O at a given P and T,
and aH2O (at the same P and T) is to be determined. Albeit
not commonly applied to mantle rocks, a method to cal-
culate water activity is the use of H2O-buffering equilibria
among the end-member components of peridotite minerals
(olivine, orthopyroxene, clinopyroxene, spinel/garnet and
amphibole; see ‘‘Dehydration equilibria’’ section in Popp
et al. 2006).
Following the criteria reported in Popp et al. (2006), and
keeping in mind the uncertainties involved in this approach
(Popp et al. 2006; Lamb and Popp 2009), we determined
the aH2O for BR218Amph by fixing the location of uni-
variant H2O-buffering equilibria as a function of P, T and
aH2O using the THERMOCALC software (Holland and
Powell 1990, 1998). Starting from the composition of the
co-existing minerals in BR218* (olivine, ortho- and
clinopyroxene and spinel plus amphibole, Table 2), the
values of aH2O were calculated for the following reactions
at 900 �C and 0.9 GPa.
2trþ 2fo ¼ 4diþ 5enþ 2H2O ð8Þ2trþ 2sp ¼ 2diþ 2catsþ 5enþ 2H2O ð9Þ2trþ 2sp ¼ 4diþ 3enþ 2mgtsþ 2H2O ð10Þ2trþ 3catsþ 2sp ¼ 7diþ 5mgtsþ 2H2O ð11Þ2trþ 2mgtsþ 2sp ¼ 4catsþ 7enþ 2H2O ð12Þ5trþ 2pargþ 7cats ¼ glþ 21diþ 9mgtsþ 6H2O ð13Þ5trþ 2parg ¼ glþ 14diþ 7enþ 2mgtsþ 6H2O ð14Þ7trþ glþ 12sp ¼ 2pargþ 10catsþ 21enþ 6H2O ð15Þ
where tr = tremolite, fo = fosterite, di = diopside,
en = enstatite, sp = spinel (MgAl2O4), cats = Ca-tscher-
mak, mgts = Mg-tschermakite, parg = pargasite and
gl = glaucophane are the relevant mineral end-members.
The aH2O values calculated for the dehydration equi-
libria (8)–(15) vary from a 0.02 (reaction 12) to 0.11
(reaction 8), except the reaction (11) for which the calcu-
lated aH2O is 0.25. The mean value of aH2O is 0.06 and
the1r of 0.02.
This estimate is consistent with the crystal-chemical
constraints (see above) that imply amphibole crystalliza-
tion in a low aH2O environment.
On the basis of aH2O (0.06) and KH2O (at appropriate
P and T; Bandura and Livov 2006), the fO2 conditions of
amphibole crystallization, and hence of the metasomatizing
agent can be estimated by the Eqs. (6) and (7) and result in
a value of Dlog fO2 = -1.71 log-bar units. The minimum
uncertainty on this value (±1 log-bar units) is mainly due
to the uncertainties involved in the method used to estimate
aH2O and fH2.
Discussion
Oxygen fugacity in northern Victoria Land lithospheric
mantle
Calculated fO2 values cluster below the FMQ buffer, and
Dlog fO2 varies from -1.52 to -0.23 log-bar units
(Table 7) well within the range accepted for subcontinental
1062 Contrib Mineral Petrol (2012) 164:1053–1067
123
lithospheric mantle (Dlog fO2 from -2.0 to ?1.0 log-bar
units; Ionov and Wood 1992; Ballhaus 1993; Woodland
et al. 2006).
No sample lacking metasomatic overprint has been yet
recovered at Baker Rocks; however, it is reasonable to
consider the less cryptically metasomatized sample
(BR219) as the best constraint to pre-metasomatic fO2.
Under this assumption, the lithospheric mantle underlying
both localities has a similar pre-metasomatic oxidation
state as testified by the close agreement between the
Dlog fO2 values obtained from BR219 (-1.27 log-bar
units) and those from GP40 and GP42, representative of
Greene Point unmetasomatized lithospheric mantle (-1.35
and -1.20 log-bar units, respectively).
Partial melting should lead to reduction of residual
mantle peridotite due to the preferential partitioning of
Fe3? into the produced melt (Bryndzia and Wood 1990;
Arculus 1994; Kadik 1997; Lee et al. 2003; McCammon
and Kopylova 2004 and reference therein); this in turn
should yield a negative correlation between fO2 and indi-
cators of the residual nature of peridotite (i.e., Cr# in spi-
nel). Contrary to this prediction, no clear correlations could
be found between fO2 values and the degree of depletion in
NVL peridotites. Rather, the samples from Greene Point
show a roughly mutual increase of Dlog fO2 and spinel Cr#.
Within this suite, the unmetasomatized GP42 and GP40
samples whose degree of partial melting F was estimated to
be 2 and 8 %, respectively, indicate virtually no change of
the local fO2 induced by partial melting event process
(Table 7). The other selected GP samples which have a
higher refractory character (harzburgites GP6, GP22 and
GP3), according to what stated above, should document a
local decrease of oxidation state; in contrast, they yield
values of Dlog fO2 higher than those obtained from GP42
and GP40 (Fig. 5). It should be noted that these harzburgite
samples are also those cryptically metasomatized, whose
spinel analysis provided the highest degree of oxidation
(z = 19–26 %; Fig. 5). This finding suggests that, although
no apparent correlation between estimated Dlog fO2 values
and the enrichment in incompatible elements could be
found, the high Dlog fO2 values obtained for GP metaso-
matized xenoliths could have been induced by the Ceno-
zoic metasomatism.
Several authors (Menzies et al. 1987; Ballhaus 1993 and
reference therein) have noted a fO2 versus Cr# correlation
in subcontinental mantle xenoliths, similar to that defined
by GP samples. The correlation has been ascribed to a
higher activity of metasomatizing oxidized fluids/melts on
a refractory harzburgite rather than on a fertile lherzolite
‘‘even if the amount of oxygen or Fe3? added to fertile and
refractory domains is the same’’ (Ballhaus 1993). Ionov
and Wood (1992), instead, did not detect any relationship
between fO2 values and the degree of depletion and/or
metasomatism in spinel peridotites from continental rift
environments. Nevertheless, within our samples, we
observe that peridotite xenoliths with comparable degree of
depletion (e.g., the unmetasomatized GP40 with F = 8 %,
the metasomatized GP31 or BR218* with F = 10 and
9 %), show variations in Dlog fO2 (-1.35 log-bar units,
-0.65 log-bar units and -1.52 log-bar units, respectively)
that cannot be explained by the low fO2-buffering associ-
ated to the depleted character of these xenoliths. This
observation suggests that, when associated with variable
chemical enrichments, Cenozoic metasomatism induced
local oxidation within GP lithospheric mantle, whereas at
Baker Rocks, the redox state of lithospheric mantle was not
altered by the metasomatic event. Hence, we infer that the
metasomatic melts acting in the two sites were different in
fO2 conditions.
Oxygen fugacity of metasomatizing melts
At Greene Point, the distinctive metasomatic overprint
on trace element patterns points to a silicate metasomatic
agent resembling the host lava of the xenoliths (SAX20,
Perinelli et al. 2006); however, textural features of the
GP xenoliths and the fast magma ascent rates exclude
that the metasomatic event and the entrapment of the
xenoliths are contemporary. Nevertheless, host lava
SAX20 can be used to bracket the oxygen fugacity
during metasomatism.
In porphyritic rocks, the estimated fO2 value may not
represent the redox conditions of host lava at its origin;
indeed, it is related to conditions prevailing during the
crystallization; in fact, fractionation of olivine and/or
clinopyroxene, whose Fe3?/Fetot ratio is lower than that of
melt, can promote relative oxidation (Ballhaus 1993).
However, the low content of crystals (\10 % vol. pheno-
crysts, Orlando et al. 1997) of SAX20 allows a reliable
estimate of the upper limit of fO2 using the Kress and
Carmichael (1991) model. The Fe2? and Fe3? content in
the melt has been derived from the experimental data on
Cr-spinel-silicate melt equilibria through the equation
proposed by Maurel and Maurel (1982):
log Fe2þ=Fe3þ� �sp¼ 0:764� log Fe2þ=Fe3þ� �
melt�0:343
ð16Þ
Using the compositions of chromium-bearing spinels
(Cr# = 0.63) in olivine phenocrysts (Fo = 78–81), the
calculated value of fO2 in SAX20, expressed as Dlog fO2,
ranges from ?1.1 to ?1.5 log-bar units, at T = 1095 �C
(olivine-spinel geothermometer, Ballhaus et al. 1991) and
P = 1.3 GPa (the mean value of equilibrium pressures
estimated for the GP xenoliths). The relatively high oxygen
fugacity inferred for this possible metasomatic melt(s) is
Contrib Mineral Petrol (2012) 164:1053–1067 1063
123
compatible with the increase of about 1 log-bar unit
observed in the metasomatized GP xenoliths (Fig. 6).
At Baker Rocks, the crystallization of amphiboles in the
metasomatic vein in the BR218 xenolith points to redox
conditions of Dlog fO2 = -1.71 log-bar units; this value
fairly matches the fO2 conditions estimated for the peri-
dotite matrix adjacent to the vein (BR218*; Fig. 6) and
suggests a similar oxidation state for both metasomatizing
melt(s) and the lithospheric mantle in this area.
Coltorti et al. (2004) proposed that a melt similar to
nephelinite SAX20 could represent a possible metasomatic
agent also at Baker Rocks. However, the experimental
study of Perinelli et al. (2008) did not provide any clear
evidence in support of this hypothesis because: (1) the
changes induced in the composition of primary minerals
only in part matched those found in minerals from natural
metasomatized xenoliths and (2) no run produced an
amphibole-bearing paragenesis.
Moreover, the high oxygen fugacity conditions esti-
mated for SAX20 metasomatic melt (Dlog fO2 = ?1.1 to
?1.5 log-bar units) are in contrast with those indicated by
both the amphibole-bearing vein in BR218 xenolith
(Dlog fO2 = -1.71 log-bar units) and the peridotite matrix
(Dlog fO2 = -1.52 log-bar units close to the vein, and
-1.14 log-bar units far from the vein). Therefore, at Baker
Rocks, a SAX20-like metasomatic silicate melt can be
excluded.
At Baker Rocks, the lack of Cr-spinel phenocrysts in the
less evolved magmas erupted in the Mt. Melbourne Vol-
canic Province prevents the application of the approach
used for SAX20 host lava to derive the fO2 conditions of
the lithospheric mantle. However, the titanomagnetite-
ilmenite pairs occurring in the groundmass of basanites/
olivine-basalts erupted in the area (Armienti et al. 1991)
can be used for this purpose. In fact, the application of the
titanomagnetite-ilmenite oxybarometer provides an esti-
mation of the range of fO2 at which basic magmas evolved
and hence provides an upper limit to the oxidation state of
shallow mantle beneath Baker Rocks. The Dlog fO2, cal-
culated by the titanomagnetite-ilmenite oxybarometer
proposed by Sauerzapf et al. (2008), varies from -1.6 to
-0.9 log-bar units, close to the range estimated for both
BR xenoliths and amphibole-bearing vein and far from
Dlog fO2 estimated for SAX20. These results strongly
support the conclusion that different melts are responsible
for the distinct styles of metasomatism of lithospheric
mantle of Greene Point and Baker Rocks recorded by the
xenoliths.
In summary, we can suggest that at Greene Point, a
SAX20-like melt metasomatized the peridotite portions
closest to the magma conduits (vein and/or dyke); in
contrast, at Baker Rocks, the metasomatism can be
described as a continuous differentiation process of ba-
sanitic/olivine-basalt melts that during their rise within
the lithospheric mantle, generated anhydrous and hydrous
veins plus Fe–Ti enrichment or cryptic enrichment of
incompatible elements in the surrounding peridotite. This
is in agreement with the mechanisms of formation of
hydrous/anhydrous metasomatic veins in the lithospheric
mantle proposed by several authors (i.e., Harte et al.
1993) and with the experimental studies of Pilet et al.
(2009), which suggest that the formation of amphibole-
bearing metasomatic veins can be explained by the
percolation and differentiation of small-melt fraction,
produced by low-degree partial melting of a depleted
mantle source.
Metasomatism and geodynamic context
As stated previously, the metasomatic event documented in
GP and BR mantle xenoliths is related to magmatic activity
during the Cenozoic Ross Sea rifting. The development of
the Ross Sea rift system and associated magmatic activity
in northern Victoria Land had been linked to dextral
transtensional movements connected with an important
reorganization in plate kinematics in the Southern Hemi-
sphere (Rocchi et al. 2002, 2005; Storti et al. 2007). Iso-
topic and geochemical features of NVL Cenozoic basalts
point to a model for which the source of these near-primary
melts is a sublithospheric mantle, metasomatized during
the initial extensional event that affected the West Ant-
arctic Rift System in the Late Cretaceous (Nardini et al.
2009). After the first phase of Ross Sea opening, at the
edge of the lithospheric step between the thick East Ant-
arctic craton and the thinned crust of the Ross Sea, an
‘‘edge effect’’ in mantle circulation (Faccenna et al. 2008)
may have provided the heat source to warm up the
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
GP6
GP Host lava
GP22
GP31
GP40
GP42
BR213
BR219
BR218
BR218*
BR218 Amph
Δlo
gfO
2
FMQ buffer
cryptically metasomatized
unmetasomatized
close to amphibole-bearing vein
crypticallymetasomatized
SAX20
Fig. 6 A summary of oxygen fugacity values estimated for Greene
Point and Baker Rocks mantle samples. fO2 values, expressed as
deviation from FMQ buffer, estimated from amphibole of BR218
xenolith and from the SAX20 melanephelinite are reported
1064 Contrib Mineral Petrol (2012) 164:1053–1067
123
lithospheric mantle beneath northern Victoria Land
(Armienti and Perinelli 2010).
During Eocene–Oligocene, the reactivation of Palaeo-
zoic lithospheric discontinuities in northern Victoria Land
was due to the increase in differential velocity across the
Southern Ocean fracture zones (Rocchi et al. 2002, 2005;
Storti et al. 2007). This induced local mantle decompres-
sion and melting providing magma that initially was em-
placed as plutons and dyke swarms (Rocchi et al. 2002).
From Late Miocene to Present, the craton-ward mantle
flow led to collapse of the rift shoulder and normal faulting
which favored the rise of magmas to the surface (Nardini
et al. 2009).
In this frame a ‘‘short-term metasomatic’’ mechanism
(Pilet et al. 2004, 2008) has been proposed to account for
the Sr–Nd–Pb isotopic ratios of NVL near-primary melts
(Nardini et al. 2009) and for isotopic heterogeneity of
parental and metasomatizing melts revealed by the geo-
chemistry of Browning Pass cumulates (Perinelli et al.
2011). The ‘‘short-term metasomatic’’ model envisages a
vein-plus-wall mechanism similar to that proposed by Fo-
ley et al. (2006) for magmatism linked to the Phanerozoic
Lambert-Amery Rift in eastern Antarctica, in which melts
produced during decompression mantle melting in the early
phase of rifting form veins in overlying lithosphere by a
percolative fractional crystallization process. These enri-
ched veins are probably more oxidized with respect to
surrounding depleted mantle. As the rifting proceeds, the
progress of mantle decompression and/or the onset of local
thermal perturbation promote melting of the low-solidus
enriched veins characterizing the chemistry of the early
magmas. While the rifting advances, more and more heat is
provided by the upward movement of isotherms and by
convection inducing the melting in the relatively reduced
peridotite matrix.
Thus, the differences in oxygen fugacity caused by
distinct metasomatic melts acting in Greene Point and
Baker Rocks, possibly reflect the contributions of two end-
members. The former represents the melting of metaso-
matic veins/domains emplaced during the amagmatic phase
of Ross Sea rifting, while the latter is the effect of partial
melting induced in the mantle wedge by edge-driven con-
vection of asthenospheric mantle, developed at the
boundary between thick East Antarctic Craton and thin
Ross Sea lithosphere.
Acknowledgments We wish to thank both the Editor, C. Ballhaus,
and the two reviewers, I. Parkinson and anonymous, for their careful
work and their very constructive comments. We gratefully acknowl-
edge funds provided by the project PRIN 2008 ‘‘SPIN GEO-TECH’’
and PRIN 2009 ‘‘Structure, microstructures and cation ordering: a
window on to geological processes and geomaterial properties’’.
M. Serracino (CNR-IGAG) kindly helped during EMP analyses.
References
Andreozzi GB, Lucchesi S (2002) Intersite distribution of Fe2? and
Mg in the spinel (sensu stricto)-hercynite series by single-crystal
X-ray diffraction. Am Miner 87:1113–1120
Arculus RJ (1994) Aspects of magma genesis in arcs. Lithos
33:189–208
Armienti P, Perinelli C (2010) Cenozoic thermal evolution of
lithospheric mantle in northern Victoria Land (Antarctica):
evidences from mantle xenoliths. Tectonophysics 486:28–35
Armienti P, Civetta L, Innocenti F, Manetti P, Tripodo A, Villani L,
Vita G (1991) New petrological and geochemical data on Mt.
Melbourne volcanic field, northern Victoria Land, Antarctica. (II
Italian Antarctic expedition). Mem Soc Geol It 46:397–424
Ballhaus C (1993) Redox state of lithospheric and asthenospheric
upper mantle. Contrib Miner Petrol 114:331–348
Ballhaus C, Berry RF, Green DH (1991) High pressure experimental
calibration of the olivine-orthopyroxene-spinel oxygen barometer:
implications for the oxidation state of the upper mantle. Contrib
Miner Petrol 107:27–40 (corrected in Contrib Mineral Petrol
(1991) 108:384–384 and Contrib Mineral Petrol (1994) 118:109)
Bandura AV, Livov SN (2006) The ionization constant of water over
wide ranges of temperature and density. J Phys Chem Ref Data
35:15–30
Behrendt JC, LeMausurier W, Cooper AK, Tessensohn F, Trehu A,
Damaske D (1991) Geophysical studies of the West Antarctic
Rift System. Tectonics 10(6):1257–1273
Bosi F, Andreozzi GB, Ferrini V, Lucchesi S (2004) Behavior of
cation vacancy in kenotetrahedral Cr-spinels from Albanian
eastern belt ophiolites. Am Miner 89:1367–1373
Brown ID, Shannon RD (1973) Empirical bond strength-bond length
curves for oxides. Acta Crystallogr A29:266–282
Bryndzia LT, Wood BJ (1990) Oxygen thermobarometry of abyssal
spinel peridotites: the redox state and C-O-H volatile composition
of the Earth’s sub-oceanic upper mantle. Am J Sci 290:1093–1116
Canil D, O’Neill HSTC (1996) Distribution of ferric iron in some
upper-mantle assemblages. J Petrol 37:609–635
Canil D, Virgo D, Christopher M, Scarfe CM (1990) Oxidation state
of mantle xenoliths from British Columbia, Canada. Contrib
Miner Petrol 104:453–462
Coltorti M, Beccaluva L, Bonadiman C, Faccini B, Ntaflos T, Siena F
(2004) Amphibole genesis via metasomatic reaction with
clinopyroxene in mantle xenoliths from Victoria Land, Antarc-
tica. Lithos 75:115–139
De Grave E, Van Alboom A (1991) Evaluation of ferrous and ferric
Mossbauer fractions. Phys Chem Miner 18:337–342
Faccenna C, Rossetti F, Becker TW, Danesi S (2008) Recent
extension driven by mantle upwelling beneath the Admiralty
Mountains (East Antarctica). Tectonics 27:TC4015. doi:
10.1029/2007TC002197
Foley S, Andronikov AV, Jacob DE, Melzer S (2006) Evidence from
Antarctic mantle peridotite xenoliths for changes in mineralogy,
geochemistry and geothermal gradients beneath a developing
rift. Geochim Cosmochim Acta 70:3096–3120
Harte B, Hunter RH, Kinny PD (1993) Melt geometry, movement and
crystallization, in relation to mantle dykes, veins and metaso-
matism. Philos Trans R Soc Lond Ser A 342:1–21
Hawthorne FC, Oberti R (2007) Classification of amphiboles. In:
Hawthorne FC, Oberti R, Della Ventura G, Mottana A (eds)
Amphiboles: crystal chemistry, occurrence, and health issues.
Reviews in Mineralogy and Geochemistry, vol 67, pp 55–88
Hellebrand E, Snow JE, Dick HJB, Hofmann AW (2001) Coupled
major and trace elements as indicators of the extent of melting in
mid-ocean-ridge peridotites. Nature 410:677–681
Contrib Mineral Petrol (2012) 164:1053–1067 1065
123
Hellebrand E, Snow JE, Hoppe P, Hofmann AW (2002) Garnet-field
melting and late-stage refertilization in ‘‘residual’’ abyssal
peridotites from the Central Indian Ridge. J Petrol 43:2305–2338
Holland TJB, Powell R (1990) An enlarged and updated internally
consistent thermodynamic data set with uncertainties and
correlations: the system K2O-Na2O-CaO-MgO-FeO-Fe2O3-
Al2O3-TiO2-SiO2-C-H2-O2. J Metamorph Geol 8:89–124
Holland TJB, Powell R (1998) An internally consistent thermody-
namic data set for phases of petrological interest. J Metamorph
Geol 16:309–343
Ionov DA, Wood BJ (1992) The oxidation state of subcontinental
mantle: oxygen thermobarometry of mantle xenoliths from
central Asia. Contrib Miner Petrol 111:179–193
Kadik A (1997) Evolution of Earth’s redox state during upwelling of
carbon-bearing mantle. Phys Earth Planet Int 100:157–166
Kress VC, Carmichael ISE (1991) The compressibility of silicate
liquids containing Fe2O3 and the effect of composition, temper-
ature, oxygen fugacity and pressure on their redox states. Contrib
Miner Petrol 108:82–92
Kyle PR (1990) McMurdo Volcanic Group-Western Ross Embay-
ment: introduction. In: LeMasurier WE, Thomson JW (eds)
Volcanoes of the Antarctic plate and Southern Oceans American
Geophysical Union, Washington DC, pp 19–25
Lagarec K, Rancourt DG (1998) RECOIL. Mossbauer spectral
analysis software for Windows, version 1.0. Department of
Physics, University of Ottawa, Canada
Lamb WM, Popp RK (2009) Amphibole equilibria in mantle rocks:
determining values of mantle aH2O and implications for mantle
H2O contents. Am Miner 94:41–52
Leake BE, Woolley AR, Arps CES, Birch WD, Gilbert MC, Grice JD,
Hawthorne FC, Kato A, Kisch HJ, Krivovichev VG, Linthout K,
Laird J, Mandarino JA, Maresch WV, Nickel EH, Rock NMS,
Schumacher JC, Smith DC, Stephenson NCN, Ungaretti L,
Whittaker EJW, Guo Y (1997) Nomenclature of amphiboles:
report of the subcommittee on amphiboles of the international
mineralogical association, commission on new minerals and
mineral names. Can Miner 35:219–246
Lee CA, Brandon AD, Norman M (2003) Vanadium in peridotites as a
proxy for paleo-fO2 during partial melting: prospects, limitations,
and implications. Geochim Cosmochim Acta 67:3045–3064
LeMasurier WE, Thomson JW (1990) Volcanoes of the Antarctic
plate and Southern Oceans. Antarctic Research Series, 18.
American Geophysical Union, Washington, DC, p 487
Lenaz D, Andreozzi GB, Mitra S, Bidyananda M, Princivalle F (2004)
Crystal chemical and 57Fe Mossbauer study of chromite from the
Nuggihalli schist belt (India). Miner Petrol 80:45–57
Maurel C, Maurel P (1982) Etude experimentale de l’equilibre Fe2?–
Fe3? dans les spinelles chromiferes et les liquides silicates
basiques coexistants, a 1 atm. CR Acad Sci Paris 295:209–212
McCammon CA, Kopylova MG (2004) A redox profile of the Slave
mantle and oxygen fugacity control in the cratonic mantle.
Contrib Miner Petrol 148:55–68. doi:10.1007/s00410-004-
0583-1
McCammon CA, Griffin WL, Shee SR, O’Neill HSC (2001)
Oxidation during metasomatism in ultramafic xenoliths from
the Wesselton kimberlite, South Africa: implications for the
survival of diamond. Contrib Miner Petrol 141:287–296
McDonough WF, Sun S–S (1995) The composition of the Earth.
Chem Geol 120:223–253
McGuire A, Dyar M, Nielson J (1991) Metasomatic oxidation of
upper mantle peridotite. Contrib Miner Petrol 109:252–264. doi:
10.1007/BF00306483
Melchiorre M, Coltorti M, Bonadiman C, Faccini B, O’Reilly SY,
Pearson NJ (2011) The role of eclogite in the rift-related
metasomatism and Cenozoic magmatism of Northern Victoria
Land, Antarctica. Lithos 124:319–330
Menagazzo G, Carbonin S, Della Giusta A (1997) Cation and vacancy
distribution in an artificially oxidized natural spinel. Mineral
Mag 61:421–441
Menzies MA, Rogers N, Tindle A, Hawkesworth CJ (1987) Meta-
somatic and enrichment processes in lithospheric peridotites, an
effect of asthenosphere-lithosphere interaction. In: Menzies MA
(ed) Mantle metasomatism. Academic Press, London, pp 313–
361
Nardini I, Armienti P, Rocchi S, Dallai L, Harrison D (2009) Sr-Nd-
Pb-He-O isotope and geochemical constraints to the genesis of
Cenozoic magmas from the West Antarctic rift. J Petrol
50:1359–1375
Oberti R, Hawthorne FC, Cannillo E, Camara F (2007) Long-range
order in amphiboles. In: Hawthorne FC, Oberti R, Della Ventura
G, Mottana A (eds) Amphiboles: crystal chemistry, occurrence,
and health issues. Reviews in Mineralogy and Geochemistry, vol
67, pp 125–171
Orlando A, Armienti P, Conticelli S, Vagelli G, Manetti P (1997)
Petrologic investigations on the primitive Cainozoic lavas of
Northern Victoria Land, Antarctica. In: Ricci CA (ed) The
Antarctic region: geological evolution and processes. Terra
Antarctica Publication, Siena, pp 523–530
Parkinson IJ, Arculus RJ (1999) Redox state of subduction zones:
insights from arc peridotites. Chem Geol 160:409–423
Perinelli C, Armienti P, Dallai L (2006) Geochemical and O-isotope
constraints on the evolution of lithospheric mantle in the Ross
Sea rift area (Antarctica). Contrib Miner Petrol 151:245–266
Perinelli C, Orlando A, Conte AM, Armienti P, Borrini D, Faccini B,
Misiti V (2008) Metasomatism induced by alkaline magma on
upper mantle of the Northern Victoria Land (Antarctica): an
experimental approach. In: Coltorti M, Gregoire M (eds) Mantle
metasomatism in intra-plate and suprasubduction settings. Geo-
logical Society. Special Publications, London, vol 293,
pp 197–221. doi:10.1144/SP293.10
Perinelli C, Armienti P, Dallai L (2011) Thermal evolution of the
lithosphere in a rift environment as inferred from the geochem-
istry of mantle cumulates; Northern Victoria Land, Antarctica.
J Petrol 52:665–690
Pilet S, Hernandez J, Bussy F, Sylvester PJ (2004) Short-term
metasomatic control of Nb/Th ratios in the mantle sources of
intraplate basalts. Geology 32:113–116
Pilet S, Baker MB, Stolper EM (2008) Metasomatized lithosphere and
origin of alkaline lavas. Science 320:916–919. doi:10.1126/
science.1156563
Pilet S, Ulmer P, Villiger S (2009) Liquid line of descent of a
basanitic liquid at 1.5 Gpa: constraints on the formation of
metasomatic veins. Contrib Miner Petrol 159:621–643
Popp RK, Bryndzia LT (1992) Statistical analysis of Fe3?, Ti, and OH
in kaersutite from alkalic igneous rocks and mafic mantle
xenoliths. Am Miner 77:1250–1257
Popp RK, Virgo D, Hoering TC, Yoder HS Jr, Phillips MW (1995)
An experimental study of phase equilibria and Fe oxy-compo-
nent in kaersutitic amphibole: implications for the fO2 and aH2O
in the upper mantle. Am Miner 80:534–548
Popp RK, Hibbert HA, Lamb WM (2006) Oxy–amphibole equilibria
in Ti–bearing calcic amphiboles: experimental investigation and
petrologic implications for mantle–derived amphiboles. Am
Miner 91:54–66 (corrected in Am Mineral (2006) 91:216)
Quintiliani M, Andreozzi GB, Graziani G (2006) Fe2?and Fe3?
quantification by different approaches and fO2 estimation for
Albanian Cr-spinels. Am Miner 91:907–916
Rocchi S, Armienti P, D’Orazio M, Tonarini S, Wijbrans J, Di
Vincenzo GD (2002) Cenozoic magmatism in the western Ross
embayment: role of mantle plume vs. plate dynamics in the
development of the West Antarctic Rift System. J Geophys Res
107(B9):2195. doi:10.1029/2001JB000515
1066 Contrib Mineral Petrol (2012) 164:1053–1067
123
Rocchi S, Armienti P, Di Vincenzo G (2005) No plume, no rift
magmatism in the West Antarctic Rift. In: Foulger GR, Natland
JH, Presnall DC, Anderson DL (eds) Plates, plumes, and
paradigms. Geological Society of America, Special Papers, vol
388, pp 435–447
Sauerzapf U, Lattard D, Burchard M, Engelmann R (2008) The
titanomagnetite-ilmenite equilibrium: new experimental data and
thermo-oxybarometric application to the crystallization of basic
to intermediate rocks. J Petrol 49:1161–1185
Storti F, Salvini F, Rossetti F, Phipps Morgan J (2007) Intraplate
termination of transform faulting within the Antarctic continent.
Earth Planet Sci Lett 260:115–126
Tessensohn F, Worner G (1991) The Ross Sea Rift System
(Antarctica): structure, evolution and analogues. In: Thomson
MRA, Crame JA, Thomson JW (eds) Geological evolution of
Antarctica. Cambridge University Press, Cambridge, pp 273–277
Tonarini S, Rocchi S, Armienti P, Innocenti F (1997) Constraints on
timing of Ross Sea rifting inferred from Cainozoic intrusions
from Northern Victoria Land, Antarctica. VII ISAES. The
Antarctic Region: Geological evolution and processes,
pp 511–522
Trehu A, Holt T, Behrendt JC, Fritsch J (1989) Crustal structure in the
Ross Sea, Antarctica: preliminary results from GANOVEX V.
EOS 43(Suppl 70):1344
Wood BJ (1990) An experimental test of the spinel peridotite oxygen
barometer. J Geophys Res 95:15845–15851
Woodland A, Kornprobst J, Tabit A (2006) Ferric iron in orogenic
lherzolite massifs and controls of oxygen fugacity in the upper
mantle. Lithos 89:222–241. doi:10.1016/j.lithos.2005.12.014
Worner G (1999) Lithospheric dynamics and mantle sources of
alkaline magmatism of the Cenozoic West Antarctic Rift
System. Glo Planet Change 23:61–77
Xu YG, Bodinier JL (2004) Contrasting enrichments in high- and
low-temperature mantle xenoliths from Nushan, Eastern China:
results of a single metasomatic event during lithospheric
accretion? J Petrol 45:321–341
Contrib Mineral Petrol (2012) 164:1053–1067 1067
123