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A review of Antarctic granulite-facies rocks
7c,~rf,nf,p~~.\rts. 105
171
(19X4)177- 191
I
A REVIEW OF ANTARCTIC
PrInted m The Netherlands
GRANULITE-FACIES
ROCKS
ABSTRACT
Grew.
ES..
1984. A review of Antarctic
Balakrishna (Editors).
Precambrian
Lithosphere:
granulite-facies
shield. Ages of metamorphic
rocks. In: SM.
rocks occur in significant proportion
pressures.
the approxrmateiy
pressure estimates A
(errant:
sapphirine-quartz+
of
3500 m.v. ages for crust formation
Antarctica.
metamorphism is
interest
garnet, sillimanite-orthopyroxene.
with pyroxene-granulite-facies 7 -9 khar. andpn?,,
indicate
exceptional
rocks. Metamorphic
< 0.5 kbar. Metamorphism
H.K.
in the Elrst Antarcttc
assemblages over most of the area are typical of the hornblende
temperature
Naqvi.
Gupta
and S.
%c~tonr~~h~~.s,c~s. 105: 177 191. Precambrian
events range from 2500 m.v. to about 500 m.y.. hug wmc
and deformational
rocks are much older. notably Mineral
granuhte-facies
Structure. Dynamics and Evolution.
at 700-X(K)°C
the
Napier
osumilitc.
granulite
in linderhv
Land.
facies. and sparse
and 5 X kbar at reduced uater
complex
of
Endcrhv
and inverted
pigeonite
Land.
where
arc dssociared
conditions are estimated to have reached 9003 -9XO’C.
in the Napier
complex. and possibly in other parts of Kast
may he associated with large loss of fluid rather than massirc influx of CO,.
INTRODUCTION
Precambrian crystalline rocks are exposed along the Perimeter of East Antarctica (Fig. I). Much of the exposed portions of the Precambrian crystalline rocks are high-grade metamorphics having one of the following characteristics: (1) granulitefacies mineralogy (R in Fig. 1). (2) polymetamorphic granulite and amphibolite facies (go ). or (3) amphibolite-facies mineralogy retaining evidence of a prior granulite facies mineralogy or appearing to grade into granulite-facies mineralogy with increasing metamorphic intensity (a) (e.g. Windmill Islands. Blight and Oliver. 1982). A few areas consist of greenschist and amphibolite-facies rocks of probable Precambrian age that have not been subjected to granulite-facies event or arc unrelated to granulite-facies terranes (m in Fig. 1). Geologists of several nations have studied virtually all the areas where PrcCambrian rocks are exposed, at least in reconnaissance, most notably geologists from the Soviet Union. Australian geologists have studied many of the exposures between Present address: lnstitut
0040- 1951/84/%03.00
fiir Mineralogie.
Ruhr Universitht.
Postfach 10214X. D-4630.
‘C 1984 Elsevier Science Publishers B.V.
Bochum (F.R.C;.).
17x
45 and
170”E. while Belgian
eastern
Queen
LtitzowrPHolm
Maud
Bay, and
petrologic
studies
favourably
in quality
and Japanese
Land
based
(20” -45”E).
the Windmill on electron
and quantity
America,
Madagascar,
petrology
of the granulite-facies
own unpublished GFi’iERAl.
have worked
Islands
portions
have been analyses.
to the published
literature
and parts of Africa. The present
These
in
Land.
of detailed
data
compare
on South India. South
re\ieu,
rocks is based on the literature and laboratory
intensively
of Enderby
the object
microprobe
field observations
GEOL.O~~Y
geologists Moreover.
of the metamorphic supplemented
by rn>
work.
Ai%I> Pb.7ROLO
The granulite-facies terranes are composed largely of gneissic and granulitic metamorphic rocks: quartzofeldspathic gneisses. pyroxene granulites. and diverse
Fig. 1. Map of Antarctica terranes.
showing
given only where geochronologic Soloviev
(1966). Craddock
Grikurov
data
and earliest Phanerozoic
available.
(1972), Ravich
and Grew (1982a). Other sources above
Precambrian
(ages > 500 m.y.) metamorphic
Note: In areas for which more than one rock type indicated, General
and Kamenev
not mentioned
sources
most abundant is listed first. Ages are Ravich et al. (1965). Ravich and
(1972, 197S), Kamenev
(1978). Tingey et al. (1981). and Grew (1982~). Sources of mineral
references)
are Fig. 2, Segnit (1957).
Tingey (1972), Matsumoto
(1982). Collerson
(1977), Tingey
in text are Michot (1962), Clarkson
Van Autenboer
et al. (1964).
et al. (1983) and Grew (1983).
localities McCarthy
(19X2),
(1972). Ravich and (in addition
to the
and Trail (1964).
179
metasediments. enderbite,
The quartzofeldspathic
charnockite,
cally the most abundant (perthitic
K-feldspar,
referred
(leucosome)
rocks. These gneisses consist plagioclase,
as well as variable Garnetiferous
gneisses,
or vein component
amounts
or mesoperthite),
of biotite,
quartzofeldspathic
gneisses
and feldspar
orthopyroxene.
clinopyroxene,
pyroxene
as
are volumetri-
largely of quartz
and subordinate
hornblende, lacking
to by Soviet geologists
of migmatites,
and
garnet.
are also an important
rock type. Pyroxene granulites, probably the second most abundant rock type, consist largely of plagioclase, pyroxene, hornblende, and biotite; quartz and Kfeldspar are minor or absent; and garnet is an important constituent locally. Migmatitic varieties are not rare. Metasediments include (1) metapelitic gneisses and granulites, commonly migmatitic, containing garnet, biotite, cordierite, sillimanite, or accessory graphite; much less common are sapphirine or osumilite; (2) quartzites; (3) marbles and talc-silicate granulites; and (4) ironstones. These metasedimentary rocks probably
constitute
no more than 25 or 30% of the metamorphic
complexes.
Plutonic rocks of charnockitic and enderbitic affinities are generally subordinate to the metamorphics, although widespread (Figs. 1 and 2). Bodies up to 4000 km’ have been mapped
(Ravich
X @
Osumilite Osumilite-garnet
A 0
Sillimanite-orthopyroxene, Sapphirine Sapphirine *garnet-quartz
and Soloviev,
1966; Ravich
and Kamenev,
1972, 1975;
sapphirine
s*P
Fig.
2. Mineral
Offe
(1977),
communications
6 Isolated Wollastonite Charnockitic
localities rocks
localities in Enderby Land. Sources are Ravich and Kamenev (1972, 1975), Sheraton and Grew
(1979,
from EN.
198Oa. 1981b. Kamenev
1982b),
Ellis et al. (1980).
(1978) and J.W. Sheraton
Sheraton
et al. (1980).
(1980). and Grew (unpublished
personal data).
Sheraton,
1982). Ultramafic
also widespread.
and
abundant
1972).
Queen
are
tens of meters)
rocks are local; larger bodies (to 900 km’ ) are
and mafic plutonic
from central
Kamenev.
of which have been metamorphosed.
but mostly in lenses or dikes a few meters (locally
thick. Anorthositic only known
rocks. many
Maud
Land (Ravich
Metamorphosed
and
in many areas but conspicuously
and Soloviev.
unmetamorphosed
absent
1966; Ravich
dolerite
dikes
are
from others.
Early Paleozoic plutonic rocks include pegmatites, which are widespread (Grew. 1982a). granitic rocks (y in Fig. 1). local mafic rocks (6). and a fayalite-bearing charnockite
at Mirny
Station.
Detailed
structural
investigations
indicate
that rocks
in the granulite-facies terranes have been deformed more than once and recumbent folds are described from several areas (Yoshida. 1978: James and Black. 1981: Oliver et al.. 1982; Blight and Oliver, 1982). For example. James and Black (1981) report the Napier Complex rocks were deformed into a recumbent gneiss terrane by intense flattening at the peak of metamorphism; these structures were later deformed into a dome and basin pattern. Antarctic granulite-facies rocks are intersected in numerous exposures
by zones
pegmatite
activity
of cataclasis,
(e.g. Ravich
retrograde
and Soloviev.
metamorphism (diaphorites). and 1966: Grew. 1978. 1981a: Kamenev,
1982b). RADIOMETRIC
AGES
Most of the published geochronologic data on East Antarctica are K-Ar dates (see Picciotto and Coppez, 1964; Grew, 1982a). These dates provide little information as to either the crust-formation age or ages of granulite-facies metamorphism. However, Rb-Sr isochron, U-Pb, and Sm-Nd data have been reported for a few areas. Assignment Cambrian (mostly
of Archean (>, 2500 m.y.). Proterozoic (600-2500 500-600 m.y.) ages in Fig. 1 are based on the Rb-Sr
data. The Napier complex of Enderby and is unique to contain sapphirine
m.y.), and and U-Pb
Land (Fig. 2) is the oldest metamorphic complex with quartz or garnet, orthopyroxene sillimanite,
and osumilite. Whole rock Rb-Sr, U-Th-Pb, and Sm-Nd isotope data are consistent with crust formation (in this case, volcanism and associated sedimentation) about
3500 m.y. ago; a more
precise
estimate
is not possible
because
the three
isotopic systems were disturbed by the subsequent granulite-facies metamorphism (Grew and Manton. 1979a; DePaolo et al.. 1982). U-Pb data on zircons and other minerals from Napier complex granulites and pegmatites indicate that the present metamorphic fabric in the Napier complex is the result of granulite-facies metamorphism and associated deformation, accompanied by pegmatite emplacement, 2500 m.y. ago. Grew et al. (1982) suggest that the recumbent gneiss terrane developed during the 2500 m.y. event, at the peak of metamorphism, whereas James and Black (1981) suggest a 3000 m.y. age for the peak of metamorphism and recumbent structures, and the 2500 m.y. age for the dome and basin structures. Collerson et al.
1x1
(1983)
report
2800-3000
Sm-Nd
and
and 2400-2500
Rb-Sr
data
indicating
m.y. ago in the Vestfold
and Vestfold Hills are the only Archean
granulite-facies
The Napier
Archean
complex
is unique
among
in the large (1000 m.y.) interval
between
granulite-facies
metamorphism
Hills. Thus, the Napier terranes
granulite-facies
crust formation
complex
known in Antarctica. terranes
world-wide
age and metamorphic
age
(DePaolo et al., 1982). A belt of granulite-facies rocks exposed west, south, and east of the Napier complex (Rayner complex of Ravich and Kamenev, 1972, 1975) and extending at least
as far east
as the Ingrid
Christensen
Coast,
has been
affected
Proterozoic (800-1100 m.y.) metamorphism, deformation, and 1978, 1982a; Tingey, 1982). Zircon U-Pb and whole-rock Rb-Sr
by a late
plutonism (Grew, data indicate that
the metamorphic rocks in this Proterozoic terrane appear to be largely derived from pre-existing metamorphics, possibly Archean in age. On the other hand, the plutonic charnockites (n on Fig. 1) originated during the Proterozoic event, possibly by remelting of granulite-facies rocks near the base of the Earth’s crust (Sheraton, 1982). Although the Napier complex and Vestfold Hills Archean rocks are intersected
by tholeiitic
dikes (1190 t_ 200, 2350 t 48, and 2400 -t 250 m.y. old in the
Napier complex (Sheraton and Black, 1981), 1030 f 220, 1400, and 2170 f 217 m.y. old in the Vestfold Hills (Harding and McLeod. 1967; Tingey, 1982; Hofmann et al., 1980)) no such dikes have been found in the neighboring Proterozoic terrane. Rb-Sr isochron and U-Pb ages of 1100-1400 m.y. are reported from the Bunger Hills
and
Windmill
Commonwealth further
Islands,
and
Bay in Wilkes
Rb-Sr
Land.
west, rocks in the Bunger
biotite
In contrast
Hills and
ages
of 1500-1700
to the Proterozoic
Windmill
Islands
m.y.
near
complexes
are intersected
by
unmetamorphosed mafic dikes. However, these dikes may not be related to the tholeiitic dikes in the Napier complex and Vestfold Hills (Grew, 1982a). The granulite-facies
rocks of Wilkes
from the sector including Limited
geochronologic
Enderby
Land
may belong
to a geologic
Land and the Ingrid
data precludes
meaningful
Christensen comparison
province
distinct
Coast. of the metamor-
phic complexes of central Queen Maud Land with other parts of East Antarctica. However, the presence of a large anorthosite complex and of fayalite-bearing charnockitic rocks (Ravich and Soloviev, 1966) suggests that the mountains of central Queen Maud Land constitute a distinct geologic province. Anorthosites are virtually absent in other parts of East Antarctica (two small bodies in Enderby Land, Fig. 2) while the charnockites at Mirny of Cambrian fayalite-bearing plutonic rocks reported in East Antarctica.
age are the only other
Widespread pegmatite activity, local emplacement of granitic and gabbroic rocks, and metamorphism and deformation (particularly in discrete tectonic zones) during the interval 500-650 m.y. ago are well documented in eastern Queen Maud Land, Enderby Land, MacRobertson Land, and the Ingrid Christensen Coast, that is, west of 78”E (except the Mirny charnockite at 90’E). Moreover, in this sector, a thermal event has reset most K-Ar dates to 400-600 m.y. On the other hand, K-Ar dates on
granulite-facies reset.
and
rocks in the sector between 7X”E and 1SO”E have only been partially
there
metamorphism,
is much
or deformation.
in the topography. 2000&3000 generally
low-lying
for Paleozoic
The distinction
West of 7X”E. the terrane
m above
mean
plutonism
between
is bdm
mountainous
between
and
Nichols,
1972).
Wilkes
Land and other parts of East Antarctica
feature
from the Proterozoic
up to relatively
Mirny). (peaks
7X” and
during
the geological appears
to
15O”E is
sea level. As the present
is most likely due to movements
(e.g. Calkin
(except
the two sectors 1s reflected
IS generally
sea level) while the terrane
and a fair proportion
phy of East Antarctica Quaternary
less evidence
topogra-
the Tertiary
distinction
01
between
to have been a persistent
recent times (Grew.
1982a).
Antarctic granulite facies rocks have been the subject of a few regional and several detailed petrologic and mineralogic studies (e.g.. Banno et al.. 1964: Suwa and Tatsumi, 1969; Suwa. 1968; Ravich and Kamenev. 1972. 1975: Ravich et al.. 1978; Yoshida. 1978: Suzuki 1979; Kanisawa et al.. 1979; Ellis et al.. 1980: Grew 1980a and b. 1981a and b, 1982b; Blight and Oliver. 1982). Whole rock analyses have also been published by Sheraton (1980) and DePaolo et al. (1982). Orthopyroxene and clinopyroxene are important constituents not only of mafic granulites and many quartzofeldspathic gneisses, but also in metapelitic rocks and ironstone. Orthopyroxenes range in composition from enstatite to ferrohypersthene ( X, ~,= mol. Fe/(Fe + Mg) = 0.07 to 0.67) and in Napier complex metapelites containing
sapphirine.
osumilite.
to 0.5 Al per six oxygens).
or cordierite, Clinopyroxenes
it contains
ultramafics,
and some are augite in mafic granulites.
in relatively
iron-rich
to be inverted Antarctic
metasediments
pigeonite
granulite-facies
about 6-- 11.5 wt.% Al ,O, (up
are diopside
of the Napier
or salite in metamorphosed
Coarse pyroxene complex
(Grew. 1982b). the only reported
intergrowths
(Fig. 2) are interpreted
metamorphic
pigeonite
in
rocks.
Qlivine is characteristic of metamorphosed ultramafic rocks and of marble and talc-silicate rocks. It is not known to occur with plagioclase, but 1 found olivine with K-feldspar. pyroxenes and biotite in Napier complex ultramafic near Mount Torckler (Fig. 2). Humite-group minerals occur in marble and talc-silicate rocks in central Queen Maud Land (Ravich and Soloviev, 1966: Ravich and Kamenev. 1972. 1975) and in an ultramafic rock at Latham Peak in Enderby Land (Sheraton and Offe. 1977). Wollastonite is a rare, but locally important component of talc-silicate (Figs. 1, 2); while scapolite is a common component throughout the area.
rocks
Hornblende and biotite are found in of mafic granulites and quartzofeldspathic rocks. These minerals appear to have crystallized in equilibrium with orthopyroxene (e.g., Grew, 1978; Yoshida, 1979; Sheraton et al., 1980). However, in the Napier complex exposed in eastern Casey Bay, Scott and Tula mountains (Fig. 2) primary
183
rocks and pyroxene granuiites, Hornblende does occur in some quartz-free mafic and ultramafic rocks, and biotite is common in uitramafics and magnesian metapehtes in this area. This part of the Napier complex is thus the only pyroxene-granulite facies hornblende
terrane
and
biotite
in Antarctica;
appear
to be absent
other terranes
from
quartzofeldspathic
are hornblende-granulite
facies. Most Antarctic
hornblendes are pargasitic hornblende or pargasite (terminology of Leake, 1978). These hornblendes contain up to 2.5 wt.% TiOZ and 0.10-0.38 wt.% F (Liitzow-Holm Bay, Kanisawa
et al., 1979) or 0.59-1.39
pers. commun., 1982). Biotite ranges in composition 0.57) and is typically titanian (0.32-1.27 varieties
from the Napier content
Bay and
complex,
of biotite
(that is, in rocks saturated
complex,
H.R. Westrich.
from phlogopite to iron-rich biotite (X,, = 0.04 to (to 6.6 wt.% TiOz). Fluorine is generally present
wt.%. Liitzow-Holm
The Al,O,
wt.% F (Napier
Molodezhnaya),
1.56-5.29s
associated
in the magnesian
F have been reported
with quartz
in SiO, and Al,(&)
but
(Grew, 1982b).
and sillimanite
decreases
or sapphirine
with metamorphic
grade.
Garnet occurs not only in pelitic rocks and quartzofeldspathic gneiss, but also in talc-silicate granulites, mafic granulites and ironstones. Garnet-clinopyroxene ( i orthopyroxene f plagioclase I quartz) associations are widespread, and are not restricted to zones of high-pressure metamorphism or polymetamorphism (cf. Kamenev, 1977, 1982a; Grikurov et al., 1979). For example, this association overlaps the areas where sapphirine-quartz occurs in western Enderby Land (Fig. 2). Garnet from pelitic rocks and quartzofeldspathic gneiss is largely almandine-pyrope (X,, = 0.43-0.86), in which grossular content rarely exceeds 15 mol.% (mostly < 10%) and spessartine contents, 7% except for the garnets from the Windmill Islands (up to 15% is found-Blight The metapelitic the only Al,SiO, assemblages (Ravich
and Oliver, 1982). rocks are by far the mineralogically most diverse. Sillimanite is mineral that is in textural equilibrium with the granulite-facies
in pelitic
and Soloviev,
rocks.
Kyanite
(Sheraton et al., 1980; Kamenev, where in most cases it is confined metamorphism. Liitzow-Helm
occurs
sporadically
in Queen
1966; Grew, 1983; Hiroi et al., 1983), western
Andalusite Bay (Hiroi
Maud
Land
Enderby
Land
1982b), and Bunger Hills (Ravich et al., 1965), to mylonitic zones or zones of intense retrograde
has been found at Schirmacher Hills (Grew, 1983). near et al.. 1983), and in the northern Prince Charles Moun-
tains (Tingey, 1972), and its formation can be attributed to polymetamorphism. Cordierite-garnet-biotite-sillimanite and less commonly. cordierite-orthopyroxene are characteristic assemblages of metapelitic rocks, except in the pyroxenegranulite facies rocks of the Napier complex, where most cordierite appears to be secondary (Sheraton et al., 1980). Cordierite iron contents range from intermediate values (X,, = 0.29-0.42) in Windmill Islands metapelites to tow values (X,, = 0.07-0.14) in magnesian Napier complex metapelites. Cordierite from Molodzhnaya and the Napier complex contains little Na, K, or Ca (e.g. 0.01-0.16 wt.% Na,Q), but a secondary cordierite associated with beryllium minerals in Casey Bay, Enderby
1 wt.% Na:O.
Land. contains (Grew. 1981b). Sapphirine macher
sapphirine
occurs
it is associated
localities. tion
from undersaturated
Hills (sapphirine-garnet)
complex, where
is known
rocks at Mawson
in both quartz-bearing
with garnet.
Station.
for AI the Schir-
Hills (Fig. 1). In the Napier
and quartz-free
a rare assemblage
at other
(1972. 1975) report a forsterite
complex- undersaturated
Antarctica or elsewhere. sample Kamenev gave
to (Na + Be) substitution
and in the Vestfold
Ravich and Kamenev
in a Napier
I attribute
which
rochs (Fig. 2). world
sapphirine
sapphirine
rock. This association
associa-
is not known
in
Sapphirine and olivine are present in the \ame section of a to me. but do not touch and do not appear to be in
equilibrium. In the saturated rocks of Napier complex sapphirine is found with sillimanit~-orth~~pyr(~xeile associations and osumihte on a regional scale (Fig. 2). ~sulnil~t~. a mineral structurally akin to cordierite, is generally found in low-pressure, high-temperature osumilite is magnesian Napier
complex
environments (volcanic ( X, c = 0.03 -0.21). rocks
containing
sapphirine.
osumilite are unusual in their high Mg/Fe content (e.g.. some are rich in C‘r and Sheraton, depositional a magnesian
1980)). These unusually environments source
rocks. contact
magnesian
compositions precursors
(such as ultramafic
rocks). but are not the result of changes
sillimanite-
The Antarctic
orthopyroxene.
and
ratios and Mg content and trace element Ni. others much depleted in these (see
for the sedimentary
terrane
aureoles).
during
may be due to unusual in the early Archean.
or to
or hydrothermally
altered
igneous
the granulite-facies
metamorphism
(Sheraton, 1980). Rocks of similar composition are rare. but not unkn{~~~ll in other parts of East Antarctica. e.g. Mawson Station (Sheraton. 19X0) and Schirmacher Hills. Unusual accessory minerals in the granulite-facies rocks and associated metamorphic segregations and pegmatites include perrierite and chevkinite (Grew and or polycrase (Mount Manton. 1979a and b: DePaolo et al.. 1982). aeschynite surinami~e, taaffeite. chrysoberyl, and wagnerite C‘ronus). heryllian sapphirine. (Grew. 1981b) (Fig. 2). Kornerupine has been reported from an erratic in Commonwealth
Bay (Mawson.
1940) and from central
Queen
Maud
Land (Ravich
and
1966) (Fig. 1). but identification in Mawson’s section could not be 1982). A rock consisting of tephroite and confirmed (R. Oliver, pers. commun.. minor spessartine. rhodonite and barite occurs in cordierite .sillimaI~i~e-garI~et gneiss in the Windmill Islands (Mason, 1959). Mn-rich ironstone containing magSoloviev.
netite,
spessartine-rich
Fyfe hills (M. Sandiford,
garnet,
Mn-rich
pers. commun..
PRESSURES AND TEMPERATURES
clinopyroxene
and celsian
are found
in the
19X2).
OF ~~TAMt~RPHISM
Estimates of the physical conditions of metamorphism based on mineral chemistry and phase relations have been discussed in detail for four areas in hornblende-
185
granulite
facies
terranes
complex. Generalized blende-granulite
and
one
kbar
(two events
30”C, 5.5 + 1 kbar (Molodezhnaya Islands-Blight
Indian granulite-facies phirine-garnet-sillimanite temperatures
facies Napier
in the pyroxene-granulite
temperature-pressure
facies are 730”-8OO”C,
88O”C, 8.8-13 (Windmill
area
estimates
for four areas
5-8 kbar (Schirmacher
at Liitzow-Holm Station-Grew,
in the horn-
Hills-Grew,
Bay-Yoshida,
1979);
1981a) and 760°C
and Oliver, 1982). Using a petrogenetic
1983), 700” +
5.5-6.5
grid proposed
of 730”-800°C
and 5-8 kbar. For Lutzow-Holm
1979). These associations
and the Windmill
Islands
tures are estimated
Bay, temperatures
are characteristic
of Molodezhnaya
to be less than 8OO”C, but are absent
in the Tula
suggest
temperaMountains,
are estimated to be 900°C. Moreover, the presence Bay metapelitic rocks implies pressures did not
exceed 9 kbar (for T = 75O’C) or 10 kbar (T = XOO’C) (Holdaway, data
of and Bay
(Grew, 1978)
(Blight and Oliver, 1977), for which metamorphic
where metamorphic temperatures of sillimanite in Liitzow-Holm available
for
rocks (Grew, 1982d), the Schirmacher Hills cordierite-sap(no quartz) assemblage is estimated to have formed at
700”-800°C and pressures of 6 kbar appear to be more reasonable. Hornblende biotite are associated with quartz in charnockitic rocks at Lutzow-Holm (Yoshida,
kbar
that metamo~hism
1971). In sum,
in the ho~blende-granulite-faci~s
ter-
ranes of Antarctica probably occurred over a temperature range of 700”-800°C and pressure range of 5-8 kbar. Metamorphic conditions in the Napier complex pyroxene granulite-facies rocks of the Tula Mountains
are estimated
to be 900” rtr 30°C and 7 ~fr:1 kbar (Grew, 1980a),
and 940” f 40°C and 9 f 1 kbar (Eilis, 1980). These estimates chemistry and are consistent 1980) and inverted pigeonite complex
cooled isobarically
after peak metamorphic
cooling is reflected in the 600”-770°C by garnet and secondary cordierite. Pressure-temperature m.y. metamorphic
are based on mineral
with the presence of mesoperthitic (Grew, 1982b). Ellis (1980) proposed
conditions
temperatures
conditions
were attained.
(at p = 7.1-8.4
varied from one area to another
event in the Napier
complex
and probably
feldspars (Ellis, that the Napier This
kbar) recorded during
the 2500
also during
the 1000
my. event in the Rayner complex (see Sheraton et al., 1980). For example, increase in metamorphic pressures southwest from the Tula Mountains towards Casey Bay, where Sandiford by development
and Wilson (1983) estimate of garnet-clinopyroxene
limanite-orthopyroxene,
and
changes
pressure to be 8-10 kbar, are indicated rocks, increasing abundance of sil-
in osumilite
composition
and
parageneses
(Sheraton et al., 1980; Grew, 1980a, 1982b). Moreover, there is no evidence for any secular trends in the geothermal gradient (cf. Kamenev, 1977, 1982a). For example, my T-p estimates for the 2500 m.y. event in the Tula Mountains indicate a gradient of 30*-#*C/km, while my estimates for the 1000 m.y. event at Molodezhnaya yield 2%46”C/km (Grew, 1981a). The Napier complex assemblages may not be the result of an unusually high geothermal gradient for granulite-facies terranes, but of the exposure of a deeper crustal level and gradients of this magnitude are not unique to Archean metamorphism in Antarctica.
METAMORPHIC‘FLUIDS
Metal~orph~sm in the granulite facies is believed by some to he accompanied by H,O-poor. CO?-rich fluids (e.g., Janardhan et al., 1982). Estimates of plric, in Antarctic granulites are about 2 kbar or 0.4 p,,,,.,, at Molodezhnaya (Grew. 19Xla). 3 kbar in the Windmill
Islands
the Tula
(Sheraton
Mountains
attempted, appears
et al.,
1980).
1982), and possibly No
nor have there been any fluid inclusion
as a primary
at Mawson
(Blight and Oliver,
phase in talc -silicate inclusions
and in calcsilicate
layers associated
estimates studies.
< 0.5 kbar in
of p< (), have However,
at two localities
been
wollastonite in charnockite
with sapphirine-bearing
granulitea
at Forefinger Point in Enderby Land (Figs. I and 2). The appearance of wollastonite instead of calcite-quartz implies P(.~,, < P-,,_:~,_ For example. Valley and Essene (1980) calculate that cafcite-quartz is stable to 1010”c‘ at 8 kbar for pc f) = p Irl,,,,. Moreover. there is no evidence. such as secondary carbonates. that the low water partial pressures indicated for Antarctic increased partial pressure of C’O,.
granulite-facies
rocks
are the result
of
,411 alternative explanation of the above observations is that I-‘,, ,() t pc ().
isotopic
as proposed
ages at h&h ambient by Harte
temperatures
ct al. (19X1 ). My proposal
at the base of the Earth’s is consistent
features in the Napier complex. For example. one group of post-tectonic with an Rb-Sr isochron age of 2400 f 250 m.y. are granuloblastic gr~lllulite-facies
mineralogy
(Sheraton
nl~t~~n~~rph~sed at high ambient
mafic dikes and have a
and Black. 1981). These dikes may have been
pressures
dike rock itself, while the fluid-depleted
with several
and temperatures country
by fluids present
rocks underwent
in the
no chttnge.
On the other hand, a large quantity of fluid must have passed through the rocks of the Napier complex at some time when peak metamorphism conditions were except possibly K ?t.9. were not mohihzed attained. Although major components. (Sheraton, 19g0). some trace elements were highly mobile. such as Rb. U. Sm and Nd (DePaolo et al.. 1982) and therefore introduced uncertainty into Sm end age determination. Moreover. the Be. Nb, and rare earth element mineralization mentioned above may be due to partial removal of these elements from the metamorphic rocks and subsequent concentration in pegmatites and segregations by an active fluid phase. Earlier I had suggested that a non-magmati~ source of the beryllium in the Casey Bay pegmatites was unlikely as there was no obvious mechanism for transporting and concentrating beryllium under granuiite-facies conditions (Grew. 1981b). However. in view of the high mobility of the trace elements (dePaoi(~et al..
187
1982) from
conclusive the Tula
between
evidence
the beryllium
beryllium
for beryllium
Mountains-Grew, pegmatites
in the pegmatites
from the country
in quartzofeldspathic
1983)
and
absence
and
plutonic
rocks,
was derived by transport
rock by fluids passing
through
gneiss (in sapphirine
of any visible I now
connection
suggest
and concentration the rocks during
that
the
of beryllium granulite-facies
metamorphism. CONCLUSION
International features
studies
of the Napier
in Enderby complex
Land have sufficiently
that this complex
elucidated
the classic pyroxene-granulite facies terranes of the world. Certain notably osumilite-sapphirine-quartz, and beryllium blages, (surinamite-taaffeite-Be-sapphirine) in granulite-facies pegmatites, the Napier earth
complex.
elements
It is the first granulite-facies
during
metamorphism
systematics. The rare earth element the importance of fluid, while
has been
the petrologic
can now be recognized
terrane shown
as one of
mineral assemmineralization are unique
in which mobility to disturb
Sm-Nd
to
of rare isotope
mobility and beryllium mineralisation illustrate the mineral assemblages (e.g. sapphirine-
osumiliteequartz) can form only at low water partial pressures. Massive influx of COZ has been proposed as a means of driving water from rocks during granulite-facies metamorphism in other terranes, but this hypothesis is not consistent with some features of the Napier complex, such as appearance of wollastonite in talc-silicate rocks. Although
the main focus of this review is to summarize
information
accumulated
that
this review
on Antarctica
will stimulate
further
the considerable
body of
over the last 20 years, it is the author’s hope work.
Many
areas
of potential
petrologic
interest have to date been covered only in regional surveys, or in reconnaissance. Detailed work on the better studied areas such as Enderby Land has only begun. ACKNOWLEDGEMENTS
The present review is distillation of my 10 years of Antarctic studies, including five trips to the Antarctic. I thank the Antarctic Division of the Department of Science and Environment (Australia) for enabling me to participate in two Australian National Antarctic Research Expeditions (1977-1978 and Antarctic Scientific Research Institute (USSR), Soviet Antarctic Expeditions; and the U.S. Antarctic Research Programme (1981-1982). for providing unpublished analyses, R.C. Museum, Sydney, for a piece of Mawson’s E.N. Kamenev and M.A. Sandiford for discussions and exchange of information
and 1979-1980); the Arctic in the 18th, 19th, and 22nd
National Science Foundation, in the U.S. I thank H.R. Westrich and M. Yoshida Newton for calculations, the Australian kornerupine-bearing sample (lOOA), and samples from Enderby Land. Fruitful with many scientists have contributed
IX8
much
to the ideas
DePaolo,
presented
R.B. Hargraves,
in this paper.
EN.
Kamenev,
in particular
K.D.
C‘ollerson.
D.J.
R.L. Oliver. M.A. Sandif(~rd. J.W. Shera-
ton. and M. Yoshida. An earlier version of this manuscript B.F. Windley.
was reviewed by E.J. Essene. P.C. Grew. 2nd
Their thoughtful
comments
of this review
has been
have lead to a substantial
improvement
of
the paper. Preparation Foundation
Grant
supported
through
U.S. National
Science
DPPXO-19527.
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interest
garnet, sillimanite-orthopyroxene.
with pyroxene-granulite-facies 7 -9 khar. andpn?,,
indicate
exceptional
rocks. Metamorphic
< 0.5 kbar. Metamorphism
H.K.
in the Elrst Antarcttc
assemblages over most of the area are typical of the hornblende
temperature
Naqvi.
Gupta
and S.
%c~tonr~~h~~.s,c~s. 105: 177 191. Precambrian
events range from 2500 m.v. to about 500 m.y.. hug wmc
and deformational
rocks are much older. notably Mineral
granuhte-facies
Structure. Dynamics and Evolution.
at 700-X(K)°C
the
Napier
osumilitc.
granulite
in linderhv
Land.
facies. and sparse
and 5 X kbar at reduced uater
complex
of
Endcrhv
and inverted
pigeonite
Land.
where
arc dssociared
conditions are estimated to have reached 9003 -9XO’C.
in the Napier
complex. and possibly in other parts of Kast
may he associated with large loss of fluid rather than massirc influx of CO,.
INTRODUCTION
Precambrian crystalline rocks are exposed along the Perimeter of East Antarctica (Fig. I). Much of the exposed portions of the Precambrian crystalline rocks are high-grade metamorphics having one of the following characteristics: (1) granulitefacies mineralogy (R in Fig. 1). (2) polymetamorphic granulite and amphibolite facies (go ). or (3) amphibolite-facies mineralogy retaining evidence of a prior granulite facies mineralogy or appearing to grade into granulite-facies mineralogy with increasing metamorphic intensity (a) (e.g. Windmill Islands. Blight and Oliver. 1982). A few areas consist of greenschist and amphibolite-facies rocks of probable Precambrian age that have not been subjected to granulite-facies event or arc unrelated to granulite-facies terranes (m in Fig. 1). Geologists of several nations have studied virtually all the areas where PrcCambrian rocks are exposed, at least in reconnaissance, most notably geologists from the Soviet Union. Australian geologists have studied many of the exposures between Present address: lnstitut
0040- 1951/84/%03.00
fiir Mineralogie.
Ruhr Universitht.
Postfach 10214X. D-4630.
‘C 1984 Elsevier Science Publishers B.V.
Bochum (F.R.C;.).
17x
45 and
170”E. while Belgian
eastern
Queen
LtitzowrPHolm
Maud
Bay, and
petrologic
studies
favourably
in quality
and Japanese
Land
based
(20” -45”E).
the Windmill on electron
and quantity
America,
Madagascar,
petrology
of the granulite-facies
own unpublished GFi’iERAl.
have worked
Islands
portions
have been analyses.
to the published
literature
and parts of Africa. The present
These
in
Land.
of detailed
data
compare
on South India. South
re\ieu,
rocks is based on the literature and laboratory
intensively
of Enderby
the object
microprobe
field observations
GEOL.O~~Y
geologists Moreover.
of the metamorphic supplemented
by rn>
work.
Ai%I> Pb.7ROLO
The granulite-facies terranes are composed largely of gneissic and granulitic metamorphic rocks: quartzofeldspathic gneisses. pyroxene granulites. and diverse
Fig. 1. Map of Antarctica terranes.
showing
given only where geochronologic Soloviev
(1966). Craddock
Grikurov
data
and earliest Phanerozoic
available.
(1972), Ravich
and Grew (1982a). Other sources above
Precambrian
(ages > 500 m.y.) metamorphic
Note: In areas for which more than one rock type indicated, General
and Kamenev
not mentioned
sources
most abundant is listed first. Ages are Ravich et al. (1965). Ravich and
(1972, 197S), Kamenev
(1978). Tingey et al. (1981). and Grew (1982~). Sources of mineral
references)
are Fig. 2, Segnit (1957).
Tingey (1972), Matsumoto
(1982). Collerson
(1977), Tingey
in text are Michot (1962), Clarkson
Van Autenboer
et al. (1964).
et al. (1983) and Grew (1983).
localities McCarthy
(19X2),
(1972). Ravich and (in addition
to the
and Trail (1964).
179
metasediments. enderbite,
The quartzofeldspathic
charnockite,
cally the most abundant (perthitic
K-feldspar,
referred
(leucosome)
rocks. These gneisses consist plagioclase,
as well as variable Garnetiferous
gneisses,
or vein component
amounts
or mesoperthite),
of biotite,
quartzofeldspathic
gneisses
and feldspar
orthopyroxene.
clinopyroxene,
pyroxene
as
are volumetri-
largely of quartz
and subordinate
hornblende, lacking
to by Soviet geologists
of migmatites,
and
garnet.
are also an important
rock type. Pyroxene granulites, probably the second most abundant rock type, consist largely of plagioclase, pyroxene, hornblende, and biotite; quartz and Kfeldspar are minor or absent; and garnet is an important constituent locally. Migmatitic varieties are not rare. Metasediments include (1) metapelitic gneisses and granulites, commonly migmatitic, containing garnet, biotite, cordierite, sillimanite, or accessory graphite; much less common are sapphirine or osumilite; (2) quartzites; (3) marbles and talc-silicate granulites; and (4) ironstones. These metasedimentary rocks probably
constitute
no more than 25 or 30% of the metamorphic
complexes.
Plutonic rocks of charnockitic and enderbitic affinities are generally subordinate to the metamorphics, although widespread (Figs. 1 and 2). Bodies up to 4000 km’ have been mapped
(Ravich
X @
Osumilite Osumilite-garnet
A 0
Sillimanite-orthopyroxene, Sapphirine Sapphirine *garnet-quartz
and Soloviev,
1966; Ravich
and Kamenev,
1972, 1975;
sapphirine
s*P
Fig.
2. Mineral
Offe
(1977),
communications
6 Isolated Wollastonite Charnockitic
localities rocks
localities in Enderby Land. Sources are Ravich and Kamenev (1972, 1975), Sheraton and Grew
(1979,
from EN.
198Oa. 1981b. Kamenev
1982b),
Ellis et al. (1980).
(1978) and J.W. Sheraton
Sheraton
et al. (1980).
(1980). and Grew (unpublished
personal data).
Sheraton,
1982). Ultramafic
also widespread.
and
abundant
1972).
Queen
are
tens of meters)
rocks are local; larger bodies (to 900 km’ ) are
and mafic plutonic
from central
Kamenev.
of which have been metamorphosed.
but mostly in lenses or dikes a few meters (locally
thick. Anorthositic only known
rocks. many
Maud
Land (Ravich
Metamorphosed
and
in many areas but conspicuously
and Soloviev.
unmetamorphosed
absent
1966; Ravich
dolerite
dikes
are
from others.
Early Paleozoic plutonic rocks include pegmatites, which are widespread (Grew. 1982a). granitic rocks (y in Fig. 1). local mafic rocks (6). and a fayalite-bearing charnockite
at Mirny
Station.
Detailed
structural
investigations
indicate
that rocks
in the granulite-facies terranes have been deformed more than once and recumbent folds are described from several areas (Yoshida. 1978: James and Black. 1981: Oliver et al.. 1982; Blight and Oliver, 1982). For example. James and Black (1981) report the Napier Complex rocks were deformed into a recumbent gneiss terrane by intense flattening at the peak of metamorphism; these structures were later deformed into a dome and basin pattern. Antarctic granulite-facies rocks are intersected in numerous exposures
by zones
pegmatite
activity
of cataclasis,
(e.g. Ravich
retrograde
and Soloviev.
metamorphism (diaphorites). and 1966: Grew. 1978. 1981a: Kamenev,
1982b). RADIOMETRIC
AGES
Most of the published geochronologic data on East Antarctica are K-Ar dates (see Picciotto and Coppez, 1964; Grew, 1982a). These dates provide little information as to either the crust-formation age or ages of granulite-facies metamorphism. However, Rb-Sr isochron, U-Pb, and Sm-Nd data have been reported for a few areas. Assignment Cambrian (mostly
of Archean (>, 2500 m.y.). Proterozoic (600-2500 500-600 m.y.) ages in Fig. 1 are based on the Rb-Sr
data. The Napier complex of Enderby and is unique to contain sapphirine
m.y.), and and U-Pb
Land (Fig. 2) is the oldest metamorphic complex with quartz or garnet, orthopyroxene sillimanite,
and osumilite. Whole rock Rb-Sr, U-Th-Pb, and Sm-Nd isotope data are consistent with crust formation (in this case, volcanism and associated sedimentation) about
3500 m.y. ago; a more
precise
estimate
is not possible
because
the three
isotopic systems were disturbed by the subsequent granulite-facies metamorphism (Grew and Manton. 1979a; DePaolo et al.. 1982). U-Pb data on zircons and other minerals from Napier complex granulites and pegmatites indicate that the present metamorphic fabric in the Napier complex is the result of granulite-facies metamorphism and associated deformation, accompanied by pegmatite emplacement, 2500 m.y. ago. Grew et al. (1982) suggest that the recumbent gneiss terrane developed during the 2500 m.y. event, at the peak of metamorphism, whereas James and Black (1981) suggest a 3000 m.y. age for the peak of metamorphism and recumbent structures, and the 2500 m.y. age for the dome and basin structures. Collerson et al.
1x1
(1983)
report
2800-3000
Sm-Nd
and
and 2400-2500
Rb-Sr
data
indicating
m.y. ago in the Vestfold
and Vestfold Hills are the only Archean
granulite-facies
The Napier
Archean
complex
is unique
among
in the large (1000 m.y.) interval
between
granulite-facies
metamorphism
Hills. Thus, the Napier terranes
granulite-facies
crust formation
complex
known in Antarctica. terranes
world-wide
age and metamorphic
age
(DePaolo et al., 1982). A belt of granulite-facies rocks exposed west, south, and east of the Napier complex (Rayner complex of Ravich and Kamenev, 1972, 1975) and extending at least
as far east
as the Ingrid
Christensen
Coast,
has been
affected
Proterozoic (800-1100 m.y.) metamorphism, deformation, and 1978, 1982a; Tingey, 1982). Zircon U-Pb and whole-rock Rb-Sr
by a late
plutonism (Grew, data indicate that
the metamorphic rocks in this Proterozoic terrane appear to be largely derived from pre-existing metamorphics, possibly Archean in age. On the other hand, the plutonic charnockites (n on Fig. 1) originated during the Proterozoic event, possibly by remelting of granulite-facies rocks near the base of the Earth’s crust (Sheraton, 1982). Although the Napier complex and Vestfold Hills Archean rocks are intersected
by tholeiitic
dikes (1190 t_ 200, 2350 t 48, and 2400 -t 250 m.y. old in the
Napier complex (Sheraton and Black, 1981), 1030 f 220, 1400, and 2170 f 217 m.y. old in the Vestfold Hills (Harding and McLeod. 1967; Tingey, 1982; Hofmann et al., 1980)) no such dikes have been found in the neighboring Proterozoic terrane. Rb-Sr isochron and U-Pb ages of 1100-1400 m.y. are reported from the Bunger Hills
and
Windmill
Commonwealth further
Islands,
and
Bay in Wilkes
Rb-Sr
Land.
west, rocks in the Bunger
biotite
In contrast
Hills and
ages
of 1500-1700
to the Proterozoic
Windmill
Islands
m.y.
near
complexes
are intersected
by
unmetamorphosed mafic dikes. However, these dikes may not be related to the tholeiitic dikes in the Napier complex and Vestfold Hills (Grew, 1982a). The granulite-facies
rocks of Wilkes
from the sector including Limited
geochronologic
Enderby
Land
may belong
to a geologic
Land and the Ingrid
data precludes
meaningful
Christensen comparison
province
distinct
Coast. of the metamor-
phic complexes of central Queen Maud Land with other parts of East Antarctica. However, the presence of a large anorthosite complex and of fayalite-bearing charnockitic rocks (Ravich and Soloviev, 1966) suggests that the mountains of central Queen Maud Land constitute a distinct geologic province. Anorthosites are virtually absent in other parts of East Antarctica (two small bodies in Enderby Land, Fig. 2) while the charnockites at Mirny of Cambrian fayalite-bearing plutonic rocks reported in East Antarctica.
age are the only other
Widespread pegmatite activity, local emplacement of granitic and gabbroic rocks, and metamorphism and deformation (particularly in discrete tectonic zones) during the interval 500-650 m.y. ago are well documented in eastern Queen Maud Land, Enderby Land, MacRobertson Land, and the Ingrid Christensen Coast, that is, west of 78”E (except the Mirny charnockite at 90’E). Moreover, in this sector, a thermal event has reset most K-Ar dates to 400-600 m.y. On the other hand, K-Ar dates on
granulite-facies reset.
and
rocks in the sector between 7X”E and 1SO”E have only been partially
there
metamorphism,
is much
or deformation.
in the topography. 2000&3000 generally
low-lying
for Paleozoic
The distinction
West of 7X”E. the terrane
m above
mean
plutonism
between
is bdm
mountainous
between
and
Nichols,
1972).
Wilkes
Land and other parts of East Antarctica
feature
from the Proterozoic
up to relatively
Mirny). (peaks
7X” and
during
the geological appears
to
15O”E is
sea level. As the present
is most likely due to movements
(e.g. Calkin
(except
the two sectors 1s reflected
IS generally
sea level) while the terrane
and a fair proportion
phy of East Antarctica Quaternary
less evidence
topogra-
the Tertiary
distinction
01
between
to have been a persistent
recent times (Grew.
1982a).
Antarctic granulite facies rocks have been the subject of a few regional and several detailed petrologic and mineralogic studies (e.g.. Banno et al.. 1964: Suwa and Tatsumi, 1969; Suwa. 1968; Ravich and Kamenev. 1972. 1975: Ravich et al.. 1978; Yoshida. 1978: Suzuki 1979; Kanisawa et al.. 1979; Ellis et al.. 1980: Grew 1980a and b. 1981a and b, 1982b; Blight and Oliver. 1982). Whole rock analyses have also been published by Sheraton (1980) and DePaolo et al. (1982). Orthopyroxene and clinopyroxene are important constituents not only of mafic granulites and many quartzofeldspathic gneisses, but also in metapelitic rocks and ironstone. Orthopyroxenes range in composition from enstatite to ferrohypersthene ( X, ~,= mol. Fe/(Fe + Mg) = 0.07 to 0.67) and in Napier complex metapelites containing
sapphirine.
osumilite.
to 0.5 Al per six oxygens).
or cordierite, Clinopyroxenes
it contains
ultramafics,
and some are augite in mafic granulites.
in relatively
iron-rich
to be inverted Antarctic
metasediments
pigeonite
granulite-facies
about 6-- 11.5 wt.% Al ,O, (up
are diopside
of the Napier
or salite in metamorphosed
Coarse pyroxene complex
(Grew. 1982b). the only reported
intergrowths
(Fig. 2) are interpreted
metamorphic
pigeonite
in
rocks.
Qlivine is characteristic of metamorphosed ultramafic rocks and of marble and talc-silicate rocks. It is not known to occur with plagioclase, but 1 found olivine with K-feldspar. pyroxenes and biotite in Napier complex ultramafic near Mount Torckler (Fig. 2). Humite-group minerals occur in marble and talc-silicate rocks in central Queen Maud Land (Ravich and Soloviev, 1966: Ravich and Kamenev. 1972. 1975) and in an ultramafic rock at Latham Peak in Enderby Land (Sheraton and Offe. 1977). Wollastonite is a rare, but locally important component of talc-silicate (Figs. 1, 2); while scapolite is a common component throughout the area.
rocks
Hornblende and biotite are found in of mafic granulites and quartzofeldspathic rocks. These minerals appear to have crystallized in equilibrium with orthopyroxene (e.g., Grew, 1978; Yoshida, 1979; Sheraton et al., 1980). However, in the Napier complex exposed in eastern Casey Bay, Scott and Tula mountains (Fig. 2) primary
183
rocks and pyroxene granuiites, Hornblende does occur in some quartz-free mafic and ultramafic rocks, and biotite is common in uitramafics and magnesian metapehtes in this area. This part of the Napier complex is thus the only pyroxene-granulite facies hornblende
terrane
and
biotite
in Antarctica;
appear
to be absent
other terranes
from
quartzofeldspathic
are hornblende-granulite
facies. Most Antarctic
hornblendes are pargasitic hornblende or pargasite (terminology of Leake, 1978). These hornblendes contain up to 2.5 wt.% TiOZ and 0.10-0.38 wt.% F (Liitzow-Holm Bay, Kanisawa
et al., 1979) or 0.59-1.39
pers. commun., 1982). Biotite ranges in composition 0.57) and is typically titanian (0.32-1.27 varieties
from the Napier content
Bay and
complex,
of biotite
(that is, in rocks saturated
complex,
H.R. Westrich.
from phlogopite to iron-rich biotite (X,, = 0.04 to (to 6.6 wt.% TiOz). Fluorine is generally present
wt.%. Liitzow-Holm
The Al,O,
wt.% F (Napier
Molodezhnaya),
1.56-5.29s
associated
in the magnesian
F have been reported
with quartz
in SiO, and Al,(&)
but
(Grew, 1982b).
and sillimanite
decreases
or sapphirine
with metamorphic
grade.
Garnet occurs not only in pelitic rocks and quartzofeldspathic gneiss, but also in talc-silicate granulites, mafic granulites and ironstones. Garnet-clinopyroxene ( i orthopyroxene f plagioclase I quartz) associations are widespread, and are not restricted to zones of high-pressure metamorphism or polymetamorphism (cf. Kamenev, 1977, 1982a; Grikurov et al., 1979). For example, this association overlaps the areas where sapphirine-quartz occurs in western Enderby Land (Fig. 2). Garnet from pelitic rocks and quartzofeldspathic gneiss is largely almandine-pyrope (X,, = 0.43-0.86), in which grossular content rarely exceeds 15 mol.% (mostly < 10%) and spessartine contents, 7% except for the garnets from the Windmill Islands (up to 15% is found-Blight The metapelitic the only Al,SiO, assemblages (Ravich
and Oliver, 1982). rocks are by far the mineralogically most diverse. Sillimanite is mineral that is in textural equilibrium with the granulite-facies
in pelitic
and Soloviev,
rocks.
Kyanite
(Sheraton et al., 1980; Kamenev, where in most cases it is confined metamorphism. Liitzow-Helm
occurs
sporadically
in Queen
1966; Grew, 1983; Hiroi et al., 1983), western
Andalusite Bay (Hiroi
Maud
Land
Enderby
Land
1982b), and Bunger Hills (Ravich et al., 1965), to mylonitic zones or zones of intense retrograde
has been found at Schirmacher Hills (Grew, 1983). near et al.. 1983), and in the northern Prince Charles Moun-
tains (Tingey, 1972), and its formation can be attributed to polymetamorphism. Cordierite-garnet-biotite-sillimanite and less commonly. cordierite-orthopyroxene are characteristic assemblages of metapelitic rocks, except in the pyroxenegranulite facies rocks of the Napier complex, where most cordierite appears to be secondary (Sheraton et al., 1980). Cordierite iron contents range from intermediate values (X,, = 0.29-0.42) in Windmill Islands metapelites to tow values (X,, = 0.07-0.14) in magnesian Napier complex metapelites. Cordierite from Molodzhnaya and the Napier complex contains little Na, K, or Ca (e.g. 0.01-0.16 wt.% Na,Q), but a secondary cordierite associated with beryllium minerals in Casey Bay, Enderby
1 wt.% Na:O.
Land. contains (Grew. 1981b). Sapphirine macher
sapphirine
occurs
it is associated
localities. tion
from undersaturated
Hills (sapphirine-garnet)
complex, where
is known
rocks at Mawson
in both quartz-bearing
with garnet.
Station.
for AI the Schir-
Hills (Fig. 1). In the Napier
and quartz-free
a rare assemblage
at other
(1972. 1975) report a forsterite
complex- undersaturated
Antarctica or elsewhere. sample Kamenev gave
to (Na + Be) substitution
and in the Vestfold
Ravich and Kamenev
in a Napier
I attribute
which
rochs (Fig. 2). world
sapphirine
sapphirine
rock. This association
associa-
is not known
in
Sapphirine and olivine are present in the \ame section of a to me. but do not touch and do not appear to be in
equilibrium. In the saturated rocks of Napier complex sapphirine is found with sillimanit~-orth~~pyr(~xeile associations and osumihte on a regional scale (Fig. 2). ~sulnil~t~. a mineral structurally akin to cordierite, is generally found in low-pressure, high-temperature osumilite is magnesian Napier
complex
environments (volcanic ( X, c = 0.03 -0.21). rocks
containing
sapphirine.
osumilite are unusual in their high Mg/Fe content (e.g.. some are rich in C‘r and Sheraton, depositional a magnesian
1980)). These unusually environments source
rocks. contact
magnesian
compositions precursors
(such as ultramafic
rocks). but are not the result of changes
sillimanite-
The Antarctic
orthopyroxene.
and
ratios and Mg content and trace element Ni. others much depleted in these (see
for the sedimentary
terrane
aureoles).
during
may be due to unusual in the early Archean.
or to
or hydrothermally
altered
igneous
the granulite-facies
metamorphism
(Sheraton, 1980). Rocks of similar composition are rare. but not unkn{~~~ll in other parts of East Antarctica. e.g. Mawson Station (Sheraton. 19X0) and Schirmacher Hills. Unusual accessory minerals in the granulite-facies rocks and associated metamorphic segregations and pegmatites include perrierite and chevkinite (Grew and or polycrase (Mount Manton. 1979a and b: DePaolo et al.. 1982). aeschynite surinami~e, taaffeite. chrysoberyl, and wagnerite C‘ronus). heryllian sapphirine. (Grew. 1981b) (Fig. 2). Kornerupine has been reported from an erratic in Commonwealth
Bay (Mawson.
1940) and from central
Queen
Maud
Land (Ravich
and
1966) (Fig. 1). but identification in Mawson’s section could not be 1982). A rock consisting of tephroite and confirmed (R. Oliver, pers. commun.. minor spessartine. rhodonite and barite occurs in cordierite .sillimaI~i~e-garI~et gneiss in the Windmill Islands (Mason, 1959). Mn-rich ironstone containing magSoloviev.
netite,
spessartine-rich
Fyfe hills (M. Sandiford,
garnet,
Mn-rich
pers. commun..
PRESSURES AND TEMPERATURES
clinopyroxene
and celsian
are found
in the
19X2).
OF ~~TAMt~RPHISM
Estimates of the physical conditions of metamorphism based on mineral chemistry and phase relations have been discussed in detail for four areas in hornblende-
185
granulite
facies
terranes
complex. Generalized blende-granulite
and
one
kbar
(two events
30”C, 5.5 + 1 kbar (Molodezhnaya Islands-Blight
Indian granulite-facies phirine-garnet-sillimanite temperatures
facies Napier
in the pyroxene-granulite
temperature-pressure
facies are 730”-8OO”C,
88O”C, 8.8-13 (Windmill
area
estimates
for four areas
5-8 kbar (Schirmacher
at Liitzow-Holm Station-Grew,
in the horn-
Hills-Grew,
Bay-Yoshida,
1979);
1981a) and 760°C
and Oliver, 1982). Using a petrogenetic
1983), 700” +
5.5-6.5
grid proposed
of 730”-800°C
and 5-8 kbar. For Lutzow-Holm
1979). These associations
and the Windmill
Islands
tures are estimated
Bay, temperatures
are characteristic
of Molodezhnaya
to be less than 8OO”C, but are absent
in the Tula
suggest
temperaMountains,
are estimated to be 900°C. Moreover, the presence Bay metapelitic rocks implies pressures did not
exceed 9 kbar (for T = 75O’C) or 10 kbar (T = XOO’C) (Holdaway, data
of and Bay
(Grew, 1978)
(Blight and Oliver, 1977), for which metamorphic
where metamorphic temperatures of sillimanite in Liitzow-Holm available
for
rocks (Grew, 1982d), the Schirmacher Hills cordierite-sap(no quartz) assemblage is estimated to have formed at
700”-800°C and pressures of 6 kbar appear to be more reasonable. Hornblende biotite are associated with quartz in charnockitic rocks at Lutzow-Holm (Yoshida,
kbar
that metamo~hism
1971). In sum,
in the ho~blende-granulite-faci~s
ter-
ranes of Antarctica probably occurred over a temperature range of 700”-800°C and pressure range of 5-8 kbar. Metamorphic conditions in the Napier complex pyroxene granulite-facies rocks of the Tula Mountains
are estimated
to be 900” rtr 30°C and 7 ~fr:1 kbar (Grew, 1980a),
and 940” f 40°C and 9 f 1 kbar (Eilis, 1980). These estimates chemistry and are consistent 1980) and inverted pigeonite complex
cooled isobarically
after peak metamorphic
cooling is reflected in the 600”-770°C by garnet and secondary cordierite. Pressure-temperature m.y. metamorphic
are based on mineral
with the presence of mesoperthitic (Grew, 1982b). Ellis (1980) proposed
conditions
temperatures
conditions
were attained.
(at p = 7.1-8.4
varied from one area to another
event in the Napier
complex
and probably
feldspars (Ellis, that the Napier This
kbar) recorded during
the 2500
also during
the 1000
my. event in the Rayner complex (see Sheraton et al., 1980). For example, increase in metamorphic pressures southwest from the Tula Mountains towards Casey Bay, where Sandiford by development
and Wilson (1983) estimate of garnet-clinopyroxene
limanite-orthopyroxene,
and
changes
pressure to be 8-10 kbar, are indicated rocks, increasing abundance of sil-
in osumilite
composition
and
parageneses
(Sheraton et al., 1980; Grew, 1980a, 1982b). Moreover, there is no evidence for any secular trends in the geothermal gradient (cf. Kamenev, 1977, 1982a). For example, my T-p estimates for the 2500 m.y. event in the Tula Mountains indicate a gradient of 30*-#*C/km, while my estimates for the 1000 m.y. event at Molodezhnaya yield 2%46”C/km (Grew, 1981a). The Napier complex assemblages may not be the result of an unusually high geothermal gradient for granulite-facies terranes, but of the exposure of a deeper crustal level and gradients of this magnitude are not unique to Archean metamorphism in Antarctica.
METAMORPHIC‘FLUIDS
Metal~orph~sm in the granulite facies is believed by some to he accompanied by H,O-poor. CO?-rich fluids (e.g., Janardhan et al., 1982). Estimates of plric, in Antarctic granulites are about 2 kbar or 0.4 p,,,,.,, at Molodezhnaya (Grew. 19Xla). 3 kbar in the Windmill
Islands
the Tula
(Sheraton
Mountains
attempted, appears
et al.,
1980).
1982), and possibly No
nor have there been any fluid inclusion
as a primary
at Mawson
(Blight and Oliver,
phase in talc -silicate inclusions
and in calcsilicate
layers associated
estimates studies.
< 0.5 kbar in
of p< (), have However,
at two localities
been
wollastonite in charnockite
with sapphirine-bearing
granulitea
at Forefinger Point in Enderby Land (Figs. I and 2). The appearance of wollastonite instead of calcite-quartz implies P(.~,, < P-,,_:~,_ For example. Valley and Essene (1980) calculate that cafcite-quartz is stable to 1010”c‘ at 8 kbar for pc f) = p Irl,,,,. Moreover. there is no evidence. such as secondary carbonates. that the low water partial pressures indicated for Antarctic increased partial pressure of C’O,.
granulite-facies
rocks
are the result
of
,411 alternative explanation of the above observations is that I-‘,, ,() t pc ().
isotopic
as proposed
ages at h&h ambient by Harte
temperatures
ct al. (19X1 ). My proposal
at the base of the Earth’s is consistent
features in the Napier complex. For example. one group of post-tectonic with an Rb-Sr isochron age of 2400 f 250 m.y. are granuloblastic gr~lllulite-facies
mineralogy
(Sheraton
nl~t~~n~~rph~sed at high ambient
mafic dikes and have a
and Black. 1981). These dikes may have been
pressures
dike rock itself, while the fluid-depleted
with several
and temperatures country
by fluids present
rocks underwent
in the
no chttnge.
On the other hand, a large quantity of fluid must have passed through the rocks of the Napier complex at some time when peak metamorphism conditions were except possibly K ?t.9. were not mohihzed attained. Although major components. (Sheraton, 19g0). some trace elements were highly mobile. such as Rb. U. Sm and Nd (DePaolo et al.. 1982) and therefore introduced uncertainty into Sm end age determination. Moreover. the Be. Nb, and rare earth element mineralization mentioned above may be due to partial removal of these elements from the metamorphic rocks and subsequent concentration in pegmatites and segregations by an active fluid phase. Earlier I had suggested that a non-magmati~ source of the beryllium in the Casey Bay pegmatites was unlikely as there was no obvious mechanism for transporting and concentrating beryllium under granuiite-facies conditions (Grew. 1981b). However. in view of the high mobility of the trace elements (dePaoi(~et al..
187
1982) from
conclusive the Tula
between
evidence
the beryllium
beryllium
for beryllium
Mountains-Grew, pegmatites
in the pegmatites
from the country
in quartzofeldspathic
1983)
and
absence
and
plutonic
rocks,
was derived by transport
rock by fluids passing
through
gneiss (in sapphirine
of any visible I now
connection
suggest
and concentration the rocks during
that
the
of beryllium granulite-facies
metamorphism. CONCLUSION
International features
studies
of the Napier
in Enderby complex
Land have sufficiently
that this complex
elucidated
the classic pyroxene-granulite facies terranes of the world. Certain notably osumilite-sapphirine-quartz, and beryllium blages, (surinamite-taaffeite-Be-sapphirine) in granulite-facies pegmatites, the Napier earth
complex.
elements
It is the first granulite-facies
during
metamorphism
systematics. The rare earth element the importance of fluid, while
has been
the petrologic
can now be recognized
terrane shown
as one of
mineral assemmineralization are unique
in which mobility to disturb
Sm-Nd
to
of rare isotope
mobility and beryllium mineralisation illustrate the mineral assemblages (e.g. sapphirine-
osumiliteequartz) can form only at low water partial pressures. Massive influx of COZ has been proposed as a means of driving water from rocks during granulite-facies metamorphism in other terranes, but this hypothesis is not consistent with some features of the Napier complex, such as appearance of wollastonite in talc-silicate rocks. Although
the main focus of this review is to summarize
information
accumulated
that
this review
on Antarctica
will stimulate
further
the considerable
body of
over the last 20 years, it is the author’s hope work.
Many
areas
of potential
petrologic
interest have to date been covered only in regional surveys, or in reconnaissance. Detailed work on the better studied areas such as Enderby Land has only begun. ACKNOWLEDGEMENTS
The present review is distillation of my 10 years of Antarctic studies, including five trips to the Antarctic. I thank the Antarctic Division of the Department of Science and Environment (Australia) for enabling me to participate in two Australian National Antarctic Research Expeditions (1977-1978 and Antarctic Scientific Research Institute (USSR), Soviet Antarctic Expeditions; and the U.S. Antarctic Research Programme (1981-1982). for providing unpublished analyses, R.C. Museum, Sydney, for a piece of Mawson’s E.N. Kamenev and M.A. Sandiford for discussions and exchange of information
and 1979-1980); the Arctic in the 18th, 19th, and 22nd
National Science Foundation, in the U.S. I thank H.R. Westrich and M. Yoshida Newton for calculations, the Australian kornerupine-bearing sample (lOOA), and samples from Enderby Land. Fruitful with many scientists have contributed
IX8
much
to the ideas
DePaolo,
presented
R.B. Hargraves,
in this paper.
EN.
Kamenev,
in particular
K.D.
C‘ollerson.
D.J.
R.L. Oliver. M.A. Sandif(~rd. J.W. Shera-
ton. and M. Yoshida. An earlier version of this manuscript B.F. Windley.
was reviewed by E.J. Essene. P.C. Grew. 2nd
Their thoughtful
comments
of this review
has been
have lead to a substantial
improvement
of
the paper. Preparation Foundation
Grant
supported
through
U.S. National
Science
DPPXO-19527.
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