Content uploaded by M. Qasim Jan
Author content
All content in this area was uploaded by M. Qasim Jan on Feb 05, 2016
Content may be subject to copyright.
I .l
Proc. Pakistan Acad. Sci. 36(2): ll9-I34.1999
PETROGRAPHY AND GEOCHEMISTRY OF ROCKS FROM THE SOR.RONDANE
MOI]NTAINS, DRONNING MAUD LANDO EASTERN ANTARCTICA
rS. Shafiqur Rehman,2M. Thhir Shah, 2M. Qasim Jan and 'M. Majid
rDepartment of Geolog1,, Universin, of Peshawar, Pakistan and 2NCE Geologl', Universitl, of Peshawati Pakistan
Atrstract: Many lock specimens, were collected from the Sor-Rondane mountains and Breid B ay area
of Dronning Maud Land, eatsren Antarctica, during the 2nd Pakistan Antarctic Expedition, 1992-93.
Petrography and geochemical studies suggest that the rocks are essentially of igneous origin. The
samples dredged from ocean-bottom include olivine basalts, amygdaloidal volcanics, dacites and
rhyodacites. A majority of these rocks are calc-alkaline and formed by the fractionation of olivine,
clinopyroxene and plagioclase + titanomagnetite. Most of these rocks apparently formed in an island
arc or continental margin set up. However, volcanics showing ocean floor basalt character are also
present. A metamorphosed and deformed basement consisting of amphibolites, calc-silicate rocks
and gneisses is intruded by undeformed or only slightly deformed granites with a minor arkosic sandstone
cover. The granites are chemically distinguished as I-type, originated at deeper crustal level by
collisional/subduction related processes during orogenic environments.
Keywords : Petrography, geochemistry; eastern Antarctica
Introduction
Antarctica is the 5th largest continent of the
Earth with a total area of - 14 million km2.
Climatically, it lies in a cold desert environment
where mean annual temperature is - -50 oC,
rainfall < 5 cmlyr, andblizzards reaching up to
300 km/hr. Ninety percent of the world's ice is
stored in the Antarctic icecaps having an average
thickness of 24OO m and covering - 98 Vo of its
land surface. These extreme weather conditions
have made it the least known and exploited part
of the earth. After the International Geophysical
Year (1958), all scientific research endeavours
carried out in isolation were abandoned and an
integrated international research programme was
implemented. This has substantially improved
our understanding of the area and has opened
more fields in applied and basic research.
Part of the supercontinent - Gondwana -
Antarctica gradually moved to the extreme south
of the globe following Gondwanic disintegration
rAddress for correspondence: Dr. M. Qasim Jan, Director /
Chancellor, University of Peshawar, Peshawar, Pakistan.
nearly 180 million years ago [1]. Very little has
been known about its geology due to limited rock
exposure (only 2 Vo surface areais exposed) and
hostile weather conditions. Yet general
reconnaissance andexploratory work spreading
over the last 50 years has brought many facts to
light. Accordingly, the continent is sub-divided
longitudnally into two major geological
provinces - the Gondwana Province of East
Antarctica and the Andean Province of West
Antarctica [2]. The former is characterized by
magmatic and metamorphic rocks ranging in age
from Protetozorc to Archeozoic, whereas, the
latter is made up of Mesozoic-Cenozoic
sedimentary rocks.
2nd Pakistan Antarctic expedition
Pakistan has undertaken a modest polar
research programme since 1990. So far, two
major independent research expeditions have
been launched to study meteorology, glaciology,
oceanography, geology/geophysics and ecology
of a relatively small part of the Dronning Maud
vice- Land (DML), eastern Antarctica. The first
expedition conducted in December 1990,
Petrography and geochetnistry, eastern Antractica
established a ground station (Jinnah-I) at Iatitude
70" 24' S, longitude 25" 45' E, at a distance of
about Z2kminland from the edge of the ice shelf.
During this expedition rock specimens were
collected from the Molle-Rock of Casey Bay
area. Petrographic studies revealed that almost
all samples were of garnet-biotite gneiss (A.R.
Tabrez, pers. comm.).
Subsequent to a partially successful first
trip, the second expedition was lanuched from
Karachi two years later in December, 1992. After
a 25 days voyage through the Indian Ocean, the
team arrived at the Breid Bay of Princess
Ragnhild Coast (Dronning Maud Land, eastern
Antarctica) on January 22,1993. Besides several
oceanographic and terrestrial experiments, the
objectives of the 2nd expedition included revival
of Jinnah-1 and establishment of two new
stations, Jinnah-Il and the lqbal Observatory,
during a total stay period of 25 days.
Inadequate logistic support and bad weather
--blizzards and snow storms which continued
during 80%o of the time -- thwarted all efforts to
carry out extensive land operations. Geological
investigations were, therefore, restricted to
collecting rock samples from the scarce outcrops
exposed in the immediate vicinity of our ground
stations without any geological mapping or
stmctural measurements. Jinnah-II and the Iqbal
Observatory were, thus, established at lat. 70"
50' S, long. 25" l0'E and lat.77" 27' 5,1ong.25"
l8' E, located approximately 72 and 140 km
inland from the shelf edge, respectively.
A proYninent physiographic feature of the
Dronning Maud Land is a - 250 km long east-
west wedge-shaped coastal range, called Sor
Rondane mountains. The mountain front starts
appearing from the ice sheet as nunataks some
140 km inland from the ice edge. Accoiding to
some workers [3, 4], the range comprises two
120
distinct zones -- the Gneissic Series and the
Intrusive Series and belongs to the shield area of
the eastern Antarctica. The site of the Iqbal
Observatory (study area of this paper) has been
referred to as Nordtoppen in maps produced
during Belgian expedition 1 95 8-60. Radiometric
ages determinedon biotite and zircon of granitic
and dioritic samples foom Nordtoppen show these
rocks to be in the range of 481+15 to 555+20
Ma [4].
Several other studies have been conducted
in different parts of the Dronning Maud Land.
For instance the - 1080 m.y., old Ritscherfiya
supergroup has been described as molasse
deposits intruded by the - 1000 m.y. old
Borgmassivet continental tholeiites of the
western DML [5]. Grantham et al. [6) have
studied the -47O m.y. oldDalmatian granites and
identified two varieties with magnetite and
tourmaline nodules- They have shown that these
granites form sheet-like bodies and have been
emplaced syntectonically inro - 1000 m.y. old
orthogneisses, paragneisses and calcareous rocks.
Kirwan basalts and Mesozoic dolerite dykes of
the western DML have been discussed by Harris
et al. l7 ,81. Barton et al. [9] have described the
Annandgstoppane granite from the western DML
as a part of the basement complex, emplaced
during 31 15 to 2945 m-y. ago. This granite was
intruded by the Annandgstoppane gabbro about
- 1200 m.y. ago.
Petrographic Studies
This paper presents the results of the
petrographic study of two categories of rock
samples. Those collected from the nunataks of
the lqbal Observatory have been classified as
"terrestrial", whereas the remaining, which were
dredged out from the sea floor of the Brekilen
Bay area (Iat. 70'08' S, long. 2611'E atadepth
of 235 m), are termed as "ocean bottom"
t21
specimens. Accordingly, their samples numbers
have been prefixed with the letter "T" and "O.B"
respectively, for ease of reference' The collection
consists, predominantly of igneous rocks with
only one sample identified as sandstone.
Ocean Bottom SamPles
Samples dredged from the Brekilen Bay can
be divided into granitic and volcanic rocks. The
formef are described with continental rocks
because (i) normal granites are atypical of oceanic
environments, and (ii) their KrO contents
resemble continental granophyres. It is possible
that these rocks were rifted from continental areas
and dumped in the ocean by melting icebergs.
As shown, even the volcanic rocks may not
entirely have originated in oceanic setting and
for the sake of convenience are here lumped
together. They range from flows (olivine basalts
and rhyodacites) with few amygdules to those
highly amygdaloidal.
i) Olivine basalts: These contain
phenocrysts of olivine (with or without
plagioclase and clinopyroxene) in a matrix of
plagioclase, clinopyroxene and iron oxide, as
well as glass in some. The texture of the
groundmass ranges from intersertal to
intergranular, but the clinopyroxene is locally
subophitic.
Olivine phyenocrysts reach up to 3 mm in
length and all are invariably altered to chlorite +
serpentine. In a few cases, the pseudomorphs
also contain some talc, rare carbonate and reddish
iron oxide along margins and fractures.
Plagioclase is only locally cloudy and
saussuritization may be accompanied by minor
carbonate. It shows some normal zoning, with
core compositions ranging from Anu, to Anuo in
different samples. Clinopyroxene is also mostly
fresh and augitic in composition. Glass is locally
S. Shafiqur Rehman el. a/
devitrified and charged with granules of black
iron oxide. Alteration to hematite imparts the
glass a reddish colour in some sections.
All the samples contain tiny amygdules
filled with material similar to that
pseudomorphing the olivine. More complicated
amygdules, up to 5 mm in length, occur in some
samples. These consist of an outer thin rim of
radial serpentine and an inner shell of chlorite
with or without a core of coarse grained felsic
material, carbonate and (?) zeolite. Microveins
of the chlorite/serpentine occur locally; one
sample contains a 2 to 4 mm thick vein of
radiating chlorite and serpentine fibers.
ii) Dacitic rocks: These are characterized
by a low quantity of ferromagnesian minerals and
abundance of felsic minerals. They display
textures typical of quickly cooled rocks: prismatic
phenocrysts ranging from euhedral to subhedral
in outline, displaying high length to breadth
ratios, and radial to lnterlocking disposition, in a
micro- to cryptocrystalline/glassy groundmass.
The phenocryst phase is typically plagioclase,
ranging from oligoclase to andesine in
composition and constituting up to 4 mm long
needles in one rock. In another sample,
clinopyroxene also forms phenocrysts up to 6 mm
in length.
The felsic groundmass contains sparse
grains of clinopyroxene and iron oxide. Some
devitrified parts contain slender microlites of
feldspar in a brown cryptocrystalline matrix.
From modal and chemical analyses we deduce
that the groundmass consists of plagioclase, K-
feldspar, andquafiz. In some samples it appears
to consist of a micrographic microperthitic
intergrowth. There are local pools of slightly
coarser-grained quartz. These may represent tiny
amygdules. Other larger amygdules may be filled
by quartz with variable amounts of epidote,
Petrography and geochemistry, eastern Antractica
carbonate, chlorite/serpentine and iron oxide but
in most sections amygdules do not exceed a few
percent by volume. Most rocks are only slightly
weathered but in rare cases the feldspar grains
are cloudy with local growth of epidote.
iii) Amygdaloidal volcanics.. Three of the
ocean bottom samples are highly amygdaloidal
and merit independent description. Despite being
weathered, OBl0 clearly displays a quenched
texture. It consists of tiny (< 0. 5 mm) but
abundant prisms of cloudy plagioclase in a light
green chloritic matrix (after glass) dotted with
leucoxene (after ilmenite). A quarter of the
sample is occupied by rounded amygdules up to
4 mm across. These contain epidote and quartz
grains up to 2 mm in length, but some may have
iron oxide, carbonate and chlorite.
A microporphyritic basalt (OBl7) consists
of plagioclase, clinopyroxene, partly devitrified
brown-green glass and iron oxide dust. The
plagioclase is zoned from medium labradorite
cores to calcic-andesine margins. About 30Vo of
this sample consists of fragments of a highly
amygdaloidal basalt. This consists of plagioclase
1- Anr) and clinopyroxene (up to 2 and 1.5 mm
long, respectively) and some opaque grains in a
partly devitrified matrix charged with plagioclase
microlites and reddish pink dust. The contact of
the fragments with the host basalt does not appear
to be sharp. The bulk of these fragments ,
(reaching up to 8 mm in size) is made up of
amygdules consisting of feldspar, quartz, zeolite
(? pectolite) + chlorite + ?amphibole. In many
cases these minerals are wrapped around by thin
envelopei of.chlorite (inner), chalcedony and,
sparingly, reddish iron oxide (outer).
One basalt (OB 18) consisrs of
microphenocrysts of abundant plagioclase and a
little clinopyroxene in a red-stained glassy
groundmass. A few plagioclase grains are
122
distinctly coarser than the rest (up to a millimeter)
and may be xenocrysts. A third of this sample is
occupied by amygdules consisting essentially of
a colourless mineral with low relief, first order
white interference colour and small negative 2V.
Small amounts of quartz, feldspar, chalcedony
and carbonate may occur in some amygdules.
Cont inen t al Rock Sam ple s
With the limited rock samples and scarce
field data at hand, we assume that the area
consists of basement intrudedby granitic plutons,
which was possibly overlain by continental
sediments.
i) The basement:Thebasement rocks are
characteri stically metamorphic, with deformation
fabric (commonly plastic) displayed by some
samples. The collected specimens are divisible
into gneisses, amphibolites, and calc-silicates.
Mutual relationships of these rocks are not clear.
The amphib"olites are dark medium-grained
and foliated which apparently host the gneisses.
They may be the product of a continental
magmatism predating the emplacement of the
granites. They consist of hornblende and
plagioclase with reliable amounts of quartz,
biotite, sphene, opaque oxide, apatite + epidote/
allanite + zircon. Plagioclase is generally fresh
and may display good albite twining. It ranges
from Anro to An, in different samples and may
locally have less calcic margins. The hornblende
may contain quartz droplets and plagioclase.
Sphene occurs in association with opaque grains
(probably ilmenite) as well as independently.
The calc-silicate rocks are coarse-medium-
grained, locally foliated and/or banded. These
consist principally of clinopyroxene, quartz +
plagioclase, with minor amounts of hornblendic
amphibole, sphene, carbonate, epidote/allanite +
I
t?3
birxitc+opaque oxide + oxidized sulphide. One
sample contains abundant hornblende
{>>clinopyroxene), a lot of black oxide and
seh€ne-
The clinopyroxene is green and locally
replaced by bluish green amphibole. Hornblende
is greenish and biotite is chloritized. Although
some carbonate appears to be replacing other
minerals, there also are intergrowths of
clinopyroxene and carbonate. Plagioclase is
variably zoned and deformed, with core
compositions ranging from labradorite to
andesine. Sio-ne plagioclase is much cloudy and
contains epidote, sericite + calcite, and a few
grains have many inclusions of quartz. In one
rock sample (T25), the clinopyroxene,
plagioclase and quartz have inclusions of each
other.
The gneisses appear to be a suite of
granitoids ranging from quartz diorite to granite.
They are generally medium-grained, foliated, and
display banding. Some bands are very rich in
biotite + hornblende and may represent mafic
schlieren, metasediments or metasomites. The
quartz diorite consists of plagioclase (An.,,), green
hornblende, qtJartz, biotite and subordinate
sphene, ilmenite, apatite, and secondary chlorite,
epidote and prehnite. This rock apparently
intrudes amphibolites. The silicic rocks contain
perthite and/or microcline , qurattz, intermediate
plagioclase, olive green hornblende, biotite, and
small amounts of apatite, opaque oxide, zircon
+ sphene + tourmaline. But one of the fine
medium-gr,ained granitic rocks (T29) is devoid
of hornblende'and has a plagioclase of An'
composition.
ii) Granitic Rocks: These are commonly
undeformed and medium-grained, displaying a
t1'pical granitic fabric. They range from
equigranular to porphyritic, with K-feldspar
S. Shafiqur Rehman er. nl
phenocrysts over a centimeter in length. Their
colour is grey but some weathered surfaces look
pinkish.
The rocks consist of potash feldspar,
plagioclase, quartz, and biotite, with minor
amounts of myrmekite, opaque oxide, sphene,
apatite, and zircon. The K-feldspar may be
perthite (with or without microcline twining) and/
or microcline. The plagioclase ranges from sodic
oligoclase to sodic andesine. Most rocks are
fresh, but locally the feldspars may be cloudy and
replaced by white mica, epidote+ carbonate, and
biotite by chlorite + muscovite + sphene. Only
in rare cases the muscovite may appear primary.
Both modally and chemically, the rocks can
be classified as granite [10]. One sample (OB9)
is a leucogranite with a very small amount of
mafic minerals and higher amount of feldspars
(note the low FerOr* and high alkalis of the
analysis in Table 3). This sample is coarse-
grained with up to 1,5 cm long, light-pink potash-
feldspar. It is possible that these may represent a
slightly youngerphase of the granite magmatism.
In at least one granite sample, there is a thin (<
1.0 cm) vein of similar composition.
The petrography of the rocks clearly
suggests that (i) the basement rocks are deformed
and have been metamorphosed under upper
amphibolite facies conditions, and (ii) the granitic
rocks are unmetamorphosed and show little or
no deformation. We conclude that the latter were
probably emplaced af.ter the basement passed
through various phases of deformation and
metamorphism.
iii) Sedimentary Rocks: Sandstone is the
only sedimentary rock in the studied samples
(OB 14) and belongs to the category of samples
collected from the ocean bottom. The sandstone
is dominantly composed of quartz (10Vo).
Petrography and geochemistry, eastern Antractica
Feldspar grains (plagioclase + alkali feldspar)
constitute the remaining 3OVo of the rock.
Sphene, carbonate and muscovite are present in
traces.
The quartz grains are bimodal in size and
sub-rounded to rounded in shape.
Monocrystalline quafiz is the most abundant
variety with only a few grains of polycrystalline
nature. The grains have interpenetrative contacts
due to compaction, with rims of qtJattz
overgrowth. The rock is texturally and
compositionally submature and is classified as
an arkose. Brunn [11] has reported some
outcrops of well-bedded arkoses and arenites
from the western part of the Dronning Maud Land
which may well be the source of sandstone
dredged out from the Breid Bay area.
Geochemistry
General Statement
Six granites, ten volcanics, three
Table 1. Chemical analyses of the volcanic rocks from the Antarctica.
124
amphibolites, three basement-gneisses, three
calc-silicate rocks and one arkosic sandstone
samples were analysed for major elements. The
results along with CIPW norms are listed in
Tables 1,2 and 3. SiO2, Al2O3, TiO' and prO,
have been determined by the colorimetric method
by using UV visible spectrophotometer and the
rest of the oxides by an atomic absorption
spectrophotometer. All these analyses were
performed at the Geochemistry Lab., NCE in
Geology, University of Peshawar, after
calibrating the machines by using G-2,W2 and
AGVI as internal standards. Loss on ignition
(LOD was determined by heating abour 2 g
sample at 950 - 1050 "C for more than 4 hours.
Ocean bottom rocks
Among the volcanic rocks the olivine
basalts and amygdaloidal rocks have greater
ignition loss (up to 8Vo, Table 1). Their analyses
are, therefore, recalculated to anhydrous basis.
This anhydrous data is then used for calculation
of CIPW norms and further interpretation. Out
of ten samples of volcanic rocks, five samples
Olivine basalts Amygdaloidal volcanics Rhyodacites
oB4 OB5A 086 0815 0810 oBlT 0Bl8 oB8 0816 CB12
l
j
I
l
n
I
si02
Ti02
Al201
FerO.
MnO
Mgo
CaO
Naro
KrO
PrO,
Ig loss
Total
54.60
0.64
17.45
6.43
0.14
4.31
5.91
3.21
2.94
0.16
3.59
99.38
69.34
o.41
14.r2
2.43
0.09
L88
2.22
3.95
3.'78
0.08
1.10
100.06
50.6'7 47.45
0.6 r 0.50
15.45 15.67
8.57 8.45
0.11 0.15
10.36 12.99
6.54 9.34
2.92 2.18
0.51 0.2s
0.20 0.12
3.18 3.15
99.78 100.25
46.23 s2.10
0.13 0.66
t'7.24 t7.45
7.12 8.57
0.19 0.11
6.59 6.83
10.67 7.10
2.39 3.61
1.48 1.58
0.20 0.25
7.99 3.44
100.83 t}t.'76
51.23 54.34
0.61 0.52
18.56 16.4s
8.39 7.4s
0.15 0.13
6.30 4.22
8.78 5.84
2.92 4.45
0.94 1.51
0.19 0.18
1.50 5.45
99.57 100.60
68.89 69.30
0.49 0.40
13.24 13.45
2.81 3.65
0.08 0.08
2.60 t.71
2.84 3.04
3.76 2.93
3.59 3.35
0.20 0.06
0.98 1.60
99.54 99.63
lg5
(bF|l.trrg me amygdaloidal volcanic) are of
Mhic mrnposition (< 53 wtTo SiOr), two
nygdanomU volcanics have basaltic - andesitic
oqmitlon (53 - 57 wt%o) and three samples
hmm nhyodacite composition (69 wtTo) on the
bmis of SiO, contents [2].
Thesnrdied basalts (Table 2) can be divided
into two main classes on the basis of MgO
content: a) high-magnesia basalt with MgO
ourtent greater than 9 wtVo, andb) low-magnesia
basalt with MgO content less than 9 wt%o ll3l.
Chemically the olivine basalts have SiO, in the
tange of 46 to 52 wt%o, Al2Oj is 15.45 to 17 .45
wt%. Fe,O., is 7 to 8.57 wt%o, MgO is 6.59 to
1?.99 wt%o, CaO is 6.54 to 70.67 wtVo, NarO is
?.18 to 3.61 wtVo and KrO is 0.25 to 1.58 wt%o.
TiO, and PrO, vary from 0.50 to 0.73 wt%o and
O. 12 to 0.25 wt%o,respectively. All the analysed
S. Shafiqur Rehman er. c/
basalts are silica-undersaturated (olivine
normative) but the presence of hypersthene (up
to 32.11 Vo) in the norms, together with the
absence of titanium augite, suggests that they are
non-alkaline in nature.
Amygdaloidal rocks have basalt to basaltic-
andesite composition with SiO, ranging from
52.24 to 57 .ll wt 7o, Al2O3 from l7 .29 to 18.93
wtVo, FerO. from 6.71 to 8.56 wt7o, MgO from
4.44 to 6.42 wt%o, CaO from 6.T4 to 8.95 wtTo,
NarO from 2.98 to 4.68, and KrO from 0.96 to
3.07 wt Vo.
The CIPW norms on anhydrous basis
suggest that the amygdaloidal rocks of basaltic
composition are olivine-normative, while that of
basaltic-andesite composition are quartz-
normative. All these samples are diopside (up
Thble 2' Chemical analyses along with C.I.P.W norms (recalculated on anhydrous basis.; for the volcanic rocks of Antarctica.
Olivine basalts Amygdaloidal volcanics Rhyodacites
OB4 OB5A 086 0Bl5 0810 0817 0818 oB8 0816 CBtz
siq
rot
Al.o.
Fe=O,
MnO
ItdeO
CaO
Nqo
KO
Pro,
52,18 48.81
0.64 0.51
16.09 16.14
8.93 8.70
0.18 0.15
10.79 13.38
6.81 9.62
3.04 2.25
0.53 0.26
0.2r 0.12
0.00 0.00
3.16 L55
- 25 .90 19. 16
28.89 33.39
3.01 11.16
32.19 12.57
3.35 19.22
1.75 t.1l
1.23 0.98
0.46 0.26
49.81 52.99
o.79 0.67
18.58 17.75
1.67 8.72
0.20 0.11
'7.07 6.95
11.50 7.22
2.58 3.67
1.59 1.61
0.22 0.25
0.00 0.00
9.41 9.61
21.21 31.30
34.97 21.41
17.06 5.19
0.51 14.49
13.21 7.84
1.52 1.73
l.51 1.28
0.48 0.55
52.24 57.11
0.62 0.55
18.93 17.29
8.56 7.83
0.15 0.14
6.42 4.44
8.95 6.14
2.98 4.68
0.96 1.6s
0.19 0.19
0.00 1.68
5.72 9.83
2s.37 39.82
35.65 21.40
6.45 6.6r
23.15 l7 .64
0.36 0.00
1.69 1.55
1.19 1.05
0.42 0.42
69.90 70.69
0.50 0.41
13.43 13.72
2.91 3.12
0.08 0.08
2.64 1.81
2.88 3.10
3.81 2:.99
3.64 3.42
0.20 0.06
23.18 29.42
21.60 20.28
32.33 25.34
8.16 13.93
3.44 0.92
1.78 0.46
8.12 8.47
0.57 0.73
0.95 0.78
0.44 0,13
57.00
0.67
18.22
6.71
0.15
4.50
6.17
3.35
'3.01
0.11
3.54
18.27
28.48
25.71
3.26
11.76
0.00
1.33
1.28
0.31
70.50
0.48
14.36
2.41
0.09
1.91
2.26
4.02
3.84
0.08
24.04
22.18
34.02
9.78
0.75
0.39
7.06
0.48
0.91
0.18
CIPW norms on anhydrous basis
a
Or
Ab
An
Di
Hy
or
Mt
I
Ap
Petrography and geochemistry, eastern Antractica
to 6.6lvo) and hypersthene (up to 23.75Vo)
norrnative. Rhyodacites have negligible variation
in SiO, (68.89 - 69.34 wtVo),Al 2Or 03.25 1 4.12
wt Vo) and K2O (3.35 - 3.78 wt 7o). Among the
rest of the oxides FerO, varies from2.43 to 3.65
wt%o, ldgO from 1 .77 to 2.84 wtVo, CaO from
2.22 to 3.04 wt%o and NarO from 2.93 to 3.95
wt7o. CIPW norm calculations (Table 2) show
that these rocks have normative Q in the range
of 23.78 to 29.42 wt%o, ot from20.28 to 22.78
wt%o, Ab from 25.34 to 34.02 wt%o, and An from
8.76 to 13.93 wtVo. Both diopside (up to3.44Vo)
and hypersthene (up to 8.47Vo) are present in all
the analyses.
The major oxides of the studied volcanics
are plotted against silica in Figure 1 There is a
big compositional gap between 57 and 68 wt%o
SiOr. This can be attributed to the lack of proper
sampling. There is a continuous decrease of TiO'
A1293, MgO, FerO. and CaO and an increase of
KrO and total alkalis (NarO+KrO) with increase
of SiO' The NarO, however, increases up to 57
wtTo SiO' The decreasing behaviour of major
oxides against SiO, suggest the fractionation of
6liuin" and clinopyroxene followed by
plagioclase along with titanomagnetite during
differentiation of magma (the validity of this
conclusion is entirely dependent on the
assumption that the dredged volcanic rocks
belong to the same suite. It is also possible that
the basalts and rhyodacites are mutually
unrelated). Assuming that the samples belong
to the same suite, a decrease of FerO., and TiO,
with increase of SiO, during differentiation
typifies them as calc-alkaline [14]. On the AFM
diagram (Fig. 2) almost all the volcanics (except
one) fall within the calc-alkaline field of Irvine
and Baragar [15]. The calc-alkaline nature of
these volcanics is also clear in FeO(t)/ MgO vs
SiO, (FiS. 3).
In order to identify the tectonic affinity of
volcanics, various discrimination diagrams, using
t26
major oxide data, are used. All olivine basalts
and amygdaloidal volcanics plot within the field
of calc-alkaline basalts on Mullen's [17] diagram
(Fig. 4a). Most of these (except two samples)
are confined to the narrow field or orogenic basalt
(both of island arc and continental margin) of
Pearceet aL t18l (Fig. 4b). However, two olivine
basalts plot within the ocean floor basalts. Very
similar island arc of calc-alkaline character of
these volcanics is also evident from Yoder's [19]
diagram (Fig. 4c). The studied volcanics are poor
in TiO, and, therefore, scattered within the field
of island arc volcanics of Miyashiro [20] (Fig.
4d).
Continental rocks
As already mentioned in the petrography
section the amphibolites can be divided into two
groups. Sample nos. T26 and T2l have very
similar chemical composition but are
significantly different from sample no. T33. The
former samples have lower SiO' AlrO' and
higher P2O., MnO and especially FerO, and TiO,
than the latter. Sample no. T33 is an andesitic-
basalt similar to some volcanic and plutonic rocks
of continental region although it is a little
depleted in KrO. It contains quarrz, diopside (11
Vo) and hypersthene (21 Vo) in the CIPW norrns
and shows tholeiitic character on AFM diagram
(Fig. 2). We have not been able to find chemical
analogues of the other two amphibolites (T2l and
T26) in igneous rocks of continental regions. For
rocks with only SOVo SiO,, they have rather low
Mg number and show difference in total alkali
and TiOr. It is thus possible that they are some
sort of CaO and FeO rich sediments. If so, then
they may well be a part of the metasedimentary
basement to which the calc-silicate rocks also
belong.
The clac-silicate rocks have variable
concentration of almost all the oxides (Table 3).
SiO, varies from 44 to 59.12 wt%o,TrO rfrom 0.40
S. Shafiqur Rehman er. a/
(€
o
o
L
cJ
j
a
ag
EO
^6
.trr
H>\
q -C,
-vr
8il
!x
o-
co
or:
OO
>=
o>
l'd
(ko
Fd
eg9
qo0
bo >,
6d
9d
a^ ll
Ya
a -^
@(d
Oa
.Y o-l
xtr
€rr
ax
E'n
h
o
\o N
o
.!l
0
d
.-
-A
ra
e
tr
rn
\9
o
F
ln
\c
\o
tfl c
=tao--la)€ OBJ
ra(ac
r'{:-
tl
t* tt
IF :r
to'
oErnt
v)r"r€3
o'x+d"N
b
e€
IY
€'€
Gl-
e
)
0
Petrography and geochemistry, eastern Antractica
red
x
CALC-ALKALINE
NqO+Kp
Fig.2. AFM diagram for the volcanic rocks from the
DML, Antarctica. Fields are after Irivine and
Baragar [15]. Symbols as for Fig.l.
t28
Fig. 3. FeO(t)/MgO vs SiO, diagram for the volcanic
rocks from DML, Antarctica. Fields are after
Miyashiro [16]. Symbols as for Fig. L
o
0
FeO(t)nvlgO
Tio, FeO(t)
-:#lA
(MoRr) " ^f$\
MnOxl0 P p.x10
o
o0
H
2
5
1
3
2
t
o
Fr
d
Y)/
.v.,
ISIIND AIC VOI'AT{ICS
FeO+Fe O
,r FeO(t/MgO
Fig.4. Plotof a)TiO,-MnO-PrO' afterMullen [17];b)MgO-FeOO-Al2O3afterPearceetal. [8];c)MgOvsFeO
+ FerO, after Yoder [9]; and d) TiO,vs FeO(t) AvIgO after Miyashiro [20], for the volcanic rocks from DML,
Antarctica. CAB = Calc-Alkaline Basalt, IAI = Island Arc Tholeiites, MORB = Mid-Ocean Ridge Basalts. OIT
= Oceanic lsland Tholeiites, OIA = Oceanic Island Alkali basalt, Symbols as for Fig. 1.
tr!9
i*t-Chemical analyses of continental rocks from Antarctica.
S. Shafrqur Rehman et a/
Amphibolites Calc-silicates Gneisses Arkosicsandstone
T21 T23 oB14
sno!
imo"
Aqq
Fep.
tjlno
DtsO
cs
!{qO
qo
P_O_
l!
tglss
Total
53.45
0.66
16.58
9.68
o.21
5.60
9.30
2.46
0.81
0.13
0.80
99.68
49.23 s0.34 s5.89
2.32 1.67 0.59
14.8"t 12.43 5.12
14.45 14.12 15.66
0.40 0.46 0.42
6.01 6.23 4.81
9.43 9.89 11.31
1.22 2.64 0.38
0.92 1.49 0.16
0,40 0.48 0.28
0.45 0.73 0.09
99.10 100.48 100.71
59.12 63.23
0.40 1.09
15.34 14.23
1.12 8.94
0.31 0.16
3.23 0.41
11.54 2.86
2.08 3.21
0.25 4.69
0.00 0.41
0.37 0.27
99.76 99.50
69.67 18.12
0.68 0.45
12.04 10.34
4.89 0.63
0.11 0.04
1.20 0.46
1.87 2.04
3.78 2.12
4.98 3.27
0.28 0.08
0.1 1 1.58
99.61 99.73
44.40
2.81
9.22
21.80
0.47
5.84
12.31
1.81
0.94
0.47
0.83
100.90
74.67
0.56
1?.s6
2.31
0.03
1.05
3.20
3.37
1.6r
0.08
0.40
99.84
oBl oB3 OB9A OB9 T27 . T28
Granites
siq
TO,
aro,
FerO,
MnO
blgO
CaO
NEo
K"O
P,05
Ig loss
Total
CIPW norms
a
Or
Ab
NarO/CaO wt%
Na,O/KrO wtTo
MgO/FeO(t) wtTo
MgO/I\4nO wt%
.A,lO/(Na,O+K"O) mole
A,O/(NarO+KrO) mole
12.43 72.90
0.24 0.00
14.23 14.76
1.99 0.58
0.05 0.02
0.14 0.03
0.11 1.25
3.96 3.84
4.90 5.69
0.08 0.00
0.28 0.48
99.01 99.55
28.53 26.00
29.41 34.00
33.96 32,78
3.05 6.24
1.32 0.00
0.00 0.02
0.00 0.01
2.10 0.85
0.40 0.11
0.46 0.00
0.18 0.00
5.58 3.01
0.81 0.67
0.08 0.06
2.80 1.50
1.09 1.00
1.20 r.18
73.80 72.23
0.38 0.33
12.89 12.46
2.80 2.69
0.40 0.08
0.44 0.90
1.28 2.37
3.01 3.11
3.97 5.45
0.08 0.10
0.47 0.43
99.52 100.15
36.84 27.43
23.81 32.41
25.80 26.42
5.91 3.92
1.51 0.00
0.00 6.01
0.00 3.03
4.70 2.38
0.52 0.s3
0.73 0.63
0.l8 0.22
2.35 1.31
0.'t6 0.57
0.11 0.31
l.l0 11.25
l.l l 0.81
1.39 1.13
71.76
0.24
12.23
2.18
0.05
0.72
2.20
4.15
4.74
0. r0
o.67
99.04
25.35
28.56
35.73
o.72
0.00
8. r5
4.06
0.37
0.44
0.46
0.22
1 .89
0.88
0.37
14.40
0.77
1.02
71.00
0.24
14.78
1.99
0.05
0.37
1.60
3.55
5.r2
0.10
0.34
99.14
26.39
30.11
30.42
7.39
0.72
0.00
0.00
3.29
0.39
0.46
0.22
2.22
0.69
0.21
1.40
l.03
r.30
An
C
Di
wo
Hy
Mt
l
Ap
)
T
Petrography and geochemistry, eastern Antractica
to 2.81 wt%o, Al2Oj from 5.12 to 15.34 wtEo,
FerO, fromT .72 to 21.8 wtVo,MgO from 3.23 to
5.84 wt%o, CaO from 1 1.54 to 17 .31 wt%o,NarO
from 0.38 to 2.08 wt%o, \O from 0. 16 to 0.94
wtVo and PrO, is up to 0.47 wt7o. MnO in these
rocks is relatively higher (0.47 wt%o).
The basement gneisses have greater
variation in SiO, (63.23 - 74.67 wt%o), FerO.
(2.31 - 8.94 wt%o) and KrO (1.61 - 4.98 wt%o),
but the rest of the oxides have little variation.
Al2Or varies from 12.04 to 14.23 wt%o,TrO rfrom
0.56 to 1.09 wt%o, MgO from 0.41 to 1.2 wtVo,
CaO from 1.87 to 3.2 wtVo and NarO from3.2l
to 3.18 wt%o.
One sample of arkosic sandstone has been
analysed (Table 3) which has SiOr: J8.12 wt%o,
A1 rO.,: 10.34 wt%o,FerOr: 0.63 wtVo,MgO: 0.46
wt%o, CaO: 2.04 wt%o, NarO: 2.7 2 wt%o and KrO:
3.27. wt%o . PrO, and MnO are negligible and TiO,
is 0.45 wt%o.
Major oxides analyses of granites in Table
3 indicate that there is little variation of SiO,
content, ranging from 7 I .00 to 73.8 wt%o. Al2Oj
varies from12.28to 14.78wtVo,FerO. from 0.58
to2.69 wtVo, MgO from 0.14 to 0.80 wt Vo,CaO
from 0.71 to 2.37 wt Vo, and NarO from 3.01 to
3.96 wt%o. The granites have higher content of
KrO (3.87 to 5.69 wt%o) relatle to NarO (3.01 to
4.15 wt%o). The ratios of NarO/CaO, NarO/KO,
MgO/FeO(,) and MgO/MnO vary from 1.31 to
5.58, 0.57 to 0.88, 0.06 to 0.37 , and I .50 to 14.40,
respectively. The ranges of selected CIPW values
are 25 t"o 29Vo q\artz (Q), 28 to 34Vo orthoclase
( or), 25 t"o 3 6Vo al bi te (Ab), 0 .7 2 to 8Vo anorthite
(An). Corundum (C), up to l.lSVo, is present in
norms of three analyses. Normative hypersthene
(Hy) is present in all and diopside (Di) in half of
the analyses.
The major oxide data of the granites were
plotted on various geochemical diagrams to see
130
their variation. The major oxides of these
granites are plotted against SiO, in Fig. 5. TiO,
and FerO, have systematic variation and increase
with increase in SiOr. The rest of the oxides (i.e.,
A1rO3, MgO, CaO, NarO and I!O) show scatter,
suggesting that these granite samples may be
polygenic in nature.
According to the classification scheme of
Chappell and White [21], these granites are I-
type granitoids fmolecular AlrOrl(KzO + NarO
+ CaO) < 1.ll with no or very low corundum.
The I-type nature of these rocks is also evident
in the discrimination diagram (Fig. 6) of Garrels
and Mackenzie 1221. In this diagram all the
samples of granites and basement gneisses plot
in the field of igneous rocks, thus indicating the
involvement of igneous source in the formation
of these rocks. AA{-K vs A/CNX diagram (Fig.
7) shows that three samples plot in the field of
peraluminous and two samples in metaluminous
fields. One granite has the sharing characteristics
and plot at the boundary of these two fields.
Maniar and Piccoli [23] have used a variety
of major element diagrams to distinguish between
granitic rocks formed in different tectonic
settings. Plots of our analyses on their Al2Oj VS
SiO, and FeO(t)/FeO(t)+MgO vs SiO, produce
contradictory results and are not shown here.
Their ACF (Fig. 8a) and AFM (Fig. 8b) ternaries
are, however, very conclusive as all the granite
samples plot in the combined field of IAG, CAG
and CCG of group I of Maniar et al.l23l in both
these diagrams. It is likely that the studied
granites have formed in orogenic setting.
The depth of magma generation for granitic
rocks can be obtained by comparison to water*
saturated minimum in the granite system,
provided the magma has experienced minimal
changes in composition since generation [24].
The studied granites are plotted in Figure 9,
where the water-saturated minimum
=s\€F\our
bx+o'B\I oErnr OBJ
9.o e - eg : I S =
ob'n.{ UIY
bn
S. Shafiqur Rehman er. a/
d
o
o
I
(6
o
o
$.i
a
J4
o
o
L
O
d
k
bo
C)
I
.o
cd
L
bo
(d
U)
a
o
'd
x
o
o
'a
z
rf)
C,b
Frr
Petrography and geochemistry, eastem Antractica
Fig. 6. NarO/AlrO. vs I!O/A12O. plot for the granitic rocks
from DML, Antarctica. Fields are after Garrels and
Mackenzie[22).
Fig.7. A/CNK vs A/NK diagram fbr the granitic rocks
from DML, Antarctica. Fields are after Maniar
' .andPiccoli 1231. A=AlrO.,, C=CaO, N=Na:O
andK = K.O.
r32
Fig. 8. Plotting of granitic rocks from DML, Antarctica,
in the ACF and AFM discrimination diagrams of
Maniar and Piccoli [23]. Orogenic granitoid
rocks: CAG = Continental arc granitoids, CCG =
Continental collision granitoids, CEUG =
Continental epiorganic granitoids, IAG = Island
arc granitoids, OP = Oceanic plagiogranite, pOG
= Post-orogenic granitoids; Anorganic granitoid
rocks: RRG = Rift-related granitoids..
o
o
G
z
IGNEOUS
+
l-++
-1---------...-----_--_
SEDIMENTARY / METASEDIMENTARY
KO/ALO
223
o
bo
tt
z
o
rat N
(r)oes
rn
ol
oBrru+(l)oeu
L
6l
o
l!{
a
rl
z
Metdunlnour
.+
Perelunrlnour
+
+
Pcrdk llnc
.0 l5
A/CNK (Molar)
l,
)f
d
=
=
d
J
d
Fig. 9. Normative quartz (Q) albite (Ab) orthoclase (Or)
composition for the granitic rocks from DML,
Antarctica, and their comparison to experimental
HrO-saturated minimum melt data as summarized
in Anderson and Cuellers f251.
compositions at various Prro are given. This
diagram clearly indicates that five Antarctic
granite samples fall near 7-10 kb minima [at An/
An + Ab = 0.11,0.26 and 0.361. One sample
plots within 2-4 kb minima. This sample has
either quaftz veining in it or it might not be linked
w ith the other granites. It can be concluded that
the granitic magma may have originated at
slightly deeper crustal level.
Conclusions
It has already been mentioned that this study
is based on limited amount of samples collected
tiom the.immediate vicinity of the observatory
and dredged rnaterial from the sea bottom.
Because of poor rock exposures and hostile
u'eather conditions, geological mapping could
not be carried out in a systematic manner.
Therefore, there is no information on the mutual
relationship of the studied rocks in the context
of their origin. Despite these shortcomings, some
important. thou-eh preliminary, conclusions can
S. Shafiqur Rehman et. a/
be drawn from the petrographic and geochemical
studies performed during the course of present
investigation. Thus we conclude that:
a) The study area (Dronning Maud Land)
is apparently a part of a basement, deformed and
metamorphosed during the Precambrian. It may
have consisted of volcanic and sedimentary rocks
which were intruded by a suite of quartz diorite
to granite. This package was metamorphosed to
amphibolites, calc-silicate rocks and gneisses
before the emplacement of a younger group of
granites during the Late Precambrian or Cambro-
Ordovician thermal episode, possibly towards the
end of Pan-African orogeny. Granthamet al.16l
and Groenewald et aI. 1261, have advocated a
similarity in age between the granites found in
DML and those reported from Mozambique and
Natal orogenic provinces of southern Africa. It
may not be totally out of context to mention that
this also is the age of the Lesser Himalayan
cordierite granite belt. Granites of this age also
occur in Australia and the 500 Ma magmatic
event in southern Asia is related to a thermal
episode of Gondwana scale (? Late Pan-African)
1271.
b) The volcanic rocks are mainly of calc-
alkaline nature and basaltic to rhyodacitic
composition. They suggest the prevalence of
island arc or continental margin type set up. They
may have been rafted to the ocean bottom by
melting icerbergs/glaciers in the vicinity. We are
not in a position at this stage to discuss the
relationship of these rocks with the continental
granitoids described above.
Acknowledgements
The first author (SSR) gratefully
acknowledges the help and support of the
members of the 2nd Pakistan Antarctic
Expedition, especially, Maj. M. Zafar and Mr.
lqbal Khan, for their co-operation in field
'0.16 0.26 o.re
i/-?*
?/?7F= ""o
Fig.9.
Petrography and geochemistry eastern Antractica
sampling. Financial support for the expedition,
provided by the Ministry of Science &
Technology, Government of Pakistan, is also duly
acknowledged.
References
l. King, L. and Downard, T. W. 1964. Importance of
Antarctica in the hypothesis of continental drift. In:
Antarctica Geology. Ed. Adie, R.J. pp. 727-'132.
Amsterdam, North-Holland.
2. Adie. R.J. 1964. Stratigraphic correlation in Wesr
Antarctica. In: Antarctic Geology. Ed. Adie, R.J. pp.
307 -313. Amsterdam, North-Holland .
3. Autenboer, T.V., Michot. E. and Picciotto, B, 1964.
Outline of the geology and petrology of the Sor-
Rondane Mountains, Dronning Maud Land. In:
Antarctic Geology. Ed. Adie, R.J. pp. 501-514.
Amsterdam, North-Holland .
4. Picciotto, H., Deutach, S. and Pasteels, P. 1964.
Isotopic ages from the Sor-Rondane mountains,
Dronning Maud Land. In: Antarctic Geology. Ed.
Adieed, R.J. pp. 510-578. Amsterdam, North-Holland.
5. Moycs,A.B., Krynauw,J.R.andBarton,J.M. 1995.
The age of Rilseherflys supergroup and Borgmassivet
intrusions, Dronning Maud Land, Antarctica. Jour
Antarctic Sci. 7 (1): 87 -97
6. Grantham, G.H., Moyes, A.B. and Hunter, D.R.
1991. The age, petrogenesis and emplacement of the
Dalmatian Granite, H.U. SverdrnpfJella, Dronning
Maud Land, Antarctica. Antarctic Science 3(2): 197-
204.
7. Harris,C., Marsh, J.S., Duncan, A.R. and Erlank,
A.J. 1990. The petrogenesis of Kirwan basalts of
Dronning Maud Land, Antarctica. Jour Petrol.3l(2):
341-369.
8. Harris,C., Walters, B.R. and Groenewald, P.B.
1991. Geochemistry of the Mesozoic basic dykes of
western Dronning Maud Land. Antarctica. Contrib.
Mis. Petrol 107(1): 100-1 11.
9. Barton , J.M. Jr., Kiend, R., Allsopp, H.L., Asret,
S.H. and Copperthwaite, Y.E. 1987. The geology and
geochronology of use Annaudgiloppane granite,
western Drosning Maud Land, Antarctica. Contrib.
Min. F etrol. 97 (4): 488-496.
10. Le Bas, M.J., Le Maitre, R.W., Streckeisen, A. and
Zanettin, B. 1986. A chemical classification of
volcanic rocks based on the total alkali-silica diagram.
Jour FetroL 21 : 1 45-7 50.
11. Brunn,V. 1964. Note on some basic rocks in western
Dronning Maud Land. In: Annrctic Geology. Ed. Adie,
R.J. pp. 415-418. Amsterdam, North-Holland.
12. GiIt, J.B. 1981. Orogenic andesites and plate tectonics.
Springer-Verlag, New York.
t34
13. Myers,J.D. 1988. Possible petrogenetic relations
between low and high-MgO Aleutian basalts. Geot.
Soc. Amer Bull. IOO:1040-1053.
14. Miyashiro, A. 1975. Classification, characteristics &
origin of ophiolites. Jour. Geol. 83:249-281.
15. Irvine, T.N. and Barager, W.R.A. 1971. A guid to
the chemical classification of the common volcanic
rocks. Canad. Jour Sci. 8: 523-548.
16. Miyashiro, A. 7974. Volcanic rock series in island
arc and active continental margins. Amer Jour. Sci.
274:321-355.
17. Mullen, 8.D., 1984. MnO/TiOr/PrOr,: a minor
element discriminate for basaltic rocks of oceanic
environments and its implications for petrogenesis.
Earth-Planet. Sci. Len. 62:53-62.
1 8. Pearce,T.H., Gorman, B.E. and Birkelt, T.C.197j .
The relationship between major element chemistry and
tectonic environments of basic and intermediate
volcanic rocks. Earth. Plnnet. Sci. Lett.36 l2l-132.
19. Yoder, H.S. 1969. Cale-alkatine andesites:
experimental data bearing on the origin of their
assumed characteristics. In: Proceedings of the
Andesite Conference, Oregon Dept. Ed. MeBirney,
A.R. Geol. Mineral Industry Bull.65 72-89.
20. Miyashiro, A. 1977. Subduction zone ophiolites and
island arc ophiolites. In Energetics of geological
processes. Eds. Saxena, S.K. and Bhattachargi, S.
Sprin ger-Verlag, New York.
21. Chappell. B.W. and White, A.J.R. 19j4. Two
contrasting granite types. Pac. Geol. 8: 173-175.
22. Garrels, R.M. and Mackenzie, F.T. l9j I . Evolution
of Sedimentary rocks. WW. Norton, New York.
23. Maniar, P.D. and Piccoli, P.M. 1989. Tecronic
discrimination of graniloids. Geol. Soc. Amer Bull.
101:635-643.
24. Anderson, J.L. and Cutters, R.L. 1918.
Geochemistry and evolution of.the Wolf River
batholith, a Late Precambrian rapakivi massif in North
Wisconsin, USA. Precamb. Res. 7 : 281 -384.
25. Anderson, J.L. and Bender, E.E. 1989. Nature and
origin of Proterozoic A-type granule magmatism in
the south western United States of America. Lithos
23:19-52.
26. Groenewald, P.B., Grantham, G.H. and Walkeys,
M.K. 1991 . Geological evidence for a Proterozoic to
Mesozoic link between southeastern Africa and
Dronning Maud Land, Antarctica. Jour Geol. Soc.
1 48(6): 1115-1123.
27. LeFort, P., Debon, P., Pecher, A., Sonet, W. and
Vidal, P. 1986. The 500 Ma magmaric evenr in the
alpine southern Asia, a thermal episode at Gondwana
scale. In: Evolution des domaines orogeniques d'Asic
meridionale. Ed. LeFort, P. N., Sclence de la Tbrre,
Memoires. 41:l9l-209.
