Majalah Geologi Indonesia, Vol. 26 No. 1 April 2011: 19-28
Microstructure Deformation of Metamorphic Rocks
in the Biru Area, South Sulawesi, Indonesia
Deformasi Mikrostruktur Batuan Malihan di Daerah Biru,
Sulawesi Selatan, Indonesia
Asri Jaya1 and Osamu Nishikawa2
1
Department of Geological Engineering, Hasanuddin University, Makassar, Indonesia
Department of Geosciences, Geotechnology, and Materials, Graduate School of Engineering
and Resource Science, Akita University, Akita, Japan
2
ABSTRACT
A small exposure of metamorphic rocks (Biru metamorphic rocks) occurs in the Biru area, South
Sulawesi, lying adjacent to a prominent topographic lineament along the West Walanae Fault (WWF) on
the east side, which is divided into western mountain range and the Sengkang Basin. The metamorphic
rocks are mainly metabasite, adjacent to Cretaceous sedimentary rocks (Marada Formation), and
contact with the Miocene plutonic rocks. Chemical analyses by electron microprobe for establishing
mineral assemblages and chemical composition indicate higher greenschist to amphibolites facies
for their metamorphic grade. A sequence of the microstructural development of the metamorphic
rocks has been reconstructed associated with metamorphism, deformation, and plutonism. During the
UHJLRQDOPHWDPRUSKLVP0WKHPDLQVFKLVWRVLW\LVGH¿QHGE\SUHIHUUHGRULHQWDWLRQRIFROXPQDUDQG
platy minerals, and quartz pools with lenticular shape was developed. The older schistosities are also
inferred with the obliquely arrayed mineral inclusions to the main schistosity in the garnet, epidote,
and plagioclase porphyroblasts. Epidote porphyroblasts have often shown microboudin of which
SXOODSDUWVSDFHVDUH¿OOHGZLWKTXDUW]VXJJHVWLQJDQH[WHQVLRQVXESDUDOOHOWRWKHPDLQVFKLVWRVLW\
during a posthighest metamorphic stage. Quartz grains show polygonal shapes with straight grain
boundaries and seem free from the intracrystalline strain, indicating that the Biru metamorphic rocks
have experienced an annealing process in a contact metamorphism probably caused by intrusion of
plutonic rocks during Miocene (M2). Numerous brittle faults occur along WWF in the Biru area.
Occasionally the associated cataclastic deformation also develops in the Biru metamorphic rocks.
These evidences of deformation in the metamorphic rocks may have been connected to the West
Walanae Fault or regional extension during uplift of western mountain range.
Keywords: deformation, microstructure, Biru metamorphic rocks, South Sulawesi
SARI
Suatu singkapan batuan malihan yang tidak luas (batuan malihan Biru) di daerah Biru, Sulawesi
6HODWDQ PHQJKDPSDU EHUGDPSLQJDQ GHQJDQ NHOXUXVDQ WRSRJUD¿ \DQJ PHQRQMRO VHSDQMDQJ VLVL
WLPXU6HVDU:DODQDH%DUDW::)PHPLVDKNDQ-DMDUDQ3HJXQXQJDQ%DJLDQ%DUDWGDQ&HNXQJDQ
Sengkang. Jenis batuan malihan terutama adalah metabasit yang berdampingan dengan batuan
sedimen Formasi Marada serta bersentuhan dengan batuan plutonik yang berumur Miosen. Analisis
NLPLDPLFURSUREHXQWXNPHQHQWXNDQDVRVLDVLPLQHUDOGDQNRPSRVLVLNLPLDPHQJLQGLNDVLNDQGHUDMDW
PHWDPRUI IDVLHV VHNLV KLMDX KLQJJD IDVLHV DP¿EROLW 6XDWX VHNXHQ SHUNHPEDQJDQ PLNURVWUXNWXUDO
batuan malihan telah direkonstruksi berasosiasi dengan pemalihan deformasi, dan plutonisme.
6HODPDPHWDPRU¿VPHUHJLRQDO0VHNLVWRVLWDVXWDPDGLWHQWXNDQROHKRULHQWDVLPLQHUDOPHQLDQJ
dan mineral pipih serta kumpulan kuarsa berbentuk melensa yang berkembang. Sekistositas yang
lebih tua disimpulkan dari mineral-mineral inklusi yang tersebar miring terhadap sekistositas utama
GDODPSRU¿UREODVSRU¿UREODVJDUQHWHSLGRWGDQSODJLRNODV3RU¿UREODVSRU¿UREODVHSLGRWVHULQJ
Naskah diterima: 03 Januari 2011, revisi terakhir: 30 Maret 2011
19
Majalah Geologi Indonesia, Vol. 26 No. 1 April 2011: 19-28
memperlihatkan boudinmikro dan rongga tarik regang diisi oleh kuarsa, yang PHQXQMXNNDQDGDQ\D
regangan subparallel terhadap sekistositas utama selama tahap pasca pemalihan tertinggi. Butiranbutiran kuarsa memperlihatkan bentuk yang poligon dengan batas-batas butir yang lurus dan terlihat
WDQSDUHJDQJDQDQWDUNULVWDO\DQJPHQXQMXNNDQEDKZDEDWXDQmalihan Biru telah mengalami suatu
SURVHVSHPDQDVDQGDQSHQGLQJLQDQGDODPNDLWDQGHQJDQPHWDPRU¿VPHNRQWDN\DQJNHPXQJNLQDQ
GLVHEDENDQ ROHK LQWUXVL EDWXDQ SOXWRQLN VHODPD 0LRVHQ 0 6HMXPODK VHVDU JHWDV WHUEHQWXN
VHSDQMDQJ6HVDU:DODQDH%DUDWGLGDHUDK%LUX%XNWLEXNWLGHIRUPDVLSDGDEDWXDQmalihan bisa
EHUNDLWDQGHQJDQ6HVDU:DODQDH%DUDWDWDXSHUHQJJDQJDQUHJLRQDOVHODPDSHQJDQJNDWDQMDMDUDQ
3HJXQXQJDQ%DJLDQ%DUDW
Kata kunci: deformasi, mikrostruktur, batuan malihan Biru, Sulawesi Selatan
INTRODUCTION
Numbers of study on Pre-Tertiary basement
rocks in South Sulawesi have been done in
two main locations, Bantimala and Barru
areas. The metamorphic rock assemblages
from these two areas show that both metamorphic blocks were accreted slices from
a wide range of tectonic environments
(Maulana et al., 2010). A small exposure of
Pre-Tertiary basement accompanying metamorphic rocks has been also known in Biru
area, South Sulawesi. The metamorphic rock
has been described as contact metamorphic
rocks associated with a Miocene plutonism
(van Leeuwen, 1981; Sukamto & Supriatna,
1982), although both adequate petrographic
investigation and structural analysis on
them have not been performed yet. Biru is
ORFDWHGLQDWHFWRQLFDOO\VLJQL¿FDQWSRVLWLRQ
adjacent to the assumed suture zone of collision between Sundaland and Australian
microcontinent and Walanae Faults.
Our recent research found the presence
of multiple deformation texture including
synmetamorphic one in the rocks, indicating that they were not formed by a local
intrusion event of plutonic rocks but may
be associated with a regional metamorphism
and later tectonic events.
In this paper, the mineral assembly, chemistry of metamorphic minerals, and deformation structure of Biru metamorphic rocks are
20
described in order to elucidate the type of
the metamorphism and deformation condition of them.
GEOLOGICAL SETTING
The geology of eastern and western parts
of South Sulawesi is distinctly different,
that are separated from each other by the
West Walanae Fault (van Leeuwen, 1981).
The oldest rocks; the Bantimala and Barru
Tectonic Complex are found on the western
side as the basement complex in this region,
and consist of high pressure metamorphic
URFNVDQGXOWUDPD¿FDQGVHGLPHQWDU\XQLWV
of Jurassic to Cretaceous age. The sequence
has been interpreted as representing Cretaceous subduction of a microcontinent underneath Sulawesi, and the tectonic stacking
RI WKLV FRPSOH[ UHÀHFWV D ODWHU 1HRJHQH
collisional event (Parkinson, 1996; Wakita
et al., 1996).
A correlative geological body has also been
found in Biru area, metamorphic rocks
believed as hornfels and Marada Formation consisting of Late Cretaceous clastic
sediments. The age of the metamorphic
rocks is not present, but they may be correlative to the Marada Formation (Sukamto
& Supriatna, 1982). These basement rocks
are unconformably overlain by the Langi
Volcanics consisting of volcanic rocks of
Paleocene to Oligocene age (van Leeuwen,
Microstructure Deformation of Metamorphic Rocks in the Biru Area, South Sulawesi, Indonesia
(A. Jaya and O. Nishikawa)
1981). The metamorphic rocks are intruded
by Miocene plutonic rocks; Biru intrusive
complex (BIC) that consist of syenite with
8.4 Ma of K/Ar age (Elburg et al., 2002)
DQGJUDQRGLRULWHZLWK“0DRI¿VVLRQ
track age (van Leeuwen, 1981). Numerous
numbers of basalt-andesite dikes, aplite,
and quartz vein with their width ranging
from several cm to 3 m occur as intrusion,
striking N 25° - 70° E and N 32° - 82° W.
The basement rocks covered by youngest
potassic volcanic rocks (Elburg et al., 2002)
are shown on Figure 1. These volcanic rocks
are equivalent to the Pammusureng and
Walanae Volcanics (van Leeuwen, 1981).
The West Walanae Fault (WWF) trending
NNW, commonly interpreted as a left lateral movement, probably took place during
the Middle Miocene (van Leeuwen, 1981;
Grainge and Davies, 1985). It coincides with
block faulting carbonate platform, juxtaposition of the Bone Groups against Salokalupang Groups along the East Walanae Fault
20o00 E
(EWF) in the eastern part of South Sulawesi
(van Leeuwen et al., 2010).
METHODS
Field observations were carried out in the
two main locations; a small river in the
Pammusureng Village and the Bulubuluk
River (Figure 1). Oriented samples were
FROOHFWHG LQ WKH ¿HOG DQG VWUXFWXUDO HOHments such as strike and dip of foliation
and fold axis were recorded. Collected
samples (Table 1) were cut perpendicular
to foliation and parallel to lineation (XZ
plane), and also perpendicular to lineation
(YZ plane) for observation of deformation
texture. Chemical analyses of metamorphic
minerals were performed by Electron Probe
Micro-Analyzer (EPMA), JEOL JXA-8800
55/6XSHU3UREHXVLQJȘ$RIEHDPFXUrent, 15 kv. Representative analyses are
shown on Table 2.
o
WWF
25 00 S
o
BV : Bila Volcanics
MI : Marara Ignimbrite
BV
PM-30
UV
25o00 E
5O3’ S
Syenite (8.4 Ma)
Granodiorite (19 +3.4Ma)
-
&
20o00 E
S. Bulubulu
Biru Instrusive Complex
10o00 S
10o00 S
Elburg et al., 2002
LV
BB-11
BB-10
KV
5 00 S
o
Makassar
~7.6-6.2 Ma
UV : Ulubila Volcanics
KV : Kabu Volcanics
Sulawesi
5 00 S
LV : Lemo Volcanics
~11.2-10.3 Ma
o
0 00
0o00
Volcanics Units
o
20 00 E
Metamorphic Rocks
Marada Formation
PM-02
PM-05
PM-07
PM-08
PM-09
PM-09
la
Bi MI
S.
LV
Pammusureng
0
20
PM-07
Garnet Amphibolite
BB-10
BB-11
Amphibolite
PM-08
PM-09
N
UV
Epidote Amphibolite
&
PM-02
PM-30
PM-05
LV
KV
Biru Area
Makassar
5o00 S
5o00 S
BV
U. Cretaceous
Mica Schist
0
40
0.5
Kilometres
1
Kilometres
o
20 00 E
120O 3’ E
)LJXUH6LPSOL¿HGJHRORJLFDOPDSRIWKH%LUXPHWDPRUSKLFURFNVPRGL¿HGIURP/HHXZHQ(OEXUJet
al., 2002).
21
Majalah Geologi Indonesia, Vol. 26 No. 1 April 2011: 19-28
Table 1. Mineral Assemblages of the Metamorphic Rocks in the Biru Area
Sample No
PM – 02
PM – 05
PM – 06
PM – 30
PM – 07
PM – 08
PM – 09
PM – 10
PM - 11
Rock Name
Metabasite (Epidote Ampibolite)
Amphibolite
Amphibolite
Amphibolite
Amphibolite
Garnet Amphibolite
Mica Schist
Metasediment (Greenschist)
Muscovite Schist
Metabasite (Amphibolite)
Amphibolite
Amphibolite
Ep
Chl Act Hbl Ms Grt
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
FIELD OBSERVATION
The outcrops of the metamorphic rocks
were found in Pammusureng area and
along Bulubuluk River (Figure 1). In Pammusureng area, three different lithologies
crop out along a small valley. In the upper
stream of the valley, amphibolites which
contain abundance of epidote porphyroblasts with elongate shape and their long
axis of up to 30 mm in length occur. Garnet
amphibolite occurs in the middle part of the
stream. Downstream, near the contact with
granodiorite, weakly folded mica schist
is found. Metamorphic rocks in this location commonly have an evidence of shear
deformation, representatively, mylonitic or
cataclastic foliations generally dipping to
SE. In some localities, lineation oriented to
S-SE also develops (Figure 2).
Unlike in the Pammusureng location,
metamorphic rocks in the Bulubuluk River
generally consist of amphibolites.
Distinct compositional banding developed
LQWKHURFNGH¿QHVVFKLVWRVLW\ZKLFKGLSV
15 - 52° to SE. Deformation structures pervasively develop in the rocks. Two groups
of fold structure with different orientation
and style are distinguished (Figure 2); SSW
trending tight fold (F1) and ENE-WSW
trending gentle-open fold (F2).
22
O
O
O
O
O
O
O
O
O
O
O
O
O
O
Pl
Qtz
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
Rt Mag
Py
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
Cal
O
O
PETROGRAPHY AND MINERAL
CHEMISTRY
On the basis of mineral assemblages, the
PHWDPRUSKLF URFNV FDQ EH FODVVL¿HG LQWR
three facies; epidote amphibole facies
and amphibolite facies in the metabasites,
greenschits facies in the metasediments
(Table 1).
The epidote amphibolite facies consist of
three kinds of litologies; garnet amphibolite,
amphibolite, and mica schist. The amphibolite is characterized by mineral assembly of
albite + hornblende + actinolite + epidote
+ chlorite + quartz. Large plagioclase and
epidote crystals include hornblende, quartz,
and chlorite (Figure 3a, 3b), which often
show oriented inclusion array. Chlorite also
SUHVHQWVDV¿OOLQJRUDOWHULQJWKHULPRIPD¿F
minerals. The contents of major constituent
are 30 - 35% of plagioclase (albite), 15 25% of hornblende, 15 - 20% of epidote,
10 - 15% of quartz, and 10%< of chlorite.
The garnet amphibolite is characterized by
the mineral assembly of hornblende + garnet + plagioclase + epidote + muscovite +
chlorite + quartz. Garnet commonly occurs
as black coloured porphyroblasts of up to 4
mm in sizes and has a euhedral-subhedral
shape with abundant microfractures (Figure
3c). Chemical composition indicate that
1.85
0.20
0.03
0.00
0.00
14.11
Ca
Na
K
Cr
Ni
Total
Oxigens
3.41
97.89
23.00
Total
Mg
0.04
NiO
0.04
0.02
Cr2O3
Mn
0.14
K2O
0.58
0.73
Na2O
Fe
12.25
CaO
0.00
16.26
MgO
Ti
0.30
MnO
0.89
10.28
FeO
Al
7.34
Al2O2
7.11
0.06
0.03
TiO2
Si
55.20
50.50
SiO2
14.97
0.00
0.00
0.03
0.48
1.70
2.98
0.02
0.79
0.01
1.35
7.60
23.00
98.69
0.03
0.02
0.16
1.80
11.50
14.52
0.20
6.89
8.31
Act
Hbl
Mineral
Sample
19.90
0.00
0.00
0.01
0.01
0.00
7.38
0.03
2.03
0.01
4.65
5.78
28.00
85.99
0.00
0.01
0.05
0.02
0.00
24.80
0.18
12.18
19.75
0.06
28.95
Chl
Ab
4.99
0.00
0.00
0.01
0.97
0.01
0.00
0.00
0.00
0.00
1.01
2.99
8.00
101.75
0.00
0.00
0.10
11.71
0.18
0.00
0.00
0.03
20.02
0.00
69.71
PM-02
7.97
0.00
0.00
0.00
0.00
1.94
0.01
0.00
0.57
0.00
2.39
3.05
12.50
97.09
0.00
0.00
0.00
0.00
23.15
0.08
0.06
8.70
25.96
0.08
39.06
Ep
1994
0.00
0.00
0.00
0.00
0.02
6.86
0.04
2.63
0.00
4.65
5.74
28.00
82.54
0.01
0.00
0.01
0.01
0.09
21.69
0.24
14.84
18.59
0.02
27.06
Chl
4.99
0.00
0.00
0.00
0.97
0.01
0.00
0.00
0.00
0.00
1.00
3.00
8.00
112.37
11.60
0.00
0.07
11.60
0.23
0.00
0.00
0.03
19.57
0.01
69.26
Ab
Ep
7.98
0.00
0.00
0.00
0.00
1.97
0.01
0.00
0.45
0.01
2.52
3.03
12.50
97.87
0.00
0.00
0.02
0.00
23.76
0.08
0.04
6.97
27.68
0.12
39.20
PM-05
7.98
0.00
0.00
0.00
0.00
0.89
0.31
0.03
1.68
0.01
1.98
3.04
12.00
100.18
0.03
0.00
7.69
1.73
1.31
30.47
0.00
0.00
20.80
0.09
38.06
Grt
Table 2. Representative Microprobe Analyses of Minerals of the Metamorphic Rocks in the Biru Area
7.08
0.00
0.00
1.02
0.04
0.00
0.24
0.00
0.18
0.02
2.33
3.26
11.00
101.53
0.28
0.02
0.00
2.43
0.02
3.17
0.00
0.02
29.67
0.34
49.06
Ms
PM-07
7.97
0.00
0.00
0.00
0.00
1.95
0.01
0.00
0.37
0.01
2.60
3.03
12.50
97.76
0.00
0.00
0.01
0.01
23.62
0.08
0.05
5.78
28.65
0.15
39.41
Ep
15.56
0.00
0.00
0.16
0.24
1.96
1.59
0.07
3.19
0.03
1.40
6.91
23.00
99.34
0.80
0.04
11.68
6.82
0.51
19.03
5.86
0.02
7.57
0.26
44.06
Hbl
15.10
0.00
0.01
0.02
0.07
1.94
3.85
0.08
2.01
0.01
0.36
7.75
23.00
100.71
0.24
0.01
12.42
13.12
0.66
14.44
2.25
0.05
2.09
0.07
53.18
Act
BB-11
7.99
0.00
0.00
0.00
0.00
1.97
0.00
0.04
0.67
0.00
2.27
3.03
12.50
100.71
0.00
0.00
0.00
0.02
23.34
0.03
0.63
10.24
24.43
0.06
38.53
Ep
Microstructure Deformation of Metamorphic Rocks in the Biru Area, South Sulawesi, Indonesia
(A. Jaya and O. Nishikawa)
23
Majalah Geologi Indonesia, Vol. 26 No. 1 April 2011: 19-28
N
N
N
Figure 2. Lower hemisphere equal-area stereographic projections of structure of metamorphic rocks in the Biru
area; fold axis (a), foliation of metamorphic rocks (b), mineral lineation (c).
these garnets are dominated almandine
component (Xalm = 57 - 68 % and Xgrs = 20
- 30 %). Analyzed amphiboles fall in the
ferrohornblende with XMg = 0.02 - 0.18 and
actinolite with XMg =0.61 – 0.78 for the amphibolite in the epidote amphibolites facies.
Plagioclase is almost pure albite (> 98 %).
The mica schist is composed of actinolite,
epidote, muscovite, chlorite, and quartz.
Preferred orientation of muscovite and acWLQROLWHGH¿QHVVFKLVWRVLW\EURNHQWKLQOD\HU
Epidote occurs as porphyroblast (Figure
3d). All samples in this facies contain small
amounts of rutile, magnetite, and pyrite as
secondary minerals.
Mica schist in greenschist facies is composed
of quartz + muscovite + chlorite, with small
amounts of plagioclase (Figure 3e). Magnetite and pyrite occur as accessory minerals.
Muscovite and chlorite show strong preIHUUHG RULHQWDWLRQ DQG GH¿QHG VFKLVWRVLW\
Rocks exposed in the Bulubuluk River are
of amphibolite facies. Amphibolite samples
(BB-10 and BB-11) contain mainly plagioclase, hornblende, actinolite, chlorite, and
TXDUW]6FKLVWRVLW\LVGH¿QHGE\WKHSUHIHUUHG
orientation of hornblende and actinolite (Figure 3f). Plagioclase shows elongate shape as
porphyroblast in which hornblende, actinolite, chlorite, and quartz inclusion show weak
linear alignments. Epidote occur as minor
component. As accessory minerals, rutile,
magnetite, and pyrite occur.
24
MICROSTRUCTURE
AND DEFORMATION
6FKLVWRVLW\LVGH¿QHGE\SUHIHUUHGRULHQWDtion of major component of minerals. The
amphibolites in samples PM-02 and PM-05
included in large epidote and albite porphyroblasts show subhedral grain shape. They
often align with its long axis parallel to
main schistosity (S1), partially random oriented, cross cut by actinolite, linearly aligned
chlorite and quartz inclusion oriented (So)
as shown in Figure 4a. Large grains in the
rocks are fractured. Epidote porphyroblast
is extended in brittle manner forming microboudin subparallel to S1. The spaces of the
ERXGLQVDUHRIWHQ¿OOHGE\TXDUW]SRROV(DFK
grain composing quartz pool shows an equant
grain shape without evidence of deformation
)LJXUHESRVVLEO\LQÀXHQFHGE\KHDWLQJ
of intrusion event (M2). Brittle deformation
features in the rock of Pammusureng area
(Figure 4c) may be caused by a cataclastic
shear process (D2).
The schistosity S o in porphyroblast of
garnet amphibolite (Sample PM-07) is
GH¿QHG E\ VKDSH SUHIHUUHG RULHQWDWLRQ RI
epidote, hornblende, muscovite, and array
of garnet (Figure 3c). Epidote occasionally
VKRZVHORQJDWHGVKDSHDQGIUDFWXUHV¿OOHG
by quartz. Garnet porphyroblasts are surURXQGHGE\WKH\RXQJHVWVFKLVWRVLW\GH¿QHG
by muscovite (S1). Garnet porphyroblast
Microstructure Deformation of Metamorphic Rocks in the Biru Area, South Sulawesi, Indonesia
(A. Jaya and O. Nishikawa)
Chl
a
b
Act
Hb
Mag
Ep
Hb
Rt
Ab
Chl
Act
Ab
Act
Ep
Ep
0,5 mm
0,5 mm
Ms
c
d
Ep
Rt
Ep
Grt
Ms
Chl
Ms
Qtz
Qtz
Ep
0,5 mm
0,5 mm
e
Chl
f
Hbl
Py
Qtz
Atc
Pl
Pl
Hbl
Ms
Qtz
0,5 mm
0,5 mm
Atc
Figure 3. Photomicrograph (plane-polarised light) showing representative of epidote amphibolite facies;
amphibolite (a-b), garnet amphibolite (c), greenschist (d); amphibolite facies; amphibolite (f); greenschist
facies; mica schist (e).
often exhibits striate or slightly curved
inclusion trails which are discordant with
external fabric. Some porphyroblasts include S-shape inclusion trails, indicating
rotation (Figure 4d).
In the mica schist (sample PM-09), asymmetry of pressure shadows around quartz
SRUSK\URFODVWVDQGPXVFRYLWH¿VKHVLQGLFDWH
a dextral sense of shear (Figure 4e). The
evidence of intense fracturing and fragmentation in this rocks indicates cataclastic
ÀRZ'3\ULWHDQGPDJQHWLWHJUDLQVDOVR
present aligning parallel to schistosity but
without pressure shadows surrounding.
25
Majalah Geologi Indonesia, Vol. 26 No. 1 April 2011: 19-28
Therefore, they developed in a hydrothermal
process (M2) and possibly no more deformation after emplacement of plutonic rocks
(Figure 5). Whereas mica schist sample PM-
a
08 (epidote amphibolites facies) exhibits a
sinistral sense of shear evidenced by asymmetry of pressure shadows around epidote
porphyroblasts (Figure 4f).
b
Ep
Ms
Qtz
0,5 mm
c
Chl
Hb
0,5 mm
SO
d
Ep
SO
0,5 mm
e
0,5 mm
f
Grt
Qtz
Ep
SO
Ep
0,5 mm
S1
1 mm
Figure 4. Deformation microstructures: Fracture in epidote porphyroblats (a); cataclastic texture showing dextral
VKHDUELQFOXVLRQWUDLOLQHSLGRWHSRUSK\UREODVWFHSLGRWHSRUSK\UREODVWLVUHÀHFWLQJVLQLVWUDOVHQVHRIVKHDU
(d); S-shape inclusion trails of garnet porphyroblast are indicating sinistral sense of shear (e); microboudin neck
¿OOHGZLWKUHFU\VWDOOL]HGTXDUW]I
26
Microstructure Deformation of Metamorphic Rocks in the Biru Area, South Sulawesi, Indonesia
(A. Jaya and O. Nishikawa)
M1
Metamorphism
M2 (intrusion)
F1 , F2
Folding
Schistosity
Post
Metamorphism
So
S1
Cataclasite Formation
Annealling
Deformation
DO
D1
D2
Figure 5. Diagram illustration of deformation and metamorphism phases.
In contrast, texture of the amphibolite (sample BB-11, BB10) in the Bulubuluk River
does not show evidences of intense shear
deformation and cataclasis. Long axis of
grains in these rocks are commonly oriented
parallel to axial plane of fold (F1 and F2).
(1998) proposed that the Pompangeo schist
complex in central Sulawesi probably generated in the same subduction system as well
as Bantimala-Barru and other accretionary
complex in western Sulawesi.
CONCLUSIONS
DISCUSSION
The Biru metamorphic rocks were experienced a metamorphism that is simultaneous
with deformation (Figure 5). Pervasive cataclastic texture found in the Pammusureng
area indicates that these rocks were consequently sheared when uplifted at a shallow
level. The shearing may be related to uplift
event and activity of WFZ, which was
formed during a regional extension in the
Mid-Miocene (van Leeuwen et al., 2010).
Probably, the emplacement of plutonism
was also facilitated by uplifting.
The Biru metamorphic rocks may be formed
contemporaneously with the metamorphic
complex in the Bantimala-Barru area. Both
metamorphic bodies consist of high pressure metamorphic rocks (Miyazaki et al.,
1996; Maulana, 2009). The general trends
of the metamorphic rocks are NW and NE
striking, respectively (Berry and Grady,
1987), which are roughly conformable with
those of Biru metamorphic rocks. Parkinson
'HWDLOHG ¿HOG VWXG\ DQG WH[WXUDO DQDO\VLV
allow the authors draw the following conclusions about the Biru metamorphic rocks:
Metamorphic rocks in this area are
mainly metabasic rocks which are of
epidote amphibolite, amphibolite, and
greenschist facies. Metasediment of
greenschist facies also occur in a few site.
The Biru metamorphic rocks have experienced multiple deformation and metamorphic stages. Main metamorphism
(M1) was simultaneous with high degree
of deformation under the differential
stress, which resulted in formation of
schistosity and various deformation
structures.
The metamorphic textures in the rocks
have slightly altered in a contact metamorphism probably caused by intrusions
of plutonic rocks during Miocene (M2).
In the latest deformation stage, cataclastic
to low temperature mylonitic texture is
overprinted on the rocks in the Pammusu27
Majalah Geologi Indonesia, Vol. 26 No. 1 April 2011: 19-28
reng area by an intense shear deformation,
which may be associated with the activity
of Walanae Fault Zone or regional extension during uplift of the western mountain
range.
ACKNOWLEDGEMENTS
The authors thank Dr. Daizo Ishiyama and Dr.
Takashi Ucida for their constructive advises. The
authors thank Azuza Kondou for his guidance
and assistance of EPMA analyses. This study was
conducted by using the research fund granted by
UNHAS-JBIC Loan No. IP-541.
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