Uttaradit, Sra Kaeo and Bentong–Raub Suture Zones, which have been interpreted as representing the main
Palaeo-Tethys Ocean Metcalfe, 1999; Metcalfe et al., 1999. Its eastern boundary in Sumatra is contentious.
Hutchison 1975, 1983 and Gasperon and Varne 1995 suggest, principally on the distribution of granite types,
that the Bentong–Raub Suture extends southeast-wards through the tin islands of Bangka and Billiton. Tjia 1985,
1989a, Tjia and Zaiton Harun 1985 and Metcalfe 1988, 1996, 1998 have suggested, on structural and stratigraphic
grounds, that the suture extends into the Bengkalis Graben see Hutchison, 1993; Metcalfe, 1996 for discussions.
2.1.2. Indochina terrane The eastern part of Peninsular Malaysia, east of the
Bentong–Raub Suture, has a different pre-Jurassic tectonos- traigraphy and evolution to the Sibumasu terrane. It was
interpreted by Stauffer 1973 as part of an “East Malaya Block”, but is now regarded as a southwards extension of
the Indochina Terrane Metcalfe, 1998. This terrane is bounded to the northeast by the Song Ma Suture Zone,
and to the west by the Uttaradit-Nan–Sra Kaeo and Bentong–Raub sutures in Thailand and Malaysia, respec-
tively. It is here taken to include what has previously been referred to as the “East Malaya Block” excepting Borneo
of Stauffer 1974, 1983 and Metcalfe 1988.
2.1.3. Terrane origins and dispersal from Gondwanaland Palaeobiogeographic and tectonostratigraphic data for
both Sibumasu and Indochina indicate that these continental blocks formed part of the India–Australian margin of Gond-
wana in the Lower Palaeozoic Metcalfe, 1988, 1990, 1993c, 1996, 1998; Burrett et al., 1990; Rong et al.,
1995. Gondwana biogeographic affinities of faunas and floras on Sibumasu continue up to the Early Permian
Sakmarian, and the presence of Lower Permian glacial- marine diamictites, associated with cold climate indicators
and Gondwana faunas and floras Fig. 2, dictate that this terrane was still attached to the margin of Gondwana up
until the Early Permian. This is supported by gross tecto- nostratigraphical
comparisons between
the Sibumasu
Terrane and the Canning Basin of NW Australia Fig. 3, suggesting that the Cambrian to Lower Permian stratigraphy
of Sibumasu is an extremely good fit for a position outboard of NW Australia during that period. In the Assellian–Early
Sakmarian, brachiopods on the Sibumasu Terrane belong to the Gondwanan Indoralian Province, but shortly after
separation from Gondwana in the Late Sakmarian-Midian, the brachiopods developed their own Sibumasu Province
faunas with endemics. By Wujiapingian–Changxingian times, the brachiopod faunas had become assimilated into
the Cathaysian Province. These changes of provincial affi- nities of the brachiopod faunas of Sibumasu document the
northwards drift of the terrane during the Permian Shi and Archbold, 1998.
Ordovician and Silurian faunas of Indochina show Gond- wana affinities, but by Lower Carboniferous and younger
times there appears to be no Gondwana connections Metcalfe, 1988, 2000c; Fig. 2. It seems most likely that
the Indochina Terrane, along with South and North China and Tarim, separated from Gondwana in the Devonian.
2.2. Palaeomagnetic data Palaeomagnetic summaries and studies of the Sibumasu
and Indochina terranes and of Peninsular Malaysia have been made by Richter and Fuller 1996 and Richter et al.
1999. Palaeozoic and Mesozoic palaeomagnetic data from SE Asia remain problematic, due to widespread Mesozoic
and Cenozoic overprints, and the Palaeozoic and Early Mesozoic rocks often carry Late Triassic or Late Cretaceous
overprints Metcalfe, 1994; Richter and Fuller, 1996; Rich- ter et al., 1999. Palaeolatitude data do, however, provide
some constraints on terrane positions at certain times.
I. Metcalfe Journal of Asian Earth Sciences 18 2000 691–712 695
40 30
20 10
-10 -20
-30 -40
-50 ✽
✽
▲ ▲
▲ ▲
▲ ▲
▲ ▲
▲ ▲
▲
● ●
● ●
● ●
● ●
S. CH INA
AUSTRALIA S
IB U
M A
S U
Carboniferous Devonian
Permian Triassic Jurassic
Cretaceous Tertiary
PALAEOLATITUDE
✽ ●
▲ Sibumasu
Block Ref. at 18N, 95E
Observations E. Sumatra
E. Malaya Predicted from
South China Predicted from
Australia ✽
✽
▲ ▲
▲
Fig. 4. Rapid northwards drift of the Sibumasu Terrane interpreted from palaeolatitude data from Van der Voo, 1993 and supported by the more recent data of Richter et al., 1999.
There is a general paucity of Palaeozoic data from the Sibumasu Terrane. Results considered reliable i.e. passing
reversal and fold tests indicate that the Sibumasu Terrane moved from about 42
8S in the Late Carboniferous to around 15–20
8N in the late Triassic Van der Voo, 1993; Fig. 4. This is consistent with the late Early Permian separation and
Permo-Triassic northwards drift of Sibumasu as part of the Cimmerian Continent, interpreted from other data.
The majority of the palaeomagnetic data for the Indo- china Terrane has been collected from the Upper Palaeozoic
and Mesozoic of the Khorat Plateau. All pre-Late Triassic rocks appear to have been remagnetised during the Late
Triassic Indosinian Orogeny Richter and Fuller, 1996. A palaeolatitude of 25
8N is indicated for the Khorat Plateau in the Late Triassic. The Virtual Geomagnetic Pole VGP
presented for these data is indistinguishable from the VGP of remagnetised Permian Limestones. Interestingly, this
also coincides with the mean VGP for remagnetised Permian and Triassic limestones of the Sibumasu Terrane,
suggesting that a Late Triassic remagnetisation of these rocks is most likely. Unfortunately, available palaeomag-
netic data for the Indochina Terrane provide little informa- tion on its pre-Late Triassic latitudinal position.
2.3. Volcanic arcs The Bentong–Raub Suture Zone represents the main
Palaeo-Tethys Ocean, which would have been at least 2000 km wide at some point during its history. Long lived
subduction subsequently destroyed the Palaeo-Tethys beneath either Indochina, Sibumasu, or both, resulting in
destruction of the ocean, and the eventual collision of these two continental lithospheric blocks. Since subduction
is required to destroy the Palaeo-Tethys, there must have been one or more volcanic arcs related to this subduc-
tion process. Two Late Palaeozoic volcanic arcs can be identified in the vicinity of the Bentong–Raub Suture; a
Lower to Middle Permian volcanic arc Peusangan-Pale- pat Volcanic Arc distributed as an elongate, fault-
bounded strip to the west of the suture along the western edge of the Sibumasu Terrane in Sumatra,
and a Middle to Upper Permian and Triassic volcanic arc East Malaya Volcanic Arc, identified as an elon-
gate strip to the east of the suture through eastern Peninsular Malaysia, and possibly extending to Bangka
and Billiton, along the western edge of the Indochina Terrane.
2.3.1. Peusangan-Palepat Volcanic Arc This Lower? to Middle Permian plutonic-volcanic arc is
interpreted as subduction-related Katili, 1973; Pulungono and Cameron, 1984. McCourt et al. 1996, quoting
Fontaine and Gafoer 1989, suggested that the faunas asso- ciated with the andesitic volcanics of this arc indicated
warm climate and Cathaysian affinities, in contrast to typical Sibumasu Gondwana sequences. They suggested that the
arc was an oceanic island arc, subsequently accreted to Sibumasu through northerly directed subduction and the
closure of a marginal ocean basin, in the Late Permian, or more likely Early Triassic. If the Peusangan-Palepat Volca-
nic Arc was already in existence in the early Early Permian, then the Sibumasu Terrane must have already separated
from Gondwana prior to the Early Permian. However, we have substantial evidence that this was not the case, and that
it only separated at the end of the Early Permian see Metcalfe, 1996, 1998. This suggests that this poorly
dated arc is probably of late Lower to Middle Permian, rather than early Lower Permian to Middle Permian age.
This is critical when making comparisons with the Gond- wana faunas, floras and the stratigraphy of the Sibumasu
Terrane. This is because cold-climate glacial-marine sedi- ments, faunas and floras are present on Sibumasu in the
Asselian–Sakmarian, but soon after this, and certainly by Kungurian times, due to separation and northwards drift of
the terrane, and climatic amelioration following retreat of the Gondwana glaciation in the late Sakmarian, sediments,
faunas and floras become warm climate TethyanCathaysian types see Shi and Archbold, 1998. The only unequivocal
early Lower Permian Asselian Cathaysian fauna and flora known in Sumatra is that of the Jambi area, and I have
stressed in previous publications that this region formed part of the Cathaysian Indochina terrane during the Early
Permian. Late Lower and Middle Permian and younger faunas of Sumatra, whether on the volcanic arc or on the
Sibumasu or Indochina portions of the island, will be of warm climate Cathaysian type. The assertion, based on
faunal and floral comparisons, by Hutchison 1993 that the “West Sumatra Block” comprising the Alas, Kluet,
and Kuantan Formations together with the Peusangan-Pale- pat Volcanic Arc could not have been contiguous with
Sibumasu in the Carboniferous to Early Permian is thus flawed. A single K–Ar age of 248 10 Ma Early Triassic
from the volcanics Nishimura et al., 1978 was used by McCourt et al. 1996 to indicate the probable age of colli-
sion of this arc with Sibumasu. Clearly, precise dating of the Peusangan-Palepat Volcanic Arc volcanics is essential for
constraining models for its evolution, and for Late Palaeo- zoic palaeogeographic reconstructions of the region. In
addition, it is important to determine if this volcanic arc was constructed on the margin of Sibumasu presence of
late Lower Permian warm climate fossils do not preclude this or if it was, as suggested by Wajzer et al. 1991 and
McCourt et al. 1996, an oceanic island arc which was accreted to Sibumasu in the Triassic. In any case, this volca-
nic arc appears to have no direct relationship with subduc- tion processes during the closure of the Palaeo-Tethys,
represented by the Bentong–Raub Suture Zone, but it does, however, have important implications for a better
understanding of the evolution of the Sibumasu terrane, and hence indirectly the suturing of this terrane to Indo-
china, and to the interpretation of the Permian palaeogeo- graphy of the region.
I. Metcalfe Journal of Asian Earth Sciences 18 2000 691–712 696
2.3.2. East Malaya Volcanic Arc The Middle to Upper Permian and Triassic East Malaya
Volcanic Arc comprises intermediate to acidic volcanics, distributed in eastern Peninsular Malaysia and extending
southeastwards to the islands of Bangka and Billiton. Ande- sitic and acidic volcanism occurs in the Upper Permian, and
acidic volcanism predominates in the Triassic Metcalfe et al., 1982. The age of this arc may also extend down into the
Carboniferous, as abundant volcaniclastics and some volca- nics of this age are widely distributed in Carboniferous
rocks in eastern Peninsular Malaysia Fig. 2. The arc was constructed on the margin of the Indochina Terrane and
would have been the result of eastwards but originally northwards subduction of the Palaeo-Tethys Ocean. The
subduction polarity suggested, is consistent with that indi- cated by tectonic transport directions see below, and as
time progressed, the volcanic arc probably migrated south- westwards. I-type granitoids of Late Permian to Triassic age
east of the Bentong–Raub Suture, represent the plutonic elements of the volcanic arc Hutchison, 1977; see below.
3. The accretion phase and description of the Bentong– Raub suture
