556 RODINIA, GONDWANA AND ASIA

Deformational Historv of the Eastern Belt, Peninsular Malaysia J

Ibrahim Abdullah and Heru Sigit Purwanto Geology Program, National University of Malaysia, Malaysia

It was generally been understood that the oldest rock formations in the eastern belt of Malaysia Peninsula are Carboniferous and Permian age and that they consist mainly of clastics and volcanics. Limestone is also present. Carboniferous- Permian rocks were intruded by pre-granite mafk to intermediate igneous rocks, followed by biotite granites of late Permiadearly Triassic and late Triassic and finally by doleritic dykes of Jurassic- Cretaceous age. Continental deposits unconformably overlie this rock formation. Plant fossils found in these continental rock successions indicate that these continental deposits are of Late Permian age. Again during Jurassic-Cretaceous time another sequence of continental sediments were deposited

In the eastern belt, these pre-granite rock formations show complex structures and have undergone at least two episodes of folding characterized by inclined or recumbent folds and thrust faulting. Strike slip and normal faulting are also very commonly observed. However, in some areas, this rock formation shows very low grade of metamorphism (shale, slate and sandstone) and rather simple structures. This indicates that the supposed Carboniferous metasediments (quartzite, phyllite and occasional schist) could be of older age. The Late Permian continental sediments are folded into open folds and have two sets of fracture cleavage. Apart from normal and strike slip faults, reverse faults are also present in this older continental rock formation. The late Cretaceous continental deposits are only gently tilted.

Doleritic dykes are aligned in either "W or ENE direction.

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The "W dykes are cut and sometimes displaced dextrally by ENE dykes and strike slip faults. The dextral ENE faults are also displaced; NNW strike slip fault are observed in the supposed Carboniferous-Permian metasediments and late Permian continental deposits.

From structural point of view, it is believed that the oldest sediments in this belt are of pre-Carboniferous age. These sediments were subjected to the earliest deformation (orogeny?) producing inclined to recumbent folds and associated thrust faults, and this deformation was responsible for regional low-grade metamorphism. Following that, the Carboniferous-Permian clastics, limestone and volcanics were deposited. Apparently, towards the end of the Permian, there was an episode of folding, producing open to tight folds and reverse faults together with regional low-grade metamorphism followed by "W dextral wrenching and uplifting giving rise to a continental condition for the deposition of the late-Permian continental deposits. Late- Triassic granite intrusion was followed by post Triassic uplift that was responsible for the deposition of the younger continental deposits in the area. Following that, there was an episode of almost E-W extension giving way for "W doleritic dykes intrusion. Within a short period of time, the extensional nature changed from almost E-W to almost N-S, which was responsible for the formation of almost ENE doleritic dykes that cut the "W dykes. At a later stage, the NNW dykes were displaced by ENE dextral fault as a result of almost E-W compression.

Cretaceous - Eocene Volcanism Along Eastern Coast, India - Its Implications S. Acharya 155, VIP Colony, Bhubaneswar - 751015, India

An outlier of unmetamorphosed vesicular basalt is traced west of Chilika lake, Orissa, India to unconformably overlie the khondalites of Eastern Ghat Super Group (EGSG). In addition to this unit, there are two thin cross - cutting basic dykes in the railway cuttings between Rambha and Khallikote stations not very far from the first out crop. The mineralogy of these two rock types are identical and in the absence of any metamorphism, the rocks are considered co-genetic because of their identical composition and similar occurrence (Acharya, 2001).

The flow and the two small dykes have geological significance because of their possible genetic connection with the bysmalith and dykes of Naraj and Mundali respectively as they are the nearest basic igneous rocks intruding into the upper Jurassic Gondawana sandstone (Kittoe, 1838). Recent studies in Bay of Bengal by Oil and Natural Gas Commission for Oil India Ltd,. has reported Eocene basic traps on the floor of Bay of Bengal

at about 1000 m depth. Naraj-Mundali igneous activity may, therefore, be correlated with the Eocene flows of the sea, east of the Mahanadi-Brahmani-Baitarani tri-delta and hence are to be considered as upper Cretaceous lower Eocene age that witnessed the initial igneous activity (harbinger) of Deccan traps in the eastern part of India. Rajmahal traps of Bihar and Rajmahendry basalts of A.F? are considered equivalent to upper - Cretaceous and lower eocene time. Naraj intrusiver should therefore be of equivalent age and connects the Rajmahal - Rajmahendry bridge. Chilika flow and intrusives should, therefore, be another span joining the two places.

Naraj dykes are almost on the surface and the flows of Chilika, therefore, suggests that Eocene seafloor flows and the supra - khondalite flow at Chilika are of the same age and in the absence of any central type, are to be regarded as of fissure eruption. Thus, it has to be somewhat deep and join the two flows on both

Gondwana Research, V. 4, No. 4,2001