PRE - TERTIARY TECTONO - STRATIGRAPHY AND PALEOGEOGRAPHY OF THE SUMATRA TERRANES, SOUTHEAST ASIAN, INDONESIA

Abstract

Sumatra is part of the sole southeast Asian terranes, which composed of mixed affinity block (mixed Gondwana and Cathaysian flora), and was formed by the amalgamation of allochtonous, microplates, continental fragments, island arc, and accretionary/ foreland complex assembled prior to the Tertiary. the allochtonous rocks (terrane) can be devided into 4(four) terranes i.e the Bohorok - Tigapuluh Mountains, Kluet - Kuantan, Gunungkasih - Tanjung karang and Sikuleh - Garba terranes, They are different lithology, origin, ages and separated one another by relatively NW-SE trending faults or suture.

The Bohorok - Tigapuluh Mountain terrane is dominantly by association of diamictities/ pebbly mudstone with a glacio marine of fluvio glacial origin and a cool water enviroments with having Permo - Carboniferous in age, the lithology of the clasts indicates a Continetal provenance, occupied in the eastern part of Sumatra. the Kluet - Kuantan terrane consist metamorphic clastic sediment, volcanic and carbonates rocks, which contain rich of Jambi flora (Cathaysian Flora), with Carboniferous - Triassic in age, in warm water condition, continent - transitional enviroments, the terranes occuryed in the middle part of Sumatra, the Gunung kasih - Tanjungkarang terrane is composed of the pre-Carboniferous metamorphic complex i.e schist, amphibolite, quartzite, gneiss, migmatit and marble, which all originaly drived from sedimentary and igneous / volcanic rocks. The terrane occupied in the southern part of Sumatra. Meanwhile Sikuleh - Garba (Woyla) terrane which is occupied of Jurassic - Creteceous of tectonite/melange, metasediment, carbonate, oceanic tholeiites volcanic and I-Type granitoid rocks, The terrane is situated in along the western part of Sumatra.

Based on of the measurement paleomagnetic of the Permo - Carbonifereous the diamictit/ pebbly mudstone Mentulu Formation from Tigapuluh Mountains showed that it to have lain 410 South, part of N.W. Australia. The Evidence that the Bohorok - Tigapuluh Mountains terrane (East Sumatra Block) was a part of Sibumasu/Sinoburmalaya drived from the Gondwana land, while the Permo - Carboniferous the Jambi/Cathaysian Flora Mengkarang Formation from Batang - Merangin showed that it to have lain 300 North and the Triassic Tuhur formation shown 240 N. The Evidence that Kluet - Kuantan terrane/ West Sumatra Block was part of terrane of Cathaysian affinity (East Malaya/Indosinia terrane) The Bohorok - Tigapuluh Mountain terrane had drifted / travelled from south to northwards, nearer to the paleo - equator, while the Kluet- Kuantan terrane drifted/traveled from north to southwards, these terrane have been collided and amalgamated most prohably in Early Triassic and saparated by middle Sumatra Fault Zone / suture (Medial Sumatra Tectonic Zone), marked by a wide zone deformed rocks and Gunungkasih - Tanjung Karang by the Lalang fault zone (the continoues from Uttaradit - Bentong - Raub line) and led to the formation of Proto Sundaland. The measurement paleomagnetic of Jurassic - Cretaceous Sedimentary rocks from Sikuleh - Garba (Woyla) terrane showed that it to have lain 320 - 310 - 300 South.

Probably during Late Cretaceous - Early Tertiary the oceanic Plate of Sikuleh - Garba terrane has Subducted with Proto Sundaland Continental plate. Probably in this time all the terranes were joined together / amalgamated to form a present Sumatra Island.

AAPG Datapages/Search and Discovery Article #90226 © 2015 European Regional Conference and Exhibition, Lisbon, Portugal, May 18-19, 2015