Tectonics of the Indonesian Region

Abstract

The plate-tectonic evolution of a region can be deduced by following the assumptions that subduction zones are characterized by ophiolite, melange, wildflysch, and blueschist, that intermediate and silicic calc-alkaline igneous rocks form above Benioff zones, and that truncations of orogenic belts indicate rifting. Interrelatioships provide crosschecks, as do marine geophysical data. Southeast Asia and "Sundaland" are an aggregate of small continental fragments. Late Paleozoic subduction westward beneath Malaya and Thailand (recorded by granites in eastern Malaya, and by melanges in western Laos and Cambodia) ended when Indochina collided with them. Early and Middle Triassic subduction was eastward, beneath the west side of the aggregate. Late Triassic and Jurassic subduction from the north ended in collision of the aggregate with China. Early Cretaceous subduction was again from the west. Late Cretaceous subduction was beneath the east side of the aggregate and followed continental rifting there. Cenozoic subduction, from the west once more, ended in the north when the aggregate collided with India, but subduction still continues in the south. Borneo similarly reflects changing subduction patterns. The Philippines, Sulawesi, and Halmahera consist wholly of upper Mesozoic(?) and Cenozoic island-arc subduction and magmatic complexes and lack old continental foundations. The scrambled fragments of the Philippines came from several arc systems, including two extending to Borneo. Sulawesi and Halmahera record primarily subduction from the east and may be rifted and contorted fragments initially continuous with southeast Borneo and central Java. In the early Tertiary, Australia and New Guinea, which then had a stable-shelf northern margin, moved northward until they collided with a southward-migrating island arc, behind which had formed the Caroline oceanic plate. Late Cenozoic tectonics in New Guinea have been dominated by southward subduction fo the Caroline oceanic plate beneath the Australian New Guinea continent, and by left-lateral strikeslip faulting. Such faulting tore the Sula Islands from northwest New Buinea and carried them to Sulawesi. The islands of the outer Banda arc are formed of melanges of the shallow-water sediments of the New Guinea and Australian continental shelf, which is now disappearing beneath the active arc.

Mammalian species richness on islands on the Sunda Shelf, Southeast Asia

“…Tanabala, Tanamasa, Pini, Tuangku, and Bangkaru lie off the west coast of Sumatra, an area of great tectonic activity (Hamilton 1979), so they were not used in this study. Finally, I suspect that three islands used by Wilcox (Bali, Penang, and Singapore) were heavily disturbed before sampling took place, and so I do not include them.…”

Seasonal sediment transport and deposition in the Rajang River delta, Sarawak, East Malaysia

“…1) drains part of the Central Borneo Massif, which is dominated by CretaceousEocene age sediments. These rocks are accretionary complexes and forearc basin deposits that formed during the Tertiary opening and spreading of the South China Sea (Hamilton, 1979;Hutchison, 1989Hutchison, , 1996. They are composed of folded and faulted, finegrained siliciclastics, with minor amounts of carbonates.…”

Evidence for active subduction at the New Guinea Trench

“…Further to the west, the tectonic setting becomes more complicated with interactions between Halmahera, the Molucca Sea Plate and Sulawesi while east of 148°E subduction of the Solomon Sea Plate occurs beneath the South Bismarck Plate on the New Britain Trench [Hamilton, 1979].…”

“…[4] Previous studies have suggested that convergence may occur on the NGT [e.g., Hamilton, 1979;Cooper and Taylor, 1987;Puntodewo et al, 1994;Tregoning et al, 2000] along with partitioning of normal convergence and left-lateral slip in the FTB [e.g., Abers and McCaffrey, 1988;Puntodewo et al, 1994] (Figure 1). The lowlands of New Guinea south of the FTB are part of the rigid Australian Plate [Hamilton, 1979;Kreemer et al, 2000].…”

“…[3] The New Guinea Trench is a deep trench, clearly defined in bathymetry and gravity anomaly data, that extends about 700 km along the northern coastline of New Guinea from the eastern margin of the Ayu Basin near the Mapia Ridge at $134.5°E [Milsom et al, 1992] to 143°40 0 E [Hamilton, 1979] (Figure 1). Further to the west, the tectonic setting becomes more complicated with interactions between Halmahera, the Molucca Sea Plate and Sulawesi while east of 148°E subduction of the Solomon Sea Plate occurs beneath the South Bismarck Plate on the New Britain Trench [Hamilton, 1979].…”