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Alpine-Himalayan Orogens |
Indonesian Institute of Sciences, Djl. Teuku Tjik Ditiro No. 43, Djakarta, Indonesia
The late Mesozoic to Tertiary orogenic belt of the Greater Sunda Islands lies between the ‘foreland’ of the early Mesozoic Thai-Malay orogen (Sunda Shelf) and the Indian Ocean. Traced laterally, the belt is linked to the north-west via the Andaman-Nicobar arc with the Indoburman Ranges and towards the east with the Banda Arcs; both are also of late Mesozoic to Tertiary date. The contact of the Sunda and Thai-Malay orogens lies in the very poorly exposed region of East Sumatra: the gentle folds of zone 1 (see below) appear to gradually die out towards this contact. The width of the Sunda orogen from this margin to the south-western Trench (fore-deep) zone reaches 450 km.
Segment: an E-W strip across the orogen in South Sumatra, some 500 km in length when measured parallel to the strike, has been selected for description (Fig. 1).
Zones: six NW-trending zones are recognized. Three are on Sumatra (East Sumatran Basin, Proto-Barisan and Barisan zones). The others lie to the south-west—the islands of the Non-volcanic outer arc between the submarine trenches of the Inter-deep and Trench (fore-deep) zones.
History: the oldest dated rocks are marine strata of Permo-Carboniferous age (zone 2), but the undated crystalline schists of zones 2 and 3 may be older. Andesitic volcanism was important in early Permian times, limestone deposition in later Permian times, then shale and sandstone, followed by limestone and marl deposition in the Triassic. Jurassic strata are rare, but thick, sedimentary and andesitic volcanic rocks accumulated locally in zone
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