The Rajang Group, composed of the Belaga and Lupar Formations of Sarawak and the Embaluh Group and Selangkai Formation (in part) in Kalimantan, had a turbidite sedimentation history from Early Cretaceous to Late Eocene. These rocks generally young northwards. Inliers within the eastern Miri Zone have been mapped as the Kelalan and Mulu Formations. The Rajang Group was compressed into a steeply dipping quartz-veined phyllite-quartzite complex by the Sarawak orogeny and unconformably overlain locally in the north by the Upper Eocene continental to neritic Tatau Formation, extensively in the south by Middle to Upper Eocene basal continental sequences of the Ketungau, Mandai and Melawi basins, and widely in the north by the Upper Oligocene coastal to marine Nyalau Formation. In Sabah and East Kalimantan, the Upper Cretaceous to Upper Eocene Mentarang, Sapulut, Trusmadi, and possibly the East Crocker Formations, also belong to the Rajang Group. The West Crocker Formation demonstrates rapid facies changes into the more shaly Temburong Formation, and was deposited as sandy turbidites throughout the Oligocene. To the south their equivalents are the nearshore Kelabit and Long Bawang Formations. The West Crocker Formation was folded and uplifted in several Miocene pulses, resulting in regional unconformities and igneous events at Mount Kinabalu. The West Crocker Formation has not been metamorphosed, and dips are shallower than in the Belaga and Trusmadi Formations. Its provenance probably was from the uplifted Upper Cretaceous to Eocene Lurah and Kelalan formations of NE Kalimantan and East Sarawak. It is therefore proposed that the West Crocker and Temburong formations be excluded from the Rajang Group. Middle to Late Miocene Crocker Formation uplift and deformation, herein called the Sabah orogeny, was synchronous with spectacular basin inversion throughout the South China Sea and in the Meratus Mountains of Kalimantan. Uplift ceased in the Late Miocene and undeformed post-inversion formations unconformably overlie inverted folded structures. The Rajang Group flysch-belt may be interpreted as a north-facing accretionary prism. The Schwaner Mountains represent a subduction-related Lower to Upper Cretaceous volcanoplutonic arc. Scattered Eocene volcanism, Miocene Sintang intrusives and Pliocene Metalung volcanics in Central Kalimantan and Sarawak post-date subduction. The Rajang Basin (Danau Sea) rapidly narrowed and by Eocene time subduction was transformed to collision as the Rajang Group was compressed between the Schwaner Mountain Zone and the Luconia-Balingian-Miri block. The Ketungau Basin is in sharp contact with the Rajang Group along the bounding Lupar Fault, which can be traced northwards into the East Natuna region. Palaeocurrents show that the Upper Eocene basal sandstones have a provenance in the metamorphosed Sibu Zone. The Melawi and Mandai basins of Kalimantan also unconformably overlie the flysch-belt. The basins are not forearc and were formed after transformation of the accretionary prism to a landmass formed of a collisional orogenic complex.

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Three principal granite provinces are defined across SE Asia, as follows. (1) The Western Thailand–Myanmar/Burma province consists of hornblende–biotite I-type granodiorite–granites and felsic biotite–K-feldspar (± garnet ± tourmaline) granites associated with abundant tin mineralization in greisen-type veins. New ion microprobe U–Pb dating results from Phuket Island show zircon core ages of 212 ± 2 and 214 ± 2 Ma and a thermal overprint with rims of 81.2 ± 1.2 and 85–75 Ma. (2) The North Thailand–West Malaya Main Range province has mainly S-type biotite granites and abundant tin mineralization resulting from crustal thickening following collision of the Sibumasu plate with Indochina during the Mid-Triassic. Biotite granites around Kuala Lumpur contain extremely U-rich zircons (up to 38000 ppm) that yield ages of 215 ± 7 and 210 ± 7 Ma. (3) The East Malaya province consists of dominantly Permian–Triassic I-type hornblende–biotite granites but with subordinate S-type plutons and A-type syenite–gabbros. Biotite–K-feldspar granites from Tioman Island off the east coast of Malaysia also yield a zircon age of 80 ± 1 Ma, showing Cretaceous magmatism in common with province 1. Geological and U–Pb geochronological data suggest that two east-dipping (in present-day coordinates) subduction zones are required during the Triassic, one along the Bentong–Raub Palaeo-Tethyan suture, and the other west of the Phuket–Burma province 1 belt. Supplementary material: A full description of U–Pb analytical methods used and data tables are available at www.geolsoc.org.uk/SUP18523 .

Subduction followed by underthrusting of continental lithosphere, driven by Oligocene–Early Miocene spreading in the South China Sea marginal basin, account for the tectonic features of Sabah. Isostatic rebound then caused Late Miocene uplift of the Western Cordillera. The strata were buried under 4–8 km of overburden then rapidly exhumed and cooled at >10°C Ma −1 . A rate of exhumation of 0.5–0.7 mm a −1 is deduced from thermochronology. The same order of uplift in the Labuk Highlands has exposed metamorphic rocks of the epidote-glaucophane facies. Rapid erosion of the Western Cordillera supplied abundant clastic sediments to the Miocene–Pliocene Baram Delta oil-bearing basin and to the Eastern Lowlands and Sulu Sea. The Eastern Lowlands were affected by Miocene rifting of the Sulu Sea marginal basin. In contrast to the Western Cordillera, the strata contain apatite crystals whose fission track ages pre-date the containing rocks, indicating burial by only about 2–3 km of overburden. The terrain has been isostatically stable. Some apatite and all zircon crystals, extracted from Tertiary strata, yield Cretaceous fission track provenance ages.

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