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.

A late Jurassic to early Cretaceous (Neocomian) age is most likely for the ophiolite basement of Sabah, consistent with the Barremian-Aptian age of the overlying ribbon cherts. Attempts at dating have been confined to the K:Ar method, unfortunately unsuited to this rock suite because of its low potassium and high atmospheric argon contents. Our data confirm the need for interpreting part of the extensive ophiolite terrane of the Segama Highlands as consisting of continental lithosphere of Jurassic age-only limited exposures of calc-alkaline granite are known in the Litog Klikog Kiri vicinity ofUlu Segama. The ophiolite suite of the Labuk and Segama Highlands is oflow-K tholeiitic affinity and the trace element geochemistry indicates MORB characteristics, typical of magma formation at a mid ocean ridge spreading centre. Before uplift, the Sabah ophiolitic basement may be interpreted as having formed an integral part of either the western Pacific or the eastern Indian Ocean, extant beneath sea level in the Argo Abyssal Plain west of Australia.

No abstract