Origin, emplacement and tectonic relevance of the Mt. Kinabalu granitic pluton of Sabah, Borneo

The generation of granitic melts, their evolution and emplacement in the crust are investigated here through a detailed multi-disciplinary study on the geology of the Mt Kinabalu pluton in the Malaysian state of Sabah, North Borneo. Implications of our findings for the tectonic history of SE Asia and the generation of continental crust are also discussed. New field data, geochemical analyses and gravity interpretations conclude that the ophiolitic basement of Sabah is not underlain by felsic crust. The ophiolite’s geochemistry and existing geochronological data support initial ophiolite emplacement at approximately 200 Ma during early Pacific subduction. A new geological map and field observations on Mt Kinabalu show construction in a laccolith style but with complex three-dimensional forms of its composite units. AMS and structural data indicate emplacement during regional NW-SE extension. Geochemical data disputes an anatectic origin. The magma of Mt Kinabalu was produced by crystallisation of hornblende and plagioclase rich cumulates from an enriched basaltic primary melt with simultaneous assimilation of biotite-rich meta-sediments. The primary melt was derived by low degree melting of a fertile mantle source, probably through extensional melting. Similar melts have occurred across South China and the South China Sea region since at least the Jurassic. Implications of the results for the generation of continental crust show both the upper and lower crust to be derived through variable degrees of fractional crystallisation from mantle melts, not through intra-crustal differentiation.