Cretaceous and Neogene lavas of Sabah - origin and tectonic significance

Abstract

A combination of field and geochemical investigations of the Cretaceous and Neogene lavas of Sa bah (CNLS) allow some control on the relative timing of events in its tectono-magmatic history. The low-K tholeiitic lava (Telupid basalt of Cretaceous age) or so-called 'boninitic suite', interpreted as a product of partial melting of hydrated oceanic lithosphere in the mantle wedge, suggesting that the first magma formed in response to intra-oceanic subduction. As subduction proceeded, the magma composition changed to the calc-alkaline suite (high-K calc-alkaline lavas of Neogene Tungku and Tanjung Batu andesites), probably because of the hydrated asthenosphere of the mantle wedge confirming an oceanic, supra-subduction zone origin for this volcanic arc assemblage. An evolutionary sequence can be envisaged for the CNLS which begins with the establishment of an oceanic island arc where supra-subduction zone extension led to the genesis of tholeiitic lava and/or boninitic (Telupid basalt) and followed by formation of the volcanic arc (Tungku andesite). Next, followed by Tungku arc-splitting, as extension continued, a marginal basin (Sulu Sea) developed. Later, incomplete closing of the Sulu Sea caused the southwards subduction beneath the older arc and formation of the Tanjung Batu andesite.