Early to middle paleozoic volcanism of Western Peninsular Malaysia / Quek Long Xiang

Quek , Long Xiang (2018) Early to middle paleozoic volcanism of Western Peninsular Malaysia / Quek Long Xiang. PhD thesis, University of Malaya.

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Abstract

This study reports new whole-rock major and trace elements data with zircon U-Pb age and Lu-Hf isotope data from the Early to Middle Paleozoic meta-volcanic rocks in Western Peninsular Malaysia, consisting of Gerik-Dinding meta-volcanic rocks, meta-dolerite intrusions and Rephens meta-volcanic rocks. The Early Paleozoic meta-volcanic rocks are represented by the Gerik-Dinding meta-volcanic rocks, which crystallized in the Early to Middle Ordovician (480-460 Ma). They are comparable to high-K calc-alkaline rhyolite and enriched in Th, U, and light rare-earth elements (LREEs). They are also depleted in Nb, Ta, Ti, and P, which are typically observed in arc-related rocks. Their zircon εHf(T) values vary from +0.85 to −15.7, with TDM2 ages from 1.3 to 2.4 Ga. Accordingly, the meta-volcanic rocks are interpreted as resulting from the partial melting of Mid-Mesoproterozoic to Mid-Paleoproterozoic crustal material with minor mantle-derived material. We propose that the Gerik-Dinding meta-volcanic rocks were formed in a lithospheric delamination tectonic setting following the crustal thickening from the final amalgamation of Asian micro-continental fragments (AMF) onto the East Gondwana Proto-Tethys margin. Meta-dolerite intrusions that occur irregularly on Western Peninsular Malaysia are associated with Early Paleozoic meta-sedimentary formations and could be constrained to Late Cambrian until Early Silurian (500-430 Ma). They have weak to absent Nb-Ta negative anomalies on the primitive mantle normalized spidergram, low La/Nb (<2), low Th/Ce and low Th/La, which suggest the absence of subduction signature. Their trace element geochemical data patterns, supported by tectonic discrimination plot, indicate that the magma was likely emplaced in an active continental rift or a within-plate setting. The lithospheric delamination event (475-460 Ma) in East Gondwana following the continental collision with AMF and lithospheric thickening may have caused an extensional regime at the East Gondwana Proto-Tethys margin, which permitted the meta-dolerite magma to intrude into the thinned continental crust. The Middle Paleozoic meta-volcanic rocks are represented by the Rephens meta-volcanic rocks, which crystallized in the Early Carboniferous (~342 Ma and ~354 Ma). Two types of Rephens meta-volcanic rocks have been observed: (1) meta-andesite and (2) meta-lithic tuff. Both meta-volcanic rocks have trace element geochemical features suggesting a subduction-related origin (depletion in Nb, Ti, and P). The meta-andesite zircon εHf(T) values range from +3.4 to +10.3, with TDM2 ages from 0.6 to 1.1 Ga while the meta-lithic tuff zircon εHf(T) values vary from +10.5 to −13.9, with TDM2 ages from 0.7 to 2.2 Ga. The formation age of the meta-volcanic rocks coincides with extension magmatic event (365-330 Ma) from the prolonged southern Paleo-Tethys Ocean subduction. The roll-back of Paleo-Tethys oceanic slab may have caused the upwelling of asthenosphere which resulted in the melting of the continental crust.

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