Abstract
Establishing the location (where), timing (when) and reasons for the development (why) for the Mesozoic subduction along the western Paleo-Pacific that extended from Coastal South China to SE Vietnam has proven problematic due to the difficulty in the identification of the fore-arc igneous rocks. This paper firstly presents a set of zircon U-Pb and whole-rock 40Ar/39Ar geochronological, zircon in-situ Lu-Hf isotopes, and whole-rock elemental and Sr-Nd-Pb isotopic data for the Mesozoic igneous rocks from the Sabah ophiolites and Segama non-ophiolitic basement in NE Borneo. Our work documents major phases of the formation of these rock units at ∼185–140 Ma, ∼135–112 Ma and ∼130–85 Ma for the Telupid, Kudat and Darvel Bay ophiolites in Sabah, respectively. The mafic rocks within the ophiolites are classified into the MORB-, high-Nb, Nb-enriched and arc-like rocks, with the similar Sr-Nd (εNd(t) = +6.4–+10.2) and Atlantic-Pacific Ocean MORB-like Pb isotopic compositions. Their generation is related to input of slab-derived melt in the MORB mantle wedge source in an arc-trench gap setting. The Segama non-ophiolitic igneous rocks were dated at 251–178 Ma, with zircon in-situ εHf(t) = +9.5–+17.5, and are classified as high-Si and low-Si adakite, and high-mg andesite. They are the fractional products of the wedge-derived magma with the source being modified by slab-derived fluids. The magmatic flare-ups at ∼251–203, ∼185–153 Ma, ∼135–112 Ma and ∼95–85 Ma in Sabah are comparable with those in Coastal South China and West Borneo, indicating the Jurassic-Cretaceous accretionary orogenesis in Sabah. Sabah was tectonically located at the East Cathaysia margin of South China in the Mesozoic. It was a long-lived (>150 Ma) Andean-type active continental margin with multi-staged pulsed subduction and rollback in East Asia. Such a subduction system initiated no later than the earliest Triassic (∼251 Ma) and continued till the Late Cretaceous (∼85 Ma).
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