?Where, when and why? for the arc-trench gap from Mesozoic Paleo-Pacific subduction zone: Sabah Triassic-Cretaceous igneous records in East Borneo

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 iso-topes, 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 classi-fied into the MORB-, high-Nb, Nb-enriched and arc-like rocks, with the similar Sr-Nd (eNd(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 eHf(t) = +9.5-+17.5, and are clas-sified 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).(c) 2023 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.