Early Cretaceous subduction in NW Kalimantan: Geochronological and geochemical constraints from the Raya and Mensibau igneous rocks

Abstract

The Kuching zone in NW Kalimantan and Malaysia Sarawak might be the southerly-extending segment of the paleo-Pacific subduction that is developed along the Coastal South China and SE Vietnam, and separated the Sundaland “old-land” from the Cenozoic Sibu zone. However, establishing this link is hindered by the lack of data on the Mesozoic orogenic history in NW Kalimantan. This paper presents zircon U-Pb geochronological and Hf-O isotopic data as well as whole-rock elemental and Sr-Nd-Pb isotopic results for the Raya Volcanics and their equivalents, as well as the Mensibau batholith in NW Kalimantan. The Raya Volcanics and Mensibau granitoids formed at 130–144 Ma, synchronous with the Menunuk Volcanics, but significantly older than the Pakong-Serabang mafic rocks and Serian Volcanics (~77–98 Ma) in the Sarawak Kuching zone. The Raya Volcanics and their equivalents belong compositionally to tholeiitic to low-K calc-alkaline series, and exhibit “spiky” PM-normalized patterns with Nb/La = 0.16–0.32, (87Sr/86Sr)i = 0.70187–0.70671 and εNd(t) = +0.9 to +3.6. Their (206Pb/204Pb)i, (208Pb/204Pb)i and (207Pb/204Pb)i range from 18.49 to 18.83, 38.39 to 39.19 and 15.57 to 15.70, and zircon εHf(t)-δ18O values from +4.1 to +16.1, and 5.21‰ to 6.05‰, respectively. They are derived from mantle wedge modified by recycled sediments. The Mensibau batholith is dominated by I-type granodiorite and granite. They share similar elemental ratios and Sr-Nd-Pb-Hf-O isotopic compositions with the Raya Volcanics, and originated from wedge-derived juvenile mafic crust. The temporal-spatial and geochemical accordance for the Raya Volcanics and Mensibau batholith document the extensive development of the early Cretaceous igneous rocks in NW Kalimantan. The Kuching zone is a northeasterly-propagated Cretaceous accretionary system that developed in response to the subduction of the paleo-Pacific plate.