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

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 (similar to 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, (Sr-87/Sr-86)(i) = 0.70187-0.70671 and epsilon(Nd)(t) = +0.9 to +3.6. Their (Pb-206/Pb-204)(i), (Pb-208/Pb-204)i and (Pb-207/Pb-204)i range from 18.49 to 18.83, 38.39 to 39.19 and 15.57 to 15.70, and zircon epsilon(Hf)(t)-delta O-18 values from +4.1 to +16.1, and 5.21 parts per thousand to 6.05 parts per thousand, 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. (C) 2021 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Automated summary

The research indicates that the Raya Volcanics and Mensibau batholith in NW Kalimantan were formed in the Early Cretaceous, derived from a mantle wedge modified by recycled sediments and juvenile mafic crust. This confirms the geological evolution pattern of the Kuching zone.