Provenance study of the Lubok Antu Mélange from the Lupar valley, West Sarawak, Borneo: Implications for the closure of eastern Meso-Tethys?

Abstract

The Lubok Antu Mélange is exposed along one of the most important tectonic lineaments, the Lupar Line in Sarawak, Borneo. However, the depositional age of the Lubok Antu Mélange is poorly known, and no provenance studies have been conducted so far. Here, we use geochemical, Nd isotopic and detrital zircon UPb analyses of samples from the Lubok Antu Mélange to constrain provenance and routing in order to better understand Borneo's evolution history. Bulk rock geochemistry reveals that the Lubok Antu Mélange was deposited in a continental arc setting related to the Paleo-Pacific subduction margin. New UPb detrital zircon data suggest that the maximum depositional age for the Lubok Antu Mélange is ca. 115 to 105 Ma. The Lubok Antu Mélange with a strongest Jurassic peak is interpreted to be sourced from the Mesozoic continental arc related to the Paleo-Pacific subduction, with contributions from West Borneo, the Malay Peninsula and possibly Sumatra. Compared with the detrital zircon data of the uppermost Cretaceous sedimentary rocks in Sarawak, our study records a change in source in the latest Cretaceous from erosion of basement magmatic rocks of the Paleo-Pacific subduction-related arc that was probably located offshore of what is now South Vietnam and West Borneo, to the Schwaner Mountains arc of SW Borneo. This indicates that the rapid uplift and exhumation of the Schwaner Mountains could have initiated in the latest Cretaceous, which may imply the arrival of SW Borneo and the closure of the eastern Meso-Tethys at that time.