Temporal-spatial patterns of Mesozoic Paleo-Pacific and Tethyan supra- subduction systems in SE Asia: Key observations and controversies in Borneo and its surroundings

The Mesozoic tectonic regime of the Indonesian Archipelago holds the key to decoding the development of the East Asia continental margin and unraveling the temporal-spatial pattern of the Paleo-Pacific and Tethyan supra-subduction systems in SE Asia. However, no consensus has been reached on the “intersected location (where), timing (when) and mechanism (why)” of the two supra-systems in the “narrow knot zone”. This paper presents an overview of key geological observations in Borneo and its surrounding areas in the heart of the Indonesian Archipelago with respect to its Mesozoic tectonics. Available data collectively show that the western segment of west Borneo, along with west Sumatra, have Sundaland affinities, representing the southernmost segment of the Paleo-Tethyan active continental margin. West Borneo was overprinted by the Paleo-Pacific-related accretionary orogenesis in the Jurassic and Cretaceous periods. The Mesozoic rock-units in Sabah (NE Borneo) exhibit Cathaysia-like affinities and their generation in an earliest Triassic-Late Jurassic arc-trench gap setting. The Mesozoic igneous rocks in NE, NW and SW Borneo define magmatic flare-ups at ca. 190 Ma, ca. 150 Ma, ca. 130 Ma and ca. 85 Ma that are comparable to those in Coastal South China. This magmatic activity represents a long-lived active continental margin derived by the pulsed Paleo-Pacific subduction and rollback. This oceanwardly-propagating accretionary orogen extends from the Lupar-Palangkaraya of west Borneo into Coastal South China, and extends as far as the Russian Far East via SE Vietnam and Sabah (NE Borneo)-Palawan (Philippine) arc-trench system. In NW and SW Borneo, the Jurassic and Cretaceous arc-like igneous rocks, whether mafic-intermediate or felsic, mostly share similar Sr-Nd-Hf-O and Pacific-like Pb isotopic compositions, which originated from the subduction-related mantle wedge or its juvenile crust source in a convergent plate margin setting. All the data indicate that Paleo-Pacific subduction had at least initiated by the earliest Triassic in NE Borneo and likely Coastal South China, and earliest Jurassic in NW and SW Borneo, but likely ceased at ca. 80 Ma. SE Borneo represented the easternmost segment of the Neo-Tethyan Ocean, along which northward subduction initiated at ca. 140 Ma and ceased at ca. 90 Ma. Such a Neo-Tethyan subduction system was cold and rapid, and was followed by the rapid exhumation at ca. 133–110 Ma along the Central Indonesian Accretionary Collision Complex as defined by the presence of HP/LT clockwise P-T-t metamorphism. Tectonic overprinting in East Asia since the Late Cretaceous might have driven the twist of the Paleo-Tethyan tectonic zone in west Sumatra and the intersection of the Paleo-Pacific and Neo-Tethyan systems in the Palangkaraya area between SW and SE Borneo. The Mesozoic stratigraphic framework is herein updated but validation will be required in the future. Integrating all available observations, and uncertainties a tectonic model is reconstructed for the interaction of Paleo-Pacific and Tethyan supra-subduction systems in SE Asia from the Triassic to Cretaceous.