An Ophiolite Perspective on Asian Orogeny: Propagating Subduction Initiation from Sabah to Taiwan

Abstract

Ophiolites that occur in orogenic belts commonly display island arc geochemical features suggestive of sea-floor spreading related to subduction zone processes. These are referred to as supra-subduction zone (SSZ)-type ophiolites, which form within the upper plate at the initial stage of subduction, yielding a characteristic magma association as that observed from the Eocene Izu-Bonin-Mariana forearc or around younger marginal basins in the western Pacific. This study explores its broader implication by examining the age and nature of SSZ-type ophiolites circum the South China Sea, including those from the Banggi Island, Sabah (~55-50 Ma), Palawan (~40-34 Ma), Mindoro (~33-23 Ma) and eastern Taiwan (~17-14 Ma). We propose that the Banggi Island ophiolite was produced in the forearc regime when the proto-South China Sea plate began subducting southward to a vanished ocean basin (part of the East Asian Sea?). The subduction initiation propagated stepwise from Sabah to Palawan and then Mindoro, and eventually terminated as the result of demise of the proto-South China Sea, arrival of the Luzon Island sitting on the Philippine Sea plate, and collision of the rifted Eurasian continental fragments derived from opening of the South China Sea. One such continental fragment split off and drifted to the western margin of the Philippine Sea, or the Huatung Basin, thus facilitating the initiation of eastward subduction of the nascent South China Sea plate in the mid-Miocene to form the protolith of Eastern Taiwan ophiolite and succeeding northern Luzon magmatic arc. All these later accreted together to the attenuated Eurasian continental margin giving rise to the orogeny in Taiwan.