Natural observations of subduction initiation: Implications for the geodynamic evolution of the Paleo-Asian Ocean

Abstract

Initiation of new subduction zones is an integral part of Earth's plate tectonics regime. It is generally accepted that the negative buoyancy of sufficiently old oceanic lithosphere provides the primary driving force for subduction initiation. However, the dynamic processes of the subduction initiation are still debated. In this paper, we summarize representative geological records of subduction initiation, including supra-subduction zone (SSZ) ophiolitic mélanges, forearc basalts and metamorphic soles, and review four typical mechanisms of the subduction initiation using natural examples from circum-Pacific and Tethyan subduction zones, including Izu-Bonin-Mariana (IBM), Oman, Caribbean and Solomon examples for subduction initiation by transform fault collapse, mid-ocean ridge inversion, plume-induced, and polarity reversal, respectively. Above three rock records were also preserved in different stages of evolution of the Central Asian Orogenic Belt (CAOB), which is one of the largest and long-lived accretionary orogenic belts on Earth, and indicated that the subduction initiation began at 1.02 Ga in the northern Paleo-Asian Ocean (PAO), but started at the Early Cambrian in the southern PAO. The plume-induced subduction initiation might play the dominant role prior to Cambrian, and other models were also operated in the evolution of the CAOB. More importantly, this study highlights a crucial link between SSZ ophiolitic mélanges associated with metamorphic rocks and subduction initiation in the CAOB. Therefore, we recommend that future research in this direction focuses on the SSZ ophiolitic mélanges, forearc basalts and metamorphic soles in the CAOB, this will open the door for geologists to contribute fundamentally to understanding subduction initiation in the PAO.