Dynamics of closure of the Proto-Tethys Ocean: A perspective from the Southeast Asian Tethys realm

Highlights

• The Pan-Cathaysian blocks witnessed the entire Proto-Tethys evolution.

• The Proto-Tethys evolution narrates a cycle of supercontinent break-up and assembly.

• Pacific-type continental margins occurred during closure of the Proto-Tethys ocean.

• ARRs or SSSs formed and transported toward the Gondwana during closure of the Tethys ocean.

• Stratified mantle convection as the driving mechanism of closure of the Tethys ocean.

Abstract

The force that drives continental drift has been one of the most challenging subjects of the plate tectonics theory in the last decades. The Proto-Tethys evolution exemplifies a scenario of drifting of continental plates during closure of the Proto-Tethys Ocean. The Pan-Cathaysian blocks in the Southeast Asian tectonic realm (SATR) derived from break-up of the Rodinia supercontinent witnessed the entire process of the Proto-Tethys evolution. The blocks and suture zones between them offer crucial information on the dynamics of continental drifting linked to shallow mantle convection and deep mantle flow.

Break-up of the Pan-Cathaysian blocks from the Rodinia and opening of the Proto-Tethys Ocean, e.g., the Changning-Menglian (CM) Ocean and the Tam Ky-Phuoc Son-Po Ko (TPP) Ocean, is evidenced by the volcano-sedimentary records in the SATR and their source affinities. Subsequent convergent tectonics occurred during the subduction of the Proto-Tethys CM oceanic plate beneath the northern margin of the Gondwana and of the oceanic plate of the TPP subsidiary ocean beneath the Truong Son and Kontum blocks. Occurrence of tectonic mélanges, e.g., the Lancang mélange, and extensive arc (continental or intra-oceanic) magmatic rocks attests the switch from passive to active plate margins, forming advancing subduction zones (Andean-type) along both the distal and proximal margins of the CM Ocean, and within the TPP Ocean. Jinshajiang-Ailao Shan-Song Ma (JAS) rifting proceeded and Dapingzhang back-arc rifting occurred during or subsequent to the transition from advancing to retreating subduction along the southern margin of the Indochina block. Closing of the CM and TPP oceans in the SATR by suturing of the oceans and collision of the continental blocks occurred in the late early Paleozoic, which is evidenced by, e.g., existence of high-pressure rocks along the CM suture and post-collisional magmatic rocks along the TPP suture zone.

The Proto-Tethys evolution in the SATR narrates a scenario of supercontinent break-up and assembly through continental drifting. Progressive Gondwana-centered convergent drifting of the Pan-Cathaysian blocks induced progressive closure of the Proto-Tethys main and subsidiary oceans, and rifting and closing of the rift basin and back-arc basin. Advancing subduction-ridge spreading-retreating subduction systems (ARRs) or subduction-spreading-subduction systems (SSSs) were formed and transported toward the Gondwana during the convergent drifting of the continental blocks. It is suggested that coupled shallow- and deep mantle flow, i.e., stratified mantle convection, is the major driving mechanism of the Gondwana-centered convergence of the Pan-Cathaysian blocks. In the model, the shallow-mantle convections directly control the subduction geometries and plate kinematics, while the deep-mantle convection is responsible for the drifting of the continental blocks, formation and migration of the SSSs and ARRs.

Introduction

The dynamics of plate tectonics has been one of the most challenging problems since the birth of the theory more than 50 years ago (McKenzie and Parker, 1967; Morgan, 1968; Bokelmann, 2002). The forces that drive continental drift and subduction of lithospheric plates become hotly debated in recent studies (Moores and Twiss, 1995; Collins, 2003; Capitanio et al., 2010; Becker and Faccenna, 2011; van Summeren et al., 2012; Doglioni and Panza, 2015; Sun, 2019). One or more forces, e.g., slab pull, slab drag, ridge push etc., in the force balance model (Forsyth and Uyeda, 1975; Moores and Twiss, 1995) have been widely accepted as important candidates for the drifting and subduction of particular plates. The slab-pull force from negative buoyancy of the subducting plate, as one of the most popularly accepted forces has been widely applied in interpreting many ocean-continent and continent-continent lithosphere subduction processes (Capitanio et al., 2010; Becker and Faccenna, 2011; van Summeren et al., 2012; Sun, 2019). Differential displacements between the Gondwana domains, for example, were suggested to be triggered by slab pull at the northern subduction margin of the Paleo-Tethys Ocean that caused localized deformation along their borders (Vizán et al., 2017). The excess potential energy of a mid-ocean ridge due to its higher elevation than the surrounding oceanic lithosphere, at the same time, gives rise to the ridge push force (Bott, 1991). The force partly contributes to the drifting of oceanic plates, although it may not be high enough or an order of magnitude less than the slab-pull force (Schellart, 2004; Ghosh et al., 2006; Wessel and Müller, 2007; Faccenna et al., 2012; van Summeren et al., 2012). Taking the Tethys evolution in Permian to Late Jurassic as an example, Kazmin (1991) argued that simultaneous occurrence of rifting and collision cannot be explained, if only the forces applied to plate margins, i.e., slab-pull and ridge-push, are considered as the plate-driving forces.

The mantle convection model presents a general framework of mantle flow-driving plate interactions, yet how convection operates in the mantle is highly controversial (Morgan, 1971; Wilson, 1973; Conrad and Lithgow-Bertelloni, 2004; Chen et al., 2016). Convective mantle flow at the base of the subducting lithospheric plates, for example, may exert a shear force, i.e., the mantle drag, and promote or oppose motions of the overlying plates (Forsyth and Uyeda, 1975; Bokelmann, 2002). The sustained convergence of the Tethys belt, for example, is explained to be associated with a long-term drag exerted by larger-scale, whole mantle flow (Alvarez, 2010; Cande and Stegman, 2011; van Hinsbergen et al., 2011). Global scale mantle convection systems in Phanerozoic may also promote slab-pull at local scales (Collins, 2003). Conveyor-belt process of transportation of continental masses from the passive to the active margin, e.g., of Tethys, was suggested to be governed by north-directed convective flow in the asthenosphere (Kazmin, 1991). For the dynamics of Tethys collisional system, Becker and Faccenna (2011) indicated that plume-associated “conveyor-belt” represents the primary mechanism and suggested that the most important force contribution is related to deep-rooted mantle flow. Numerical simulation revealed that the Pangea was assembled in a downwelling hemisphere (Zhong et al., 2007).

Doglioni, 1990, Doglioni, 1991, Doglioni, 1993, Doglioni and Panza (2015), Crespi et al. (2007) addressed the significant westward drift of the lithosphere relative to the asthenosphere to interpret e.g., the subduction asymmetries, contrasting structural patterns, subduction kinematics and related tectonic processes across the Pacific and the Mediterranean. High-angle subduction and trench-arc-back-arc basin along their western margins, and low-angle subduction and trench-arc system along the eastern margins are correlated to differential rotation between lithosphere and mantle (Doglioni et al., 2015a, b). The Earth's rotation and tidal torque probably provides a sufficiently energetic mechanism to drive this motion (Riguzzi et al., 2010, Scoppola et al., 2006). Doglioni and co-authors suggested that easterly-directed horizontal mantle flow may partly provide explanations to the above mentioned evidence and processes (Doglioni and Panza, 2015; Ficini et al., 2017). The mechanism is also accountable for the late Mesozoic retreating subduction along the eastern Eurasian continental margin and advancing subduction along the western North American continental margin (Liu et al., 2021).

Closure of the Proto-Tethys unfolds a scenario of an early-stage rifting and a late-stage closure of the Proto-Tethys Ocean (Fig. 1a, b), and assembly of the Pan-Cathaysian (including North China, South China, Indochina, etc.) blocks on to the Gondwana (Fig. 1c). During the period, the Pan-Cathaysian blocks drifted, the advancing subduction-ridge spreading-retreating subduction systems (ARRs) formed and the subduction-spreading-subduction systems (SSSs) between the blocks transported toward the Gondwana (see Fig. 1b to Fig. 1c). What contributed to the surface plate interactions (spreading, subduction), the drifting of continental blocks, the migration of ARRs and the transportation of the SSSs during closure of the Proto-Tethys? Here we focus on progress of recent studies on the Proto-Tethys tectonics in the Southeast Asia Tethys domain (SATR). We show that various shallow-level plate interactions occurred during the Proto-tectonic evolution as a consequence of supercontinent assembly that is nonetheless attributed to deep mantle convection processes. It is proposed that stratified mantle convection involving shallow- and deep-mantle convections may have controlled the surface plate interactions, e.g., the ARRs and migration of the SSSs, during the Proto-Tethys evolution in the SATR.