Subduction Initiation During Collision‐Induced Subduction Transference: Numerical Modeling and Implications for the Tethyan Evolution

Abstract

The collision‐induced subduction transference is a composite dynamic process including both the terrane collision/accretion and the subduction initiation (SI) at the neighboring passive margin. This process occurred repeatedly during the evolution of Tethyan systems, with multiple ribbon‐like continents or microcontinents drifting from Gondwana in the southern hemisphere and accreting to the Eurasian continent since Paleozoic. In the previous numerical studies, the dynamics of terrane collision and induced SI are investigated individually, which however need to be integrated to study the controlling factors and time scales of collision‐induced subduction transference. Systematic numerical models are conducted with variable properties of converging plates and different boundary conditions. The model results indicate that the forced convergence, rather than pure free subduction, is required to trigger and sustain the SI at the neighboring passive margin after terrane collision. In addition, a weak passive margin can significantly promote the occurrence of SI, by decreasing the required boundary force to reasonable value of plate tectonics. The lengths of subducted oceanic slab and accreting terrane play secondary roles in the occurrence of SI after collision. Under the favorable conditions of collision‐induced subduction transference, the time required for SI after collision is generally short within 10 Myr, which is consistent with the general geological records of Cimmerian collision and the following Neo‐Tethyan SI. In contrast, the stable Indian passive margin and absence of SI in the present Indian Ocean may be due to the low convergent force and/or the lack of proper weak zones, which remains an open question.

Reviewing subduction initiation and the origin of plate tectonics: What do we learn from present-day Earth?

“… Conversion of oceanic transform faults/fracture zones: (Uyeda and Ben‐Avraham, 1972; Casey and Dewey, 1984; Toth and Gurnis, 1998; Doin and Henry, 2001; Hall et al, 2003; Gurnis et al, 2004; Baes et al, 2011; Maffione et al, 2017; Guilmette et al, 2018; Zhong and Li, 2020); Inverse at (extinct) spreading ridges (Gurnis et al, 2004; Duretz et al, 2016; Keenan et al, 2016) or detachment faults (van Hinsbergen et al, 2015; Maffione et al, 2015); Inverse at COB (Zhong and Li, 2019); Episodic subduction (Crameri et al, 2020). ii) Externally driven forcing with self‐nucleated shear zone Plate rupture within an oceanic plate under compression forcing (McKenzie, 1977; Cloetingh et al, 1989; Shemenda, 1992; Thielmann amd Kaus, 2012; Zhong and Li, 2019; Crameri et al, 2020); Plate reorganization with sedimentary loading (Erickson and Arkani‐Hamed, 1993); Compression forcing with various localization mechanisms, including shear heating (Crameri and Kaus, 2010; Thielmann and Kaus, 2012) and grain‐size reduction (Bercovici and Ricard, 2005, 2013, 2014; Rozel et al, 2011); Plate rupture induced by plate acceleration (Agard et al, 2007); Subduction zone transference/trench jump (Mitchell, 1984; Stern, 2004; Tetreault and Buiter, 2012; Vogt and Gerya, 2014; Wan B et al, 2019; Wu et al, 2020); Subduction polarity reversal (Mitchell, 1984; Cooper and Taylor, 1985; Pysklywec, 2001; Stern, 2004; Faccenda et al, 2008; von Hagke et al, 2016; Crameri et al, 2020); Conversion of passive margin to subduction zone with suction force imposed at bottom boundary (Baes and Sobolev, 2017);…”

“…Conversion of oceanic transform faults/fracture zones: (Uyeda and Ben‐Avraham, 1972; Casey and Dewey, 1984; Toth and Gurnis, 1998; Doin and Henry, 2001; Hall et al, 2003; Gurnis et al, 2004; Baes et al, 2011; Maffione et al, 2017; Guilmette et al, 2018; Zhong and Li, 2020);…”

Kinematic Boundary Conditions Favouring Subduction Initiation at Passive Margins Over Subduction at Mid-oceanic Ridges

“…As loads of 16 TN/m are needed to initiate subduction at passive margins (Zhong and Li, 2020) additional forces are required next to ridge push for the formation of a new subduction zone. It is, therefore, expected that stress levels in excess of ridge push would be relaxed through deformation of the mid-oceanic ridge, where the lithospheric strength is low.…”

“…Previous studies have emphasized that deformation at the passive margin through spontaneous margin collapse is an unlikely mechanism for subduction initiation, because stresses acting on the passive margin lithosphere are never at yield (Cloetingh et al, 1984;Mueller and Phillips, 1991). It is thus more likely that the nucleation of a subduction zone at a passive margin occurs upon additional external forcing to reach stress levels of at least 16 TN/m (Zhong and Li, 2020) to induce failure of the passive margin lithosphere. Numerical modelling studies simulating the shortening of an oceanic basin (Auzemery et al, 2020;Candioti et al, 2020;McCarthy et al, 2020;Zhong and Li, 2020) emphasise that such stress levels can only be supported by thick oceanic lithospheres, suggesting that subduction initiation is only feasible in case of shortening of an old oceanic basin.…”

Flat Subduction Versus Big Mantle Wedge: Contrasting Modes for Deep Hydration and Overriding Craton Modification

“…An initial weak zone is set between the oceanic and continental plates, used for localizing the initial subduction. The dynamics of subduction initiation at oceanic‐continental plate boundary is not the focus of this study but has been systematically investigated in Zhong and Li (2019, 2020). The initial temperature of the sublithospheric mantle is set with a constant adiabatic gradient of 0.5°C/km.…”