Subduction initiation (SI) at passive continental margin plays a key role in the Wilson cycle of plate tectonics; however, the long‐lived, stable Atlantic‐type margin challenges this hypothesis. The spontaneous SI at passive margin is difficult, which could be instead induced by far‐field tectonic forces. Previous analog and numerical models are generally conducted with constant convergent velocity, which may lead to extremely large boundary force in order for SI. In this study, we focus on numerical models with constant convergent force/stress to investigate the conditions for SI at typical passive margin without any type of prescribed weak zones. The result indicates that the SI at young passive margins with thin oceanic lithosphere is much easier than that at old margins. It reveals the dynamics of multiple newly formed subduction zones in the young oceanic plates of Southeast Asia and Southwest Pacific, but generally no SI for the old Atlantic‐type passive margin.

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.

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In the general history of the earlier Tethyan evolution, the younger oceanic plate began subduction shortly after the terrane collision and closure of the neighboring older ocean (Table S1 in the Supporting Information S1). For example, the subduction of Neo-Tethyan oceanic plate initiated at about 10-20 Myrs after the collision of Cimmerian terranes with Eurasia (Stampfli & Borel, 2002;Wan et al., 2019;Zhong & Li, 2020). However, there is no clear sign for subduction initiation (SI) in the present-day northern Indian Ocean, although it has been more than 50 Myrs since the collision between Indian and Eurasian continental plates (Stern, 2004;.The absence of SI in the Indian Ocean is thus a puzzling and widely debated issue. One possible reason is the high strain localization in the relatively weak Tibetan plate, which thus hinders the stress building in the Indian oceanic plate. However, this explanation is challenged by the high gravitational potential energy of the present

The understanding of subduction initiation (SI) remains ambiguous due to limited geological records. The metamorphic sole, generally considered to be generated by oceanic crustal metamorphism during SI, is characterized by high temperature condition (∼800°C) at shallow depths (<40 km). However, the exact tectonic setting of the metamorphic sole with such a high geothermal gradient is still controversial. The petrological and geochemical signatures of ophiolites and metamorphic soles in nature indicate three different types: (a) supra‐subduction zone (SSZ)‐type ophiolite with mid‐ocean ridge basalt (MORB)‐type metamorphic sole; (b) SSZ‐type ophiolite with SSZ‐type metamorphic sole; and (c) MORB‐type ophiolite with MORB‐type metamorphic sole. To clarify the conditions of metamorphic sole generation in different tectonic settings, a series of numerical models are conducted. The model results indicate that the SI at a (back‐arc) spreading center or spontaneous SI at a transform fault provides the favorable high‐temperature condition for formation of the metamorphic sole underlying the ophiolite. The former regime generates SSZ‐type ophiolite with SSZ‐type sole, whereas the latter generates SSZ‐type ophiolite with MORB‐type sole. The P‐T conditions of natural metamorphic soles may not represent the characteristic subduction channel condition for the majority of ophiolites, but stand for the end‐member high‐temperature regime that facilitates weakening, detachment and further exhumation of metamorphic soles. It thus illustrates the less widely distributed metamorphic soles than ophiolites in nature. The model results are further compared with three present‐day back‐arc basins on the Earth to evaluate the likelihood of future metamorphic sole generation and preservation in these basins.

The India–Asia collision, starting from 55 ± 5 Ma, leads to the formation of the Himalayas and Tibetan Plateau with great gravity potential energy and large forces acting on the surrounding blocks. However, the subduction transference/jump does not occur in the southern Indian continental margin or the northern Indian oceanic plate as supposed to happen repeatedly during the preceding Tethys evolution. Instead, the continental collision and orogeny continues until present day. The total amount of convergence during the India–Asia collision has been estimated to be ∼2,900–4,000 km and needs to be accommodated by shortening/extrusion of the Tibetan plate and/or subduction of the Greater Indian plate, which is a challenging issue. In order to study the collision mode selection, deformation partition, and continental mass conservation, we integrate the reconstruction-based convergence rate of the India–Asia collision into a large-scale thermomechanical numerical model and systematically investigate the effects of overriding Tibetan lithospheric strength and the amount of convergence. The model results indicate that the absence of subduction transference during the India–Asia collision may be attributed to strain localization and shortening of the rheologically weak Tibetan plate. In case of the India–Asia collision for ∼50 Myr with a total convergence of ∼2,900 km, the model with the intermediately weak Tibetan plate could reconcile the general deformation partition and continental mass balance of the Himalayan–Tibetan system. However, the longer period of India–Asia collision for ∼55 Myr leads to significant shortening of the overriding plate that is not consistent with the Tibetan observations, in which case an oceanic basin may be required for the Greater Indian continent.

Subduction initiation (SI) remains a confusing problem today, especially for how and where the subduction zones begin (

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