Search

Tethys tectonic system has experienced a long-term evolution history, including multiple Wilson cycles; thus, it is an ideal target for analyzing plate tectonics and geodynamics. Tethyan evolution is typically characterized by a series of continental blocks that separated from the Gondwana in the Southern Hemisphere, drifted northward, and collided and accreted with Laurasia in the Northern Hemisphere. During this process, the successive opening and closing of multistage Tethys oceans (e.g., Proto-Tethys, Paleo-Tethys, and Neo-Tethys) are considered core parts of the Tethyan evolution. Herein, focusing on the life cycle of an oceanic plate, four key geodynamic processes during the Tethyan evolution, namely, continental margin breakup, subduction initiation (SI), Mid-Ocean Ridge (MOR) subduction, and continental collision, were highlighted and dynamically analyzed to gather the following insights. (1) Breakup of the narrow continental margin terranes from the northern Gondwana is probably controlled by plate subduction, particularly the subduction-induced far-field stretching. The breakup of the Indian continent and the subsequent spreading of the Indian Ocean can be attributed to the interactions between multiple mantle plumes and slab drag-induced far-field stretching. (2) Continental margin terrane collision-induced subduction transference/jump is a key factor in progressive Tethyan evolution, which is driven by the combined forces of collision-induced reverse push, far-field ridge push, and mantle flow traction. Moreover, lithospheric weakening plays an important role in the occurrence of SI. (3) MOR subduction is generally accompanied by slab break-off. In case of the considerably reduced or temporary absence of slab pull, mantle flow traction may contribute to the progression of plate subduction. MOR subduction can dynamically influence the overriding and downgoing plates by producing important and diagnostic geological records. (4) The large gravitational potential energy of the Tibetan Plateau indicates that the long-lasting India-Asia continental collision requires other driving forces beyond the far-field ridge push. Further, the mantle flow traction is a good candidate that may considerably contribute to the continuous collision. The possible future SI in the northern Indian Ocean will release the sustained convergent force and cause the collapse of the Tibetan Plateau. Based on the integration of these four geodynamic processes and their driving forces, a "multiengine-driving" model is proposed for the dynamics of Tethyan evolution, indicating that the multiple stages of Tethys oceanic subduction provide the main driving force for the northward drifting of continental margin terranes. However, the subducting slab pull may be considerably reduced or even lost during tectonic transitional processes, such as terrane collision or MOR subduction. In such stages, the far-field ridge push and mantle flow traction will induce the initiation of new subduction zones, driving the continuous northward convergence of the Tethys tectonic system. [ABSTRACT FROM AUTHOR]

The recent statistics suggests that over 60% of active Cenozoic subduction initiation (SI) cases are related to the strike‐slip fault. A number of previous studies have shown that the lithospheric weak zone is a necessary condition for the SI. However, the direct effect of strike‐slip motion on lithospheric weakening and SI has rarely been investigated in numerical models due to the challenge of complex 3D boundary conditions. In this study, a new 3D model has been built with both strike‐slip and compression boundary conditions. The model results indicate that the compression at a strike‐slip boundary provides a favorable condition for the SI, with producing and maintaining a lithospheric‐scale weak zone that facilitates strain localization and SI. In addition, the high strike‐slip velocity and buoyant overriding plate contributes to the SI of young oceanic plate. This mechanism satisfies a large number of natural SI cases in the Cenozoic. Plain Language Summary: Subduction zone is one of the most important elements of plate tectonics on the present Earth. How to form a new subduction zone, that is, subduction initiation (SI), is still a challenging issue in geodynamics. The lithospheric weak zone is a necessary condition for SI; otherwise, the required force for breaking the lithosphere is too high. The strike‐slip fault is a natural weak zone, and is thus a favorable place for SI. However, the strike‐slip fault is generally set as a simple weak zone in the previous models, because the strike‐slip motion itself is challenging for the numerical simulation. In this study, we have built a new 3D model with complex boundary conditions, including both strike‐slip and compression components. Based on the systematic numerical studies, we find that the compression at a strike‐slip boundary provides a favorable condition for the SI. We also find that the high strike‐slip velocity and buoyant overriding plate contributes to the SI of young oceanic plate. This mechanism satisfies and explains a large number of natural SI cases in the Cenozoic. Key Points: A new 3D model has been developed with both strike‐slip and compression boundary conditionsSubduction initiation (SI) prefers transpression with both compression and shear componentsCenozoic SI favors strike‐slip fault with buoyant overriding plate and young subducting plate [ABSTRACT FROM AUTHOR]

The closure of a subduction zone with continental terrane collision and accretion is generally thought to be followed by the initiation of a new subduction zone in the neighboring oceanic plate, which is suggested to happen repeatedly during the evolution of Tethyan system. Although the Indian‐Asian continental collision has occurred for >50 Myrs, there is still no clear sign for subduction initiation (SI) of the northern Indian oceanic plate, which is a puzzling issue and requires further investigations. This problem is studied here by systematic 3‐D thermo‐mechanical numerical models with a constant stress boundary condition. The model results indicate that the lack of proper weak zones at passive continental margin plays a critical role in hindering the collapse and SI of the northern Indian oceanic plate. In addition, the wedge‐shaped southern Indian continental margin provides an additional resistance for the SI. However, the strain localization with shortening of the Tibetan Plateau does not have a significant effect on the SI of Indian oceanic plate in the current models, which requires further studies with wider Tibetan plate. The numerical results explain why no SI has occurred in the northern Indian Ocean with pushing from the high gravitational potential energy of the uplifted Tibetan Plateau and seafloor spreading in the Northern Indian Ocean, and further predict that the future SI is more likely to occur in the northwestern Indian Ocean than the northeastern region due to continuous counterclockwise rotation of the Indian Continent. Plain Language Summary: The collision between continental plates builds many large mountain belts on the Earth, with the Himalaya and Tibetan Plateau as the greatest one. After the mountain building, the large convergent force may lead to the formation of a new subduction zone in the neighboring oceanic plate, which was defined as "subduction transference." As the latest stage of Tethyan evolution, Indian‐Asian collision has occurred for more than 50 Myrs; however, there is still no clear sign for subduction initiation at the northern Indian oceanic plate, which is a puzzling issue. In this study, a series of 3‐D numerical models are conducted to investigate why there is no subduction transference, as well as whether and where the subduction of Indian oceanic plate is going to happen. The model results indicate that the absence of proper weak zones at the northern Indian oceanic plate is the primary factor that hinders its subduction initiation. Additionally, the wedge‐shaped geometry of southern Indian continental margin also plays a role in resisting the collapse of the margin. We further predict that the future SI is more likely to occur in the northwestern Indian Ocean than the northeastern region because of continuous counterclockwise rotation of the Indian Continent. Key Points: Series of 3‐D thermomechanical models are conducted with constant convergent stress to study subduction initiation (SI) at passive marginsDifficulty of SI at northern Indian Ocean may be attributed to the wedge‐like southern Indian continental margin without proper weaknessThe southwestern Indian continental margin is more likely for SI in the future after its continued counterclockwise rotation [ABSTRACT FROM AUTHOR]

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. Plain Language Summary: Subduction, characterized by an oceanic plate sinking into the Earth's interior, is a key process of our living planet. The formation mechanism of a new subduction zone is still widely debated because of the limited geological records. The ophiolite is a fragment of an ancient oceanic plate and widely distributed in the orogens. Beneath some of the ophiolites, there is a thin layer of metamorphosed rock, called the metamorphic sole, which is composed of the materials detached from the subducted oceanic plate. The assembly of the ophiolite and metamorphic sole provides the most important constraints for the subduction initiation process. However, the petrological and geochemical signatures of the natural ophiolites and metamorphic soles indicate very different tectonic settings. The tectonic setting and dynamic conditions for the formation of the ophiolite and metamorphic sole remain unclear. Combining with the pressure and temperature data of natural metamorphic soles, our systematic numerical modeling studies reveal that the subduction with a very young overriding oceanic plate is the key factor for the metamorphic sole generation underlying the ophiolite. Furthermore, we evaluate the possibility of future generation and preservation of ophiolites and metamorphic soles in the present‐day oceanic basins on the Earth. Key Points: Systematic numerical models are conducted to clarify the conditions of metamorphic sole generation in different tectonic settingsSubduction initiation at a (back‐arc) spreading center is a favorable setting for the formation of metamorphic sole underlying ophioliteP‐T conditions of natural metamorphic soles may represent a high temperature regime facilitating their weakening and exhumation [ABSTRACT FROM AUTHOR]

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. Plain Language Summary: Subduction, which is a plate moves under another one and sinks into the mantle, is a key process of the Earth. Subduction could cause disasters, shape magnificent natural wonders, and control the long‐term climate. However, our understanding for how and where subduction would begin between continents and oceans is still poor. This is because the beginning of subduction is just a snapshot of long‐lived geological process. Thus, the rock records are rather limited and difficult to observe. In this study, we conducted systematic numerical models to quantify the force required for the formation of a new subduction zone with variable ages of oceanic lithosphere. The result indicates that the force needed to begin subduction increases with the oceanic age, which explains that young oceanic plates in the Southeast Asia and Southwest Pacific are easier to begin subduction; however, the old Atlantic Oceanic plate is hard. Key Points: Subduction initiation at passive continental margin is studied by numerical model with convergent force/stress boundary conditionMode selection of subduction initiation and required magnitude of force are dependent on the age of passive marginal oceanic lithosphereYoung oceanic lithosphere is easier to initiate subduction with low boundary force, whereas the old Atlantic‐type margin is difficult [ABSTRACT FROM AUTHOR]