Structure, composition and dynamics of divergent and convergent plate margins

Plate margins are the dynamic boundaries where lithospheric plates interact, driving Earth’s tectonic evolution. While the asthenospheric material and energy are transported along divergent plate margins to the Earth’s surface, the surface material is transferred along convergent plate margins into the Earth’s interior. Therefore, plate divergence and convergence are two key mechanisms for the exchange of material and energy between the lithosphere and asthenosphere. A great deal of advances in understanding thestructure, composition and dynamics of divergent and convergent plate margins have been made in the past two decades. Divergent margins are manifested as seafloor spreading and continental rift zones, and they occur as mid-ocean ridges, successful and failed continental rifts in different phases. Convergent margins are manifested as oceanic subduction and continental collision zones, and their formation and evolution are dictated by the properties of converging plates. Therefore, the two types of plate margins record a series of kinematic processes and dynamic mechanisms for the Wilson cycle in plate tectonics.The thermobaric and dynamic regimes of plate margins are two critical variables in modulating the internal and external Earth systems. In general, the geothermal gradient of plate margins changes from cold through warm to hot during the transition from convergence to divergence, and it correlates with the dynamic regime of either horizontal or vertical forces via specific tectonic processes. Cold subduction proceeds at low geothermal gradients, producing low T/P Alpine-type blueschist to eclogite facies metamorphic rocks; warm collision proceeds at mediate geothermal gradients, leading to medium T/P Barrovian-type amphibolite to granulite facies metamorphic rocks; and hot rifting proceeds at high geothermal gradients, generating high T/P amphibolite to granulite facies metamorphic rocks. Oceanic plates may subduct either actively or passively beneath continental margins, giving rise to different products at the overriding continental margins. Active subduction results in accretionary wedge, andesitic arc magmatism and porphyry mineralization, which are absent in the case of passive subduction.Continental assembly progresses from soft collision through hard collision to deep subduction, producing different types of regional metamorphism along convergent plate margins. Syn-collisional orogeny during continental assembly is characterized by medium T/P Barrovian-type metamorphism in the compressional regime, whereas post-collisional orogeny during continental rifting is featured by high T/P Buchan-type metamorphism in the extensional regime. Such spatiotemporal relationships between the dynamic and thermobaric regimes are definite at plate margins. Magmatism always proceeds at high geothermal gradients and thus is associated with extensional regimes either in the late stage of oceanic subduction or in the post-collisional stage. In this regard, caution must be exercised in linking HT/LP metamorphism and felsic magmatism to continental collision and supercontinental assembly. The formation and evolution of intracontinental tectonics have the inheritance and development relationships to the structure and composition of precursor plate margins. The thermobaric and dynamic regimes are two key variables in dictating the physicochemical properties and geodynamic processes of continental margin-interior tectonics.Thethermo-mechanical coupling is significant at the plate margins, where feedback between thermobaric regimes (i.e., geothermal gradients) and dynamic forces (i.e., buoyancy vs gravity, and compression vs extension) governs a series of geological processes such as deformation, metamorphism and magmatism. Therefore, plate tectonics operate viafeedback loopswhere thermobaric anomalies (e.g., asthenospheric heating vs slab cooling) modify rock rheology, inducing these geological processes that reshape the architecture of active and fossil plate margins. As a result, continental rifting along previously convergent plate margins plays a critical role not only in physical and chemical reworking of the plate margins but also in initiating new Wilson cycles. As such, intracontinental orogeny during continental rifting is featured by high T/P Buchan-type metamorphism in the extensional regime. The relevant elements are the important components of plate tectonics theory in both kinematics and dynamics, and thus have significant linkages to resources, energy and disasters.