Convergent plate margin dynamics: New perspectives from structural geology, geophysics and geodynamic modelling

Convergent plate margins occur when two adjoining tectonic plates come together to form either a subduction zone, where at least one of the converging plates is oceanic and plunges beneath the other into the mantle, or a collision zone, where two continents or a continent and a magmatic arc collide. Convergent plate margins are arguably the most complicated and dynamic plate boundaries on Earth and have been the subject of many investigations and discussions since the advent of plate tectonic theory. This paper provides a historical background and a review of the development of geological and geodynamic theories on convergent plate margins. Furthermore, it discusses some of the recent advances that have been made in the fields of structural geology, geophysics and geodynamics, which are fundamental to our understanding of this phenomenon. These include: (1) the finding that plates and plate boundaries move at comparable velocities across the globe; (2) the emerging consensus that subducted slabs are between two to three orders of magnitude stronger than the ambient upper mantle; (3) the importance of lateral slab edges, slab tearing and toroidal mantle flow patterns for the evolution of subduction zones; and (4) clear evidence from mantle tomography that slabs can penetrate into the lower mantle. Still, many first-order problems regarding the geodynamic processes that operate at convergent margins remain to be solved. These include subduction zone initiation and the time of inception of plate tectonics, and with it convergent plate margins, on Earth. Fundamental problems in orogenesis include the mechanism that initiated Andean mountain building at the South American subduction zone, the potential episodicity of mountain building with multiple cycles of shortening and extension, and the principal driving force behind the construction of massive mountain belts such as the Himalayas–Tibet and the Andes. Fundamental questions in subduction dynamics regard the partitioning of subduction into a trench and plate component, and the distribution of energy dissipation in the system. In seismic imaging, challenges include improving resolution at mid to lower mantle depth in order to properly understand the fate of slabs, and better constraining the 3-D flow-related anisotropic structure in the surrounding mantle. Future insights into such fundamental problems and into the regional and global dynamics of convergent plate margins will likely be obtained from integrating spatio-temporal data, structural geological data, geophysical data and plate kinematic data into plate tectonic reconstructions and three-dimensional geodynamic models of progressive deformation.