About this Research Topic
The initiation, maturation and breakup of oceanic arcs and their associated backarc basins is strongly linked with far-field plate tectonic stresses, the regional geodynamic setting, local crustal structure and mantle dynamics. The reorganization of tectonic plates, for example, may initiate new subduction zones but resistance to subduction of the incoming plate due to crustal anomalies such as pre-existing arc terranes or oceanic plateaus may stop subduction or flip subduction zones.
The individual evolutionary stages of arc and backarc systems are each associated with significant changes in the physical and chemical conditions that control the compositions of melts during generation, transport and storage, and eventually volcanic eruption. These magmas are generated under variable conditions that range from fluxed melting due to the devolatilization of the slab underneath the arc to dry adiabatic decompressional melting of the mantle, especially underneath the backarc. The structure, composition and geometry of the slab thus exerts an important control on melt generation in the overlying mantle wedge. Underneath the arc, ascending melts pool in the MASH (melting-assimilation-storage-homogenization) zone at the Moho and in the lower crust. Therefore, the thickness, composition, and structure of the arc crust control the composition of the final melt erupted. Extensive differentiation of the ascending melts produces intermediate (andesite) or silicic (dacite-rhyolite) compositions, making arcs a potential site for the generation of juvenile continental crust. In the backarc, plate divergence facilitates the ascent of more primitive melts to shallow levels to generate new, commonly basaltic crust. Where arc and backarc systems interact, the resulting magmas are hybrid with variable contents of slab-derived volatiles and a wide range of melt oxidation states.
The magma compositions along with the rates of crustal growth, crustal architecture and geodynamics are thus important parameters for the potential endowment of the crust in societally relevant metals such as copper, cobalt and gold. Arc and backarc systems are prolific hosts to a broad variety of magmatic-hydrothermal ore forming systems including porphyry and epithermal systems, skarns or volcanogenic massive sulfide deposits.
Recent advances in trace element and isotope geochemistry, microanalytical methods, and modeling have significantly improved the understanding of these processes. However, the complex geodynamic settings and crustal heterogeneity of these systems, make it difficult to reconcile the variations in arc-backarc geochemical fluxes through time and space and require holistic, multi-disciplinary approaches. This Research Topic welcomes contributions dealing with the spatial and temporal evolution of oceanic arc-backarc systems and their associated mineral potentials. We particularly encourage contributions that quantify and trace elemental fluxes from the subducting slab through the mantle wedge and crust, and study the upper crustal processes that influence the composition and location of ore-forming melts and fluids as well as associated metal deposition. Relevant Earth Science disciplines may include but are not limited to: geophysics; structural geology; geochemistry; experimental, metamorphic and igneous petrology; economic geology; volcanology; sedimentology and modeling.
Keywords: arc, backarc, magmatism, geodynamics, ore forming processes
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