No seamount subduction,no magmatic arc?

Water is essential for the formation of a magmatic arc by lowering the melting temperature of materials in the mantle wedge.As such,it is logical to attribute the absence of a magmatic arc to insufficient water released from the subducting plate,although a number of other factors may cause volcanic arc quiescence as well,such as a slab window or flat slab subduction.In this contribution,we present a possible but testable correlation between the occurrence of a magmatic arc and seamount subduction in light of bathymetric data obtained near trenches.This correlation,if it holds true,in turn means that a magmatic arc is unlikely to occur when the subducting slabs have not been severely fractured and that one of the main reasons for excluding effects such as the slab window or flat slab subduction may be that the plate is not accompanied by seamounts.Therefore,the role that seamount subduction plays in recycling water back into the mantle deserves more attention from the earth sciences community.

Fault-controlled regional magmatism and mineral deposition in central Cathaysia——Evidence from ambient noise tomography

Guangdong Province in the central Cathaysian Block has two world-class metallogenic belts, namely, the Nanling and Southeastern Coastal Metallogenic Belts(NLMB and SCMB), which are spatially coincide with the major regional Ganjiang and Zhenghe-Dapu Fault Zones(GJFZ and ZDFZ). However, what roles the faults played in mineral deposition and magmatism is unclear. Using ambient noise tomography, we obtain a 3-D whole-crust shear wave velocity model. By combining available regional geophysical models, we characterize the architecture of the regional shallow lithosphere and infer its possible tectonic connection to magmatic sources, pathways and surface deposition. The results show that the study area is loosely divided by the two major faults, the GJFZ and ZDFZ, into distinct velocity domains. In the north high Vand low V/Vcrust in the NLMB imply crustal remelting, which leads to the general felsic composition. In the coastal area, the lower crustal high Vanomaly is attributed to upwelling melts associated with Cretaceous magmatic activity. Between mineral belts, a swath of crustal lowvelocity zones extend into the uppermost mantle, manifesting partial melting related to upwelling magmas that may hint at a deep origin of magma from subcrustal lithosphere and likely feed surface mineral deposits through major faults. Secondary NW-trending faults coincide with low velocities and facilitated magmatic migration. A correlation between coastward extension of low velocities and younging of the Jurassic and Cretaceous magmatism is suggestive of a combined effect of slab rollback and a change in the direction of the Paleo-Pacific subduction system. We speculate a regional fault-control model in the central Cathaysian Block for the spatial-temporal evolution of regional deformation and magmatism during the middle Mesozoic.