Crustal and uppermost mantle structure across the Lower Yangtze region and its implications for the late Mesozoic magmatism and metallogenesis, eastern South China

We present here high-resolution seismic sections of crustal and uppermost mantle structure along two dense linear arrays across the Lower Yangtze region in the eastern South China Block (SCB). Our seismic images reveal two low-velocity anomalies (LVAs) in the uppermost mantle which we interpreted as relic (still cooling) mantle magma chambers ponding and underplating beneath the base of the crust in the areas of the Dexing porphyry copper deposits and the Cretaceous South Anhui granites. The Moho and LAB discontinuities imaged also exhibit deformation directly above the two mantle LVAs, which probably indicate local mantle lithosphere destruction by asthenospheric upwelling in the Mesozoic. This local asthenospheric upwelling may have triggered melting of the mantle lithosphere and generated the observed mantle magma chamber system through interactions with lower crustal materials. Low Vs bodies revealed in the middle-upper crust at depth of ~10 km may indicate the corresponding solidified intrusive granitoids. These observations provide unambiguous seismological evidence connecting deep magmatism with surface geological features. Combined with previous petrologic and geochemical studies, the findings presented here outline a mantle magma chamber based magmatic system that was underplated beneath the base of the crust and kept supplying heat and materials in forming the voluminous Yanshanian igneous rocks and associated metallogenesis in the Lower Yangtze region.

Source: Physics of the Earth and Planetary Interiors - October 22, 2019 Category: Physics Source Type: research