On the Relationship between Basalt Underplating and Felsic Igneous Rock-Formation: A Case Study of the Volcano-Intrusive Complex in Eastern China

According to the thermal structure of the lithosphere, the continental crust is located within the range of the MBL (mechanical boundary layer) and its heat transfer is controlled by thermal conductivity of the rocks in the crust. Therefore, based on the theory of thermal conductivity and the same thermophysical parameters as those obtained in previous studies, we calculated the thermal state of the crust underplated by basaltic magma. The result suggests that a felsic magma layer, thinner than 250 m, would be generated at 850℃ by the emplacement of a basalt magma sill (1200℃, 500 m thick) into continental crust during a very short period (≤ 2700 a). Geological and geochemical characteristics and isotopic chronological data of the bimodal volcanic rock association in the Changpu Formation of the Yutian Group in the Longnan-Xunwu area of Southern Jianxi suggest that the rhyolite of this association might be derived directly from partial melting of the upper crust caused by emplacement of quartz tholeiite magma. The Mesozoic continental crust in SE China (≤50 km in thickness) was located in the MBL and the amount and formation age of the felsic magma generated by the underplating of basaltic magma would be constrained by heat conductivity of the rocks in the crust. Granite and rhyolitic rocks dominate (90%) the Mesozoic igneous rock in SE China, while basaltic rocks are minor with their formation ages different from those of felsic rocks. Therefore, the formation of the extensive felsic igneous rocks in SE China may have not been caused by the underplating of basalt.