Constraints of corundum bearing metasedimentary rocks on the Neoproterozoic evolution history of the northwest margin of the Yangtze Craton
Clarifying the Precambrian metamorphic basement exposed on the northwest margin of the Yangtze Craton is of fundamental significance for revealing the tectonic evolution history of the Yangtze Craton in the Neoproterozoic and the formation and occurrence mechanism of deep resources in the Sichuan Basin.This article reveals petrogenesis of biotite plagioclase gneiss and corundum bearing sillimanite cordierite schist in the Micangshan terrane on the northwest edge of the Yangtze Craton.Combined with metamorphic research,it is believed that the formation of corundum bearing mica schist is related to the loss of SiO2 in the deep melting process of the coexisting biotite plagioclase gneiss.The temperature and pressure during the metamorphic peak recorded by the migmatitic biotite plagioclase gneiss reached 759 ℃～770 ℃,0.48～0.55 GPa(with a geothermal gradient of 46 ℃/km～53 ℃/km),while the typical mineral assemblage of corundum bearing sillimanite cordierite schist records the P-T conditions of 580 ℃～620 ℃,0.36～0.46 GPa(with a geothermal gradient of 35 ℃/km～43 ℃/km).Metamorphic zircons have reported two sets of metamorphic ages,814±9 Ma and 736±17 Ma.Based on previous research results,this article believes that the sedimentary rocks containing corundum have further finely characterized the arc-continent collision process since～814 Ma.The high temperature gradient may be related to the involvement of mantle derived materials during the collision process,and the corresponding collision process further confirms that the Yangtze Craton is located on the periphery of the Rodinia supercontinent.
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