Geochemistry and Age of the Precambrian Metamorphic Sedimentary Rock in the Mianning, Sichuan province

Abstract:

The Precambrian metamorphic sedimentary rock may be divided into two types:metamorphic detrial sedimentary rock and metamorphic chemical sedimentary rock in the Youheimu area, Mianning, Sichuan Province. The former includes the biotite-plagioclase granulite, mica-quartz schist and metamorphic feldspar-quartz sandstone, and contains more SiO₂, Al₂O₃, Rb, Cs, Ba, U and Th, but less CaO and Sr. They show more remarkably negative Eu anomaly and slight negative Ce anomaly, the chondrite-normalized Eu/Eu^*, Ce/Ce^* and (La/Yb)CN are separately 0.64, 0.93 and 2.96. The later is only the marble, and contains more CaO and Sr, but less SiO₂, Al₂O₃, Rb, Cs, Ba, U and Th. It shows more remarkably negative Ce anomaly and slight negative Eu anomaly, the chondrite-normalized Eu/Eu^*, Ce/Ce^* and (La/Yb)CN are separately 0.91, 0.76 and 3.98. Geochemical characteristics of REE for two metamorphic sedimentary rocks indicate that their original rock was formed through hydrothermal sedimentation between Early and Middle Proterozoic in the tectonic setting of continental island arc to oceanic island arc, and the age of metamorphism is between Middle and Late Proterozoic.

Key words:

Precambrian; metamorphic sedimentary rock; hydrothermal sedimentation; island arc; Mianning, Sichuan

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