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 remarkablynegative 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, andcontains more CaO and Sr, but less SiO₂, Al₂O₃, Rb, Cs, Ba, U and Th. It shows moreremarkably 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. Geochemicalcharacteristics 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

摘要： 四川冕宁尤黑木地区前寒武纪变质沉积岩可分为碎屑沉积变质的黑云斜长变粒岩、云母石英片岩、变质长石石英砂岩及化学沉积变质的大理岩等两类。前者富SiO₂、Al₂O₃、Rb、Cs、Ba、U和Th，贫CaO和Sr，具明显的负铕异常和不太明显的负铈异常，(Eu/Eu^*)CN=0.64，(Ce/Ce^*)CN=0.93，(La/Yb)CN=2.96，∑REE=124.03×10^-6；后者富CaO和Sr，贫SiO₂、Al₂O₃、Rb、Cs、Ba、U和Th，具明显的负铈异常和不太明显的负铕异常，(Eu/Eu)CN=0.91，(Ce/Ce^*)CN=0.76，(La/Yb)CN=3.98，∑REE=15.14×10^-6。两类变质沉积岩的地球化学特征表明，它们的原岩形成于早-中元古代大洋岛弧至大陆岛弧的热水沉积环境，变质作用发生在中-晚元古代。

关键词: 前寒武纪, 变质沉积岩, 热水沉积, 岛弧, 四川冕宁