五台山地区前寒武纪变质岩石的稀土元素地球化学

REE GEOCHEMISTRY OF PRECAMBRIAN METAMORPHIC ROCKS IN WUTAISHAN REGION

五台群和滹沱群变沉积-火山岩系,可能发育于岛弧带-不稳定大陆的成岩环境中,是经受区域变质作用的中-低级变质岩石。五台群的石咀亚群和台怀亚群具有太古宙稀土地球化学的基本特征,而滹沱群(包括五台群高丸亚群)则具有后太古宙的稀土元素地球化学特征。

Metasedimentary-volcanic series of the Wutai and Hutuo groups experienced regional metamorphism and thus turned into middle-low-grade metamorphic rocks. REE abundances and REE distribution patterns in the Shizui and Taihuai Subgroup metasedimentary-volcanic rocks are typical of the Archean, whereas the Gaofan Subgroup and the Hutuo Group show post-Archean characteristics. Five types of REE distribution pattern are distinguished: (1) rightly declined smooth curves with little REE anomaly (Eu/Eu* = 0.73-0.95) and heavy REE depletion (e.g. late Archean metasedimentary rocks); (2) rightly declined V-shaped cur-ves with sharp Eu anomaly (Eu/Eu* = 0.48-0.76) and slightly higher ∑REE (e.g. post-Ar-chean metasedimentary rocks); (3) rightly declined steep curves with negative Eu anomaly (Eu/Eu* = 0.73-0.76) and the lowest ∑REE (e.g. post-Archean dolomites); (4) rightly dec-lined, nearly smooth curves with both positive Eu anomaly and unremarkable positive Eu an-omaly (Eu/Eu* = 0.95-1.25) (e.g. metabasic volcanic rocks); and (5) rightly declined curves with Eu anomaly (Eu/Eu* = 1.09-1.19) and heavy REE depletion (e.g. metaacid volcanic rocks). Strata of the two groups are considered to have been formed in an island-arc belt-an unstable continental petrogenetic environment.