Geochemistry and SHRIMP Zircon U-Pb Data of Neoproterozoic Meta-Magmatic Rocks in the Suizhou-Zaoyang Area, Northern Margin of the Yangtze Craton, Central China
摘要
///In this paper, the authors used zircon SHRIMP U-Pb technique accurately dating the rhyodacitic tuff and meta-trachyandesite of the Suizhou Group, as well as two-pyroxene troctolitic sill swarm, yielding an emplacement ages of (763±7) Ma, (741±7) Ma and (632±6) Ma, respectively. The meta-trachyandesite of the Suizhou Group show no fractionation between LREE and HREE, no negative HFSEs anomalies such as Nb and Ta, similar geochemically to most eclogites in the orogen. The troctolitic sill swarm is characterized by high Al2O3 and MgO contents, low TiO2 and alkaline contents, strong enrichment of LREE over HREE ((La/Yb)N=5.49), particular for strong positive Ba, Sr and Eu anomalies (δEu=1.22), indicating plagioclase crystallization/accumulation. No HFSEs such as Nb, Ta, U, Th, Zr and Hf anomalies for the troctolitic sill swarm show little contamination of crustal material during evolution of the magmas, and that the parent magma could be derived from partial melting of an enriched subcontinental lithospheric mantle.