苏鲁造山带岩浆岩的锆石U-Pb定年及构造意义

Zircon U-Pb Dating and Tectonic Relevance for Igneous Rocks in Sulu Orogen

锆石U-Pb定年和地球化学分析结果显示,苏鲁造山带南缘连云港锦屏山片麻状花岗岩形成于(806.0±14.0)Ma,海州群云台组变质火山岩形成于(800.8±7.8)Ma,张八岭隆起的张八岭群西冷组变质火山岩形成于(751.6±7.1)Ma和(767.0±15.0)Ma.这些岩浆岩总体上具有高钾钙碱性系列、右倾型REE(Rare Earth Elements)模式、Nb、Ta、Sr、P和Ti强烈亏损、中等负铕异常、重稀土弱到中等亏损、低Sr、高Yb等特点,与浙闽型岩浆岩反映的区域伸展环境和下地壳部分熔融是一致的.这次构造岩浆活动820～740Ma,是晋宁期主碰撞造山后Rodinia超大陆裂解和岩石圈减薄演化的记录.

Abstract： A study of LA-ICP-MS zircon U-Pb dating and geochemical analysis is performed on Neoproterozoic igneous rocks from the southern part of Sulu orogenic belt to obtain their crystallization time and tectonic control. Zircon U-Pb dating results yield weighted mean crystallization ages of （806.0 --＋_ 14. 0） Ma for the gneissic granite from Jinping Mountain, （800.8 ~ 7.8）Ma for metavolcanic rocks of the Yuntai Formation, Haizhou Group in the Lianyungang area, together with （751.6±7.1）Ma and （767.0±15.0）Ma for metavolcanic rocks of the Xileng Formation, Zhangbaling Group from the Zhangbaling belt. These igneous rocks are characterized with high K calc-alkaline series, mediumnegative Eu anomaly and medium depletion of the HREE. They are predominately depleted in Nb, Ta, Sr, P and Ti, and the concentrations of high Yb and low Sr show the same characteristics as those for Zhejiang-Fujian type granite. These are correlated with the tectonic setting of extension and partial melting from the lower crust, corresponding to the Rodinia break-up and lithospheric thinning.