苏鲁造山带岩浆岩的锆石U Pb定年及构造意义

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.

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

A combined study of LA-ICPMS zircon U-Pb dating and geochemical analysis is performed on Neoproterozoic igneous rocks from the southern part of Sulu orogenic belt in order to obtain their crystallization time and tectonic control. Zircon U-Pb dating results yield weighted mean crystallization ages of 806.0±14.0Ma for the gneissic granite from Jinping Mountain, 800.8±7.8Ma for metavolcanic rocks of the Yuntai Formation, Haizhou Group in the Lianyungang area, together with 751.6±7.1Ma and 767.0±15.0Ma for metavolcanic rocks of the Xileng Formation, Zhangbaling Group from the Zhangbaling belt. These igneous rocks are characterized with high K calc-alkaline series, medium negative 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 for them show same characteristics as those for Zhejiang-Fujian type granite. All of them are correlated with the tectonic setting of regional extension and partial melting from the lower crust. This tectomagmatic event, which succeeded the Jining orogenic collision, lasted from 820Ma to 740Ma, registers the tectonic process of the Rodinia break-up and lithospheric thinning.