西湖凹陷平湖组时代新认识:来自火山岩SHRIMP锆石U-Pb年龄的证据  

The New Geochronology Results of the Pinghu Formation in Xihu Depression:Evidence from the SHRIMP Zircon U-Pb Ages of the Volcanic Rocks

作　　者：袁伟[1,2] 徐旭辉[2] 周小进[2] 

机构地区：[1]同济大学海洋与地球科学学院,上海200092 [2]中国石化石油勘探开发研究院无锡石油地质研究所,无锡214126

出　　处：《高校地质学报》2014年第3期407-414,共8页Geological Journal of China Universities

摘　　要：文中对西湖凹陷西部武云亭构造带一口钻井中的平湖组底部火山凝灰岩开展SHRIMP锆石U-Pb同位素定年和原位Hf同位素研究。锆石U-Pb年龄结果显示，年龄分布在32～2636Ma，3颗最年轻锆石年龄加权平均值为32．6±1．3Ma（MSWD=0．29，n=3），该年龄代表了平湖组时代的下限。42～44Ma时太平洋板块运动方向由NNW转变为NWW，表明平湖组沉积时期受到近E-W向挤压应力，具有拗陷沉积的区域应力场特征。此外，该火山岩中的继承锆石原位Hf同位素特征与华夏地块同时代锆石具有相似特征，说明它们具有相似的起源。SHRIMP U-Pb ages and in situ Hf isotope compositions have been measured to constrain the timing of the volcanic tuff at the bottom of the Pinghu Formation from a core drilled at the Wuyunting structure belt, western of the Xihu depression. Zircons U-Pb ages showed the age dispersed in 32-2636 Ma. Three youngest zircon ages yield a mean weighted age of （32.6±1.3） Ma （MSWD=0.29, n= 3）, which constrains the oldest age of the Pinghu Formation. The motion direetion of the Pacific plate changed from NNW to NWW during 42～44 Ma, and then the Pinghu Formation became under compressive stress control in E-W direction, with the regional stress field characteristic of the depression deposition. Furthermore, the δHt（t） values of the inherited zircons are much similar to those of the coeval zircons from the Cathsysia Block, suggesting that they might be originated from a common source.

关 键 词：西湖凹陷 平湖组 SHRIMP U—Pb年龄 HF同位素 

分 类 号：P597[天文地球—地球化学]