川西须家河组火山岩夹层时代及其地质意义

四川盆地西部的上三叠统须家河组作为反演前陆盆地构造演化的物质基础，因缺少精确的同位素地层年龄阻碍了对盆山演化的进一步理解。作者在四川盆地西部须家河组中发现了一套火山（碎屑）岩夹层，通过 LA-ICP-MS U-Pb 同位素定量分析，获得1件凝灰岩样品中岩浆锆石的结晶年龄，其加权平均值为（214．7±1．6）Ma，属于晚三叠世诺利期。该年龄结果对四川盆地西部须家河组岩石地层单元的划分与对比可提供重要参考，同时为进一步约束龙门山隆升与川西前陆盆地的演化、古特提斯洋关闭等重大事件时限提供了新证据。基于四川盆地及周缘的区域火山活动对比结果，表明诺利期中期（210～222 Ma B．P．）是中国西部地区一次强烈的区域火山喷发阶段，其范围从羌塘地体延伸到东昆仑地体，所对应的构造事件并非传统的印支运动作用。

Chronology of the pyroclastic layer from Xujiahe Formaton in the western Sichuan Basin and its geological significance

Dating by LA-ICP-MS is carried out on the newly found interbed of pyroclastic rocks in the Upper Triassic Xujiahe Formation in the western Sichuan Basin.The U-Pb isotope measurement yields (214.7±1.6 )Ma age,indicating that the pyroclastic rock belongs to Norian age of the late Triassic.This age represents the volcanic eruptions during the Xujiahe Formation accumulation and indicates that the deposition might have stopped before the Rhaetian.The dated age of pyroclastic rocks not only provide important evidence for stratigraphic classification and correlation of the Xujiahe Formation in the western Sichuan Basin,but also provide evidence and age constraints for the evolution of the western Sichuan foreland basin and the closure of the paleo-Tethys ocean.The correlation of volcanic activity between the Sichuan Basin and its periphery indicates that there was one intense volcanic eruption in the western China in the Norian age (210 ~ 220 Ma)from the Qiangtang terrane to east Kunlun terrane.