西秦岭南缘勉略带琵琶寺基性火山岩LA-ICP-MS锆石U-Pb年龄及其构造意义

LA-ICP-MS Zircon U-Pb Dating of the Pipasi Basic Volcanic Rocks Within the Mian-Lue Tectonic Zone in the Southern Margin of West Qinlin and its Geological Implication

利用阴极发光和LA-ICP-MS微区定年分析方法,对西秦岭南缘勉略构造带琵琶寺基性火山岩进行了单颗粒锆石U-Pb同位素分析。研究确定,所测定锆石为岩浆锆石。琵琶寺基性火山岩的LA-ICP-MS锆石U-Pb同位素定年结果表明,其同位素年龄为783～754Ma,形成时代为新元古代中晚期南华纪。结合前人资料,认为勉略构造带不仅在晚古生代发育有限洋盆,且在新元古代时期还有更古老的洋盆存在。这一新资料,对进一步研究勉略构造带西段新元古代大地构造格局及演化以及探讨扬子地块北缘Rodinia超大陆裂解等大陆动力学问题具有重要意义。

The LA-ICP-MS dating technique was applied to analyze the single grain zircon of basic volcanic rocks which is from the Pipasi area of the southern margin of Western Oinlin. This research indicates that the zircons measured are magmatic ones. The LA-ICP-MS zircon dating result of the rocks show an isotopic age of 783-754Ma, which represents the Neoproterozoic. Combining previous research, we believe that not only a limited ocean basin developed in late Paleozoic, hut also a more ancient ocean basin existed in Neoproterozoic. Therefore, this study has great significance both in further studying the Mian-Lue tectonic zone structure and tectonic evolution as well as addressing continental dynamic issues such as the breakup of Rodinia supercontinent and other continents in the Yangtze block north margin.