浙西南八都群古元古代和三叠纪变质和岩浆事件的年代学证据

Geochronological Constraints on Paleoproterozoic and Triassic Metamorphism and Magmatism in the Badu Group, Southwest Zhejiang Province

本文对华夏地块浙西南八都群片麻岩和侵入其中的花岗岩进行了系统的岩石学、地球化学、LA-ICP-MS锆石U-Pb年代学以及Lu-Hf同位素研究。结果表明,八都群片麻岩中的碎屑锆石普遍发育~1882 Ma的(变质)增生边,而侵入八都群花岗岩的结晶时代集中在1861~1841 Ma。综合本文及前人获得的岩石学和同位素年代学数据可知,华夏地块在古元古代晚期(1890~1850Ma)发生了一次强烈的造山事件,该期造山很可能与Columbia超大陆的聚合作用密切相关,华夏地块可能为Columbia超大陆的一个陆块。除此之外,本研究还在八都杂岩中获得了三叠纪变质锆石年龄(235±1)Ma,综合前人发表资料可知,这些古元古代基底岩石遭受了强烈的印支期改造,可能与华南大陆印支期造山作用相关。然而,关于古元古代基底的三叠纪变形变质、抬升和出露过程及其与印支期构造演化的内在联系,仍有待进一步研究。

The authors conducted a combined study of gneisses and intrusive granites of the Badu Group in southwestern Zhejiang Province of Cathaysia Block by such means as petrology,geochemistry,LA-ICP-MS zircon U-Pb geochronology and Lu-Hf isotopic analysis.The results show that the detrital zircons in the gneiss of the Badu Group have generally developed(metamorphic)accretion rim of 1882 Ma,while the crystallization ages of the granites that intruded into the Badu Group are concentrated in the range of 1861~1841 Ma.Based on the petrologic and isotopic chronological data obtained by the authors and previous researchers,it can be concluded that a strong orogenic event occurred in the Cathaysia Block in the late Paleoproterozoic(1890~1850 Ma).The orogeny was probably related to the convergence of the Columbia supercontinent.The Cathaysia Block may be one of the Columbia supercontinents.In addition,the authors also obtained a Triassic metamorphic zircon age of(235±1)Ma from the Badu Complex.Combined with data available,the authors infer that the Paleoproterozoic basement rocks underwent intensive reworking,associated with the Indosinian orogeny in South China.However,the process of Triassic deformation,metamorphism and exhumation of the Paleoproterozoic basement rocks and its role in shaping the Indosinian structural framework of South China remain undetermined and require further research.