海南岛北西部前寒武纪花岗质岩SHRIMP锆石U-Pb年龄及地质意义

SHRIMP U-PB DATING OF ZIRCON FROM THE PRECAMBRIAN GRANITOIDS IN NORTHWEST HAINAN ISLAND AND ITS GEOLOGICAL IMPLICATIONS

对海南岛北西部戈枕地区侵位于古中元古代抱板群花岗质岩进行了CL成像制约下的SHRIMP锆石U—Pb年龄测定，获得了1455±12Ma的U—Pb谐和年龄、1454±12Ma有利的^207Pb／^206Pb中值年龄。结合该花岗质岩锆石内部结构、岩浆源区和变形变质特征，以及前人多种定年成果，认为该花岗质岩结晶年龄应为～1450Ma，随后于～1400Ma经历了一次构造-热变质事件；Rodinia超大陆聚合前，华夏地块（包括海南岛、或至少是海南岛北西部）最可能位于劳伦大陆南缘的西南延伸部分。研究结果还暗示华夏地块（包括海南岛）所经历的格林威尔造山事件可能较扬子地块偏早，古、中元古代抱板群沉积上限应约束在～1450Ma。

The Precambrian granitoid pluton emplaced in the Paleoproterozoic-Mesoproterozoic Baoban Group in Gezhen area, northwest Hainan Island, south China was dated by SHRIMP U-Pb analysis assisted by CL image. Zircon from the pluton yields a concordant SHRIMP U-Pb age of 1455 ± 12Ma with a weighted mean ^207pb/^206pb age of 1454 ± 12Ma, indicating its emplacement at -1450Ma. In connection with the zircon internal structure, the structural deformation/metamorphism and the provenance of the pluton, as well as the previously published age data by different dating methods, we suggest that a tectono-thermal metamorphic event most likely took place at - 1400 Ma, and thus the minimum depositional age for the Baoban Group should be ca. - 1450 Ma. Cathaysian Block （including Hainan Island, at least its northwest part） could be regarded as a southwestward extension of southern Laurentia before the assembly of the Mesoproterozoick-Neoproterozoic Rodinia supercontinent. Our research results also imply that Cathaysian Block （ including Hainan Island） probably underwent an earlier Grenville orogeny event, in comparison with Yangtze Block.