台湾东部未变形花岗岩LA-ICP-MS锆石U-Pb定年及其地质意义

LA-ICP-MS zircon U-Pb dating of the undeformed granite in eastern Taiwan and its geological significance

台湾源头山位于台湾岛东部太鲁阁带的北部,主体为花岗闪长岩-辉长岩"浆混岩"组合,发生了强烈变形变质,其中央分布有未变形的侵入体,具有典型岩浆岩特征,代表了变形变质期后的岩浆事件。通过开展野外地质调查和岩石学、同位素年代学研究,揭示了变形变质作用前后侵入岩在岩石特征及主量、微量元素方面存在明显差别,表明二者是不同构造岩浆事件的产物。未变形的侵入岩为石英闪长岩,具有高Pb、Rb、U、Th、Zr轻度富集特征,属典型的Ⅰ型花岗岩,其LA-ICPMS锆石U-Pb年龄为82±1Ma,属晚白垩世坎潘期。这是台湾东部地区变形变质事件结束的标志,其后台湾东部进入了一个非挤压的新构造作用阶段。

Yuantoushan is located in the north of Tailuko belt, eastern Taiwan. It is mainly composed of strongly deformed and metamorphosed granodiorite-gabbro ' slurry mixed rock' combination. Deformed intrusions are in the center and show typical magmatic features, representing magmatic events after deformation and metamorphism. The authors carried out field geological survey and petrologic as well as isotopic geochronologic studies of metamorphic intrusive rocks and intrusive rocks. It is shown that there are significant differences in rock characteristics and main trace elements between the two kinds of rocks, indicating that the two kinds of rocks are products of different tectonic magmatic events. Undeformed intrusive rock is quartz diorite, with high Pb, Rb, U, Th, Zr,exhibiting mild enrichment characteristics of Ⅰ type granite, and its LA-ICP-MS zircon U-Pb isotopic age is 82 ± 1 Ma, suggesting the Late Cretaceous Campanian period. This indicates that the deformation and metamorphism event in eastern Taiwan were ended,and the evolution then entered a non-squeezing neotectonic stage.