吉林延边地区新田石英闪长岩U-Pb年代学与岩石地球化学研究

对延边地区新田石英闪长岩进行锆石U-Pb年代学、岩石地球化学分析。获得石英闪长岩LA-ICP-MS锆石U-Pb加权平均年龄为139±2 Ma,属早白垩世。岩石地球化学特征表现为过铝质高钾钙碱性;稀土元素总量较低,轻稀土元素相对富集、轻重稀土分馏较明显,较弱的负Eu异常,大离子亲石元素(Rb、Ba、Sr)与活泼的不相容元素(U、Th)富集,高场强元素(Nb、Ta、P、Zr、Hf、Ti)亏损,微量元素比值总体接近地壳平均值,反映岩浆源区为下地壳。结合地球化学特征与区域构造演化背景,认为新田地区石英闪长岩岩体形成于与太平洋板块俯冲相关的活动大陆边缘环境。早白垩世早期是区内一个较重要的俯冲阶段,中酸性岩浆侵位活动较为发育。

Zircon U-Pb geochronology and petrogeochemistry of Early Cretaceous Xintian Quartz Diorite in Yanbian area，Jilin Province

The study of the zircon U- Pb age and petrogeochemistry of Xintian quartz diorite in Yanbian area is reported in this paper． The weighted average age of zircon LA -ICP - MS U - Pb dating for the quartz diorite is 139 ±2 Ma，indicating that it was generated in the Early Cretaceous． Geochemical characteristics of the diorte indicate of peraluminous high - - K calc- alkaline． The rocks have low ＲEE contents，and are relatively enriched in light rare earth (LＲEE)，with obvious fractionation of LＲEE and HＲEE，and weak negative Eu anomalies． They are en- riched in large ion lithophile elements (Ｒb，Ba，Sr) and incompatible elements (U，Th)，relatively depleted in high field strength elements (Nb，Ta，P，Zr，Hf，Ti)，and the trace element ratios are similar to the average value of the crust，suggesting a parent magma sourced within the lower crust． Based on the geochemical data and the regional geological background，we propose that the Xintian quartz diorite formed in active continental margin environment related to the subduction of the Paleo- Pacific Plates． The Early Cretaceous was an important subduc- tion stage with strong intermediate- acid magmatic emplacement activities．