青海三江北段治多地区印支期花岗岩的成因及锆石U-Pb定年

Indosinian granitoids in the Zhidoi area in the northern segment of the Sanjiang belt,Qinghai:Their petrogenesis and zircon U-Pb dating

青海三江北段治多地区开展的1∶25万区域地质调查显示该地区大面积出露的侵入岩的形成时代主要为晚三叠世,治多县东北部巴颜喀拉岩区内花岗闪长岩单颗粒锆石U-Pb法年龄为(212.38±7.1)Ma,似斑状二长花岗岩单颗粒锆石U-Pb年龄为(196.8±0.3)Ma:治多西南部分布于金沙江蛇绿构造混杂岩带内石英闪长岩的单颗粒锆石U-Pb年龄为(215.4±0.8)Ma。通过岩体地质特征、岩石学及岩石地球化学特征结合区域构造演化特点可以初步确定这些地区晚印支—早燕山阶段花岗岩形成于后碰撞阶段,岩浆具有多源区特点,形成可能与岩石圈的拆沉作用有关。

The regional geological survey at a scale of 1：250000 in the Zhidoi area in the northern segment of the Sanjiang belt, Qinghai Province, suggests that the extensively exposed intrusive rocks in the area mainly formed in the Late Triassic. According to the single-zircon U-Pb dating, granodiorite and porphyritic monzogranite in the Bayan Har terrane in the northeast of the Zhidoi area have ages of 212.38±7.1 Ma and 196.8±0.3 Ma respectively, and quartz diorite in the Jinshajiang ophiolitic mélange zone in the southwest of the Zhidoi area has an age of 215.4±0.8 Ma. Based on the geology, petrology and geochemistry of the protons, combined with the characteristics of regional tectonic evolution, it may be preliminarily determined that： these late Indosinian-early Yanshanian granitoids formed in a post-collisional stage; the magma has the feature of multiple sources and its formation may be related to lithospheric delamination.