大兴安岭环二库新元古代变质辉长岩的厘定及其地质意义

环二库地区位于大兴安岭大扬气林场,岩石组合为斜长角闪岩、变质辉长岩、橄榄岩和大理岩,主要以NE向呈似层状、透镜状或碎片状产出。LA-ICP-MS锆石U-Pb测年结果表明,其中变质辉长岩形成于新元古代末期(696.8±2.9 Ma);岩石地球化学分析显示,环儿库变质辉长岩具有类似N-MORB的地球化学特征,且与部分岛弧拉斑玄武岩(IAT)具有成分上的亲缘性,表明变质辉长岩的形成与俯冲作用有关。结合区域上吉峰、嘎仙蛇绿岩可知,环二库岩石组合具有类似于蛇绿混杂岩的特征,其中变质辉长岩可能代表了新元古代末期的洋壳残片,表明大兴安岭北段地区新元古代时期存在古洋盆。

Determination of Neoproterozoic meta-gabbro from Huanerku,Da Hinggan mountains and its geological significance

Huanerku rock association in the Dayangqi forest farm of the Da Hinggan mountains, is composed of amphibolite, meta-gabbro, peridotite and marble, which mainly occurr as NE-trending layers, lens and pieces. LA-ICP-MS zircon U-Pb dating of meta-gabbro samples from the Huanerku rock association yields ages of (696.8±2.9)Ma. Geochemistry analysis shows that the meta-gabbro samples are similar to N-type mid-ocean ridge basalts (N-MORB), and are also with some features of island arc tholeiite (IAT), indicating that the formation of the meta-gabbro was affected by subduction. Integrating the data from the Jifeng and Gaxian ophiolite in adjacent regions, the authors suggest that the Huanerku rock association has an affinity with ophiolitic melange. The meta-gabbro may represent the remnant of Late Neoproterozoic oceanic crust, indicating that there was a palaeo-ocean basin in the northern Da Hinggan mountains.