内蒙古翁牛特旗一带晚志留世-早泥盆世花岗闪长岩的发现及意义

Discovery and Significance of Late Silurian-Early Devonian Granodiorite in the Ongniud Banner Area,Inner Mongolia

早古生代,华北克拉通北缘发育了白乃庙岛弧岩带。前人资料显示白乃庙岛弧岩带由西(白乃庙镇)向东(四平市)经过翁牛特旗浅覆盖区,但没有确凿证据。本次工作结合地表调查及钻探调查,将工作区内(朝阳沟附近)“二叠纪花岗岩”解体出一套花岗闪长岩,采集两套样品经测试得出两组数据:SHRIMP年龄为427.0±5.6 Ma,激光烧蚀年龄为409±2.9 Ma,由此确定花岗闪长岩时代为晚志留世-早泥盆世,该岩体兼具有火山弧花岗岩的地球化学特征。本文新发现的晚志留世-早泥盆世花岗闪长岩,为研究早古生代白乃庙岛弧带地质演化提供了重要证据。

In the Early Paleozoic,the Bainaimiao island arc belt developed in the northern margin of the North China Craton.Previous work shows that this belt extends from west(Bainaimiao town)to east(Siping city),passing through the Ongniud Banner area with shallow cover,but no convincing evidence is given.Combining field investigations and drilling,this work disintegrated a suite of granodiorite from the Permian granite in the working area(near Chaoyanggou).Dating on two samples from this place yielded SHRIMP age 427±5.6Ma and laser ablation age 409±2.9Ma,and determined that this granodiorite is of Late Silurian-Early Devonian.According to its characteristics of the volcanic arc granite,the Nb and Ta differentiation in the MORB standardized cobweb is not obvious,and the Sm element in the chondrite standardized cobweb is characterized by slight loss of Sm elements.This newly found rock provides evidence for further studying the geologic evolution of the Early Paleozoic Bainaimiao island arc belt.