摘要
内蒙古狼山山脉西侧分布有零星的早古生代岩浆岩,晚志留世二长花岗岩体主要出露于潮格温都尔镇一带,侵位地层为宝音图岩群。该岩体岩性为二云母二长花岗岩,其LA-ICP-MS锆石U-Pb年龄显示,^(206)Pb/^(238)U加权平均年龄为419.6±4.5～416.0±2.0Ma。岩石为块状构造,暗色矿物为黑云母,可见原生白云母,高硅(SiO_2=73.14%～75.76%)、富碱(Na_2O+K_2O=5.85%～8.20%)、强过铝质,未见闪长质包体,显示了S型花岗岩的特点。岩石富集大离子亲石元素Sr、K、Pb,不同程度亏损高场强元素Nb、Ta、P、Ti,轻稀土略富集,重稀土平坦,Eu异常不明显;锆石负的ε_(Hf)(t)值(-8.3～-4.0)及t_(DM2)为1658～1930Ma(平均值为1759Ma),显示了古—中元古代古老地壳熔融的特点。R2-R1判别图显示了岩石具有同碰撞花岗岩的特点,因此,该岩体可能形成于同造山拼贴的构造背景,与南侧善岱庙地区晚志留世花岗岩的构造属性一致。对比白乃庙地区的晚志留世石英闪长岩,两者岩石地球化学特征具有相似性,可能反映了相同的构造背景。
Early Paleozoic magmatic rocks are sporadically distributed in the western section of Langshan Mountains of Inner Mongolia, while Late Silurian two-mica monzonitic granite pluton intruding the Baoyintu Group is mainly exposed in the Chaogewenduer region. LA-ICP-MS zircon U-Pb age shows that the 206Pb/238U weighted average age of two-mica monzonitic granite is 419.6±4.5~416.0±2.0 Ma. The monzonitic granite with dark biotite and visible muscovite shows massive structure and is characterized by high Si(SiO2=73.14%~75.76%), rich alkali(Na2O+K2O=5.85%~8.20%), strong peraluminous, and no diorite enclaves, indicating the features of S-type granite. The geochemical characteristics of the pluton shows that enrichment in Sr, K, Pb, depletion in Nb, Ta, P, Ti, slightly enrichment in LREE, without obvious Eu anomalies. Negative εHf(t) values(-8.3^-4.0) and old tDM2 values(1658~1930 Ma) of zircon imply characteristic of melting of Paleoproterozic-Mesoproterozic crust. R2-R1 diagram shows that the rocks are characterized by syn-collision granites, suggesting that the rocks likely formed in the tectonic setting of syn-collision amalgamation and are consistent with the structure nature of Late Silurian granite in the Shandaimiao area. Compared with the Late Silurian quartz diorite in the Bainaimiao area, both rocks have similar geochemical characteristics, reflecting the same tectonic setting.
作者
田健
张永
滕学建
刘洋
滕飞
郭硕
何鹏
王文龙
TIAN Jian;ZHANG Yong;TENG Xuejian;LIU Yang;TENG Fei;GUO Shuo;HE Peng;WANG Wenglong(Tianjin Center of China Geological Survey ,Tianjin, 300170)
出处
《地质学报》
EI
CAS
CSCD
北大核心
2019年第3期661-673,共13页
Acta Geologica Sinica
基金
中国地质调查局公益性基础地质调查项目(编号DD20160039)资助成果
