摘要
南祁连阳康地区分布着一套变形较强的区域低温动力变质岩系,前人将其划归为巴龙贡噶尔组。通过对该套地层进行岩石地球化学、锆石LA-ICP-MS U-Pb年代学研究,发现其与巴龙贡噶尔组的原始含义不同,对该地层中不同的岩石组合重新进行了划定,其主要由两部分组成:其中的变质砂岩、变质粉砂岩和板岩等变质变形较弱,与巴龙贡噶尔组的原始含义相吻合,时代为志留纪;而其中的片岩类岩石,变质变形较强,恢复原岩为火山岩和火山碎屑岩,SiO2含量为57.1%~68.74%,Al2O313.04~14.98%,Al2O3>(K2O+Na2O+CaO)(分子数)>1,里特曼指数(σ)在1.4~4.42之间,大多在2±,主要为钙碱性系列。稀土总量∑REE=186.17×10^-6~203.79×10^-6,稀土元素球粒陨石标准化模式曲线为向右倾斜的轻稀土富集型,铕略亏损,具负异常,亲石元素Ba和Sr富集,而Rb强烈亏损,Ba相对Rb和Th、Ti相对于Sm和Y呈明显负异常,反映出具有典型中基性-中酸性火山岩微量元素特征。在火山岩中获取锆石U-Pb测年结果表明其岩浆形成的时代为新元古代(819±2 Ma)(阳康片岩),为一套基性火山岩及火山碎屑岩建造,具有大陆裂谷盆地的特点,该片岩的发现填补了该区域未有新元古代历史记录的空白,反映了该地区与全球元古代Rodinia超大陆聚合事件的一致性。
A set of highly deformed regional low-temperature dynamic metamorphic rocks occurs in Yangkang area of South Qilian,which was classified as the Balonggonggaer Formation by predecessors.Through petrogeochemistry and zircon LA-ICP-MS U-Pb chronology of the strata,it is found that the characteristics of this set of rocks is different from the original definition of Balonggonggaer Formation.The rock assemblages in this set of rocks are thus re-delineated,which are mainly composed of two parts.The metamorphic sandstone,metamorphic siltstone and slate show weak metamorphic deformation,which coincides with the original definition of the Balonggonggaer Formation.The age is Silurian.However,the schists have strong metamorphic deformation,and the restored original rocks are volcanic rocks and volcanic clastic rocks.The content of SiO2ranges from 57.1%to 68.74%,Al2O3ranges from 13.04%to 14.98%,Al2O3>(K2O+Na2O+CaO)(number of molecules)greater than 1,and the Ritman index(σ)ranges from 1.4 to 4.42,with most around 2.The rocks mainly belong to calc-alkaline series.The total REE is 186.17×10^-6~203.79×10^-6.The standard model curve of REE chondrite shows a right-leaning LREE enrichment with slight Eu deficiency and negative anomaly.The lithophile elements Ba and Sr are enriched,while Rb is strongly depleted.Ba is obviously negative relative to Rb and Th,Ti is obviously negative relative to Sm and Y.It indicates the trace element characteristics of typical intermediate-basic to intermediate-acid volcanic rocks.Zircon U-Pb dating from volcanic rocks shows that the magma was formed in the Neoproterozoic(819±2 Ma)(Yangkang schist),which is a set of basic volcanic rock and pyroclastic rock formation with the characteristics of continental rift basin.The schist identified in this study is the first record of Neoproterozoic in this region,which indicates the consistency with global Proterozoic Rodinia supercontinent convergence event.
作者
潘建
李贵义
李广铁
PAN Jian;LI Gui-yi;LI Guang-tie(Regional Geological and Mineral Resources Survey of Jilin Province,Changchun 130022,China)
出处
《世界地质》
CAS
2019年第4期900-909,共10页
World Geology
基金
青海省地质勘查基金项目(青国土资矿[2011] 277号)
