青海省刚察地区高镁安山岩锆石U-Pb LA-ICP-MS年代学及构造意义  

LA-ICP-MS ZIRCON U-Pb GEOCHRONOLOGY AND TECTONIC IMPLICATION OF THE HIGH-Mg ANDESITES IN GANGCA AREA,QINGHAI PROVINCE

作　　者：王钦元[1] 李焕学[1] 王国良[1] 许海全[1] 李善平[1] 张金明[1] WANG Qin-yuan;LI Huan-xue;WANG Guo-liang;XU Hai-quan;LI Shan-ping;ZHANG Jin-ming(Key Laboratory for Geological Process and Mineral Resources in Northern Qinghai-Tibet Plateau/Qinghai Institute of Geologicol Survey,Xining 810012,China)

机构地区：[1]青海省青藏高原北部地质过程与矿产资源重点实验室/青海省地质调查院,青海西宁810012

出　　处：《地质与资源》2018年第4期349-359,共11页Geology and Resources

基　　金：中国地质调查局项目“青海1∶5万电泵站等4幅区调”(编号1212011121195)

摘　　要：基于青海省刚察地区1∶5万电泵站等4幅区调项目,在拉脊山蛇绿构造混杂岩带药水泉组中识别一套玄武岩、玄武安山岩、安山岩类岩石组合,其岩相学、岩石地球化学特征与高镁安山岩相类似.岩石斑晶以斜长石和辉石为主,不含橄榄石,基质也含有大量的斜长石.岩石地球化学特征表现为K_2O+Na_2O含量2.55%~5.15%,Na_2O>K_2O,K_2O含量0.22%~0.82%,为低钾;CaO含量5.31%~11.41%,TiO_2含量0.27%~0.55%,变化范围较小;MgO含量为5.78%~11.06%,变化范围不大.总体具有低硅、钛、钾,高钙、镁,富钠之特征.稀土配分曲线为右倾斜状,多呈铕正异常,为轻稀土富集型.微量元素Rb、Ba、Th、Cr、Ni等变化幅度大,反映岩浆生成和演化过程复杂,但演变仍以部分熔融为主.选取玄武岩样品,通过LA-ICP-MS U-Pb锆石微区定年,获得了451.7±1.8 Ma年龄值,其时代为晚奥陶世.总体特征表明,刚察地区火山岩为埃达克型高镁安山岩,其构造环境为活动大陆边缘的岛弧.Based on the 1：50 000 regional geological survey in Gangca area of Qinghai Province, a lithologic assemblage of basalt, basaltic andesite and andesite is recognized in the Yaoshuiquan Formation of Lajishan ophiolitic melange zone, which is petrographically and geochemically similar to the high-Mg andesite. The phenocrysts of the rocks are mainly composed of plagioclases and pyroxenes without olivine, while the matrix also contains lots of plagioclases. The lithogeochemistry is generally characterized by low K, Si and Ti, high Ca and Mg, and rich Na. The REE distribution curves are right-dipping with mostly positive Eu anomaly and enrichment of LREEs. Trace elements such as Rb, Ba, Th, Cr and Ni vary significantly, reflecting the complex formation and evolution process of magma but still dominated by partial mehing. The 451.7±1.8 Ma weighted average age of basalt samples is obtained through LA- ICP-MS zircon dating, indicating it was formed in Late Ordovician. From the above, the volcanic rocks in Gangca area belong to adakitic high-Mg andesite with the tectonic setting of island arc on active continental margin.

关 键 词：地球化学 LA—ICP—MS锆石年代学 埃达克高镁安山岩 岛弧火山岩 青海省 

分 类 号：P597[天文地球—地球化学]