昆仑山世界地质公园哈萨山蛇绿岩地球化学特征及锆石U-Pb年龄  

Age and Geochemical Characteristics of the Hasashan Ophiolite in the Mountain Kunlun UNESCO Global Geopark

作　　者：沈洪江[1] 杨林[1] 覃爽 宋伟 秦永超[1] 宁萌萌 SHEN Hongjiang;YANG Lin;QIN Shuang;SONG Wei;QIN Yongchao;NING Mengmeng(Regional Geological Surveying Party,Sichuan Bereau of Geology and Mineral Resources,Chengdu,610213)

机构地区：[1]四川省地质矿产勘查开发局区域地质调查队,成都610213

出　　处：《地质论评》2018年第4期980-992,共13页Geological Review

基　　金：青海昆仑山国家地质公园管理局委托的研究项目"青海昆仑山世界地质公园野牛沟结合带调查与国际对比研究项目"成果~~

摘　　要：哈萨山蛇绿岩位于东昆中缝合带中部,为昆仑山世界地质公园三大核心地质遗迹之一,蛇绿岩出露较为完整,通过对蛇绿岩中堆晶辉长岩进行LA-ICP-MS锆石U-Pb同位素测年研究,获得年龄值为438.5±2.6 Ma,表明蛇绿岩形成于早志留世。岩石地球化学研究显示,蛇纹岩的原岩为橄榄岩类,蛇纹岩的稀土元素总量较低,呈右倾斜的配分曲线;辉长岩显示轻稀土较重稀土富集,具有不同程度的Eu负异常,配分曲线较为平缓,略呈右倾型;玄武岩具有轻稀土较重稀土富集的特征,具有明显的Eu负异常,相对富集大离子亲石元素,高场强元素呈平坦型,Nb、P轻微亏损,各样品配分曲线大致平行于E-MORB谱线,显示为同源岩浆,主要表现为E-MORB特征,并具有洋中脊向洋岛过渡的特征,其形成的构造环境应属初始小洋盆,可能为原特提斯洋洋壳残迹,形成于洋陆转换早期。Objectives：The Hasashan ophiolite is located in the middle of suture belt in central East Kunlun,which is one of the three core geological relics of the Mt. Kunlun UNESCO Global Geopark, The combination of ophiolite is relatively complete, but the times and tectonic attributes of the ophiolite in this area are still controversial, and lack of dating data, which leads to various understandings of the tectonic setting and evolution history of the region.Methods：On the basis of detailed field geological surveys and microscopic observations,we chose to collect fresh gabbro samples from the ophiolite in Hasashan for zircon U Pb isotopic age analysis. And systematically collected fresh ophiolite components for Petrogeochemical analysis. this paper combines the occurrence of the zircon U Pb age and the main trace elements in the field to investigate the formation age and tectonic setting of the ophiolite. This study provides basic geological data for identifying the Kunlun Suture Zone and studying on the formation and evolution of the East Kunlun Orogenic Belt .Results：The LA-ICP-MS zircon U-Pb dating of the gabbro in cumulate ophiolite shows that the age is 438.5 ± 2.6 Ma, which indicates that the ophiolite was formed in the Early Silurian;Detailed petrogeochemical studies show that the protolith of serpentines is peridotite and the total amount of rare earth elements of serpentine is lower, with a right oblique distribution curve. Gabbro showed that the light rare earth has a higher concentration of heavy rare earth with varying degrees of Eu anomalies. The distribution curve is more gentle with slightly to the right. The light rare earth of basalt is relatively higher than heavy rare earth. And it shows systematic enrichment of LILE, there are obvious Eu negative anomalies, no differences of HFSE and slight depletion of Nb and P. Each sample distribution curve is roughly parallel to the E MORB line, which suggests that the magma is homologous magma. It has features of E MORB and the mid ocean ridge transition

关 键 词：昆仑山世界地质公园 蛇绿岩 锆石U-PB测年 E-MORB 初始小洋盆 

分 类 号：P587[天文地球—岩石学]