西昆仑苦子干新生代透辉石正长岩和透辉石花岗岩地球化学特征及年代学研究  

Geochemical characteristics and geochronology of the Cenozoic diopside syenite and diopside granite from Kuzigan,Western Kunlun area

作　　者：袁亚娟 陈玮岩 夏斌[3] 张玉泉[4] 肖敬国 周厚云[1] YUAN Yajuan;CHEN Weiyan;XIA Bin;ZHANG Yuquan;XIAO Jinguo;ZHOU Houyun(School of Geography,South China Normal University,Guangzhou,510631;Research Institute of Petroleum Exploration and Development,PetroChina,Beijing,100083;School of Marine Sciences,Sun Yat-sen University,Guangzhou,510275;Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou,510640)

机构地区：[1]华南师范大学地理科学学院,广州510631 [2]中国石油勘探开发研究院,北京100083 [3]中山大学海洋学院,广州510275 [4]中国科学院广州地球化学研究所,广州510640

出　　处：《地质学报》2020年第10期2978-2993,共16页Acta Geologica Sinica

基　　金：国家自然科学基金项目(41776056);广东省自然科学基金项目(2017A030310395);中国博士后科学基金(2020M672671)资助的成果。

摘　　要：苦子干钾质碱性杂岩体主要由正长岩类和花岗岩类组成,其中透辉石正长岩主要造岩矿物为钾长石和透辉石,透辉石花岗岩主要造岩矿物为钾长石、斜长石、石英和透辉石。杂岩体中赋存的透辉石和钙铁辉石,均属于钙质辉石。两种岩石均属于钾质碱性岩,具有富碱、高钾、富钙的特征;富集Rb、Ba、Th、U等大离子亲石元素和Pb,贫Nb、Ta、Zr、Hf、Ti等高场强元素;稀土元素含量高(ΣREE=372.37×10^-6~1218.07×10^-6),富集轻稀土(LREE/HREE=21~37),具有轻微的铕负异常(Eu/Eu*=0.66~0.84)。锆石U-Pb定年显示,透辉石正长岩成岩年龄为11.7±0.1 Ma,透辉石花岗岩成岩年龄为11.0±0.3 Ma,均属于喜马拉雅期,相当于中新世末。两类岩石锆石εHf(t)范围在-9.4^-5.5之间,介于球粒陨石与下地壳之间。研究表明,印度大陆与欧亚大陆碰撞,导致西昆仑-喀喇昆仑地区岩石圈大幅度缩短并加厚,引发加厚岩石圈拆沉引起软流圈物质上涌底侵,使得加厚下地壳物质的重熔,伴随地壳的拉张和抬升,最终形成苦子干钾质碱性杂岩体。Kuzigan potassic alkaline complex mass is composed of alkali syenite and granite.Syenite is mainly composed of potassium feldspar and diopside,while granite is composed of potassium feldspar,plagioclase,quartz and diopside.The pyroxenes in the rocks are identified as calcium pyroxene,including diopside and hedenbergite.Petrogeochemical analysis shows that these rocks belong to potassic alkaline series with high alkali,potassium and calcium.Moreover,the rocks are enriched in the large-ion lithophile elements(LILE,Rb,Ba,Th,U and Sr)and Pb,but depleted in high field strength elements(HFSE,Nb,Ta,Zr,Hf and Ti).Rare earth element(REE)content ranges from 372.37×10^-6 to 1218.07×10^-6.The ratio of LREE/HREE is relatively high(21~37),and weak Eu negative anomalies(Eu/Eu*=0.66~0.84).Systematic LA-ICP-MS and SHRIMP U-Pb zircon dating results indicate ages of diopside syenite and diopside granite are 11.7±0.1 Ma and 11.0±0.3 Ma,respectively,which belong to the Himalayan period,equivalent to the end of the Miocene.TheεHf(t)values of the zircons from the two types of rock range from-9.4 to-5.5,which plot between those of chondrite and the lower crust.The results show that the collision between the Indian continent and the Eurasian continent caused the lithosphere in the West Kunlun and Karakoram area to be shortened and greatly thickened,leading to the delamination of the thickened lithosphere and the upwelling of the asthenosphere material and the re-melting of the thickened lower crust material.With the extension and uplift of the crust,Kuzigan potassic alkaline complex mass was formed.

关 键 词：地球化学 锆石U-Pb年龄 锆石HF同位素 钾质碱性杂岩体 苦子干 

分 类 号：P534.6[天文地球—古生物学与地层学] P588.12[天文地球—地质学]