摘要
本次研究以东昆仑西段开木棋河东地区的花岗闪长岩及其闪长质微粒包体为研究对象,开展年代学和地球化学研究,探究其成因机制和构造背景。岩石学研究发现,花岗闪长岩与微粒包体具有相似的矿物组成,但微粒包体发育石英和长石斑晶,具有明显的岩浆混合印记。LA-ICP-MS锆石U-Pb年代学分析揭示,花岗闪长岩的结晶年龄为240.1±1.5 Ma,属中三叠世早期。暗色微粒包体w(SiO_(2))54.89%-56.08%,平均55.66%,MgO相对较低;寄主花岗闪长岩与暗色包体LaN/YbN分别为6.77-13.41和5.01-7.79,δEu均<1或接近1;二者均富集为大离子亲石元素Rb,K和不相容元素U,Th;寄主花岗闪长岩Nb/Ta均值为10.98,与地壳Nb/Ta平均值相近,Sr均值为334×10^(-6),Yb均值为1.63×10^(-6),表现为低Sr低Yb型,推测寄主花岗闪长岩起源于含角闪石—石榴石—辉石的高压麻粒岩熔融。暗色微粒包体Nb/Ta值为13.87-16.19,均值为14.8,Rb/Sr值为0.22-0.34,具有壳幔混源特征。综合区域地质资料,本次研究认为开木棋河东地区含暗色微粒包体的花岗闪长岩形成于俯冲—碰撞转换阶段,即中三叠世早期阿尼玛卿古特提斯洋俯冲闭合和巴颜喀拉与昆仑陆块发生碰撞的构造转换阶段。
In this paper,the geochronological and geochemical study of granodiorite and its associated diorite microgranular inclusions from the east Kaimuqihe area in the western part of east Kunlun are carried out so as to investigate their genetic mechanism and tectonic background.Petrological observation reveals that the granodiorite and microgranular inclusions have similar mineral compositions,but the microgranular inclusions possess quartz and feldspar phenocrystals and show obvious magmatic mixed imitations.LA-ICP-MS zircon U-Pb dating for the granodiorite yields a crystallization age of 240.1±1.5 Ma(early Middle Triassic).The content of SiO_(2) in the dark microgranular inclusions ranges from 54.89%to 56.08%,with an average of 55.66%,and the rock has relatively low MgO.The La_(N)/Yb_(N) values of host granodiorite and dark inclusion are 6.77-13.41 and 5.01-7.79,respectively,with δEu<1 or close to 1.Both of them are enriched in large ion lithophile elements Rb and K and incompatible elements U and Th.The average Nb/Ta ratio of the host granodiorite is 10.98,which is similar to the average Nb/Ta of the crust.The average Sr and Yb of the host granodiorite are 334×10^(-6) and 1.63×10^(-6),respectively,showing a low Sr and low Yb type.It is inferred that the host granodiorite was originated from high-pressure granulite melting material containing amphibole,garnet and pyroxene.The Nb/Ta of the dark microgranular inclusions ranges from 13.87 to 16.19,with an average value of 14.8,and Rb/Sr ranges from 0.22 to 0.34,showing the characteristics of crust-mantle mixing.Based on the regional geological data,it is considered that the granodiorite containing dark microgranular inclusions in the east Kaimuqihe area was formed during the tectonic transition stage from the subduction and closure of Anemaqing Paleo-tethys Ocean to the collision of Bayankara Block with Kunlun Block.
作者
付彦文
张金明
薛万文
王涛
康继祖
余福承
Fu Yanwen;Zhang Jinming;Xue Wanwen;Wang Tao;Kang Jizu;Yu Fucheng(The Northern Qinghai-Tibet Plateau Geological Processes and Mineral Resources Laboratory of Qinghai Province,Qinghai Institute of Geological Survey,Xining,Qinghai 810012,China)
出处
《矿物岩石》
CAS
CSCD
北大核心
2021年第3期84-94,共11页
Mineralogy and Petrology
基金
青海学者专项(QHS201802)柴达木盆地及周缘战略性矿产成矿作用及找矿突破。
作者简介
付彦文,男,35岁,工程师,资源勘查工程专业,研究方向:地质矿产调查.E-mail:379861016@qq.com;通信作者:张金明,男,39岁,高级工程师,资源勘查工程专业,研究方向:区域地质调查.E-mail:271883992@qq.com。
