摘要
川西北塔公地区位于青藏高原东部,属于松潘—甘孜造山带的东南部边缘。塔公石英闪长岩侵位于晚三叠世地层中,岩体的K-Ar同位素年龄为134~136Ma,形成于早白垩世。岩石SiO2质量分数为61.37%~62.25%,铝饱和指数为0.93~0.95,全碱质量分数为5.46%~5.77%,里特曼指数为1.62~1.74,样品属于亚碱性准铝质高钾钙碱系列石英闪长岩。岩石Mg#值较高,总体具有高Sr含量、低Nd含量的同位素地球化学特征。N(87Sr)/N(86Sr)值为0.712 589~0.713 009,初始N(87Sr)/N(86Sr)值为0.709 503~0.709 878,N(143 Nd)/N(144 Nd)值为0.512 135~0.512 196,εNd(t)值均为负(-8.6^-7.5),Nd模式年龄为1.33~1.41Ga,Hf模式年龄为1.13~1.37Ga。该岩体是早白垩世期间,川西北地区陆缘-陆内造山环境下由松潘—甘孜造山带古老的下地壳镁铁质物质局部熔融形成的晚碰撞-碰撞后非分异Ⅰ型花岗岩类。
Tagong area of Northwest Sichuan is located in the east of Qinghai-Tibet Plateau,and belongs to the southeast margin of Songpan-Ganzi orogenic belt.The quartz diorites in Tagong area form in Early Cretaceous with K-Ar isotopic ages of 134-136 Ma,and emplace into Late Triassic strata.Mass fractions of SiO2 are 61.37%-62.25%,A/CNK values are 0.93-0.95,mass fractions of total alkali are 5.46%-5.77%,Rittmann indexes are 1.62-1.74,so that the samples belong to subalkaline metaperaluminous high-K calc-alkaline series quartz diorites.The rocks have relative high Mg# values with the isotopic geochemical characteristics of high contents of Sr and low contents of Nd.N （87 Sr）/N （86 Sr）is 0.712 589-0.713 009 with the initial N （87 Sr）/N （86 Sr）of 0.709 503-0.709 878,N （1 43 Nd）/N （1 44 Nd）is 0.5 12 135-0.5 12 1 96 with negativeεNd （t）of -8.6--7.5;Nd and Hf model ages are 1.33-1.41 Ga and 1.13-1.37 Ga,respectively. The quartz diorites belong to undifferentiationⅠ-type granitoids with late- to post-collision caused by partial melting of ancient lower crust mafic materials at the continental margin-intercontinental orogenic setting in Northwest Sichuan.
出处
《地球科学与环境学报》
CAS
2015年第3期1-13,共13页
Journal of Earth Sciences and Environment
基金
国家自然科学基金项目(41372067)
国家自然科学基金重大研究计划项目(41190072)
国家自然科学基金创新研究群体项目(41421002)
教育部创新团队发展计划项目(IRT1281)
关键词
石英闪长岩
早白垩世
地球化学
岩石成因
花岗岩
下地壳局部熔融
松潘—甘孜造山带
川西北
quartz diorite
Early Cretaceous
geochemistry
petrogenesis
granite
partial melting of lower crust
Songpan-Ganzi orogenic belt
Northwest Sichuan
