阿尔金北缘新太古代TTG片麻岩的成因及其构造意义  

Petrogenesis and tectonic implications of the Neoarchean TTG gneiss in the North Altyn Tagh area,southeastern Tarim Craton

作　　者：叶现韬[1] 张传林 YE XianTao;ZHANG ChuanLin(College of Oceanography,Hohai University,Nanjing 210098,China)

机构地区：[1]河海大学海洋学院,南京210098

出　　处：《岩石学报》2020年第11期3397-3413,共17页Acta Petrologica Sinica

基　　金：江苏省自然科学基金项目(BK20170873);中央高校基本科研业务费项目(B200202137);国家自然科学基金项目(41702197)联合资助。

摘　　要：塔里木克拉通前寒武纪构造演化,特别是早前寒武纪构造演化一直是地质学家讨论的焦点。本文通过对阿尔金北缘新太古代TTG片麻岩进行详细的野外调查、岩相学观察、地球化学分析以及锆石SHRIMP U-Pb定年来揭示该岩石的成因以及探讨塔里木克拉通早前寒武纪构造演化。锆石SHRIMP U-Pb定年结果显示阿尔金北缘TTG片麻岩的形成年龄为2740±19Ma,而后经历了新太古代(2494±53Ma)混合岩化作用和古元古代(1962±78Ma)麻粒岩相变质作用。阿尔金北缘英云闪长质片麻岩显示低的MgO含量(1.33%~3.08%)和Mg#(37~52),具有高Sr(469×10-6~764×10-6)含量、低Y(4.72×10-6~13.5×10-6)和Yb(0.37×10-6~0.99×10-6)含量的特点,它们的Sr/Y比值可达到41~99。岩石的这些特征与基性下地壳部分熔融形成的TTG相同。并且,该新太古代TTG片麻岩还具有正的εNd(t)值(0.2~3.6)、高的Nd同位素初始值(0.509088~0.509260)和古太古代两阶段模式年龄(3.62~3.70Ga)。因此,阿尔金北缘新太古代TTG片麻岩可能来源于基性下地壳部分熔融,并且岩浆源区有石榴石、角闪石和金红石的残留。综合前人的研究成果,对比相邻区域TTG的形成时代,变质事件的记录以及太古宙地壳增生差异都指示阿尔金北缘和敦煌-库鲁塔格地区可能来源于不同的大陆块体。The Precambrian evolution of the Tarim Craton in NW China,in particular during the Early Precambrian stage,remains enigmatic. In this contribution,we report field observation,petrography,geochemistry and zircon SHRIMP U-Pb ages of Neoarchean TTG gneiss of the North Altyn Tagh area in the southeastern margin of the Tarim Craton. Zircon SHRIMP U-Pb dating reveals that the TTG gneiss was formed at 2740 ± 19 Ma,and was later altered by Late Neoarchean( 2494 ± 53 Ma) migmatization and Paleoproterozoic( 1962 ± 78 Ma) granulite-facies metamorphism. Geochemically,the Neoarchean tonalitic orthogneisses exhibit low MgO( 1. 33% ~3. 08%) contents and Mg#values( 37 ~ 52) and characterized by high Sr( 469 × 10-6~ 764 × 10-6) contents,low Y( 4. 72 × 10-6~ 13. 5 × 10-6) and Yb( 0. 37 × 10-6~ 0. 99 × 10-6) contents,leading to high Sr/Y ratios( 41 ~ 99),displaying typical TTG rocks derived from the lower mafic continental crust. In addition,the TTG gneisses show positive εNd( t) values( 0. 2 ~ 3. 6) with Paleoarchean two-stage model ages( tDM2= 3. 62 ~ 3. 70 Ga),suggesting that the crustal materials of the basement rocks in the North Altyn Tagh area were initially extracted from a depleted mantle in the Paleoarchean and reworked in the Neoarchean. Therefore,the Neoarchean TTG gneisses were most possibly derived from partial melting of a mafic lower continental crust with residue of garnet,amphibolite and rutile. The diachronous formation ages of the TTGs from the North Altyn Tagh,Dunhuang and Kuruketage areas and the distinct features in continental growth process suggest that the Precambrian basement of the Tarim Craton is composed by independent continental terranes.

关 键 词：TTG片麻岩 锆石SHRIMP U-Pb定年 岩石成因 阿尔金北缘 塔里木克拉通 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]