塔里木盆地北缘新太古代辛格尔灰色片麻岩形成时代问题

On the Age of the Neo-Archean Qingir Gray Gneisses from the Northern Tarim Basin,Xinjiang, China

获得塔里木盆地北缘辛格尔灰色片麻岩的可靠形成年龄对研究塔里木克拉通地壳构造演化是十分重要的。本研究应用SIMS锆石U-Pb定年，获得了塔里木北缘辛格尔南托格拉克布拉克杂岩中占主要成分的灰色片麻岩的形成年龄为2565±18（2d）Ma，这一研究结果说明丁辛格尔地区的灰色片麻岩和库鲁克塔格中部的蓝石英花岗岩等均为新太古代晚期形成的TTG组份的岩浆岩。综合已有的研究结果，如灰色片麻岩中以残留包体形式存在的斜长角闪岩的Sm．Nd等时线年龄=3263±126Ma（2σ），εNd（t）=＋3．2±0．7（Huet al，1992），以及塔里木北缘范围内各种片麻岩、片岩和各种花岗岩的Nd模式年龄（TDM）分布在3200～2600Ma范围内（冯新昌等，1998；董富荣等，1999；Hu et al．，2000），完全可以确认塔里木盆地北缘普遍存在中一新太占代基底。但是，它们遭受了古元古代构造、变质和岩浆活动的强烈改造。辛格尔灰色片麻岩中～2300Ma、～2000Ma和片麻状花岗岩的～2000Ma锆石U-Pb年龄（高振家等，1993；郭召杰等，2003），以及铁门关斜长角闪岩中的锆石U-Pb年龄～1800Ma（郭召杰等，2003）等，就是两次重要构造热事件的记录。K-Ar年龄同样揭示塔里木盆地北缘新元古代至早古生代时期的地质热事件，^40At／^39Ar坪年龄或激光微区^40Ar/^39Ar等时线年龄等对该区变质岩中角闪石、黑云母及白云母的研究结果表明，塔里木北缘在大约850～500Ma期间，表现为各地段不均一整体性构造隆升（胡霭琴等，出版中）。

Precise age determination of the Qingir gray gneisses from the northern margin of the Tarim Basin is important for our understanding of crustal evolution of the Tarim Craton. The： present SIMS zircon U-Pb dating yielded an age of 2565 ± 18（2σ） Ma for the Qingir gray gneiss, which is the dominant constituent of the Tuokelakebulake complex in this region. The new result is comparable with zircon U-Pb age of blue-quartz-bearing granite from the central section of region of Kuluketage. It indicates that they are all Neo-Archean magmatites with TTG component. Together with the literature data, including a Sm-Nd isochron age of 3263 ± 126 Ma （20）, with εNd（t） = ＋ 3.2± 0.7, for amphibolite enclaves in the gray gneisses from the Qingir （Hu and Rogers, 1992）, and several Nd model ages （TDM） Of 3200 to 2600 Ma for gneisses, granites, and schists from the area （Hu et al., 2000;Dong et al., 1999; Feng et al., 1998）, it strongly suggests that the basement rocks in the northern margin of the Tarim Basin were formed in the Meso- to Neo-Archean times. However, all these Archean rocks have undergone post Archean tectonic activities and metamorphism, which are witnesses by zircon U-Pb ages of -2300 Ma and -2000 Ma for the Qingir gray gneiss, -2000 Ma for granitic gneiss intruded into the Qingir gray gneisses （Gao et al., 1993;Guo et al., 2003）, and -1800 Ma for an amphibolite from Tiemenguan （Guo et al., 2003）. K-Ar age study also reveals Neo-Proterozoic thermal events in the northern margin of the Tarim Basin. 4^40Ar/39Ar plateau ages and laser ^40Ar/39Ar isochron ages for hornblendes, biotites and muscovites from various metamorphic rocks in different parts of the northern Tarim range from 850 Ma to 500 Ma. These ages indicate that the northern Tarim probably underwent diachronous uplift in different regions during the late Neoproterozoic to early Paleozoic （Hu et al. , in press）.