U-Pb geochronological evidence for the early Precambrian complex of the Tarim Craton, NW China.
U-Pb geochronological evidence for the early Precambrian complex of the Tarim Craton, NW China.
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作者：
Zhang Zhi
塔里木盆地早前寒武纪变质杂岩主要由三种岩石组合组成：（1）灰色片麻岩，是杂岩的主体;（2）斜长角闪岩，以及局部保存的云母石英片岩和大理岩，常呈透镜体和石香肠状产出于灰色片麻岩中;兴迪群不整合覆盖于结晶基底之上。该研究为早前寒武纪杂岩提供了新的锆石U-Pb定年结果。两个斜长角闪岩样品的年龄分别为2492±19（2σ）Ma和1836±25（2σ）Ma。灰色片麻岩的锆石年龄为2337±6（2σ）Ma，花岗质片麻岩的精确年龄为1943？6（2σ）Ma。锆石U-Pb年代学资料结合前人的工作表明，灰色片麻岩中的斜长角闪岩石香肠可能是晚太古代的岩石，而灰色片麻岩则是早元古代的岩石。根据花岗质片麻岩与第一盖层星地群的不整合关系，提出星地群为中元古代，沉积时间约为1800 Ma。研究表明，塔东北地区的基底与盖层关系与华北克拉通的基底与盖层关系相似。
The Early Precambrian metamorphic complex of the Tarim basement mainly consist of three types of rock associations: (1) grey gneisses which are the main body of the complex, (2) amphibolite, and locally preserved mica-quartz schist and marble, commonly occurring as lenses and boudins in the grey gneisses, (3) granitic gneisses intruded in the grey gneisses. The Xingdi Tagh Group unconformably covers the crystalline basement. This study provides the new U-Pb zircon dating results for the Early Precambrian complex. Two samples of the amphibolite yielded different ages of 2492±19 (2σ)Ma and 1836±25 (2σ)Ma. The grey gneiss has zircons dated to be 2337±6 (2σ) Ma, whereas the granitic gneiss has a precise age of 1943 ?6 ( 2σ) Ma. U-Pb zircon geochronological data combined with the former works show that the amphibolite boudins in the grey gneisses might be Late Archean rocks, while the grey gneisses are the Early Preterozoic. Based upon the uncomformity between the granitic gneisses and the first cover - the Xingdi Tagh Group, we propose that the Xingdi Tagh Group is the Middle Proterozoic which deposited from about 1800Ma. This study shows that the relationship between the basement and the cover in the NE Tarim is alike to that of the North China craton.