南天山南缘晚泥盆世构造事件的^(40)Ar/^(39)Ar定年证据及其意义

^(40)Ar/^(39)Ar age determination on the Late Devonian tectonic event along the southern margin of the South Tianshan Mountains and its significance

南天山南缘前陆褶皱冲断带在独库公路范围内出露于铁力买提达坂一带,其构造岩片主体向南逆掩于塔里木盆地之上,构造样式以双向逆冲为特征。相关韧性剪切带中白云母矿物^(40)Ar/^(39)Ar同位素测年获坪年龄368±1Ma和等时线年龄368±6Ma。结合区域构造分析,这条作为南天山中央地块南部构造边界的大型复合式构造带,主要形成发育时限为晚泥盆世-早石炭世,并在二叠纪重新活动。前者可能是是南天山洋盆向北俯冲于伊犁地块之下的构造变形过程的痕迹,后者则可能是由伊犁-塔里木复合地体与北天山地块在晚石炭世-早二叠世发生碰撞而导致的构造变形。

Located in the Tielimaiti Daban area, the fold-thrust belt along the southern margin of the South Tianshan Mountains is characterized by thrust sheets which were southward thrusted over the Tarim basin sediments, with structural style of double-thrusting. ^(40)Ar/^(39)Ar dating for muscovite from the related ductile shear zone yields plateau age of 368±1Ma and isochron age of 368±6Ma. In combination with regional geological analysis, we proposed that the thrust belt was mainly formed in Late Devonian-Early Carboniferous time and acted as a complicated tectonic boundary south of the Central Tianshan block, which was the record of the subduction of the South Tianshan ocean floor beneath the Central Tianshan block. This fold-thrust belt was activated in the Permian, which was related to the collision between the Yili-Tarim composite block and the North Tianshan in the Late Carboniferous-Early Permian.