青藏高原西北缘郭扎错断裂~(40)Ar/~(39)Ar年代学研究——阿尔金断裂西延的新证据

采自阿尔金断裂西南端、沿郭扎错—龙木错—空喀山口一线展布的郭扎错断裂内的糜棱岩样品中同构造黑云母~(40)Ar/~(39)Ar同位素测年的坪年龄分别为105.9Ma±0.5Ma、121.5Ma±0.6Ma、150.4Ma±0.9Ma,表明其早期韧性变形事件发生在晚侏罗世和早白垩世晚期,与阿尔金断裂带主期活动的时期基本一致,为阿尔金断裂带西延提供了新的证据。研究表明,郭扎错断裂与阿尔金断裂带具有一致的变形年代学特征、构造特征等属性,前者是后者的西延部分,二者为同一构造带,均是拉萨地块整体向北运动的动力环境下所产生的脉冲式构造活动的产物。

40Ar/39Ar geochronology of the Guozhacuo fault in the northwestern margin of Qinghai-Tibet Plateau——New evidence for the western extension of Altyn Tagh fault

The samples of mylonite were collected from the Guozhacuo fault, situated in the southwestern end of Altyn Tagh fault zone, which extends from Guozhacuo to Longmuco and then to Kongkashankou. The plateau ages of the syntectonic biotite contained in the samples by means of 40Ar/39Ar isotopic dating are listed as follows: 105.9±0.5Ma, 121.5±0.6Ma, 150.4±0.9Ma, which indicated that the ductile deformation of early stage occurred in the Late Jurassic and Early Cretaceous in Guozhacuo fault, and they were consistent with main stages of activities of Altyn Tagh fault zone. Consequently new evidence has been provided for the extension of Altyn Tagh fault zone towards west. That is to say, Guozhacuo fault has the consistent characteristics of deformation geochronology and tectonic attribute with Altyn Tagh fault zone, and the former is the western extension of the latter, both of them are of the same tectonic belt and are also the results of impulsive tectonic activity caused by northward movement of Lhasa block.