Geochronology of the Hongliuxia ductile shear zone and its constraint on the closure time of the Junggar Ocean
红柳峡韧性剪切带形成时代及其对准噶尔洋盆闭合时限的约束

The Kalamaili ophiolitic belt in East Junggar is one of the important ophiolitic belts in Xinjiang, the closure time of Junggar Ocean represented by the Kalamaili ophiolitic belt is still argued and unclear. Recently, we discovered that the Hongliuxia EW-trending schistosity zone cut the Kalamaili ophiolite belt is a dextral ductile shear zone, which was formed in collision process between the Yemaquan arc and the Junggar block. The foliated granite and granitic ultramylonite in the ductile shear zone in the Boerqiangji area are selected for zircon SIMS U-Pb dating. New results show that the foliated granite has a concordia age of about 348.1±2.8Ma with a 206Pb/238U weight average age of about 348.2±2.7Ma, and the granitic ultramylonite has a concordia age of 343.2±2.6Ma with a 206Pb/238U weight average age of about 343.5±2.6Ma. Zircons from the granitic ultramylonite are new formed by metamorphic recrystallization; their ages may represent formation time of the ductile shear zone. This indicates that the Hongliuxia ductile shear zone was formed at about 343Ma BP, and that the Junggar ocean should be closed before 343Ma BP, and the East Junggar was involved in collisional orogen at the end of Early Carboniferous.