The crustal deformation during the Early Paleozoic period and the timing of orogeny in Kuruktag area on the northeast margin of Tarim Basin

Abstract：Located at the junction part between the Tianshan orogenic belt and the Tarim craton, Kuruktag area in Xinjiang is a key area for the study of the relationship between the Central Asian orogenic belt and the Tarim craton. According to structural and micro-structural investigations and Ar–Ar dating of Kuruktag area, the authors have reached the following conclusions: (1) Sinian–Early Paleozoic cap rocks were deformed obviously at the bottom with dense cleavages dipping gently northward, but they were deformed slightly at the top with sparse cleavages steeply dipping northward, forming southward spread spade-shape structural style in NS direction. (2) A decollement exists between the cover rocks and the basement stretching in EW direction with a width of 2 km, characterized by “A” type folds, mylonites, gentle mylonite foliation, whose stretching lineation plunges northwest or southeast. Studies of asymmetrical rotational structure and crystallographic preferred orientations of quartz in mylonites (EBSD analysis) indicate a movement of the hanging wall of the ductile decollement in SE direction. (3) Ar–Ar dating result of the muscovite in the mylonite from the ductile decollement shows that the decollement was formed earlier than 383 Ma. The decollement was a product of the intercontinental subduction after the collision event between the Tarim block and the Central Tianshan magmatic arc, and it means the existence of the early Paleozoic orogenic event in Kuruktag area on the northeast margin of Tarim Basin.