Significant Paleozoic tectonic events in the northern part of the East Tianshan Mountains, Xinjiang and their implications for the evolution of CAOB: New evidence from 1: 50000 geological survey of Banfanggou and Xiaoliugou sheets

Based on the new results of 1:50, 000 geological survey of Banfanggou and Xiaoliugou sheets in Hami area, Xinjiang, this paper systematically reviewed the major tectonic events and evolutionary history during Paleozoic in the northern part of the East Tianshan Mountains. There existed three major tectonic events between Ordovician and Early Silurian, between Devonian and Early Carboniferous and in the Late Carboniferous, respectively, as shown by the newly discovered angular unconformity or disconformity. Combined with a series of new records of sedimentation, magmatism and deformation reflecting tectonic transformation, the links between these tectonic events and the evolution of the Central Asian Orogenic Belt (CAOB) are discussed. It is suggested that the orogenic event that occurred at the turning time from Ordovician to Silurian was the response to collision between the Junggar-Tuha terrane and the Altay terrane following the closure of the Armantai oceanic basin. The disconformity between Devonian and Lower Carboniferous shows an epeirogenic event, probably in response to the initial closure of the Kalamaili oceanic basin to the north. This disconformity and underlying Silurian-Devonian deposits in relatively stable tectonic environment also show that the Junggar-Tuha terrane between the Kalamaili oceanic basin and the North Tianshan oceanic basin was a relatively rigid and stable continental block in the Paleo-Asian Ocean system. The study area, as the northern passive continental margin of the Junggar-Tuha block, was less affected by the convergence of the Kalamaili oceanic basin. The orogenic event in the late Carboniferous was the reflection of peak orogenesis in response to the evolution of the peripheral foreland basin after the arccontinental collision that occurred along the Kalamaili suture zone during late Devonian-early Carboniferous period. This event established the basic NW-SE trending structural framework in the East Tianshan Mountains. The authors also redefined the Moqinwula fault as the southeastern extension of the Kalamaili suture zone, the tectonic-stratigraphic boundary between the North Tianshan Mountains (or Junggar-Tuha block) and the East Junggar terranes, and discussed the spatial differences of tectonic regime in the early Carboniferous. Based on the records of sedimentation and magma of the early Carboniferous, the authors hold that a peripheral foreland basin, which was related to the closure of the Kalamaili oceanic basin, was developed in the Moqinwula Mountain, whereas a rift basin was developed in the Bogda-Harrick Mountain, which was in response to the post-collision extension related to the closure of the North Tianshan Ocean.