Primary Carboniferous paleomagnetic and geochronologic results from the Aqishan–Yamansu Belt, Eastern Tianshan: Implications for the tectonic evolution of the Paleo-Asian Ocean

• Published in: Tectonophysics Vol. 818; p. 229070
• Main Authors: Xu, Wei, Ji, Wenhua, Song, Bo, Li, Yan, Zhao, Yue, Wang, Baowen, Zhang, Huiyuan, Ye, Xiaozhou, Wei, Xiaoyan, McLachlan, Paul
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 05.11.2021; Elsevier BV
• Subjects: Andesite; Belts; Carboniferous; Central Tianshan; Chronostratigraphy; Compressive properties; Geochronology; Geomagnetic field; Hf isotope; Limestone; Magnetism; Magnetization; Oceans; Palaeomagnetism; Paleo-Asian Ocean; Paleogeography; Paleomagnetic studies; Paleomagnetism; Remanent magnetization; Stress distribution; Tectonics; Temperature; Zircon; Zircon U[sbnd]Pb dating; Siberia; Carboniferous; Paleo-Asian Ocean; Hf isotope; Zircon UPb dating; Paleomagnetism; Central Tianshan
• ISSN: 0040-1951; 1879-3266
• DOI: 10.1016/j.tecto.2021.229070

To constrain the closure time of the Paleo-Asian Ocean and better understand the movement processes of different terranes in the Northern Xinjiang region, we present a combined geochronologic and paleomagnetic study of Carboniferous andesite and limestones from the Yamansu and Dikaner Formations in the Aqishan–Yamansu Belt (AYB). Zircon UPb dating of the Dikaner Formation andesite yielded an age of 313.2 ± 2.0 Ma, and the zircon εHf(t) values ranged from −15.6 to 16.3. Stepwise thermal demagnetization successfully isolated a lower temperature component (LTC) and a stable higher temperature component (HTC) from 18 limestone beds. The LTC represents a viscous remanent magnetization of the present geomagnetic field. In comparison, the HTC is interpreted to represent Late Carboniferous magnetization, generating two paleopoles at 84.6°N, 38.3°E (A95 = 11.6°) for ~313 Ma and 77.2°N, 301.5°E (A95 = 5.5°) for 321–318 Ma. These results show that the AYB moved northward from 30.5 ± 6.5°N to 44.8 ± 8.3°N during the interval between 321–318 Ma and ~ 313 Ma. Compared to other published coeval paleomagnetic poles from surrounding blocks, it can be concluded that the western Paleo-Asian Ocean (between Tarim and Siberia) had been closed since the Late Carboniferous. In contrast, the eastern Paleo-Asian Ocean (between Siberia and Dunhuang-Alxa-NCB) was still open during this time. Besides, the counterclockwise rotations of AYB with respect to Siberia-Mongolia-Tuva and Tarim are estimated to be 88.5° ± 14.1° and 46.5° ± 13.4° since ~313 Ma respectively. Combined with other geological evidence, we propose that Yili-Junggar-Turpan-Hami-AYB had to move eastward to the still open eastern Paleo-Asian Ocean to accommodate the compressive tectonic stress field during the Late Carboniferous, and a Late Carboniferous tectono-paleogeography of the Paleo-Asian Ocean has been reconstructed. •New reliable C2 paleomagnetic poles of the Aqishan–Yamansu belt (AYB) were obtained.•The AYB moved northward from 30.5 ± 6.5°N to 44.8 ± 8.3°N between 321–318 Ma to ~313 Ma.•The western Paleo-Asian ocean (between Tarim and Siberia) had been closed since C2.•The CCW rotations of AYB were identified with respect to Siberia and Tarim since C2.