First Early Permian Paleomagnetic Pole for the Yili Block and its Implications for Late Paleozoic Postorogenic Kinematic Evolution of the SW Central Asian Orogenic Belt

Abstract

We conducted a paleomagnetic study on the Early Permian volcanic and sedimentary rocks, and the Neoproterozoic mafic dikes in the Yili Block, NW China. Magnetite and hematite were proven to be the principal magnetic remanence carriers. Demagnetizations revealed stable characteristic remanence magnetizations with a sole reversed magnetic polarity. The magnetic remanence of only the Early Permian strata turned out to be primary based on positive fold tests; meanwhile, the magnetic remanence age of the mafic dikes is ambiguous. Accordingly, the first Early Permian paleomagnetic pole for the Yili Block is calculated at λ = 81.5°N, φ = 256.5°E, N = 11, and A 95 = 10.9°. Comparisons of this new pole with published ones from the Yili, Tarim, and South Junggar blocks provide new quantitative constraints on late Paleozoic kinematic evolution of the SW Central Asian Orogenic Belt: (1) Between the Yili and Tarim blocks, significant relative movement took place along major strike-slip faults during the Late Carboniferous to Early Permian (580 ± 290 km) and the Early to Late Permian (585 ± 340 km), and the displacement rate increased from the Late Carboniferous to Early Permian (~19.3 ± 9.7 mm/yr) to the Early to Late Permian (~29.3 ± 17.0 mm/yr); (2) a significant relative rotation of 28.3°± 18.3°in the Late Permian, and a lateral displacement of 630 ± 295 km after the Late Permian occurred between the Yili and South Junggar blocks. The significant strike-slip movements played an important role in the formation of the Central Asian Orogenic Belt and should be considered with great attention in tectonic and paleogeographic reconstructions. ZHU ET AL.

Constraining the Intracontinental Tectonics of the SW Central Asian Orogenic Belt by the Early Permian Paleomagnetic Pole for the Turfan‐Hami Block

“…Similar large counterclockwise rotations were also documented for the Yili Block with respect to Tarim from the Late Carboniferous to the Late Permian and were interpreted as the result of the large-scale dextral strike-slip movements between the Yili and Tarim blocks (Wang et al, 2007;Zhu et al, 2018). In fact, large-scale strike-slip shearing and related transpression and/or transtension were documented to be the principal pattern of the intracontinental tectonics in the SW CAOB (Allen et al, 1993;Choulet et al, 2011;Choulet et al, 2013;Laurent-Charvet et al, 2002;Laurent-Charvet et al, 2003;Wang et al, 2007Wang et al, , 2009Wang et al, 2014;Zhu et al, 2018).…”

“…This hypothesis is supported by (1) structural and kinematic studies which show that ductile shearing along the MTSZ has been of dextral sense (Laurent-Charvet et al, 2002;Laurent-Charvet et al, 2003;Wang et al, 2007Wang et al, , 2014Yin & Nie, 1996) and (2) multimineral 40 Ar/ 39 Ar dating on mylonitic rocks from the MTSZ yields cooling ages ranging from 290 to 245 Ma (de Jong et al, 2009;Laurent-Charvet et al, 2003). As for the relatively small latitudinal difference of 8.3°± 5.9°between the Turpan-Hami and Tarim blocks, it can be considered as the result of a northward relative movement of the Turpan-Hami Block together with the Yili Block with respect to the Tarim Block that might have occurred as a simple "sliding" along the NE-SW-striking NF-MTSZ, instead of crustal shortening (Zhu et al, 2018). Tables 2 and S4, which are consistent.…”

“…Such discordance can be explained by a clockwise relative rotation of 21.2°± 9.4°and northward latitudinal movement of 14.7°± 7.2°of the Turpan-Hami Block with respect to the South Junggar Block since the Early Permian. According to previous paleomagnetic studies (Choulet et al, 2011;Zhu et al, 2018) (Carroll et al, 1995;Chen et al, 2015;Greene et al, 2001Greene et al, , 2005Hendrix et al, 1992;Shu et al, 2011;Wartes et al, 2002;Xie et al, 2016 . Facies analysis of the Tadjik basin indicates a total crustal shortening of 300 km within the Tianshan and Pamir ranges (Burtman, 2000).…”

“…Recently, several paleomagnetic studies were conducted in the SW CAOB and provided important constraints for the relative paleogeographic positions of the Yili and South Junggar blocks (Choulet et al, ; Choulet et al, ; Wang et al, ; Zhu et al, ). However, the paleomagnetic data are still scarce in the Turpan‐Hami Block (Figure b; Cogné et al, ; Huang et al, , Huang et al, ) and remain completely lacking for the Paleozoic.…”

Oblique Right‐Lateral Faulting Along the Northern Margin of the Ili Basin in the Northern Tian Shan, Northwest China

“…Therefore, the Ili Basin behaves more or less as a rigid block. Based on paleomagnetic declination changes, Zhu et al (2018) reported that the Ili block has presented significant counterclockwise rotation of 41.2° ± 19.1° and lateral displacements after the late Permian, which were accommodated by the major boundary shear zones.…”