Carboniferous back-arc extension in the southern Yili-Central Tianshan Block and its significance to the formation of the Kazakhstan Orocline: insights from the Wusun Mountain volcanic belt

Abstract

In Central Asia, the Carboniferous is a crucial period in the formation of the Tianshan Belt and associated bending of the Kazakhstan tectonic collage. In order to reveal Carboniferous magmatic events of the region and their tectonic implications, we conducted field investigations, zircon U-Pb dating, whole-rock geochemical and Sr-Nd isotopic studies on the Early Carboniferous Dahalajunshan Formation and Late Carboniferous Yishijilike Formation volcanic rocks of the Wusun Mountain Range (southern Yili-Central Tianshan Block). Volcanic rocks of the Dahalajunshan Formation consist of calc-alkaline basalt, andesite and dacite, yielding new zircon U-Pb ages of ~ 350 Ma. They have positive whole-rock ε Nd (t) values (+ 0.5 to + 1.6). In contrast, the Yishijilike Formation volcanic rocks dominantly comprise alkaline and calc-alkaline bimodal suites that erupted at ~ 337 Ma to 313 Ma and have higher whole-rock ε Nd (t) values (+ 2.3 to + 4.3). These two episodes of Carboniferous magmatism were correlated with partial melting of depleted mantle that metasomatized by slab-derived fluids. The late Carboniferous Wusun Mountain magmatic belt shows characteristics of a back-arc system that evolved due to trench retreat relative to the southern margin of the Yili-Central Tianshan Block. This mechanism induced an extensional regime with gradually depleting magma sources. The asymmetric retreat of the paleo-subduction zones of the South Tianshan Ocean and Junggar Ocean relative to the Yili-Central Tianshan Block was hence a vital driving force for the bending of the Kazakhstan Orocline.

Meso-Cenozoic thermo-tectonic evolution of the Yili block within the Central Asian Orogenic Belt (NW China): Insights from apatite fission track thermochronology

“…Some of these were affected by greenschist-facies metamorphism (XBGMR (Xinjiang Bureau of Geology and Mineral Resources), 1993). Carboniferous volcanic rocks are widespread within the Yili block and have local thicknesses of >3 km, their formation is considered to be related with the closure of the Paleo-Tianshan and Junggar Oceans (Wang et al, 2006(Wang et al, , 2007aZhu et al, 2009;Cao et al, 2017;Su et al, 2018Su et al, , 2021.…”

“…As an important segment of the southwestern CAOB, the Kazakhstan collage system is composed of several continental blocks with Proterozoic basement, Paleozoic continental/island arcs and accretionary wedges (Windley et al, 2007;Biske and Seltmann, 2010;Buslov, 2011;Su et al, 2021). The Yili block forms the wedge-shaped eastern extremity of the Kazakhstan collage system (Figs.…”

Late Mesozoic intracontinental deformation and magmatism in the Chinese Tianshan and adjacent areas, Central Asia

“…1; Gao et al, 2009;Han et al, 2011;Han et al, 2016b). The Yili-Central Tianshan Block is considered to be a micro-continent with a Proterozoic metamorphic basement intruded by various Paleozoic granitic plutons (e.g., Dong et al, 2011;Ma et al, 2014;Wang et al, 2014Wang et al, , 2017He et al, 2018;Zhu et al, 2019;Su et al, 2021). The North Tianshan Arc traditionally refers to the region between the Yili-Central Tianshan Block and the Junggar Arc and is an accretionary belt composed of Late Carboniferous volcanicsedimentary rocks and ophiolitic slices (Fig.…”

Correlation of geological complexes of the Khan-Tengri Mountain massif

“…According to U-Pb dating of zircons, several eruptive events with ages of 355-350 Ma, 337 Ma, and 325 Ma are identified in this part of the rock sequence. The thickness of volcanic deposits along the Tekes sequence reaches 7500 m. The volcanics are overlain with erosion by the marine terrigenous-carbonate deposits of the Akeshake Formation, with Visean corals and brachiopods (Su et al, 2022(Su et al, , 2018Xia et al, 2004).…”

“…The Early Carboniferous volcanic stage ended with intense tectonic deformations of stratified deposits (Su et al, 2022), and the intrusion of the Late Carboniferous Belbulak complex, composed, in the Ketmen Range, of large-medium crystalline pinkish-gray biotite and biotite-hornblende granites (Chakabaev et al, 1981), which marks the end of the collision of the Katyrasan-Kotanemel volcanic arc and the Kazakhstan paleocontinent, identified as the Saurian folding (Tevelev, 2001). Chinese researchers, however, believe that the Early Carboniferous volcanics of the Wusun Range and the sedimentary rocks associated with them represent a back-arc structure (Su et al, 2022). The granitoids of the Belbulak complex and volcanic rocks of the Lower Carboniferous are overlain with angular unconformity by terrestrial basalts, andesite-basalts, and trachyandesites of the Degeresk Formation (up to 400 m).…”