A new Carboniferous–Permian intra‐oceanic subduction system in the North Tianshan (NW China): Implications for multiple accretionary tectonics of the southern Altaids

Abstract

The North Tianshan in NW China is a key to understanding the accretionary history of the southern Altaids. However, the tectonic setting of the North Tianshan in the Carboniferous‐Permian is debatable, and its amalgamation history is ambiguous. We report new data on the field relations, geochronology and geochemistry of Carboniferous–Jurassic volcanic rocks and sedimentary rocks from the Shichang area in order to constrain the late Palaeozoic–Early Mesozoic tectonic evolution of the North Tianshan. New LA‐ICP‐MS zircon U–Pb dates demonstrate that the Carboniferous–Permian stratigraphy is a tectonic imbrication of Carboniferous–Permian rocks and Carboniferous volcanic rocks were emplaced in Permian volcano‐sedimentary rocks. The 311 ± 2 Ma volcanic rocks are calc‐alkaline, enriched in Light Rare Earth Elements and large‐ion lithophile elements, depleted in high‐field‐strength elements, and have low initial 87Sr/86Sr ratios with positive εNd(t)(+0.3 to +8.6)values. The geochemical‐isotopic data suggest the volcanic rocks were generated in an intra‐oceanic island arc. The turbidite samples 18SC02 (~267 Ma to ~349 Ma) and 18SC09 (~299 Ma to ~369 Ma) have a relatively narrow age range with no Devonian or Precambrian peaks. Our detrital zircon data suggest the presence of a so far unrecognized intra‐oceanic arc, which was isolated from the main Yili‐Central Tianshan and Mosuowan arcs in the Shichang area of the North Tianshan during the Late Carboniferous to Permian. The compiled detrital zircon data from Carboniferous to Jurassic indicates that the North Tianshan intra‐oceanic arc was probably amalgamated with the Mosuowan arc by the Early Triassic, and then accreted to the Yili‐Central Tianshan arc by the Middle‐Late Triassic, as revealed by the changes of zircon provenance of Carboniferous, Permian, Triassic and Jurassic sedimentary rocks. All integrated data suggest that the southern Altaids most likely formed by processes of multiple subduction–accretion and convergence similar to that in the ongoing southwest Pacific.

Defining the Huangcaopo complex and gabbroic magmatism in the northern Harlik Mountains (NW China): Late Cambrian to latest Permian accretionary growth of the East Junggar Arc?

“…Ao et al (2021) identified the youngest matrix at 234 Ma in the Kanguer mélange, suggesting continuous northward subduction of the North Tianshan oceanic lithosphere in the late Triassic. By doing provenance exchange study, Abuduxun et al (2021), Song et al (2021), Bai et al (2020), and Chen et al (2020) suggested that there was only provenance exchange at the early to late Triassic in the South Tianshan orogen, Alxa block, and North Tianshan orogen, respectively, indicating closure of the corresponding oceans in the Triassic.…”

“…Some authors suggested that these rocks were the products of backarc rifting of the Harlik‐Dananhu composite arc, but this conclusion requires re‐evaluation (Li et al, in press). Both southward and northward subduction of oceanic basins (various names were used, including the Kelameili Ocean) were proposed to be responsible for the construction of the Bogda arc or intra‐arc basin (Bai et al, 2020; Chen et al, 2013; Xie et al, 2016; Zhang et al, 2017).…”

Accretionary tectonics, deep structures and metallogeny of southern Altaids

“…Bai et al (, this issue) present new data on the field relations, geochronology and geochemistry of Carboniferous–Jurassic volcanic rocks and sedimentary rocks from the Shichang area. The detrital zircon data suggest the presence of a so‐far unrecognized intra‐oceanic arc during the Late Carboniferous to Permian in the southern Altaids, most likely formed by processes of multiple subduction–accretion and convergence similar to that in the on‐going southwest Pacific.…”

The Wulanmoren Accretionary Complex Unravels Early Devonian to Late Triassic Multiple‐Arc Amalgamation in the Tianshan Orogen (NW China)

“…It contains many accretionary prisms and is the key area to reconstruct the architecture of the Altaids because it represents the terminal suturing between the Tarim Craton and the Northern Ili Arc (NIA; Abuduxun et al., 2021). The geology and tectonic history of the Tianshan Orogen has been primarily investigated in the South Tianshan accretionary complex (STAC; e.g., Alexeiev et al., 2015; C. M. Chen et al., 1999; Gao & Klemd, 2003; B. F. Han et al., 2011; Jiang et al., 2014; Safonova, Biske, et al., 2016; Sang et al., 2020; B. Wang et al., 2011; G. X. Yang et al., 2017), located between the Tarim Craton and the Issyk Kul‐Central Tianshan Arc (CTA), and the North Tianshan Accretionary Complex (NTAC; e.g., Bai et al., 2020; Feng et al., 2018; M. Wang, Zhang, Pei, et al., 2018; Xu et al., 2005; G. X. Yang et al., 2018; Zheng et al., 2019) adjacent to the Junggar arcs and the NIA (Figure 1). Relatively less attention has been paid to the relationship between the Issyk Kul‐CTA and the NIA separated by the Terskey‐North Nalati Suture Zone which may connect to the Nikolaev line in its western branch (Gao et al., 2015; G. Q.…”

“…, located between the Tarim Craton and the Issyk Kul-Central Tianshan Arc (CTA), and the North Tianshan Accretionary Complex (NTAC; e.g., Bai et al, 2020;Feng et al, 2018;M. Wang, Zhang, Pei, et al, 2018;Xu et al, 2005; G. X.…”