![Sample our Engineering & Technology journals, sign in here to start your access, latest two full volumes FREE to you for 14 days]({"type":"image" , "src" : "/sda/5933/TOC-Subject-Sample-2021-Engineering-Tech.jpg"})
ABSTRACT
The Late Carboniferous to Early Permian tectonic evolution of the South West Junggar (SWJ), northwest China, a crucial constituent in the southwestern domain of the Central Asian Orogenic Belt (CAOB), has long been the subject of debate. Here, detailed petrographic studies, new nine LA-ICP-MS zircon U-Pb ages and forty-nine whole-rock geochemical results from six granitic plutons in the SWJ were combined with previously available data to elucidate their petrogenesis and re-decipher Late Palaeozoic tectonic evolution and accretionary process of the southwestern CAOB. The studied granites can be geochemically classified as I- and A-type granites, and the former is further subdivided into I-type and highly fractionated I-type granites. The calc-alkaline I-type amphibole-bearing granites (Group I) yield crystallization ages of ca. 317–315 Ma, and exhibit depletions in HFSEs and enrichments in LILEs with no to slight Eu anomalies and low zircon saturation temperatures, indicating that the formation of these granites may be closely related to the subduction of the Junggar oceanic slab. The Group II granite porphyries (ca. 312 Ma) contain negligible amphibole, and are characterized by evolved SiO2 but low zircon saturation temperatures with sharply negative Eu, Ba, Nb, Ta, Sr, P and Ti anomalies, belonging to highly fractionated I-type granites, and were probably produced in a tectonic transition from compressional to extensional setting. In contrast, the latest Carboniferous (ca. 304–298 Ma) alkaline A-type granites (Group III) are amphibole-absent, and are similar to Group II granites in major element compositions, but exhibit higher zircon saturation temperatures, indicating that they probably resulted in a back-arc extensional setting triggered by roll-back of the subducting Junggar oceanic slab since ca. 310 Ma.
In combination with regional geology and re-interpretation of previous data, a multi-stage subduction-accretion model is suggested to account for the Late Palaeozoic tectonic evolution of the southwestern CAOB. This model can plausibly interpret the differences in duration of subduction between the northern and southern domains of West Junggar and the coexistence of A-type granites with subduction-related sanukites in the SWJ during Carboniferous to Permian.
Graphical abstract
Highlights:
► Two episodes of granites with three genetic types have been recognized in the SWJ.
► The early episode of granites was produced in an oceanic-crust subduction setting.
► The late episode of granites as resulted in a back-arc extensional setting triggered by roll-back of the subducting Junggar oceanic slab since ca. 310 Ma.
► Multi-stage subduction-accretion model may be a plausible scenario to account for the Late Paleozoic tectonic evolution of the southwestern CAOB.
Acknowledgments
We are grateful to Professor Robert J. Stern and anonymous reviewers for their constructive reviews and comments that have substantially improved the quality of this paper. We thank Drs M.Q. Jin, Z.M. Wang and J.H. Du for their laboratory assistance. This study was supported by the National Key R & D Program of China (grant No. 2018YFC0604001), Xinjiang Geological Exploration Fund (grant Nos. A16-1-LQ14 and A17-1-XJ02) and Fundamental Research Funds for the Central Universities, CHD (300102270709).
Disclosure statement
No potential conflict of interest was reported by the author(s).
Supplementary material
Supplemental data for this article can be accessed here.