Tectonic Evolution of the West Bogeda: Evidences from Zircon U-Pb Geochronology and Geochemistry Proxies, NW China

Abstract

The Bogeda Shan (Mountain) is in southern part of the Central Asian Orogenic Belt (CAOB) and well preserved Paleozoic stratigraphy, making it an ideal region to study the tectonic evolution of the CAOB. However, there is a long-standing debate on the tectonic setting and onset uplift of the Bogeda Shan. In this study, we report detrital zircon U-Pb geochronology and whole-rock geochemistry of the Permian sandstone samples, to decipher the provenance and tectonic evolution of the West Bogeda Shan. The Lower-Middle Permian sandstone is characterized by a dominant zircon peak age at 300–400 Ma, similar to the Carboniferous samples, suggesting their provenance inheritance and from North Tian Shan (NTS) and Yili-Central Tian Shan (YCTS). While the zircon record of the Upper Permian sandstone is characterized by two major age peaks at ca. 335 Ma and ca. 455 Ma, indicating the change of provenance after the Middle Permian and indicating the uplift of Bogeda Shan. The initial uplift of Bogeda Shan was also demonstrated by structural deformations and unconformity occurring at the end of Middle Permian. The bulk elemental geochemistry of sedimentary rocks in the West Bogeda Shan suggests the Lower-Middle Permian is mostly greywacke with mafic source dominance, and tectonic setting changed from the continental rift in the Early Permian to post rift in the Middle Permian. The Upper Permian mainly consists of litharenite and sublitharenite with mafic-intermediate provenances formed in continental island arcs. The combined evidences suggest the initial uplift of the Bogeda Shan occurred in the Late Permian, and three stages of mountain building include the continental rift, post-rift extensional depression, and continental arc from the Early, Middle, to Late Permian, respectively.

Tectono-Paleogeographic Impact on the Permian Depositional Environment and Provenance around the Chaiwopu Depression in the Southern Junggar Basin, NW China

“…Thus, in this study, we investigated lithological, sedimentological, and geochemical data acquired from six outcrop sites (Figure 1c) to understand the Permian evolution of the Chaiwopu Depression. Our results build on recent studies that established the Permian basin-mountain system of the Bogda Mountains and adjacent sedimentary basins [26][27][28][29][30][31][32][33][34][35][36]. The intracontinental basin-mountain series on the southern CAOB formed mainly during the Late Paleozoic as a derivation of the closure of the Junggar Ocean [4,[16][17][18].…”

“…This is supported by the geochemical characteristics shown in Figure 10. According to previous studies [27,29,32], an abrupt change of provenance took place after the Middle Permian, which corresponds to re-sedimentation in the course of the uplift of the mountain range (e.g., [69]). The source rock properties of the Upper Permian are attributed to the recycled Middle Permian sediments from the West Bogda Mountains (Figures 7a and 11d; [29,32]).…”

“…The Bogda Mountains became an integral part of the northeastern Tian Shan orogenic belt, which separates the Junggar and Tuha Basins. The Late Paleozoic orogeny established a distinct geologic history in the West Bogda Trough to mountains and basin evolution [1,4,[7][8][9]14,15,18,27,32,33,36], arranged as four major phases, as follows (Figure 2a): (1) During the middle Carboniferous to Early Permian, the extensional phase was initiated by mantle upwelling and regional crustal extension as a delamination effect of the post-orogenic collision period. This formed an intracontinental rifting system in the paleo Bogda area, which accompanied Early Permian bimodal volcanism and syn-tectonic plutonism.…”

“…After the cessation of rifting at the end of the Early Permian, the area became a relatively stable tectonic setting with subsidence during the Middle Permian. The uplift of the West Bogda Mountains caused by strong intracontinental collision formed the basin geometry of the Chaiwopu Depression but restricted it from other major basins during the Late Permian [1,4,9,[14][15][16][17][18]27,32,33,36]. The Permian successions around the Chaiwopu Depression provide a continuous and sensitive geological record reflecting the tectonic evolution and associated paleogeographic changes.…”