Whole‐rock geochemistry and zircon Hf isotope of Late Carboniferous–Triassic sediments in the Bogda region, NW China: Clues for provenance and tectonic setting

Abstract

Detailed petrological, whole‐rock geochemical, and zircon Hf isotopic researches were conducted on the Late Carboniferous–Triassic sedimentary rocks in the Bogda region to evaluate the effects of weathering, sorting, and alteration, as well as to understand their provenance and tectonic setting. These rocks show variable major element compositions, but most are generally similar to post‐Archean Australian shales. The relatively narrow range of TiO2–Zr variation and good correlation between Th/Sc and Zr/Sc signify no obvious sorting and recycling of the sedimentary rocks. The relatively high index of compositional variability (0.8–3.1) and low chemical index of alteration values (44.4–76.4) of the sedimentary rocks indicate that they are immature and probably undergo weak to moderate chemical weathering. In the chondrite‐normalized diagrams, almost all the samples are distinguished by moderately enriched light rare earth element and flat heavy rare earth element patterns with negative Eu anomalies (Eu/Eu* = 0.5–0.8). In conjunction with their Th/Sc, Zr/Sc, La/Th, Zr/Al2O3, TiO2/Zr, Co/Th, and La/Sc ratios, we infer that the major sources of these sedimentary rocks were the intermediate–acidic igneous rocks from the North Tianshan and Yili–Central Tianshan. Combining the orientation of the Bogda region in the Palaeozoic that was roughly perpendicular to the Tianshan and/or East Junggar orogens with the sedimentologic, petrologic, and tectonic researches, we suggest that the Bogda region was a rift basin that occurs at high angles to the orogenic belt. On the other hand, the zircons from these sediments have minor Precambrian grains (<0.2%), positive εHf(t) values (mostly +7.1–+15.0) and young 2‐stage Hf model ages (major peak <1,000 Ma), suggesting that a juvenile continental crust exists as the basement of the Junggar Basin.

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

“…From this collision, the tectonic setting of West Bogeda Shan changed to intracontinental tectonic evolution stage, and the original terrain of West Bogeda formed (Figure 13b). At the end of the Early Permian, most parts of the terrain were still a submarine environment, while only small parts were lifted up [32,74,[83][84][85]. distribution of bimodal volcanic rocks in the Bogeda Shan [73] and some submarine olistostrome in the West Bogeda Shan [30].…”

“…In the Middle Permian, the depositional environment changed to terrestrial and lacustrine facies, resulting in a variable lithology of sandstone, siltstone, mudstone, and oil-bearing mudstone. The Upper Permian strata is composed of conglomerate and sandstone deposited in alluvial fan and braided river environment [28][29][30][31][32][33].…”

“…To examine the sediment provenances of the West Bogeda Shan from the Carboniferous to Triassic periods, all available detrital zircon U-Pb ages from previous studies are compiled and presented in Table S1 [24,32,[44][45][46][47]. The U-Pb ages of the Upper Permian detrital zircons from seven sandstone samples were measured in the present study.…”

Multi-Scale Quantitative Characterization of Pore Distribution Networks in Tight Sandstone by integrating FE-SEM, HPMI, and NMR with the Constrained Least Squares Algorithm

“…It extends to North Tianshan (NTS) to the south and to the Urumqi-Erie Road to the north [30] (Figure 1). [38]). The Jurassic stratum in the Southern Junggar Basin consists of the Badaowan Formation, Sangonghe Formation, Xishanyao Formation, Toutunhe Formation, Qigu Formation, and Kalazha Formation from old to young [39].…”

“…(a) Location of the study area, sampled well, and field section; (b) the stratigraphic column of the Badaowan Formation; (c) geological map of the southern Junggar Basin and the location of the study area; and (d) location of the Central Asian Orogenic Belt (modified by[38]). …”