Provenance of Middle Jurassic clastic rocks from the Bogda area of Eastern Tianshan and its implications

ABSTRACT

The siliciclastic rocks in the Xishanyao (XSY) and Toutunhe (TTH) formations recorded the Middle Jurassic palaeogeographic evolution processes of the Bogda Mountains. To explore their provenance, the geochronological, geochemical, and petrological characteristics of the Middle Jurassic sandstones from the west Bogda area are analyzed in this study. The detrital grains of sandstones are generally poorly to moderately sorted and subangular to subrounded. Low to moderate CIA* (chemical index of alteration), PIA (plagioclase index of alteration), CIW (chemical index of weathering) and relatively high ICV (index of compositional variability) values indicate the overall low to moderate weathering intensity, low sediment recycling, and abundant first-cycle siliciclastics supply. The abundant acid volcanic lithic fragments and element contents/ratios of the sandstones indicate source areas dominated by felsic rocks. The detrital zircon U-Pb age spectrum of the lower XSY Formation is dominated by a single Carboniferous age group. Multiple Palaeozoic zircon U-Pb age groups exist in the middle-upper XSY Formation. The TTH Formation has a typical age of late Middle Jurassic. Combined with the sedimentological characteristics, it reveals that (1) the Eastern Bogda Mountains (EBM) were the only provenance for the lower XSY Formation; (2) both the Yemaquan arc and the EBM provided detritus for the middle XSY Formation; (3) the Yemaquan arc became a minor provenance for the TTH and upper XSY formations. Middle Jurassic palaeogeographic evolution in the EBM is inferred as follows: (1) during the deposition of the lower XSY Formation, the EBM suffered a rapid uplift and became an obvious positive relief; (2) the palaeorelief became high in the Yemaquan arc area and low in the EBM during the deposition of the middle XSY Formation; (3) the Yemaquan arc was considerably eroded, which caused the palaeotopography to decline sharply during the deposition of the upper XSY Formation; (4) the EBM uplifted again during the TTH Formation period, accompanied by volcanic activities at ~165Ma.

KEYWORDS:

• Bogda Mountains
• Middle Jurassic
• provenance
• source weathering
• palaeogeographic evolution

Acknowledgments

We are thankful for the constructive comments from two anonymous reviewers and chief editor Dr Robert J. Stern. We are grateful to Prof. Dr Qi Wang for his constructive suggestions to our research and this manuscript. Unfortunately, Dr Qi Wang passed away unexpectedly several months ago. We cherish the memory of him deeply.

Disclosure statement

No potential conflict of interest was reported by the authors.

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Correction Statement

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Funding

This research was supported financially by Western Action Plan Project of the Chinese Academy of Sciences [grant number KZCX2‐XB3‐12], Scientific Research Foundation for PhD, East China University of Technology [grant number DHBK2018028], National Natural Science Foundation of China [grant number 41502110], Youth Innovation Promotion Association of the Chinese Academy of Sciences [grant number 2016068], and Natural Science Foundation of Gansu Province [grant number 18JR3RA396];National Natural Science Foundation of China [41502110];Natural Science Foundation of Gansu Province [18JR3RA396];Western Action Plan Project of the Chinese Academy of Sciences [KZCX2‐XB3‐12];Youth Innovation Promotion Association of the Chinese Academy of Sciences [2016068];