Geochronological and geochemical constraints on the non-ultrahigh-pressure metasedimentary blocks of North China affinity within the Sulu ultrahigh-pressure belt, eastern China, and tectonic implications

ABSTRACT

The Sulu ultrahigh-pressure (UHP) belt has been proven to form by deep northward subduction of the Yangtze Block (YB) beneath the North China Block (NCB) in the Triassic. The basement rocks originated from the YB and experienced Triassic UHP metamorphism. In this contribution, we identify for the first time tens of non-UHP metasedimentary blocks enclosed in the regional UHP granitic gneiss in the Weihai terrane in the northeastern Sulu UHP belt. They are mainly composed of paragneiss, marble and calc-silicate rocks, in which UHP-related minerals have not been identified. Detrital zircons from the non-UHP metasedimentary rocks are mostly of magmatic origin and yield U-Pb ages mainly from 2842 to 1792 Ma with two clusters of 2580–2460 Ma and 1900–1800 Ma. This zircon U-Pb age spectrum is typical of the NCB but not the YB, and matches the tectonothermal/magmatic history of the southwestern end of the Jiao-Liao-Ji belt (JLJB), eastern NCB, which lies immediately adjacent to the Weihai terrane. Furthermore, their whole-rock geochemical compositions show great resemblance to those of the Paleoproterozoic metasedimentary rocks within the JLJB. In particular, metamorphic zircons from the non-UHP metasedimentary rocks indicate widespread late Triassic-early Jurassic (213–194 Ma) metamorphic overprinting of the Paleoproterozoic (1850–1820 Ma) metamorphism that characterizes the JLJB. This means that the enclosed non-UHP metasedimentary rocks with NCB signatures in the Weihai terrane were involved in the collision-subduction process during the Triassic. They have not been carried to mantle depths during deep continental subduction. These lines of evidence prompt us to establish a Triassic tectonic erosion model to explain these new discoveries and pre-existing problems along the Sulu UHP orogenic belt.

Graphical Abstract

KEYWORDS:

• Non-UHP metasedimentary rocks
• North China
• Paleoproterozoic
• Triassic
• Weihai
• Sulu UHP belt

Highlights

• A suite of non-UHP metasedimentary blocks was identified within the UHP granitic gneiss in the Weihai terrane.

• The non-UHP metasedimentary rocks have petrologic, geochronological and geochemical affinity to North China.

• Paleoproterozoic and Triassic metamorphic events are both recorded by these non-UHP slices.

• A modified subduction erosion model is proposed to explain the subduction- exhumation process of the Sulu UHP belt.

Acknowledgments

We are grateful for the field help from Fang Wang, Jianrong Shi, Lei Ji and Hong Yang. We thank Zhonghua Tian and Lingtong Meng for their discussions during the preparation of the manuscript. Critical comments from editor-in-chief Robert J. Stern and two reviewers are highly appreciated. This paper was funded by the National Natural Science Foundation of China (Grants 41430210, 42002067 and 41890832), the Postdoctoral Science Foundation of China (2019M660789) and the Open Research Project of the Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources (J1901).

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

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Additional information

Funding

This work was supported by the National Natural Science Foundation of China [41430210, 42002067, 41890832]; China Postdoctoral Science Foundation [2019M660789]; Open Research Project of the Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources, Institute of Geology, Chinese Academy of Geological Sciences [J1901].