Geochronology and geochemistry of Late Triassic intrusions in the Liaodong Peninsula, eastern North China Craton: implications for post-collisional lithospheric thinning

ABSTRACT

Despite numerous years and avenues of investigation, the timing, evolution, and mechanism of lithospheric thinning of the North China Craton (NCC) are still highly debated. Late Triassic igneous rocks especially mantle derived mafic rocks could provide critical information related to the post-collisional lithospheric thinning of the Liaodong Peninsula in the eastern NCC. Using newly acquired geochronological data points, we determined that the intrusive rocks have emplacement ages of 219–209 Ma, which are typical of Late Triassic magmatism. The studied Qinghekou gabbros have low SiO₂ (49.43–51.86 wt.%), Na₂O+K₂O (3.59–7.20 wt.%), high MgO (3.70–8.54 wt.%) and transition metal element contents, with Mg^# values ranging from 49.2 to 69.3. While these samples are enriched in large ion lithophile elements such as Rb, Ba, and K and light rare earth elements, they are depleted in high field strength elements such as Nb, Ta, Ti, and P and heavy rare earth elements. We conclude that these gabbros samples were formed in a subduction-related tectonic setting, where the primary magmas were derived from partial melting of the lithospheric mantle that experienced metasomatism via slab-related fluids. Our Tongyuanpu granite samples have I-type granite affinity, as indicated by their high SiO₂ (73.60–75.30 wt.%) and low MgO (0.08–0.32 wt.%) contents, as well as the A/CNK values of 0.99–1.25 and the zircon saturated temperature values of 757–832°C, the parental magmas for these granites were generated by partial melting of the lower crust. Combined with the spatio-temporal distribution and rock-assemblages of the Late Triassic intrusive rocks, we conclude that these rocks were formed in an extensional environment characterized by lithospheric thinning caused by lithospheric delamination after the collision between the NCC and the Yangtze Craton. Furthermore, we infer that the initial lithospheric thinning of the eastern NCC occurred during the Late Triassic.

Graphical Abstract

KEYWORDS:

• Liaodong Peninsula
• Late Triassic
• Gabbro
• I-type granite
• Lithospheric thinning
• North China Craton

Acknowledgments

We appreciate Editor-in-Chief Robert J. Stern and two anonymous reviewers for their constructive and valuable comments, which substantially enhanced the final presentation of the paper. We are also sincerely grateful to Jun-Hui Bi of the Institute of Geology and Mineral Resources in Tianjin, China, for her advice and assistance during the Lu-Hf isotope analyses. We also thank the staff of the ALS Minerals-ALS Chemex (Guangzhou, China) for their help in major, trace element analytical works. This work was financially supported by the Project of China Geological Survey (1212011220247), the Natural Science Foundation of China (41872203) and the Graduate Innovation Fund of Jilin University (101832020CX206).

Highlights

1. The 219–209 Ma gabbros and granites occurred in the eastern NCC.

2. Mafic magma resulted from partial melting of lithospheric mantle.

3. Granitic magma is generated by partial melting of lower crust.

4. An extensional environment related to lithospheric thinning is proposed.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary materials

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was supported by the China Geological Survey [1212011220247]; National Natural Science Foundation of China [41872203]; Graduate Innovation Fund of Jilin University [101832020CX206].