Early Cretaceous mafic enclaves from the Jiaodong Peninsula of NNE China and what they reveal about lithospheric melts and granodiorite genesis: the Yashan example

ABSTRACT

Mafic microgranular enclaves (MMEs) are hosted by the Early Cretaceous granitic plutons from the Jiaodong Peninsula and are crucial for constraining the petrogenesis of these plutons and understanding the lithospheric evolution in the eastern North China Craton (NCC). This paper presents new geochronological, bulk-rock geochemistry, and Sr-Nd-Hf isotope data for Yashan granodiorite and its MMEs in an effort to build an integrated model of the geodynamic setting during the Early Cretaceous. Zircon U–Pb dating indicates that Yashan granodiorite (116 ± 0.42 Ma) is coeval with its MMEs (117 ± 0.81 Ma). The MMEs display magmatic textures and disequilibrium textures such as acicular apatites, plagioclase with reverse zoning, and overgrowth of amphibole around pyroxene, indicating magma mingling/mixing. The SiO₂ (55.64–59.9 wt.%), MgO (3.34–5.25 wt.%), Cr (74–245 ppm), and Ni (24–91.2 ppm) contents of the Yashan MMEs combined with their Sr-Nd-Hf compositions that are identical to local arc-like mafic dikes suggest that their primary magma derived from partial melting of a metasomatised lithospheric mantle. Yashan granodiorite is characterized by relatively high SiO₂ (66.93–67.63 wt.%) and low MgO (1.66–1.67 wt.%) contents, I-type, high-K calc-alkaline, metaluminous affinities, and corresponding Hf model ages from Neoarchean-Paleoproterozoic, which indicate that the felsic magma was derived from partial melting of ancient NCC lower continental crust. Our data combined with previous studies on Early Cretaceous MMEs and host granites in the Jiaodong Peninsula indicate that the Cretaceous magmatism is the result of rollback of the subducting Paleo-Pacific plate beneath the eastern NCC. Asthenospheric mantle convection generated by slab rollback induced the thinning of the lithosphere and provided necessary heat to cause partial melting of the lithospheric mantle and overlying lower crust, followed by crustal-mantle interaction. The emplacement of Yashan granodiorite and other Weideshan granites and hosted MMEs indicates the peak of lithospheric thinning.

KEYWORDS:

• Mafic microgranular enclaves
• magma mingling and mixing
• Yashan granodiorite
• lithospheric evolution
• Jiaodong Peninsula

Acknowledgments

The authors are grateful to Sanshandao Gold Mine, Jiaojia Gold mine, Linglong Gold Mine of Shandong Gold Group, and Lingnan Gold Mine of Zhongkuang Gold Industry Co., Ltd. for their necessary help during field works. Prof. Robert Stern and two anonymous reviewers are thanked for offering constructive comments and suggestions on the manuscript. Isheka S. Orr is also thanked for proofreading the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was supported by the National Key Research and Development Plan under Grant number 2016YFC0600104; and the National Natural Science Foundation of China under Grant number 41672074.