Late Neoproterozoic mafic sills in the Suizhou area of the South Qinling block: constraints for the tectonic evolution of the northern margin of the Yangtze craton

ABSTRACT

Late Neoproterozoic gabbroic-diabasic sills are widely distributed in the eastern part of the South Qinling block. Here, a comprehensive geochronological and geochemical study of these mafic sills has been conducted. LA-ICP-MS zircon U-Pb results indicate that the gabbroic-diabasic sills were formed at 632 ± 2 Ma. The sills consist mainly of tholeiitic basaltic rocks with relatively low TiO₂ contents (0.81–1.07 wt.%) and high Fe₂O₃^T/MgO ratios. These rocks display relatively flat to moderate light rare earth elements (LREE) enrichment patterns and positive Eu anomalies (Eu/Eu* = 1.15–1.41). On the primitive mantle normalized spider diagram, the samples show E-MORB-like geochemical features. All of the studied samples display similar Sm-Nd isotopic compositions with negative ε_Nd (t) values ranging from −6.2 to −5.5. Most clinopyroxenes from the mafic sills have relatively low Al/Ti ratios similar to those of typical rift-related cumulates. Therefore, Whole-rock and mineral geochemical features of the studied samples suggest that the mafic sills might have been derived from partial melting of a metasomatised subcontinental lithospheric mantle source in a continental rift setting. It can be advocated that the break-up of the Rodinia supercontinent in the northern part of the Yangtze craton might have been a long-lasting process. By comparison of the coherent Neoproterozoic magmatic events in the northern Yangtze craton and the Tarim block, it can be suggested that the Yangtze craton might have been adjacent to the Tarim block in the reconstruction model of the Rodinia supercontinent.

KEYWORDS:

• Mafic sills
• Continental rift
• Late Neoproterozoic
• Rodinia supercontinent
• South Qinling block
• Yangtze craton

Acknowledgments

This study was supported by National Science Foundation of China (Grants 41303026, 41902232). The authors are grateful to Long Zhao and Pei-Jun Lin for their considerable help during the LA-ICP-MS analyses. Discussion with Profs. Xian-Hua Li and Yuan-Bao Wu significantly improved an earlier version of this manuscript. Editor Robert Stern and three anonymous reviewers are kindly thanked for their thorough reviews and constructive criticisms. Special thanks to those medical staff who are fighting against the Novel coronavirus-2019 in Wuhan, China.

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 [41303026,41902232].