Late Cretaceous basalts and rhyolites from Shimaoshan Group in eastern Fujian Province, SE China: age, petrogenesis, and tectonic implications

ABSTRACT

Southeastern China is characterized by an extensive Late Mesozoic (Yanshanian) tectono-magmatic-metallogenic event. Although Late Cretaceous volcanism gradually weakened during the epilogue of the Yanshanian event, its petrogenesis and geodynamic processes remain unclear. In this study, we present new zircon U–Pb–Hf isotopic, whole-rock elemental, and Sr–Nd isotopic compositions data, for volcanic rocks from the Zhaixia Formation of the Shimaoshan Group in Fujian Province. The lower member of the Zhaixia Formation consists of basalts and rhyolites, and the upper member is only rhyolites. These volcanic rocks erupted in the early stage of Late Cretaceous, with basalts erupting earlier (ca. 99–98 Ma) than rhyolites (ca. 98–94 Ma). These basalts record high-K calc-alkaline to shoshonitic, light rare earth element (LREE)- and LILE-enrichment, high field strength element (HFSE)depletion with negligible Eu anomalies, and uniform whole-rock ε_Nd(t) (–3 to –6) and zircon ε_Hf(t) (–3.3 to –14.1) values. The overlying rhyolites record peraluminous and high-K calc-alkaline characteristics, LREE- and LILE-enrichment with negative Eu anomalies, and Nb–Ta depletion. The whole-rock ε_Nd(t) and zircon ε_Hf(t) values of these rhyolites both increase from the lower member (ε_Nd(t), –1.5 to –4.7; ε_Hf(t), –5.1 to –16.1) to the upper member (ε_Nd(t), –0.5 to 0.1; ε_Hf(t), –0.3 to –4.3). The features imply that these basalts were derived from the partial melting of the enriched lithospheric mantle and the overlying rhyolites from the melting of the crustal components, respectively. Data from the rhyolites in the upper member indicate that more juvenile, Nd–Hf isotopically depleted materials were injected into their source. During the Late Cretaceous, the new, fast rollback of the subducting slab triggered lithospheric extension and asthenospheric upwelling beneath the coastal regions, which induced the melting of lithospheric mantle and crustal components. As continued, the new round of basaltic underplating provided necessary heat to cause partial melting of the deep crust, including the younger, juvenile, and isotopically depleted crustal components.

KEYWORDS:

• Southeastern China
• Cretaceous
• basalt
• rhyolite
• slab rollback
• lithospheric extension

Acknowledgements

We are grateful to Editor-in-Chief Professor Robert J. Stern, Guest Editors Professor Wei-Dong Sun and Professor Xiao-Yong Yang, and two anonymous reviewers for their constructive comments. This research was supported by the National Key Research and Development Program of China (2017YFC0601401), National Natural Science Foundation of China (Nos. 41602042, U1606401, 41502185), China Postdoctoral Science Foundation funded project (No. 2016M592244), National Program on Global Change and Air – Sea Interaction, SOA (No. GASI-GEOGE-01), and Taishan Scholar Program and Aoshan Talents Program (No. 2015ASTP-0S10). We thank Dr Ye Li for constructive suggestions and discussion. We also thank Professor Fu-Kun Chen and Ping Xiao for their help in Sr–Nd isotopic analysis, and Ji-Lin Wang, Shuang Xu, and Qing-Yu Gu for their assistance with zircon U–Pb dating.

Disclosure statement

No potential conflict of interest was reported by the authors.

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Funding

This work was supported by the National Key Research and Development Program of China [2017YFC0601401]; National Natural Science Foundation of China [41602042, U1606401, 41502185]; Aoshan Talents Program [2015ASTP-0S10]; China Postdoctoral Science Foundation funded project [2016M592244]; National Program on Global Change and Air – Sea Interaction, SOA [GASI-GEOGE-01].