Cretaceous A-type volcanic–intrusive rocks and simultaneous mafic rocks along the Gan-Hang Tectonic Belt, Southeast China: petrogenesis and implications for the transition of crust–mantle interaction

ABSTRACT

Abundant evidence points to the Cretaceous crust–mantle interaction and plate subduction in the Gan-Hang Tectonic Belt (GHTB), southeastern China, but the evolutionary process remains poorly constrained. Here we conduct a comprehensive study on Daqiaowu granitic porphyry and diabase dikes in the eastern GHTB, in conjunction with previous studies on simultaneous felsic and mafic rocks along the GHTB, to demonstrate their petrogenesis and geodynamic evolutionary process. The Daqiaowu granitic porphyry (125 Ma), as well as the coeval granitic rocks, exhibits high zircon saturation temperatures, alkalis, 10⁴*Ga/Al ratios, and Zr + Nb + Ce + Y contents, concluding a distinctive belt of the Early Cretaceous (~137–125 Ma) A-type volcanic–intrusive rocks in the GHTB. Their ε_Nd(t) and zircon ε_Hf(t) values gradually increased through time from approximately −9.0 to −1.0 and −10.0 to +4.0, respectively, implying increasing contribution of mantle-derived components to their formation, and hence progressively intensified crust–mantle interaction in an intra-arc rift environment (a geodynamic transition stage from continental arc to back-arc) during the Early Cretaceous. This plausibility is further supported by the Early Cretaceous Daqiaowu diabase dikes and coeval mafic rocks which exhibit arc-like magmatic signatures and were derived from mantle wedge. In contrast, the Late Cretaceous mafic rocks show ocean island basalt-like geochemical characteristics, reflecting a depleted asthenosphere mantle source. This discrepancy of mantle sources concludes that the geodynamic setting in the GHTB may have basically transferred to back-arc regime in the Late Cretaceous. Thus, the Cretaceous geodynamic evolutionary process in the GHTB can be defined as the Early Cretaceous gradually intensified crust–mantle interaction in a geodynamic transition stage (from continental arc to back-arc extension) and the Late Cretaceous back-arc extensional setting.

KEYWORDS:

• Sr–Nd–Pb–Hf isotopes
• A-type volcanic–intrusive rocks
• mantle sources
• geodynamic transition
• Cretaceous
• Gan-Hang Tectonic Belt

Highlights

1. Daqiaowu A-type granitic porphyry and arc-like mafic dikes emplaced in 125–128 Ma

2. A distinctive belt of A-type volcanic–intrusive rocks (~137–125 Ma) in the GHTB

3. Rising ε_Nd(t) and zircon ε_Hf(t) values imply Early Cretaceous intensified crust–mantle interaction

4. Early Cretaceous geodynamic transition stage from continental arc to back-arc

5. Change of mantle sources suggests Late Cretaceous back-arc extensional setting

Supplemental data

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Acknowledgements

The authors have benefited from discussions with Prof. Wei-Zhou Shen, Dr Dan Wang, and Dr Li-Qiang Sun. Their contributions to the ideas presented here are gratefully acknowledged. We also thank reviewers for thoughtful comments which significantly improved the quality of this paper, and staffs from Geological party No. 269 of Zhejiang Province Nuclear Geological Bureau for their assistance with field works. This work was supported by Natural Science Foundation of China, under Grant 41703042; National Basic Research Program of China, under Grant 2012CB416703; State Key Laboratory for Mineral Deposits Research, under Grant 2017-LAMD-K06; and China Nuclear Industry Geological Bureau.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by Natural Science Foundation of China, under Grant 41703042; National Basic Research Program of China, under Grant 2012CB416703; State Key Laboratory for Mineral Deposits Research, under Grant 2017-LAMD-K06; and China Nuclear Industry Geological Bureau.