Early Mesozoic tectonic transition of the eastern South China Block: constraints from Late Triassic Dashuang complex in eastern Zhejiang Province

ABSTRACT

The Mesozoic tectonic transition from the Palaeo-Tethys tectonic regime to the Palaeo-Pacific tectonic regime in the eastern South China Block has long been debated. Geochemical and zircon U–Pb–Hf isotopic studies were conducted on the Dashuang complex in the eastern Zhejiang Province. The Dashuang complex consists mainly of quartz syenite in the northwestern part and quartz monzonite in the southeastern part. New laser ablation inductively coupled plasma mass spectrometry zircon U–Pb data show that the quartz syenite, the quartz monzonite, and its chilled margin (fine-grained granite) crystallized at 235 ± 4 Ma, 232 ± 3 Ma, and 230 ± 1 Ma, respectively. The Dashuang complex intrudes into the Chencai Group gneiss that postdated ~646 Ma and underwent anatexis at 443 ± 14 Ma. The quartz monzonite shows A-type granite affinity, characterized by high K₂O + Na₂O and Zr + Nb + Ce + Y, high FeO_T/(MgO + FeO_T) and Ga/Al ratios, an enrichment in light rare earth elements, and depletions in Ba, Sr, and Eu. The quartz monzonite has zircon ε_Hf(t) values of −14.2 to –11.9 and two-stage model ages of 1788–1922 Ma. Zircon ε_Hf(t) values of the chilled margin (fine-grained granite) and wall rock (gneiss) are scattered (−18.2 to –6.3 and −19.5 to 10.2). The corresponding two-stage model ages are 1482–2133 Ma and 1184–2471 Ma, respectively. The Dashuang complex was derived mainly from partial melting of Neoproterozoic clastic rocks in the Cathaysia Block. Geochemical data indicate that the quartz monzonite formed in a post-collision extensional environment. These results, considered with previous data, indicate that the transition from the Palaeo-Tethys to the Palaeo-Pacific tectonic regimes of the eastern South China Block occurred during the Late Triassic (225–215 Ma).

KEYWORDS:

• Triassic A-type granite
• zircon U–Pb–Hf isotopic composition
• Dashuang complex
• Mesozoic tectonic transition
• South China Block

Highlights

• Zircon U–Pb ages show that Dashuang complex occurred during 235–230 Ma.

• Quartz monzonite of Dashuang complex belongs to A-type granite.

• Dashuang complex was derived from partial melting of Neoproterozoic rocks.

• Quartz monzonite occurred during Late Triassic post-orogenic environment.

• Transition from Tethys to Pacific tectonic domains occurred during Late Triassic.

Acknowledgments

Three anonymous reviewers and the Editor-in-Chief Robert J. Stern are thanked for their critical and constructive comments and suggestions, which greatly improved the manuscript. Professor S.F. Lin in the University of Waterloo is appreciated for polishing English.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

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Additional information

Funding

This work was financially supported by the National Natural Science Foundation of China [41402174] and the Fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan) [G1323531799];Fundamental Research Funds for the Central Universities [G1323531799].