Metamorphic evolution and tectonic significance of Neoarchean high-pressure mafic granulites in the Central Limpopo Belt, South Africa

ABSTRACT

The Sand River area is in the northeastern part of the Central Zone (CZ) of the Limpopo Belt, and represents a key terrane to reveal early Precambrian tectonic processes in southern Africa. Based on petrology, U–Pb zircon ages, and major and trace element data of high-pressure (HP) mafic granulites from the Sand River area, the tectonic evolution of the Central Zone of the Limpopo Belt is re-evaluated here that allows revision of previous interpretations. The protoliths of the HP mafic granulites and amphibolites are sub-alkaline tholeiitic basalts similar to those formed at a mid-ocean ridge and intruded at 2.8 Ga. Based on the distinct mineral assemblages, three metamorphic stages (M₁–M₃) are recognized in the studied samples: (1) a peak HP granulite facies stage M₁ (~1.17–1.32 GPa/~825–870°C), (2) a post-peak near-isothermal decompression stage M₂ (~0.70–0.73 GPa/~835–880°C), and (3) a later, independent metamorphic stage M₃ (~0.53–0.69 GPa/~793–801°C). M₁ and M₂ define together a clockwise P–T path. It reveals important information related to the Neoarchean collisional orogeny, and its later overprinted by an independent orogeny with subsequent exhumation and cooling. U–Pb zircon dating of two mafic granulites samples yielded protolith formation of the mafic granulites is prior to ~2.72 Ga, and the two metamorphic age peaks of ~2.72 (M₁) and ~2.0 Ga (M₃), which present the peak and post-peak cooling stages, respectively. The metamorphic evolution of HP mafic granulites in the Sand River area as reconstructed in this study suggests the Neoarchean collision of the Kaapvaal and Zimbabwe cratons and a discrete Paleoproterozoic orogenic overprint followed by post-orogenic exhumation and cooling.

GRAPHICAL ABSTRACT

KEYWORDS:

• high-pressure metamorphism
• phase equilibria modelling
• U–Pb zircon age
• metamorphic evolution
• Limpopo belt

Acknowledgments

We very much appreciate the support of Profs. Alfred Kröner, Jan Kramers, and Dr. Guenther Brandt during the field trip on 28 July to 3 August 2013. We gratefully acknowledge critical reviews and thoughtful suggestions by Editor in Chief Prof. Robert J. Stern and two anonymous reviewers to earlier versions of the manuscript. This study was financially supported by the National Natural Science Foundation of China (No. 41872192, 42172213, 41972215, and 41730210) and the China Scholarship Council (No. 202006170184). We are grateful to Xiao Zhou, Erlin Zhu, and Qian Zhang of College of Earth Sciences, Jilin University, for their advice and assistance during the zircon U–Pb analyses.

Disclosure statement

We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the manuscript submitted. And we confirm that all the listed authors have participated actively in the study and have approved the submitted manuscript to your journal.

Authors’ contributions

Y. Yang and C.Y. Liang conceived of the presented idea, designed the experiments and verified the data together. The article is originally written and revised by Y. Yang and Franz Neubauer, the other authors are also responsible for many revisions. The main support for this study was mainly secured by C.Q. Zheng and C.Y. Liang. H.M. Zhang performed phase equilibria modelling and geochemistry analysis along with Y. Yang. Franz Neubauer digitalized the geological map and established the schematic model for the geodynamic evolution along with Y. Yang.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00206814.2023.2225186.

Additional information

Funding

This study was financially supported by the National Natural Science Foundation of China (No. 41872192, 42172213, 41972215 and 41730210) and the China Scholarship Council (No. 202006170184).