Deciphering a complex Neoarchean-Paleoproterozoic collisional history between the Kaapvaal and Zimbabwe Cratons: new constraints from polyphase deformation of the Central Limpopo Belt, southern Africa

The Limpopo Belt of southern Africa is a classical Paleoproterozoic orogenic belt that is believed to have resulted from the collision between the Kaapvaal and Zimbabwe Cratons. Previous studies have primarily focused on geochronology, petrology, and geochemistry of different rock assemblages, resulting in a general tectonic framework indicating at least two significant tectonothermal events from Mesoarchean to Paleoproterozoic. However, the spatial and temporal relationships between these events, as well as their overall structural patterns in the field, are poorly understood. The Central Limpopo Belt contains the best lithological exposures of different ages, making it the most promising area for detailed structural mapping and analysis, and for gaining a better understanding of these issues.
Based on the detailed field-based structural analyses, four generations of deformation were identified. The earliest D1 deformation is characterized by the penetrative S1 foliations only preserved within the 3.6-3.4 Ga anorthosites that now occur sporadically as xenoliths or boudins in the highly deformed 2.9-3.3 Ga Sand River gneiss. S2 are penetrative gneissic foliations that were extensively developed in the Sand River gneiss and were intensively superimposed by subsequent deformations into tight to isoclinal folds. After restoration of their attitude, S2 foliations strike NW-SE and dip steeply to SW at high angles, indicating that the D2 deformation experienced a roughly NE-SW-oriented compression between 2.9-2.6 Ga. D3 deformation resulted from significant NW-SE-oriented compression that intensively superimposed the earlier S2 fabrics into vertically inclined isoclinal folds and tectonites S3-L3. Strain measurements on these tectonites indicate that all pre-existing rock assemblages were stretched or sheared along the vertical orientation, resulting in the development of numerous sheath folds in the Sand River gneiss and 2.6-2.7 Grey gneiss. Associated with the zircon ages from anatexis melts, the D3 deformation most likely occurred at 2.1-2.0 Ga. SHRIMP U-Pb zircon age dating recorded these two metamorphic ages of ~2.6 Ga and 2.0 Ga on a single zircon of the foliated Sand River gneiss. A regional large scale inclined open fold F4 gently refolded the D1-D3 fabrics and marked the final deformation of the Central Limpopo Belt, occurring sometime after ~2.0 Ga. 
Detailed structural data of this study, in combination of available geochronological and metamorphic data lead us to propose that the ~2.65 Ga and ~2.0 Ga tectonothermal events occurred under different tectonic environments. The ~2.65 Ga tectonothermal event developed coevally with D2 deformation and high-grade metamorphism during the NE-SW collisional event. In contrast, the ~2.0 Ga tectonothermal event occurred during a NW-SE-oriented collisional event between the Kaapvaal and Zimbabwe Cratons, resulting in the formation of the major Limpopo tectonic linear belt seen today.

Acknowledgement
This work was financially supported by the National Natural Science Foundation of China (42025204) and National Key Research and Development Program of China (No. 2023YFF0803804).