Early Precambrian basement components of the Cathaysia Block in South China exhumed by Phanerozoic orogenic events

Ancient rock assemblages formed during the early history of the Earth are normally regarded as continental nuclei and they occur in old cratons. In recent years, they have been reported from different orogenic belts, but the reasons why they occur in orogenic belts are yet to be constained. The Cathaysia Block in South China is a continental block that witnessed multiple episodes of orogenic events and ancient basement rocks sporadically occur in the Wuyi area, where intense metamorphic alteration can be seen. This area is therefore ideal for addressing the above issue. New data, in combination with a review of previous studies, show that the ancient basement components of the Cathaysia Block formed during > 1.93 - 1.75 Ga and are mostly reworked ancient crustal materials (similar to 3.8 - 2.5 Ga). The first episode of metamorphism recorded in this area can be traced back to the Paleoproterozoic, but the features of this metamorphism are unclear. The early Paleozoic metamorphic rocks occur across the Wuyi area, and their protolith ages are dominantly Neoproterozoic, with a small amount of Paleoproterozoic rocks. This episode of metamorphism is characterized by high geothermal gradients, possibly corresponding to an arc setting. The early Mesozoic high-grade metamorphism of the Wuyi area is characterized by low geothermal gradients, indicating significant crustal thickening during the orogenic event. The spatial distribution of the early Mesozoic high-grade metamorphic rocks and the early Precambrian basement rocks of the Cathaysia Block are almost the same. Considering that the ancient basement rocks of the Cathaysia Block have been found in the Wuyi area, it is inferred that both the early Paleozoic and the early Mesozoic orogenic events should have facilitated the exhumation of the early Precambrian basement components. It is further suggested that the final exhumation of these ancient basement rocks is dominated by the early Mesozoic orogenic event because compared with other orogenic events of this continental block, this orogeny influenced rocks from deeper crustal levels (with the highest metamorphic pressures). Such a mechanism of ancient basement rocks exhumed by overprinted orogenic events might apply to many other high-grade terranes.