Paleoproterozoic tectonic evolution of the North China Craton

Abstract

The Archean North China Craton consists of two major blocks, separated by the Central Orogenic Belt. The age of collision of the two blocks along the Central Orogenic Belt is controversial. Some models suggest that the Archean blocks collided at 1.8 Ga, during the Luliang Orogeny (1.7–1.9 Ga). In this model, high-pressure granulite facies metamorphism accompanied collision at 1.8 Ga. Other models have suggested that the Eastern and Western Blocks collided at 2.5 Ga, soon after 2.6–2.5 Ga ophiolitic and arc rocks throughout the orogen were formed. We synthesize the geology, geochronology, and tectonics of the Neoarchean through Mesoproterozoic evolution of the North China Craton. We suggest that the Eastern and Western Blocks collided at 2.5 Ga during an arc/continent collision, forming a foreland basin on the Eastern Block, a granulite facies belt on the western block, and a wide orogen between the two blocks. This collision was followed rapidly by post-orogenic extension and rifting that formed mafic dike swarms and extensional basins along the Central Orogenic Belt, and led to the development of a major ocean along the north margin of the craton. An arc terrane developed in this ocean, and collided with the north margin of the craton by 2.3 Ga, forming a 1400 km long orogen known as the Inner Mongolia–Northern Hebei Orogen. A 1600 km long granulite-facies terrain formed on the southern margin of this orogen, representing a 200 km wide uplifted plateau formed by crustal thickening. The orogen was converted to an Andean-style convergent margin between 2.20 and 1.85 Ga, recorded by belts of plutonic rocks, accreted metasedimentary rocks, and a possible back-arc basin. A pulse of convergent deformation is recorded at 1.9–1.85 Ga across the northern margin of the craton, perhaps related to a collision outboard of the Inner Mongolia–Northern Hebei Orogen, and closure of the back arc basin. This event caused widespread deposition of conglomerate and sandstone of the basel Changcheng Series in a foreland basin along the north margin of the craton. At 1.85 Ga the tectonics of the North China Craton became extensional, and a series of aulacogens and rifts propagated across the craton, along with the intrusion of mafic dike swarms. The northern granulite facies belt underwent retrograde metamorphism, and was uplifted during extensional faulting. High pressure granulites are now found in the areas where rocks were metamorphosed to granulite facies and exhumed two times, at 2.5 and 1.8 Ga, exposing rocks that were once at lower crustal levels. Rifting led to the development of a major ocean along the southwest margin of the craton, where oceanic records continue until 1.5 Ga.