Meso-Neoproterozoic Multiple Rifting and Magmatism in the North China Craton

Abstract

AbstractThe North China Craton (NCC) was formed around 2.50 Ga. A 2.50–2.35 Ga period involved a time of tectonic quiescence, and then an important orogenic epoch, i.e., the period of Hutuo Orogeny. The tectonic processes of rifting, subduction and collision characterize this tectonic event, and possibly relate to development of the Supercontinents Nuna or Columbia. Three Palaeoproterozoic orogenic belts have been recognized in the NCC, which are termed as the Jiaoliaoji, Jinyü, and Fengzhen Mobile Belts, respectively. The Jiaoliaoji Mobile Belt is located in the eastern NCC, and made up mainly with the Liaohe and Fenzishan Groups. The Jinyü Mobile Belt occurs in the centro-western NCC, and made up of the Lüliang, Hutuo and Zhongtiao Groups. The Fengzhen Mobile Belt developed in the northwestern NCC, and is composed of the Fengzhen and Erdaowa Groups. The Palaeoproterozoic rocks are mostly basic and acid volcanic and sedimentary rocks, but metamorphosed into low-grade amphibolite facies-greenstone facies. Volcanic rocks show bimodal volcanic features in petrology and geochemistry, indicative of an intraplate setting for their occurrence. These orogenic belts apparently recorded the plate tectonic evolution in the Mesoproterozoic time. The NCC underwent extension in the period from 2.3 to 2.0 Ga, as evidenced by the development of rifts and oceanic basins. There happened subduction, collision, and resulting contraction during 2.01–1.95 Ga. The NCC became stabilized after the Hutuo orogeny or during the “Earth’s middle age”, and remained as a stable platform for more than 1.0 Ga. Meso-Neoproterozoic sedimentary sequences were extensively deposited on the basement. The Xiong’er Rift was formed in the centro-south NCC, and the Yanliao Rift (or called Yanliao Faulted-Depression Zone, YFDZ) occurred in the centro-north NCC. Two other rifts developed in the northwestern and eastern margins of NCC, i.e., the Zha’ertai-Bayan Obo-Huade Rift and Jiao-Liao-Xu-Huai Rift, respectively. The Meso-Neoproterozoic sequences in the Yanliao Rift record sedimentary development of the NCC, and are divided into the Pt21 Changchengian, Pt22 Jixianian, Xiamaling Formation (Pt23x) and Pt31 Qingbaikouan. The Changchengian started from the Changzhougou Formation with the age of ca. 1.67 Ga. The Xiong’er Rift began with volcanic rocks dated at ca. 1.78 Ma, indicating that the rifting developed earlier than the Yanliao Rift. The Jixianian is corresponding to the Calymmian sequences, and followed by the Xiamaling Formation (Ectasian) and then the Neoproterozoic Qingbaikouan (Tonian). Four magmatic events are recognized in the NCC during Late Palaeo-Neoproterozoic times: ① ca. 1800–1780 Ma Xiong’er magmatism; ② ca. 1730–1620 Ma anorogenic magmatism; ③ ca. 1400–1320 Ma diabase/gabbro-diabase sill/vein swarm; and ④ ca. 925 Ma mafic dyke swarm. These magmatic events suggest that the NCC was in an intraplate/intracraton setting from ca. 1800 Ma to ca. 700 Ma. Late Palaeo-Neoproterozoic ore deposits include magmatic iron deposits and REE-Nb-Fe or Pb–Zn-Cu-Fe deposits, while orogenic metal deposits are absent, and no geologic evidence exists for the Grenville or other orogenic events in the NCC. Accordingly, the NCC was probably far from the Nuna Supercontinent in the Proterozoic. The “Earth’s middle age” was a period when the Earth possessed a stable lithosphere and secular warm mantle, which could only result in multiple episodes of magmatism and rifting. It is thus suggested that the Earth experienced an evolution from non-plate tectonics through primitive plate tectonics to modern plate tectonics in the Proterozoic.KeywordsNorth China Craton (NCC)ProterozoicRiftingMagmatismPlate tectonics