Late Paleoproterozoic rift-related magmatic rocks in the North China Craton: Geological records of rifting in the Columbia supercontinent

摘要

Late Paleoproterozoic (1.84-1.62Ga) magmatic rocks including dykes/sills/intrusions and volcanic rocks occur throughout the North China Craton (NCC), which is considered to be part of the Columbia supercontinent by ca. 1.9-1.85Ga. On the basis of petrogeochemical data, these magmatic rocks can be classified into three major magma types: HN (Nb/La>0.8, Ce/Nb=1.7-3, (Th/Nb)_N=0.6-1.2), MN (Nb/La=0.8-0.5, Ce/Nb=3-5, (Th/Nb)_N=0.9-3.5) and LN (Nb/La<0.5, Ce/Nb=5-80, (Th/Nb)_N=1-60). The geochemical variation of the MN and LN rocks can be explained by lithospheric contamination of asthenosphere- (or plume-) derived magmas, whereas the parental magmas of the HN rocks did not undergo, during their ascent, pronounced lithospheric contamination. These magmatic rocks exhibit at least two characteristics: (1) most displaying a spectrum of compositions from mafic to silicic; (2) forming in an intracontinental rift setting. This Late Paleoproterozoic rift-related magmatism is the most distinguishing feature of the rifting of the Columbia supercontinent.