关键词: 华北地块北缘, 中元古界, 不整合面, 大陆边缘, 超大陆

Abstract:

There exist several depositional breaks and unconformities in the Mesoproterozoic successions in the northern margin of the North China Block. We carried out a field study of geologic characteristics and spatial distribution of five unconformities, and concluded that they resulted from different geological processes. The unconformity beneath the Dahongyu Formation is interpreted as a breakup unconformity in nature, representing the timing of transition from continental rift to passive continental margin. The unconformities beneath the Gaoyuzhuang and Yangzhuang Formations are considered as the consequence of regional eustatic fluctuations, leading to exposure of highlands in passive margin during sealevel falls and transgressive deposition on coastal regions during sealevel rise. The unconformity atop the Tieling Formation might be caused by uplift due to contractional deformation in backarc setting, whereas the uplift after deposition of Xiamaling Formation might have been attributed to a continental collision event. It is assumed that the occurrences of the unconformities in the Mesoproterozoic successions in the northern North China Block had a close bearing on the assemblage and breakup of the Columbia and Rodinia supercontinents.

Key words: northern margin of North China Block, Mesoproterozoic, unconformities, continental margin, supercontinent