LATE PALEOPROTEROZOIC EXTENSION AND A PALEOSTRESS FIELD RECONSTRUCTION OF THE NORTH CHINA CRATON

Abstract

Mafic dyke swarms and aulacogens are major anorogenic extensional events in the Late Paleoproterozoic North China Craton (NCC). The N-NNW mafic dyke swarms are widespread in the NCC, whose ages span between 1.83 and 1.77 Ga. The similar ages and orientations of ~ 1.8 Ga dyke swarms in the NCC demonstrate that the amalgamated NCC experienced widespread extension at this time. Based on the width statistics of dyke swarms on ten survey lines, an average crustal extension ratio of 0.35% was found for the NCC. The small magnitude of overall extension suggests that the mafic dyke swarms were emplaced into the elastic fractures, and indicates that the NCC had become a brittle plate prior to the emplacement of the mafic dyke swarms. Precisely dated mafic dyke swarms, when used as paleostress indicators, can be employed in the paleostress field reconstruction of Precambrian cratons. Two dimensional finite element modeling (2-D FEM) of the NCC, in which the various blocks were assigned densities and elastic constants, shows that north-south compression favors dyke intrusion along generally N-NW lines, and that deviations in dyke trends can be explained by the effects of boundary constraints and the physical properties of the crust. The best fitting model can be considered a plausible representation of the tectonic force acting on the NCC that produces the intraplate stress field that is most consistent with the observed orientation of dyke swarms. The results of modeling of the Late Paleoproterozoic stress field suggest a common tectonic setting for the emplacement of mafic dyke swarms in the Central Orogenic Zone, Western and East Blocks of the NCC. The results also show that the north-south tectonic forces play an important role in determining the paleostress field in the NCC. The widespread extension of the NCC resulted from the north-south tectonic forces which may be related to the break-up of the Late Paleoproterozoic supercontinent. The paleostress field modeling provides a possible approach to consider the supercontinent paleostress reconstruction and to reveal the mechanisms of the supercontinent break-up. © 2006 Elsevier B.V. All rights reserved.