Tectonic units of the Early Precambrian basement within the North China Craton: Constraints from gravitational and magnetic anomalies

Abstract

The tectonic divisions of the North China Craton (NCC) basement has always been a hot and yet unresolved topic. We collected the latest gravity and magnetic data, and then used a two-dimensional discrete wavelet transform method to decompose the Bouguer gravity anomaly of the NCC into the 1st to 8th Approximations and Details, respectively. We then compared the dynamic tectonic division schemes with the gravity and magnetic division schemes for the Precambrian basement at the end of the Neoarchean and Archean. Our results show that the 2nd-order Detail field of the Bouguer gravity anomalies is well consistent withthe Paleoproterozoic tectonic divisions of the NCC by Zhao et al. (2005), for it clearly outlines the 3-unit layout of the Eastern and Western blocks and the central Trans-North China Orogen, with some anomalous zones identically trending with the dike swarms. Faults and volcanic rocks generally produce magnetic anomalies, but the main anomalous zones in the magnetic field are merely distributed around the plate boundaries of the NCC. It may indicate that the amalgamation of the NCC was mostly completed in the Paleoproterozoic. The 5th-order Detail field of Bouguer gravity anomalies of the NCC corresponds well with its tectonic division at the end of the Neoarchean, for it well reflects the general boundaries and axial trends of the Archean units. These Archean units are mainly separated into three Paleoproterozoic tectonic units by Paleoproterozoic tectonic boundaries, respectively. The magnetic anomalies within the Western and Eastern blocks have separately similarities with the Trans-North China Orogen. The 6th-order Detail fields, however, match well the boundaries of the 10 continental nucleii of the Archean NCC, but the anomalous distributions in the 6th-order Detail are also divided by the Paleoproterozoic tectonic borders. In view of the gravity and magnetic anomalies, it further reveals that the NCC basement may have experienced a dynamic evolutionary process from continental nucleation to micro-continental amalgamation, and to a final unified crystalline basement.