The late Paleoproterozoic to Mesoproterozoic rift system in the Ordos Basin and its tectonic implications: Insight from analyses of Bouguer gravity anomalies

Abstract

The Ordos Basin is the largest cratonic basin in the North China Craton (NCC) with minimal intra-basin deformation in the Phanerozoic, making itself a good proxy to study the Precambrian evolution of the NCC. The distribution of the Precambrian strata and associated structural deformation in the Ordos Basin, however, remain an enigma due to the thick covering of the Phanerozoic strata. Herein, we depicted the residual thicknesses of the oldest sedimentary strata above the basement in the Ordos Basin, the late Paleoproterozoic to Mesoproterozoic Changcheng and Jixian systems, by combined forward and inverse modeling of the Bouguer Gravity Anomaly (BGA) data. The distribution of associated basement-involved faults was extracted by applying the signal-processing methods (e.g., the small sub-domain filtering and the total horizontal derivative) to the BGA data. The results were further calibrated by available geological constraints from limited borehole loggings, outcrops and seismic reflection data. They reveal an E- to NE-striking rift system with the development of plenty of syn-depositional normal faults and several uplifts and sags in the late Paleoproterozoic to Mesoproterozoic period in the Ordos Basin. The rift deposits reach ~8000 m in thickness in the southwestern Ordos Basin but thin toward north-northeast. The preexisting basement tectonics played an important role in the development of this rift system. Combined with regional tectonics, our findings imply that the late Paleoproterozoic to Mesoproterozoic extension in the Ordos Basin may not be related to the mantle plume centered in the Xiong’er Rift to the southeast, but instead likely results from the oceanic subduction beneath the southern margin of the NCC. This supports that the southern margin of the NCC may not connect with any other continental blocks in the reconstruction of the Paleoproterozoic Columbia Supercontinent.