3D inversion of the Sichuan Basin magnetic anomaly in South China and its geological significance

Abstract

The Sichuan Basin magnetic anomaly is the most striking regional aeromagnetic anomaly in South China. It is characterized by a continuous large-scale linear magnetic anomaly and contains long-wavelength constituents which could still be detected on satellites. However, Sichuan Basin is covered by 4 to 10 km thick non-magnetic sedimentary layers from Neoproterozoic to Cenozoic, which conceals the magnetic sources in the Precambrian basement and makes it difficult to explore the geological origin of the Sichuan Basin magnetic anomaly. In this study, we applied 3D inversion to the magnetic data, and then compared our inverted susceptibility model with geological maps. We found that the spatial distribution of the Sichuan Basin magnetic anomaly controls the range of the rigid basement beneath Sichuan Basin and it is surrounded by the widespread Neoproterozoic magmatic complexes. Based on our analysis, we proposed that the geological origin of the Sichuan Basin magnetic anomaly might be related to the craton-scale Neoproterozoic magmatic event, which has played an important role in the stabilization of the basement and the evolution of the deep crust in Sichuan Basin.

Magnetic Structure and its Tectonic Implication Around Longmenshan Fault Zone Revealed by EMAG2v3

“…The latitude of the study area spans six degrees, thus a differential RTP (DRTP) scheme (Blakely, 1995;Arkani-Hamed, 1988, 2007) is adopted here and the result is shown in Figure 4. As can be seen, the anomalies have a tendency to move northward after RTP, which is consistent with previous results (Wang et al, 2020). The RTP map shows better correspondence with the geological structure (compared to Figure 3).…”

“…The Precambrian basement with strong magnetism in SB is buried at depths of 8-23 km, and is overlain by a sedimentary metamorphic crystalline basement with weak magnetism (Pan et al, 2020). This strong magnetic basement is conjectured to be generated by craton-scale Neoproterozoic magmatic events rather than Neoarchean crystalline basement (Wang et al, 2020;Xiong et al, 2020). The SGFB shows as an isolated negative magnetic anomaly (Gao et al, 2021).…”

“…The southern segment of LFZ connects to the Xianshuihe fault, which delineates the boundary between the positive anomaly (40-100 nT) in the east and the weak negative anomaly (−20~-5 nT) in the west. SB is characterized by a broad high positive anomaly in the range of 50-350 nT, which is presumed to be generated by the Precambrian crystalline basement due to its high susceptibility (Wang et al, 2020). Most Precambrian shields, cratons, and platforms exhibit positive anomalies globally (Frey, 1982), and are supposed to have a similar origin (Arkani-Hamed and Strangway, 1985).…”

“…Current studies (e.g. Wang et al, 2020;Xiong et al, 2020) concluded that the basement is generated by Neoproterozoic magmatic activities according to the anomaly distribution and outcrops, which need more magnetic evidences. Meanwhile, the fluctuation of CPD may confuse the results and should be analyzed.…”

Initial scalar lithospheric magnetic anomaly map of China and surrounding regions derived from CSES satellite data

“…The Sichuan basin is covered by thick non-magnetic sedimentary layers from Neoproterozoic to Cenozoic, which conceals the Precambrian basement where the sources lie. Wang et al [36] performed a 3D inversion of the aeromagnetic data and compared the results with geological maps. They proposed that the geological origin of the Sichuan Basin magnetic anomaly be related to the cratonscale Neoproterozoic magmatic event, which has played an important role in the stabilization of the basement and the evolution of the deep crust below the Sichuan Basin.…”