This study presents a novel approach to modeling the Earth’s geomagnetic field, which originates from electric currents approximately 2,900 km beneath the surface, crucial for understanding planetary dynamics. We introduce a method for inverting a planetary-scale equivalent magnetization source and develop a 3-D equivalent electric current circulation model from this source, enhancing understanding of these deep currents. This research signifies the first use of unstructured tetrahedral magnetization inversion technology for planet-scale magnetic data interpretation and equivalent source model construction. Validated through a synthetic case study, the method is applied to the International Geomagnetic Reference Field (IGRF) and SWARM satellite datasets, comprising 35,768 magnetic vectors from two orbital altitudes. Employing various mesh configurations, we construct and compare detailed current source models from these datasets. The effectiveness of our equivalent current sources is confirmed by comparison with dynamo research findings, demonstrating significant advancements in geomagnetic field modeling, particularly in interpretability, and providing novel insights into Earth’s magnetic phenomena.

The location and origin of Neoproterozoic-Cambrian sutures provide keys to understand the formation and evolution of the supercontinent Gondwana. The Larsemann Hills is located near a major Neoproterozoic-Cambrian suture zone in the Prydz Belt, but has not been examined locally by comprehensive geophysical studies. In this study, we analyzed data collected from a 1-D joint seismic-MT array deployed during the 36th Chinese National Antarctic Research Expedition. We found that a sharp Moho discontinuity offset of 6-8 km shows up in the stacked image of teleseismic P-wave receiver function analysis; coinciding with the abrupt Moho offset, a near-vertical channel with (1) low resistivity extending to the uppermost mantle depths, and (2) a high crustal Poisson’s ratio in the crust is identified. These findings provide evidence for the determination of the location and collisional nature of the Prydz belt or a portion of it.

Data-processing methods only considering the turn-off ramp in transmitting waveforms are well established for land-based transient electromagnetic (TEM) methods. The turn-on ramp effects on late-time responses are generally neglected by data-processing methods. Our forward-modeling results of homogeneous half-space models show that the full-waveform effect which includes both effects caused by turn-on and turn-off stages is common for a wide range of conductivities. The inversion results for synthetic and field examples illustrate that the inversion algorithm which does not consider the full-waveform effects can lead to a higher resistivity in deeper parts of recovered models compared with the true model. Therefore, it is of vital importance to account for the full waveform effects in both forward modeling and inversion algorithms. We use synthetic examples to show how our inversion algorithms can improve the recovered model, and use real-data examples to show the importance of incorporating full transmitting waveforms in data-processing procedures.

Extension and rifting of the lithosphere is fundamental to the evolution of the continents, but the mechanism by which the lithosphere thins remains enigmatic. Using new dense magnetotelluric array data collected within the rifted margin and adjacent areas of Southeast China, we resolve the three-dimensional electrical structure of the lithosphere to constrain the process of rifting and thinning. Our measurements discover a brittle-ductile transition zone featuring low electrical resistivity and low seismic velocity in the Cathaysia Block. A southeast-directed dip is resolved for the Jiangshan-Shaoxing Fault that documents the Neoproterozoic suturing of the Yangtze and Cathaysia Blocks, and has been reactivated by the Early Paleozoic and Early Mesozoic intracontinental orogenies. It acted as a low-angle detachment fault during the Mesozoic-Cenozoic extension and rifting. Given the asymmetries of topography, electrical resistivity, Bouguer gravity anomaly and Mesozoic volcanism across the Gan-Hang Rift, an asymmetric simple shear extension model is proposed for the South China Mesozoic-Cenozoic rift system. Water content of up to 0.1 wt% and melt fraction of up to 1% are estimated at 70 km depth beneath the central Wuyi Mountains, suggesting hydration of the mantle lithosphere. The hydration weakening of the mantle lithosphere promoted both the gravitational instability and convective removal of the lowermost lithosphere in South China.