Three-dimensional anisotropic inversion and electrostratigraphic imaging of marine magnetotelluric data to understand the control of crustal deformations by pre-existing lithospheric structures in the Mexican Ridges Fold belt, Southwestern Gulf of Mexico

Abstract

Summary Three-dimensional (3D) imaging of the lithosphere in the Mexican Ridges fold belt is important for understanding how the crustal deformations in this basin relate to deep tectonic processes and structures inherited from extinct Jurassic seafloor spreading. Here, we use broadband (0.0001–0.4642 Hz) marine magnetotelluric data from the basin to reconstruct the 3D anisotropic resistivities of the lithosphere and their spatial gradients. The resistivity gradients maxima enabled independent definition of important geological boundaries (seen on collocated seismic reflection data) and estimation of crustal thickness. We found anomalous layered zones of low resistivity and high electrical anisotropy at 5-8 km depth (coinciding with the regional detachment zone in Eocene shales in 3D seismic data) and in the upper mantle which we interpret as indicating intense deformation and/or recent magmatic influence. We also found a banded crystalline basement structure across the fossil spreading centre comprising WSW-ENE trending, 6-10 km wide, electrically resistive sub-vertical sheets with conductive and anisotropic borders, which merge into a basal resistive stock-like body at 15-20 km depth. These are cut or bounded by later NNW trending major faults. These WSW and NNW structural trends correlate with the previously interpreted transform and normal faults that formed during the Late Jurassic opening of the Gulf of Mexico only if rotated clockwise by 25–30 degrees. Surprisingly, the rugged thrust-related seabed is offset at the projected positions of the steep resistive-conductive basement sheets (which also have spatially coincident high magnetic intensity and seismicity) enabling us to infer they represent magmatic intrusions facilitated by pre-existing faults. Their conductive borders spatially coincide with possibly fluid-filled vertical fracture-sets in the overlying sediments seen in seismic data which we interpret as hydrothermal fluid pathways. We infer that a magmatic body recently intruded our study area, its ascent controlled by pre-existing basement structures, and influenced the deformation of the Neogene sequences and the seafloor topography.

Deep Structure of the Santos Basin, Offshore Brazil From 3D Inversion of magnetotelluric Data

“…Thus, the location below these sites can be approximated from the layered‐earth model. The reversal in slope of vertical resistivity gradient from above Occam 1D models (Johansen et al., 2019; MacGregor & Sinha, 2000; Meju et al., 2023) is used for the marking of e‐Moho in our interpreted model in Figure 10b (see Text S10 in Supporting Information S1). The e‐Moho varies depths along L2 from 35 km in CHL where it lies beneath a dominantly resistive crust up to CFF appearing relatively shallow (∼23 km) below the thick conductive basin fill.…”

“…There are various approaches to defining stratal boundaries in smooth EM inversions by looking for maximum vertical resistivity gradient (MacGregor & Sinha, 2000; Meju et al., 2023), or using synthetic inversions to find the contour closest to a known boundary location (Hoversten et al., 2015). As both approaches fail in our situation, we have performed Occam 1D inversion (Constable et al., 1987) for some selected MT stations based on very low deviation in the main off‐diagonal components of apparent resistivity and phase data.…”

Using Large-Size Three-Dimensional Marine Electromagnetic Data for the Efficient Combined Investigation of Natural Hydrogen and Hydrocarbon Gas Reservoirs: A Geologically Consistent and Process-Oriented Approach with Implications for Carbon Footprint Reduction

“…The source may also be towed in between the lines of receivers (Figure 3). For studies of deep structural control or magmatic impact on the distribution of reservoirs, the receivers are typically left on the seafloor for 7 to 14 days in order to record sufficient MT periodicities and good quality data, depending on the water depth [11].…”

“…Electrical anisotropy will be expected across the prospective target depth here. Resolving the deep 3D electrical structure in such environments is important for understanding the geologic evolution of the hydrogen system [11]. [28].…”

“…It is also emerging that the gradient information in 3D resistivity images can be used to relate the structure of the objects in the m v and m h models that are derived from the above anisotropic inversion methods or simply for identifying features of interest (e.g., edge detection) for direct boundary recognition [11]. For simplicity, one can exploit the magnitude of the directional derivative of either m h or m v implemented by differing between the neighboring pixels in the 3D model.…”