A Review of Subsurface Electrical Conductivity Anomalies in Magnetotelluric Imaging

Abstract

After 70 years of development, magnetotelluric (MT), a remote sensing technique for subsurface electrical resistivity imaging, has been widely applied in resource exploration and the deep tectonic evolution of the Earth. The electrical resistivity anomalies and their quantitative interpretation are closely related to or even controlled by the interconnected high-conductivity phases, which are frequently associated with tectonic activity. Based on representative electrical resistivity studies mainly of the deep crust and mantle, we reviewed principal electrical conduction mechanisms, generally used conductivity mixing models, and potential causes of high-conductivity including the saline fluid, partial melting, graphite, sulfide, and hydrogen in nominally anhydrous minerals, and the general methods to infer the water content of the upper mantle through electrical anomaly revealed by MT.

A Review of Relationship between the Metallogenic System of Metallic Mineral Deposits and Lithospheric Electrical Structure: Insight from Magnetotelluric Imaging

“…The conductive phases in the lithosphere mainly include saline fluids, partial melts, graphite, sulfides and water (hydrogen) in nominally anhydrous minerals (NAMs). Previous studies have summarized the conducive characteristics of these phases [13,14] (Figure 1), and in this paper, these are not further described. Conductive mediums, such as graphite/graphite film, metallic oxide/sulfide, aqueous fluid and molten silicate/carbonate melt, have a conductivity that is several orders of magnitude higher than that of country rocks [15].…”

“…Furthermore, the alkali-rich, volatile-rich and/or water-rich melts (e.g., anatexis in the crust) also contribute to most types of ore deposits [6,[53][54][55][56][57][58][59]. During or after mineralization, these volatile residues may form a chlorate, sulfide and/or graphite film under specific temperature and pressure conditions, which can increase the conductivity of the rock system [13,14,60]. The ore deposits form in a specific geological time and the metallogenic events are transient; however, the most important features of metallogenic systems are shaped before the mineralization or a long period after the metallogenic event, and the evolution of metallogenic systems may be preserved for hundreds of millions to billions of years [2,12].…”

Exploring the Intersection of Geophysics and Diagnostic Imaging in the Health Sciences

“…The ratio of the vertical electric field (E z ) to the horizontal magnetic field (H y ) is used to calculate the impedance (Z) Z = Ez Hy [20,55] 14, x FOR PEER REVIEW 8 of 26 Where E is the induced electri- Detecting anomalies in the brain and assisting with pre-surgical planning for diseases like epilepsy [57,58] Functional Electrical Stimulation (FES) [59,60] FES (FES), a medical treatment used in the health sciences, uses regulated electrical currents to help paralyzed or weak muscles regain or improve their function. Electrical impulses are delivered to specific muscles or nerves during FES, prompting them to contract and produce movement.…”

The Influence of Polyvinyl Alcohol Porogen Addition on the Nanostructural Characteristics of Hydroxyapatite

“…The physicochemical characteristics of the synthesized samples are presented in Table 1, illustrating a correlation between increased porogen concentration and elevated pH values. Furthermore, as the pH shifts toward alkalinity, a concurrent improvement in electrical conductivity is observed, and the concentration of ions in alkaline solutions affects the value of electrical conductivity [37]. The data represent the average of two replicates.…”