Satellite tidal magnetic signals constrain oceanic lithosphere-asthenosphere boundary

The tidal flow of electrically conductive oceans through the geomagnetic field results in the generation of secondary magnetic signals, which provide information on the subsurface structure. Data from the new generation of satellites were shown to contain magnetic signals due to tidal flow; however, there are no reports that these signals have been used to infer subsurface structure. We use satellite-detected tidal magnetic fields to image the global electrical structure of the oceanic lithosphere and upper mantle down to a depth of about 250 km. The model derived from more than 12 years of satellite data reveals a ≈72-km-thick upper resistive layer followed by a sharp increase in electrical conductivity likely associated with the lithosphere-asthenosphere boundary, which separates colder rigid oceanic plates from the ductile and hotter asthenosphere.ISSN:2375-254

Satellite Tidal Magnetic Signals Constrain Oceanic Lithosphere-Asthenosphere Boundary Earth Tomography with Tidal Magnetic Signals

The tidal flow of electrically conductive oceans through the geomagnetic field results in the generation of secondary magnetic signals, which provide information on the subsurface structure. Data from the new generation of satellites were shown to contain magnetic signals due to tidal flow; however, there are no reports that these signals have been used to infer subsurface structure. Here we use satellite-detected tidal magnetic fields to image the global electrical structure of the oceanic lithosphere and upper mantle down to a depth of about 250 km. The model derived from more than 12 years of satellite data reveals an Approximately 72 km thick upper resistive layer followed by a sharp increase in electrical conductivity likely associated with the lithosphere-asthenosphere boundary, which separates colder rigid oceanic plates from the ductile and hotter asthenosphere

Exploring equivalence domain in nonlinear inverse problems using Covariance Matrix Adaption Evolution Strategy (CMAES) and random sampling

ISSN:0956-540XISSN:1365-246

Anomaly of the geomagnetic Sq variation in Japan: effect from 3-D subterranean structure or the ocean effect?

ISSN:0956-540XISSN:1365-246

Real-Time 3-D Modeling of the Ground Electric Field Due To Space Weather Events. A Concept and Its Validation

We present a methodology that allows researchers to simulate in real time the spatiotemporal dynamics of the ground electric field (GEF) in a given 3-D conductivity model of the Earth based on continuously augmented data on the spatiotemporal evolution of the inducing source. The formalism relies on the factorization of the source by spatial modes (SM) and time series of respective expansion coefficients and exploits precomputed GEF kernels generated by corresponding SM. To validate the formalism, we invoke a high-resolution 3-D conductivity model of Fennoscandia and consider a realistic source built using the Spherical Elementary Current Systems (SECS) method as applied to magnetic field data from the International Monitor for Auroral Geomagnetic Effect network of observations. The factorization of the SECS-recovered source is then performed using the principal component analysis. Eventually, we show that the GEF computation at a given time instant on a 512 x 512 grid requires less than 0.025 s provided that GEF kernels due to pre-selected SM are computed in advance. Taking the 7-8 September 2017 geomagnetic storm as a space weather event, we show that real-time high-resolution 3-D modeling of the GEF is feasible. This opens a practical opportunity for GEF (and eventually geomagnetically induced currents) nowcasting and forecasting.ISSN:1542-739

Crustal architecture of a metallogenic belt and ophiolite belt: implications for mineral genesis and emplacement from 3-D electrical resistivity models (Bayankhongor area, Mongolia)

Crustal architecture strongly influences the development and emplacement of mineral zones. In this study, we image the crustal structure beneath a metallogenic belt and its surroundings in the Bayankhongor area of central Mongolia. In this region, an ophiolite belt marks the location of an ancient suture zone, which is presently associated with a reactivated fault system. Nearby, metamorphic and volcanic belts host important mineralization zones and constitute a significant metallogenic belt that includes sources of copper and gold. However, the crustal structure of these features, and their relationships, are poorly studied. We analyze magnetotelluric data acquired across this region and generate three-dimensional electrical resistivity models of the crustal structure, which is found to be locally highly heterogeneous. Because the upper crust ( 1000 Ωm), low-resistivity (< 50 Ωm) features are conspicuous. Anomalous low-resistivity zones are congruent with the suture zone, and ophiolite belt, which is revealed to be a major crustal-scale feature. Furthermore, broadening low-resistivity zones located down-dip from the suture zone suggest that the narrow deformation zone observed at the surface transforms to a wide area in the deeper crust. Other low-resistivity anomalies are spatially associated with the surface expressions of known mineralization zones; thus, their links to deeper crustal structures are imaged. Considering the available evidence, we determine that, in both cases, the low resistivity can be explained by hydrothermal alteration along fossil fluid pathways. This illustrates the pivotal role that crustal fluids play in diverse geological processes, and highlights their inherent link in a unified system, which has implications for models of mineral genesis and emplacement. The results demonstrate that the crustal architecture—including the major crustal boundary—acts as a first‐order control on the location of the metallogenic belt.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung http://dx.doi.org/10.13039/501100001711Westfälische Wilhelms-Universität Münster (1056

Three-dimensional magnetotelluric modeling in spherical Earth

ISSN:0956-540XISSN:1365-246

Imaging the Whole-Lithosphere Architecture of a Mineral System-Geophysical Signatures of the Sources and Pathways of Ore-Forming Fluids

Mineral systems can be thought of as a combination of several critical elements, including the whole-lithosphere architecture, favorable geodynamic/tectonic events, and fertility. Because they are driven by processes across various scales, exploration benefits from a scale-integrated approach. There are open questions regarding the source of ore-forming fluids, the depth of genesis, and their transportation through the upper crust to discrete emplacement locations. In this study, we investigate an Au-Cu metal belt located at the margin of an Archean-Paleoproterozoic microcontinent. We explore the geophysical signatures by analyzing three-dimensional models of the electrical resistivity and shear-wave velocity throughout the lithosphere. Directly beneath the metal belt, narrow, vertical, finger-like low-resistivity features are imaged within the resistive upper-middle crust and are connected to a large low-resistivity zone in the lower crust. A broad low-resistivity zone is imaged in the lithospheric mantle, which is well aligned with a zone of low shear-wave velocity, examined with a correlation analysis. In the upper-middle crust, the resistivity signatures give evidence for ancient pathways of fluids, constrained by a structure along a tectonic boundary. In the lower lithosphere, the resistivity and velocity signatures are interpreted to represent a fossil fluid source region. We propose that these signatures were caused by a combination of factors related to refertilization and metasomatism of the lithospheric mantle by long-lived subduction at the craton margin, possibly including iron enrichment, F-rich phlogopite, and metallic sulfides. The whole-lithosphere architecture controls the genesis, evolution, and transport of ore-forming fluids and thus the development of the mineral system.ISSN:1525-202

Catalytic properties of nanofibrous carbon in selective oxidation of hydrogen sulphide

Nanofibrous carbonaceous materials (NFC) as a new class of materials having many applications, can catalyze the selective oxidation of H2S to sulfur. The correlation between NFC structure and its activity and selectivity in H2S oxidation was determined. It is demonstrated that selectivity can be improved if NFC with more ordered structure be synthesized and the portion of the original catalyst in carbon be reduced by increasing the carbon accumulated in the catalyst.<br /

Compaction‐Driven Fluid Localization as an Explanation for Lower Crustal Electrical Conductors in an Intracontinental Setting

We present electrical resistivity models, derived from magnetotelluric data, of the crust beneath the Bulnay region, Mongolia. They reveal that the lower crust contains a pattern of discrete zones (width of ~25 km) of low resistivity (<30 Ωm). Such features may be an effect of unaccounted‐for electrical anisotropy. However, when anisotropy is considered in the modeling, the features remain. We investigate an alternative explanation, based on a conceptual model of fluid localization and stagnation by thermally activated compaction, and demonstrate it is compatible with the observed low‐resistivity zones. The model explains the location, shape, and size of the zones, with plausible values of the activation energy for lower crustal creep (270–360 kJ/mol), and a viscous compaction length on the order of 10 km. The results imply tectonic deformation and compaction processes, rather than lithological‐structural heterogeneity, control the regional lower crustal fluid flow.ISSN:0094-8276ISSN:1944-800