Three-dimensional electrical resistivity structure of the Kuju volcanic group, Central Kyushu, Japan revealed by magnetotelluric survey data

AbstractTo analyze the process of subduction of the Nazca and South American plates in the area of the Southern Andes, and its relationship with the tectonic and volcanic regime of the place, magnetotelluric measurements were made through a transversal profile of the Chilean continental margin. The data-processing stage included the analysis of dimensional parameters, which as first results showed a three-dimensional environment for periods less than 1 s and two-dimensional for periods greater than 10 s. In addition, through the geomagnetic transfer function (tipper), the presence of structural electrical anisotropy was identified in the data. After the dimensional analysis, a deep electrical resistivity image was obtained by inverting a 2D and a 3D model. Surface conductive anomalies were obtained beneath the central depression related to the early dehydration of the slab and the serpentinization process of the mantle that coincides in location with a discontinuity in the electrical resistivity of a regional body that we identified as the Nazca plate. A shallow conductive body was located around the Calbuco volcano and was correlated with a magmatic chamber or reservoir which in turn appears to be connected to the Liquiñe Ofqui fault system and the Andean Transverse Fault system. In addition to the serpentinization process, when the oceanic crust reaches a depth of 80–100 km, the ascending fluids produced by the dehydration and phase changes of the minerals present in the oceanic plate produce basaltic melts in the wedge of the subcontinental mantle that give rise to an eclogitization process and this explains a large conductivity anomaly present beneath the main mountain range.

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

Earth Planets and Space ◽

10.1186/s40623-021-01400-9 ◽

2021 ◽

Vol 73 (1) ◽

Author(s):

Matthew J. Comeau ◽

Michael Becken ◽

Alexey V. Kuvshinov ◽

Sodnomsambuu Demberel

Keyword(s):

Electrical Resistivity ◽

Crustal Structure ◽

Three Dimensional ◽

Suture Zone ◽

Fault System ◽

Magnetotelluric Data ◽

Low Resistivity ◽

Ophiolite Belt ◽

Geological Processes ◽

Metallogenic Belt

AbstractCrustal 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 (< 25 km) is found to be generally highly resistive (> 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.

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Three‐Dimensional Resistivity Structure of Iwo‐Yama Volcano, Kirishima Volcanic Complex, Japan: Relationship to Shallow Seismicity, Surface Uplift, and a Small Phreatic Eruption

Geophysical Research Letters ◽

10.1029/2018gl080202 ◽

2018 ◽

Vol 45 (23) ◽

Cited By ~ 12

Author(s):

K. Tsukamoto ◽

K. Aizawa ◽

K. Chiba ◽

W. Kanda ◽

M. Uyeshima ◽

...

Keyword(s):

Three Dimensional ◽

Phreatic Eruption ◽

Volcanic Complex ◽

Resistivity Structure ◽

Surface Uplift

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Dynamic modeling of tunnel survey spatiotemporal data

Boletim de Ciências Geodésicas ◽

10.1590/s1982-21702014000200021 ◽

2014 ◽

Vol 20 (2) ◽

pp. 354-375

Author(s):

Xiaolong Li ◽

Jiansi Yang ◽

Bingxuan Guo ◽

Hua Liu ◽

Jun Hua

Keyword(s):

Survey Data ◽

Cross Section ◽

Cross Sections ◽

3D Modeling ◽

3D Model ◽

Three Dimensional ◽

Spatiotemporal Data ◽

Excavation Process ◽

Special Cases ◽

Time Stamps

Currently, for tunnels, the design centerline and design cross-section with time stamps are used for dynamic three-dimensional (3D) modeling. However, this approach cannot correctly reflect some qualities of tunneling or some special cases, such as landslips. Therefore, a dynamic 3D model of a tunnel based on spatiotemporal data from survey cross-sections is proposed in this paper. This model can not only playback the excavation process but also reflect qualities of a project typically missed. In this paper, a new conceptual model for dynamic 3D modeling of tunneling survey data is introduced. Some specific solutions are proposed using key corresponding technologies for coordinate transformation of cross-sections from linear engineering coordinates to global projection coordinates, data structure of files and database, and dynamic 3D modeling. A 3D tunnel TIN model was proposed using the optimized minimum direction angle algorithm. The last section implements the construction of a survey data collection, acquisition, and dynamic simulation system, which verifies the feasibility and practicality of this modeling method.

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