Hoël Seillé

Australian Resources Research Centre

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Gerhard Visser

Commonwealth Scientific and Industrial Research Organisation

J. Pous

Universitat de Barcelona

Jérémie Giraud

University of Western Australia

Mark Lindsay

Australian Resources Research Centre

Mark Jessell

University of Western Australia

Vitaliy Ogarko

University of Western Australia

Janelle Simpson

Geological Survey of Western Australia

Jelena Markov

Commonwealth Scientific and Industrial Research Organisation

J. Gallastegui

Universidad de Oviedo

Ivan Romero‐Ruiz

Universitat de Barcelona

Cooperative Institutions

Universitat de Barcelona

Consejo Superior de Investigaciones Científicas

Universidad de Oviedo

Commonwealth Scientific and Industrial Research Organisation

Australian National University

University of Adelaide

Geociencias Barcelona

Universidad Complutense de Madrid

Australian Resources Research Centre

Geological Survey of Western Australia

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Nuevos datos de magnetotelúrica (MT) en Tenerife

Geotemas ( Madrid ) (2012)

J. Pous Hoël Seillé Iván Vera-Romero María Candelaria Martín Luis

espanolSe han registrado 13 sondeos de magnetotelurica (MT) de banda ancha con periodos que abarcan desde 0.004 s hasta 500 s y 3 sondeos de periodo largo con periodos desde 10 s hasta 20000 s en la zona central de Tenerife. Los sondeos de banda ancha se situan en Montana Blanca en la Caldera de las Canadas. Se registraron las variaciones de los campos magneticos y electricos en las direcciones NS y EW, asi como las del campo magnetico en la direccion vertical. En este primer estudio con estos datos se han utilizado los periodos inferiores a 20 s con el fin de evitar la influencia del mar. Se ha realizado una inversion de los datos a lo largo de 2 perfiles. Los modelos resultantes de la inversion muestran la presencia de una capa conductora a 400-500 m de profundidad asociada al nivel saturado. Dentro de esta capa aparecen zonas de mayor conductividad asociadas a alteracion hidrotermal. La combinacion con sondeos MT registrados anteriormente permite correlacionar la continuidad de estas zonas de alteracion fuera de la Caldera de Las Canadas. EnglishThirteen broad band (BBMT) and three long period (LMT) magnetotelluric soundings were carried out in Montana Blanca within Las Canadas caldera in Tenerife. The periods range from 0.004 s to 500 s for the BBMT data and from 10 s to 20000 s for the LMT data. The electrical and magnetic fields were recorded in NS and EW directions as well as in the vertical direction for the magnetic field. Dimensionality analysis indicated a predominant direction of the electrical resistivity and a 2D inversion of the data was carried out along two profiles. In this preliminary study only periods lower than 20 s were used in order to avoid the sea effect. The inverse models reveal the presence of a conductive layer at 400-500 m depth associated with a main aquifer. Within this conductive layer the models show zones of highest conductivity, which are associated with hydrothermal alteration. The combination with previous existing MT sites allows identifying the continuity of these zones of hydrothermal alteration out the Las Canadas caldera.

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How to enhance Magnetotellurics resistivity model resolution using passive seismic HVSR to identify the cover-basement interface.

Zenodo (CERN European Organization for Nuclear Research) (2021)

Nuwan Suriyaarachchi Jérémie Giraud Hoël Seillé Mark Lindsay Vitaliy Ogarko

Magnetotellurics

Basement

Interface (matter)

10.5281/zenodo.7690856

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Structurally Self-Constrained Magnetotelluric Inversion, A Synthetic Study

Hoël Seillé G. Visser

Summary Many Australian metallogenic provinces are buried under thick post-mineralization cover. The detection of the depth to prospective basement or discrete mineral deposits is challenging in this type of geological environment, and common geophysical data modelling approaches requires constraints to enhance the reliability of the resulting geophysical images. In this work, we propose a probabilistic magnetotelluric (MT) data driven workflow for deriving those structural constraints. These are then used to constrain a deterministic 2D MT inversion. The workflow is assessed using synthetic data MT calculated from a realistic 2D Earth. We show that a geologically realistic image with sharp resistivity boundaries can be recovered, making the precise spatial detection of prospective basement or discrete mineral deposits possible, even in presence of a thick cover.

Magnetotellurics

Synthetic data

Basement

Mineral exploration

10.3997/2214-4609.202220164

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Análisis de la estructura alpina de la corteza del centro de la Península Ibérica: Una sección Magneto-Telúrica a través del Sistema Central (Sierra de Gredos)

J. Pous Alfonso Muñoz Martín Antonio José Olaiz Campos Hoël Seillé Gerardo de Vicente Muñoz

We present a magnetotelluric profile across the Duero basin, the Central System and the Madrid basin, acquired in the framework of the TOPO-IBERIA project. The MT profile consists of 24 magnetotelluric sites over a 200 km, NS oriented profile. Five components were measured with periods ranging from 0.001 s to 500s. The dimensional analysis reveals a dominant E-W direction and 2D joint inversion of apparent resistivity, phases and tipper was carried out. The inverse resistivity model obtained has been compared with other geological and geophysical data, and it shows a resistive and homogeneous crust that extends towards the Duero basin. The main conductive anomalies are elongated and inclined bodies that are related with the main big–scale Alpine thrusts. Other superficial conductive bodies are related with the tertiary sedimentary basins. [RESUMEN]Este trabajo muestra un nuevo perfil magnetotelurico (MT) a traves del la cuenca del Duero, el Sistema central y la Cuenca de Madrid, adquirido dentro del proyecto TopoIberia. El Perfil MT consiste en 24 sondeos a lo largo de 200 km con una orientacion NS. En cada sondeo se han medido cinco componentes con periodos de 0.001 a 500 s. El analisis dimensional revela una direccion dominante E-O y se ha realizado una inversion conjunta en 2D de las resistividades aparentes, fases y tipper. El modelo de resistividades obtenido ha sido comparado con otros datos geologicos y geofisicos, y muestra una estructura cortical homogenea y resistiva que se prolonga hacia la cuenca del Duero. En esta corteza aparecen cuerpos conductores inclinados y alargados en profundidad asociados a grandes cabalgamientos alpinos. Otros cuerpos conductores superficiales estan claramente relacionados con las cuencas sedimentarias terciarias

Magnetotellurics

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Geoelectrical characterization of the lithosphere beneath the Cantabrian Mountains and Duero Basin

EGU General Assembly Conference Abstracts (2012)

Hoël Seillé J. Pous D. Pedreira J. Gallastegui J. A. Pulgar

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Probabilistic Cover‐Basement Interface Map in Cloncurry, Australia, Using Magnetotelluric Soundings

Journal of Geophysical Research Solid Earth (2021)

Hoël Seillé Gerhard Visser Jelena Markov Janelle Simpson

Abstract In this article we propose a workflow for creating geologically realistic depth to basement maps and apply it to the undercover area of Cloncurry, located in the Mount Isa province, Queensland. A magnetotelluric (MT) survey consisting of 457 soundings was inverted using a 1D trans‐dimensional Bayesian algorithm designed to be robust to non‐1D effects present in the data. Automated change‐point analysis was then used to derive probability distributions on basement depth for each site independently. These were laterally combined, along with drill hole data and a structural model derived from aeromagnetic and geological data, using a Bayesian estimate fusion algorithm to create a region wide depth to basement probabilistic map. Combining many different constraints in this way lead to a significant reduction in posterior uncertainty. Individual MT site change‐point posteriors were highly multi‐modal in certain areas, with multiple resistivity transitions that could correspond to the cover‐basement interface. The estimate fusion process correlates these uncertainties and the combined posterior was thus much less multi‐modal. Our results show that the sedimentary cover gradually thickens toward the north, while toward the east its thickening is controlled by a two‐steps fault system. This workflow highlights the value gained from integrating different types of geoscientific data but also shows the capability of the MT method used within a probabilistic workflow to accurately image depth to basement even using limited constraints and assumptions.

Magnetotellurics

Basement

10.1029/2021jb021883

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Citations (10)

Magnetic inversion constrained by probabilistic magnetotellurics models: methodology and application

Zenodo (CERN European Organization for Nuclear Research) (2021)

Jérémie Giraud Hoël Seillé Vitaliy Ogarko Gerhard Visser Mark Lindsay

Magnetotellurics

10.5281/zenodo.7694072

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The crustal structure of the Cantabrian Mountains revealed by new magnetotelluric soundings

Tectonophysics (2022)

Hoël Seillé J. Pous D. Pedreira J. Gallastegui Ivan Romero‐Ruiz

The upper crustal structure of the central Cantabrian Mountains consists of a block of Variscan basement uplifted over the Duero basin as a consequence of a southward displacement along a major thrust during the convergence between Europe and Iberia in the Eocene-Oligocene (Alpine orogeny). We present the results of the 3-D modeling of thirteen new magnetotelluric sites, five of them being completed by long period data, over a 100 km-long, N-S oriented profile across the central Cantabrian Mountains and the Duero basin. Dimensionality analyses indicated a dominant E-W direction but with influence of 3-D structures at long periods and locally in the Cantabrian Mountains. Accordingly, we performed a 3-D joint inversion of the full impedance tensor and the geomagnetic transfer function following a sequential inversion workflow. The inverse model presents similarities with existing lithospheric models. In the southern part of the area, the conductive sediments of the Duero basin over a high resistive and homogeneous Iberian lithosphere are well delineated. Towards the north, beneath the Cantabrian Mountains, the model reveals a heterogeneous and conductive lithosphere, in which various elongated and dipping conductors in the upper and middle crust are associated with major Alpine thrusts, one being the frontal thrust of the Cantabrian Mountains over the Duero basin. At deeper depths (between 20 and 35 km depth), the Iberian crust appears as subducting to the north beneath a conductive zone interpreted as the hydrated mantle wedge of the north-Iberian continental margin.

Magnetotellurics

10.1016/j.tecto.2022.229310

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Datasets for the integration of MT data with magnetic inversion: proof-of-concept using synthetic data and field application

Zenodo (CERN European Organization for Nuclear Research) (2022)

Jérémie Giraud Hoël Seillé

This dataset is a companion dataset to the manuscript "Utilisation of probabilistic MT inversions to constrain magnetic data inversion: proof-of-concept and field application", by Jérémie Giraud, Hoël Seillé, Mark D. Lindsay, Gerhard Visser, Vitaliy Ogarko, and Mark W. Jessel. It contains models and data shown in the paper.The document was submitted for publication in Solid Earth: https://se.copernicus.org/preprints/se-2021-124/se-2021-124-manuscript-version2.pdfThe folder organisation is as follows, where bold refers to folders and subfolders, and text in italic corresponds to a succinct description of the contents.|-- Dataset_synth > synthetic dataset and results| |-- Mag > magnetic data and models: inversion and results | | |-- domains > contains the files used to define domains for inversion| | |-- inversion results > contains subfolders with inversion results for different cases | | | |-- case a | | | |-- case b| | | |-- case c| | | |-- case d| | | |-- case e| | | |-- case f | | |-- membership values > contain files with membership values for the cases (a)-(f)| | |-- responses > simulated data with and without noise| | |-- true model > true model used for simulation| |-- MT > MT probabilities, sites information and models| | |-- probabilities > MT-derived probabilities| | |-- responses > simulated MT data| | | |-- edi_noise_5p > 5% noise-contaminated data (*.edi files)| | | |-- MansfieldMT_fwd.dat > uncontaminated (ModEM format *.dat file)| | |-- model > model in ModEM format (*.mod) and WinGLink format (.out) formats| | |-- coordinates.txt > location of MT sites| |-- Rock units > contains the file with indices of the rock unit model, in 3D, of the modified Mansfield model. The indices are stored as a column vector. |-- Dataset_field > field dataset| |-- Mag > magnetic data and models: inversion and results| | |-- admm constraints > file with bound constraints used in cases 3, 4, and adjusted case 4.| | |-- data > magnetic data for inversion, x, y, z, data column format.| | |-- inverted models > folders containing inversion results for the different cases tested| | | |-- case 1 | | | |-- case 2| | | |-- case 3| | | |-- case 4| | | |-- case 4 adjusted| |-- MT > MT probabilities and sites information| | |-- probabilities > MT probabilities of interface and rock units (*.txt files)| | |-- coord_L26_sites > File containing the location of sites along ligne L26

Proof of concept

Synthetic data

10.5281/zenodo.6340159

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Structure of the mantle beneath the Alboran Basin from magnetotelluric soundings

Geochemistry Geophysics Geosystems (2015)

Xavier García Hoël Seillé J. Elsenbeck R. L. Evans Marion Jegen

Abstract We present results of marine MT acquisition in the Alboran sea that also incorporates previously acquired land MT from southern Spain into our analysis. The marine data show complex MT response functions with strong distortion due to seafloor topography and the coastline, but inclusion of high resolution topography and bathymetry and a seismically defined sediment unit into a 3‐D inversion model has allowed us to image the structure in the underlying mantle. The resulting resistivity model is broadly consistent with a geodynamic scenario that includes subduction of an eastward trending plate beneath Gibraltar, which plunges nearly vertically beneath the Alboran. Our model contains three primary features of interest: a resistive body beneath the central Alboran, which extends to a depth of ∼150 km. At this depth, the mantle resistivity decreases to values of ∼100 Ohm‐m, slightly higher than those seen in typical asthenosphere at the same depth. This transition suggests a change in slab properties with depth, perhaps reflecting a change in the nature of the seafloor subducted in the past. Two conductive features in our model suggest the presence of fluids released by the subducting slab or a small amount of partial melt in the upper mantle (or both). Of these, the one in the center of the Alboran basin, in the uppermost‐mantle (20–30 km depth) beneath Neogene volcanics and west of the termination of the Nekkor Fault, is consistent with geochemical models, which infer highly thinned lithosphere and shallow melting in order to explain the petrology of seafloor volcanics.

Seafloor Spreading

Asthenosphere

Magnetotellurics

Slab

10.1002/2015gc006100

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Citations (27)