Terrestrial Electromagnetic Induction under the Parana Basin

Abstract

The study aims to define the geoelectric characteristics of the underlying crust of the Paraná Basin, using deep geomagnetic soundings with triaxial fluxgate magnetometers. These magnetometers will be deployed in at least 60 sites, composing a grid with sounding spacing of 50-80 km, complementing similar data already collected in different parts of the study area. In this way, new and relevant geophysical information is obtained on the distribution of the electrical conductivity of the lithosphere under the Paraná Basin. The characteristics of the electromagnetic induction allow geophysical observations at distinct depths as a function of the period of the natural signal and of the conductivity of the crustal rocks. Thus, this study will provide a regional view of the main geoelectrical features of the basin (short periods) and the main resistive discontinuities at great depths (long periods). Since the resistive silicates are the predominant minerals of the crust, the proposed approach is very sensitive to the presence of anomalous conductors, generally associated with concentrations of mineralized fluids (electrolytic conduction) or the presence of minerals that are great conductors (especially graphite, by electronic conduction). In this way, at the typical crustal depths, the electric conduction is related to the inter connection of minor rock constituents that carry mineral conductors such as graphite or saline fluids.This study is linked to a FAPESP Thematic project that has the goal to make geophysical models of the lithosphere under the Paraná and Chaco-Paraná Basins. Through this work, it will be estimated new gravity gradient tensor data from ESA's GOCE (European Space Agency's Global Steady-State Ocean Circulation Explorer) satellite Mission, coalesced to models of the gravity and geoid field from terrestrial gravity data already acquired by several Brazilian institutes, other satellites (e.g. GRACE - Gravity Recovery and Climate Experiment) and global geopotential models (e.g. EGM2008). The results from this phase will be used in the design of new gravimetric maps of the entire region of the Paraná and Chaco-Paraná basins, from the shallow parts (sedimentary basins) to the lower crust and upper mantle. These data will be used as parameters of geoelectrical resistivity, phase and anisotropy, in 2D and 3D models of the basin and of the underlying lithosphere. The student activities involve magnetometer's calibration, data quality tests, estimation of inductions arrows, direct modeling of the data and interpretation of the results. All the necessary infra structure of equipments and computer facilities will become available by Geomagnetic and Induction Studies Group of the Space Geophysics Division of INPE, where the study will be conducted.