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Probing geoelectrical structures in the upper-mantle under the shield in South-Central Brazil


A four-year research program is proposed with the main focus on the understanding of deep lithospheric-scale processes in the geophysically poorly-known South American Shield. The investigation will be carried out through analyses and interpretations of data obtained from deep-probing wide-band and long-period Magnetotelluric (MT) methods, Geomagnetic Deep Soundings (GDS)and modeling of the geoid. Primary objectives are the mapping of the depth to the thermal and mechanical lithosphere-asthenosphere boundary, the detection of lateral variations of electrical anisotropy and of density in provinces with distinct lithosphere evolution, and inferences on the causes of deep Earth mass anomalies. These aspiring goals are reasonably attainable by the integration of gravimetry and induced electromagnetic methods applied in the deep upper-mantle, made possible by advanced equipment and improved data processing capabilities currently available to the participating research team. Funds are mainly needed for fieldwork, shipping and deployment of equipment, and processing of data from two areas that were selected for detailed investigations because of their distinct geologic/tectonic characteristics and advancements on their seismic, tectonic and deep-mantle petrologic knowledge: (i) the highlands of the southern São Francisco Craton and adjacent amalgamated fold belts; and (ii)the low-lying Pantanal-Chaco Basins. The former area, with a core largely composed by Archean rocks, was affected by lithospheric-scale Cretaceous magmatic and tectonic processes leading to sedimentation over its central portion and to mafic-ultramafic/alkaline/kimberlitic magmatism in the uplifted and partly eroded metasedimentary belts that were encroached around the cratonic border as a consequence of the Neoproterozoic Braziliano orogeny. This region is the site of an accentuated positive anomaly of the geoid and is in the proximity of a mapped low seismic velocity zone at depths below 200 km. Similarly, the subsided Cenozoic sediments of the Pantanal-Chaco regions display an extensive positive anomaly of the geoid, low seismic velocity at lithospheric depths and Cretaceous magmatism. Therefore, the significant questions that the investigation will seek to unravel are related to deep geologic-tectonic processes accountable for vertical and lateral movements and stresses, deep-seated magmatic source material and Earth mass anomalies. Results from the study will complement and possibly corroborate deep-mantle seismic and petrologic data and, thus, could verify prevailing mantle-related interpretations and contribute to a better knowledge of structural, igneous and metamorphic crustal processes, which might have some impact an strategies of mineral search. The proposal has an unprecedented and opportune advantage of directing, to the common goal of understanding mantle properties and dynamics, efforts of numerous experienced experts in Electromagnetic induction and Potential Fields methods, graduate and undergraduate students from four national research institutes, and leading foreign collaborators. (AU)

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Scientific publications (7)
(References retrieved automatically from Web of Science and SciELO through information on FAPESP grants and their corresponding numbers as mentioned in the publications by the authors)
LUIZ GUSTAVO RODRIGUES PINTO; NAOMI USSAMI; NELSI CÔGO DE SÁ. Aquisição e interpretação de anomalias gravimétricas do Quadrilátero Ferrífero, SE do Cráton São Francisco. Revista Brasileira de Geofísica, v. 25, n. 1, p. 21-30, . (00/00806-5)
BOLOGNA, MAURICIO S.; PADILHA, ANTONIO L.; VITORELLO, ICARO; PADUA, MARCELO B.. Signatures of continental collisions and magmatic activity in central Brazil as indicated by a magnetotelluric profile across distinct tectonic provinces. Precambrian Research, v. 185, n. 1-2, p. 55-64, . (00/00806-5)
ZEVALLOS, IVAN; ASSUMPCAO, MARCELO; PADILHA, ANTONIO L.. Inversion of teleseismic receiver function and magnetotelluric sounding to determine basement depth in the Parana Basin, SE Brazil. JOURNAL OF APPLIED GEOPHYSICS, v. 68, n. 2, p. 231-242, . (00/00806-5)
PADILHA, ANTONIO L.; ALVES, LIVIA R.; SILVA, GRAZIELA B. D.; ESPINOSA, KAREN V.. Effect of a huge crustal conductivity anomaly on the H-component of geomagnetic variations recorded in central South America. EARTH PLANETS AND SPACE, v. 69, . (09/50493-8, 00/00806-5)
PADILHA, A. L.; VITORELLO, I.; FONTES, S. L.; BOLOGNA, M. DE S.. Geoelectric crustal structures off the SW border of the Sao Francisco craton, central Brazil, as inferred from a magnetotelluric survey. Geophysical Journal International, v. 162, n. 2, p. 357-370, . (00/00806-5)
BOLOGNA, M. S.; PADILHA, A. L.; PADUA, M. B.; VITORELLO, I.; CHAMALAUN, F. H.. Paraguay-Araguaia Belt Conductivity Anomaly: A fundamental tectonic boundary in South American Platform imaged by electromagnetic induction surveys. GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS, v. 15, n. 3, p. 509-515, . (09/50493-8, 00/00806-5)
PADILHA, ANTONIO L.; ALVES, LIVIA R.; SILVA, GRAZIELA B. D.; ESPINOSA, KAREN V.. Effect of a huge crustal conductivity anomaly on the H-component of geomagnetic variations recorded in central South America. EARTH PLANETS AND SPACE, v. 69, p. 10-pg., . (00/00806-5, 09/50493-8)

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