ISC7

3D Resistivity Survey of a Weathering Profile of Metamorphic Rocks in State of Pernambuco, Brazil

  • Coutinho, Roberto (Federal University of Pernambuco)
  • BORTOLOZO, Cassiano (Centro Nacional de Monitoramento e Alertas de)
  • Andrade, Marcio (Centro Nacional de Monitoramento e Alertas de)
  • Silva, Felipe (Federal University of Pernambuco)

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This study aims to study a weathering profile of crystalline rocks in the City of Camaragibe, State of Pernambuco, Brazil. For this purpose, a survey using electroresistivity was conducted. A regular mesh was performed aiming at 3D acquisition. The electrode configuration was by the reconstruction of a two-dimensional network of parallel pseudosections. The target area of the survey has 3 meters deep probe responsible for recording soil moisture information and such information was used in the analyses. An auger soil sampler also was carried out reaching a depth of 3 meters to describe and identify the substrate. The main objectives of the study are to determine the geoelectrical characteristics of the materials and relate them to the strata crossed and the soil moisture profiles. The superficial geological context indicates residual soils of crystalline rocks, more specifically gneisses. The results made it possible to obtain a geoelectric model 8 meters deep with clear identification of an upper geoelectric layer and another lower layer. The superficial geoelectric layer has a resistivity between 1200 and 400 Ohm.m and in depth there is the lower geoelectric layer, with a resistive response between 400 and 20 Ohm.m. Said horizons are limited by a 400 Ohm.m isoline at a depth of ≅ 2 meters. The geoelectric model answers the objective of identifying soil weathering profile of metamorphic rocks. The higher resistivity values of the surface geoelectric layer can be correlated to a mature residual soil with a predominance of clay particle size fraction and lower moisture values. The lower geoelectric layer has lower resistivities and is related to a saprolite, which still presents foliations as relict rock structures. The lower resistivities may also be a response to the greater quantity of clay minerals observed and higher humidity values.