Airbone geophysical and geologic data integration and its contribution the geodynamic evolution of central Ceara domain, Borborema Province / Integração de dados aerogeofisicos e geologicos e sua contribuição a evolução geodinamica do dominio Ceará Central, Provincia Borborema

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

Advances in airborne geophysical data processing techniques and their integration with geologic data allow recovering valuable information from both geophysical surveys and, the older technology. These information represent an essential tool for geologic-structural mapping of Pre-Cambrian terrains, where the stratigraphic and structural relations are difficult to be delineated in field works. The airborne geophysical data from Rio Acaraú (1975) and Itatira (1977) projects were carried out through respectively, in the northwest and central regions of the State of the Ceará. Their processing produced products useful to indirectly identify regional geologic features. The verification and applicability of this approach was tested in an pilot-area whose limits are within the Umirim and Canindé topographic sheets, at 1: 100,000 scale. The integration between the airborne geophysical and the geologic field data supported to the geologic mapping at the same cited scale. Two main units were recognized: the Santa Quitéria Magmatic Arc - AMSQ and the para-and-orthoderivative supracrustal sequences that surround the arc. The AMSQ has four major lithologies: Np1 with anatetic granites; Np2: orthoderivated migmatites; Np3: porfiritic gneissic granites; Np4: granodioritic gneisses. The paraderivative supracrustal sequence (Ccp) consists of six mapped subunits, the paragneisses, marbles migmatites, mica-schists, quartzites and, calk-silicated rocks. The ortoderivative sequence (Cco) is formed by eight subunits, the granodiorites, leucogranitoids, mafic migmatites (diatexites and, metatexites), amphibolites, diorites and, granulites. The structural lineaments analysis at regional scale was done after the processing and interpretation of the airborne magnetic products and, the digital elevation model derived from the Shuttle Radar Topographic Mission-SRTM. The major lineaments correspond to the dextral transcurrent Paramoti Shear Zone (ZCP) of NE-SW direction and, to low angle shear zones with E-SE thrustdirection at the Northwestern sector and, another shear zone facing to W-NW direction at the Southeastern sector. About the deformation history, the main operating regime was compressive and, responsible for foliation, lineation, folds and shear zones.This history comprises three deformational phases called Fn, Fn+1, Fn+2. The Fn phase is represented by thrust toward E-SE in the Northwestern sector and towards W-NW direction at the Southeastern sector. The Fn+1 phase, of transpressional nature, marks the development of shear zones with NE-SW direction. Finally, the Fn+2 phase is related to the exhumation and consequently ruptile tectonics of the supracrustal rocks. The rocks from Santa Quitéria magmatic arc are characterized by high counting on the K-channel in its almost entire region and intermediate and low counting of Th and U. Generally, the supracrustal sequences are characterized by high values on the U-and-Th-channels and low on K-channel. The subunit Metaultramafics (Cco3) and Hornblendgnaisses and, mafics granulites (Cco4), are remarkable by the occurrence retro-eclogites bands and mafic granulites as lenses within gneisses and migmatites. These subunits present strong negative anomalies, with low counting on the three K, Th and, U channels. The best example for this negative anomalies are in the central region of the area, at south of Pentecostes city. That area also has positive magnetic anomalies, with high values of magnetic susceptibility.

ASSUNTO(S)

geofisica - processamento de dados geologia estrutural geologic mapping geophysics mapeamento geologico - borborema (ce) geotectonic

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