Airborne geophysical and tectonics of the Ceará central domain, eastern region of the Santa Quitéria magmatic ARC, Borborema Province, NE Brazil

Abstract

ABSTRACT. The airborne geophysical data gamma-spectrometric and magnetic from Itatira Project (1977) was carried out, in the central region of the State of the Ceará, Brazil. Their processing produced products useful to indirectly identify regional geologic features. The verification and applicability of this approach was tested in a 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 and the supracrustal sequences that surround the arc. 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 eTh and eU. Generally, the supracrustal sequences are characterized by high values on the eU-and-eTh-channels and low on K-channel. The subunit metaultramafics and, mafics granulites, are remarkable by the occurrence retrograde eclogites bands and mafic granulites as lenses within gneisses and migmatites.These subunits present strong negative anomalies, with low counting on the three K, eTh and eU channels. That area also has positive magnetic anomalies, and may reflect high values of magnetic susceptibility.Keywords: airborne geophysical, geologic mapping, mafics granulites, retrograde eclogites. RESUMO. Dados aerogeofísicos gamaespectrométricos e magnéticos adquiridos no Projeto Itatira (1977), região central do Estado do Ceará, foram processadose integrados com a finalidade de gerar produtos que possam ser utilizados como ferramenta indireta na identificação de feições geológicas regionais. A verificação e aplicabilidade do método foram postas em prática naárea piloto compreendida pelas folhas topográficas 1:100.000 Umirim e Canindé. A integração dos dados aerogeofísicos e geológicos de campo, dando suporte ao mapeamento geológico em escala 1:100.000, permitiu reconhecer duas principais unidades de mapeamento: o arco magmático de Santa Quitéria e as seqüências supracrustais que o bordejam. As rochas do arco magmático de Santa Quitéria foram caracterizadas por apresentarem altas contagens no canal de K em quase toda região de abrangência e contagens intermediárias e baixas de Th e U. De modo geral, a seqüência supracrustal foi caracterizada por apresentar alta contribuição dos canais de U e Th e baixa de K. As subunidades metaultramáficas e granulitos máficos, onde se destaca a ocorrência de retro-eclogitos e granulitos máficos encaixados como lentes em gnaisses e migmatitos, apresentam baixas contagens nos três canais K-eTh-eU. Na magnetometria essas rochas têm anomalias positivas e devem refletir altos valores de susceptibilidade magnética.

Occurrence and geochemistry of metamafic rocks from the Forquilha Eclogite Zone, central Ceará (NE Brazil): geodynamic implications

“…However, the real age of the Ceará Group is still uncertain. Rare HP/UHP metamorphic rocks from the Ceará Group, including garnet amphibolites, clinopyroxene-garnet amphibolites and retrograded eclogites in the Forquilha Eclogite Zone and the Itatira areas crop out, respectively, on the western and eastern sides of the Santa Quitéria magmatic arc (Figure 2; Castro, 2004;Garcia and Arthaud, 2004;Amaral and Santos, 2008).…”

Integrating geological and airborne geophysical data to review the cartography of Rio Itanguá Batholith, Araçuaí Orogen, Brazil

“…Airborne geophysical data have been widely used as a tool for the interpretation of geological features, aiding geological mapping efforts and mineral prospecting projects (e.g., Rattenbury et al 2016, Barbuena et al 2013, Reis et al 2012, Amaral & Santos 2008. Hence, magnetometry and gamma-ray spectrometry data can be combined with field data in order to better define the limits of geological units, according to their unique characteristics, as well as to mark structural features.…”