Mapeamento geológico, gravimetria e trama magnética do corpo intrusivo Córrego Seco, Anicuns-GO

Abstract

The Corrego Seco (CS) pluton is situated in the Arenópolis Magmatic Arc, located in the southern portion of the Brasília Belt (FB). It is a semi-circular intrusive body (30 km²) that intrudes rocks of the Anicuns-Itaberaí Metavolcanosedimentary Sequence and the Tonian-aged Sanclerlândia metagranite. The pluton exhibits inverse concentric zoning with a mafic core (gabbro/noritic) grading to quartz-dioritic edges with medium to coarse textural grain size variation. Additionally, studies conducted in the region using isotopic data and geological mapping indicate that the CS (Ediacaran) has a late emplacement and may crystallize from more evolved magmas derived from the final tectonic collision event of the Brasília orogen. Geological mapping, gravimetry, and anisotropy of magnetic susceptibility (AMS) data were combined to determine the emplacement mechanisms of the CS and its chronology in relation to the collision structure of the Brasília Belt. The gravimetric survey resulted in 72 stations using a Scintrex CG-5 Autograv terrestrial gravimeter. For the AMS, 28 sites were measured throughout the body. Magnetic susceptibility is quite variable (average of 4.72x10-² SI) and thermomagnetic curves indicate that magnetite is the main carrier of anisotropy. It has a high degree of anisotropy ranging from 1.012 to 1.502. The average shape parameter of anisotropy, defined as the ratio between the major and minor axes of the AMS ellipsoid, varies, with oblate ellipsoids being predominantly more abundant than prolate ones. Magnetic foliation and lineation data present concentric patterns of magnetic fabrics that cut across the regional N-S trending foliation. Hysteresis loop measurements indicate that the magnetic contribution comes from magnetite, i.e., crystals larger than 1 μm, and its susceptibility anisotropy is controlled by the external shape of the grains. The gravimetric data obtained from the field survey reflect the inversely zoned distributions, grading from the edges to the core. The data suggest that the emplacement was controlled by magma buoyancy forces, free from tectonic stresses. Therefore, the data indicate that the pluton is post-collisional, configuring an intrusion associated with the extensional phase of the Brasília Belt.