Abstract
An integrated evaluation of geology, aerogammaspectrometry and aeromagnetometry of the Sul-Riogran-dense Shield is permitted by the advanced stage of understanding of the geology and geochronology of the southern Brazilian Shield and a 2010 airborne geophysical survey. Gamma rays are registered from the rocks near the surface and thus describe the distribution of major units in the shield, such as the Pelotas batholith, the juvenile São Gabriel terrane, the granulite-amphibolite facies Taquarembó terrane and the numerous granite intrusions in the foreland. Major structures are also observed, e.g., the Dorsal de Canguçu shear. Magnetic signals register near surface crustal compositions (analytic signal) and total crust composition (total magnetic signal), so their variation as measured indicates either shallow or whole crustal structures. The Caçapava shear is outstanding on the images as is the magnetic low along the N-S central portion of the shield. These integrated observations lead to the deepening of the understanding of the largest and even detailed structures of the Sul-Riograndense Shield, some to be correlated to field geology in future studies. Most significant is the presence of different provinces and their limits depending on the method used for data acquisition - geology, aerogammaspectrometry or aeromagnetometry.
Highlights
This is an integrated evaluation of the geology and aerogammaspectrometric and aeromagnetometric survey of the Brazilian Shield in the southernmost state of Rio Grande do Sul, Brazil
These studies included field mapping, aerogeophysics (1974 survey by the Geological Survey of Brazil), petrography, structural geology, rock geochemistry, chemical analyses of minerals, and the U-Pb dating of zircon, added to the Sm-Nd isotopic determinations on rock samples
Results are presented in the sequence of a GoogleEarth image with the location of towns and highways (Figure 1), the digital terrain elevation (Figure 2), Th/K ratio (Figure 3), total gammaspectrometric signal (Figure 4), total K+eU+eTh signal (Figure 5), Dorsal de Canguçu total K+eU+eTh (Figure 6), K content (Figure 7), eU content (Figure 8), eTh content (Figure 9), analytic signal of the aeromagnetic anomaly (Figure 10) and differential reduction to pole (DRTP) (Figure 11)
Summary
This is an integrated evaluation of the geology and aerogammaspectrometric and aeromagnetometric survey of the Brazilian Shield in the southernmost state of Rio Grande do Sul, Brazil. Field mapping was integrated in recent years with voluminous zircon dating, mostly with the sensitive high resolution ion microprobe (SHRIMP), so this portion of the Brazilian Shield is known to contain limited exposures of Archean rocks. It is dominated by Paleoproterozoic and Neoproterozoic rocks, and Statherian (Paleoproterozoic) and Calymmian (Mesoproterozoic) units have been recently described (Camozzato et al 2013). Significant U-Pb (and some Lu-Hf) isotopic detrital zircon studies (e.g., Lena et al 2014, Lopes et al 2014) shed additional light on the significance of the main geotectonic provinces of the shield.
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