ABSTRACT. Airborne geophysical data are an important tool for the interpretation of geological features. The variations observed in airborne magnetic and gamma-ray spectrometric data are typically used to differentiate geological units and delimit structures. In this context, this study aims to use gamma-ray spectrometric and magnetic airborne data to support the geological mapping in the Fazenda Nova region, located in the east portion of the Arenópolis Magmatic Arc. The processing of the gamma-ray spectrometric data consisted of generating K, U, Th, total count, gamma-ray spectrometric ratios and ternary images. The anomalous magnetic field processing and enhancing generated the magnetic maps, which provided information about the structural framework of the area, while the gamma-ray profiles and images allowed the delineation of the geologic-geophysical domains. Fifteen domains were individualized, interpreted especially from ternary images, which displayed a good relation with the granite bodies mapped and indicated different rocks associated with the Goiás Alkaline Province, contributing to improving the geological knowledge of the area.Keywords: airborne geophysics, gamma-ray spectrometric, Arenópolis Magmatic Arc. RESUMO.Dados aerogeofísicos consistem em uma importante ferramenta para a interpretação de feições geológicas. Variações observadas em dados magnéticos e de espectrometria gama aéreos são usualmente utilizadas para a discriminação de unidades geológicas e delimitação de estruturas. Neste contexto, este estudo tem como objetivo o uso de imagens derivadas do processamento de dados magnéticos e gamaespectrométricos aéreos no suporte ao mapeamento geológico na região de Fazenda Nova, localizada na porção leste do Arco Magmático de Arenópolis. Para os dados gamaespectrométricos, o processamento consistiu na geração de imagens dos canais K, U, Th e Contagem Total, além das razões entre os canais e as imagens ternárias. O processamento e realce do campo magnético anômalo geraram as imagens magnéticas, as quais forneceram informações sobre o arcabouço estrutural daárea, enquanto que imagens e perfis aeroradiométricos permitiram a delimitação dos domínios litogeofísicos. Foram individualizados 15 domínios, interpretados principalmente a partir das imagens ternárias, os quais apresentaram forte correlação com os corpos graníticos mapeados na região e delimitaram diferentes rochas associadasà Província Alcalina de Goiás, contribuindo para o aprimoramento do conhecimento geológico da região.Palavras-chave: aerogeofísica, gamaespectrometria, Arco Magmático de Arenópolis.
High-quality aeromagnetic data are important in guiding new knowledge of the solid earth in frontier regions, such as Antarctica, where these data are often among the first data collected. The difficulties of data collection in remote regions often lead to less than ideal data collection, leading to data that are sparse and four-dimensional in nature. Standard aeromagnetic data collection procedures are optimized for the (nearly) 2-D data that are collected in industry standard surveys. In this work we define and apply a robust magnetic data correction approach that is optimized to these four-dimensional data. Data are corrected in three phases, with phase 1 operations on point data, correcting for spatiotemporal geomagnetic conditions, then phase 2 operations on line data, adjusting for elevation differences along and between lines and in phase 3, a line-based leveling approach to bring lines into agreement while preserving data integrity. For a large-scale East Antarctic survey, the overall median cross-tie error reduction error reduction is 93%, reaching a final median error of 5 nT. Error reduction is spread evenly between phases 1 and 3. Phase 2 does not reduce error directly but permits a stronger error reduction in phase 3. Residual errors are attributed to limitations in the ability to model 4-D geomagnetic conditions and also some limitations of the inversion process used in phase 2. Data have improved utility for geological interpretation and modeling, in particular quantitative approaches, which are enabled with less bias and more confidence. Plain Language Summary Observations of the Earth's magnetic field underpin our knowledge of geology and tectonics and are often among the first data collected in frontier regions. This work focuses on the problems experienced in remote surveys, including observation periods extending over years, and flying heights that vary over kilometers. Conventional approaches are designed for more tightly constrained survey collection and can be inappropriate for these data. A new way to process airborne observations of magnetic field intensity is developed and tested. Applied to a data set in East Antarctica, the data quality is substantially improved and the data better reveals the geology hidden beneath the ice of Antarctica.
Abstract. Gravity and three-dimensional modelling combined with geochemical analysis are used to examine the subsurface within, and below the poorly exposed Paleoproterozoic Yerrida Basin in central Western Australia. Understanding the structure of a region is important as key features indicating past geodynamic processes and tectonic activity can be revealed. However, in stable, post-depositional tectonic settings only the younger sedimentary units tend to be widely exposed rendering direct observation of basement and intrusive rocks impossible. Geophysical imaging and modelling can reveal the structure of a region under cover. High amplitude density anomalies around the basin cannot be reconciled with current geological knowledge in the case presented here. The density anomalies infer an abundance of buried and high-density material that is not indicated by the surface geology. A hypothetical causative source for the high-density anomalies is considered to be intrusion and extrusion of volcanic mafic rocks during rifting of the basin. The simplest and plausible stratigraphic attribution of these interpreted mafic rocks is to the Killara Formation within the Mooloogool Group. However, geochemistry reveals that the Killara Formation is not the only host to mafic rocks within the region. Mafic rocks present in the Juderina Formation have largely been ignored in previous descriptions of Yerrida Basin magmatism and results indicate that they may be far more substantial than once thought. Sulphur isotopic data indicates no Archean signature to the mafic rocks, a somewhat surprising result given the basement to the Basin is Archean Yilgarn Craton. It is proposed the mafic rocks were sourced from vents located to the north along the Goodin Fault or under the Bryah sub-basin and Padbury Basins. The conclusion is that the formation of the Yerrida Basin involves a geodynamic history more complex than previously thought. The utility to the approach described here is examined for application to cratonic sag-basin environments. This result highlights the value in geophysics and geochemistry to reveal complexity in the earlier geodynamic evolution of the basin that may be indiscernible from surface geology, but may have high importance for the tectonic development of the region and its mineral resources.
Abstract. Gravity and 3D modelling combined with geochemical analysis examine the subsurface within and below the poorly exposed Palaeoproterozoic Yerrida Basin in central Western Australia. Understanding the structure of a region is important as key features indicating past geodynamic processes and tectonic activity can be revealed. However, in stable, post-depositional tectonic settings only the younger sedimentary units tend to be widely exposed, rendering direct observation of basement and intrusive rocks impossible. Geophysical imaging and modelling can reveal the structure of a region undercover. High-magnitude density anomalies around the basin cannot be reconciled with current geological knowledge in the case presented here. The gravity anomalies infer an abundance of buried and high-density material not indicated by the surface geology. A hypothetical causative source for the high-magnitude gravity anomalies is mafic rocks that were intruded and extruded during basin rifting. The simplest and plausible stratigraphic attribution of these interpreted mafic rocks is to the Killara Formation within the Mooloogool Group. However, geochemistry reveals that the Killara Formation is not the only host to mafic rocks within the region. The mafic rocks present in the Juderina Formation are largely ignored in descriptions of Yerrida Basin magmatism, and results indicate that they may be far more substantial than once thought. Sulfur isotopic data indicate no Archean signature to these mafic rocks, a somewhat surprising result given the basement to the basin is the Archean Yilgarn Craton. We propose the source of mafic rocks is vents located to the north along the Goodin Fault or under the Bryah sub-basin and Padbury Basin. The conclusion is that the formation of the Yerrida Basin involves a geodynamic history more complex than previously thought. This result highlights the value in geophysics and geochemistry in revealing the complexity of the earlier geodynamic evolution of the basin that may be indiscernible from surface geology but may have high importance for the tectonic development of the region and its mineral resources.
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