Luís Gustavo de Castro

Correlation of lineaments (magnetic and topographic) and Phanerozoic brittle structures with Precambrian shear zones from the basement of the Paraná Basin, Santa Catarina State, Brazil

The objective of this article is to characterize the main directions of structures of the Parana Basin, to define the relation of deep structures (magnetic lineaments) with superficial structures [lineaments obtained over Shuttle Radar Topography Mission (SRTM) images] and analyse reactivated structures in the Phanerozoic. The magnetic lineaments at the Eastern edge of the Parana Basin, in the central-southern region of the Santa Catarina State, show a main orientation pattern NE-SW and secondarily NNE-SSW. The NE-SW pattern reflects a framework of the ductile structures of the Santa Catarina Shield that continues in the substratum of the basin. The structural NNE pattern appears in the south of the Major Gercino Shear Zone (MGSZ) and the NE pattern appears in the north of this structure. The data obtained shows that the structural NE-SW pattern of the basin, present in the MGSZ and Itajai-Perimbo Shear Zone as well as in the Tijucas Terrain (Brusque Metamorphic Complex) in Santa Catarina, clearly extends underneath the Gondwanic sequence of the Parana Basin in the region. Among the products obtained by geophysical data processing in this work, what propitiated the best definition and distinction of the magnetic structures was the tilt angle of the total horizontal gradient (TAHG) method. However, the great flight line spacing of one of the geophysical projects (7 km) makes the identification of small magnetic structures difficult, particularly in N-S and E-W directions. Such structural directions are referred to in the previous works and were confirmed through the interpretation of SRTM images and studies of brittle structures in the field.

Enhancement of the total horizontal gradient of magnetic anomalies using tilt derivatives: Part II — Application to real data

We propose a new magnetic anomaly enhancement method based on the tilt derivative of the total horizontal gradient. We illustrate the effectiveness of the method in structural mapping by applying it to reduced-to-the-pole aeromagnetic data and comparing the results to those obtained from other methods reported in literature. The anomalies generated by our method show good correlation with geological structures and Euler deconvolution results.

Arcabouço geofísico-estrutural da porção meridional do Cinturão Ribeira

The diversity of works and models presented to explain the evolution and current setting of southern portion of the Ribeira Belt reflects the complexity of the processes involved in such terrains. Based on qualitative (anomalies enhancement) and semi-quantitative (source depths detection) analysis of aeromagnetic data and gravity data modeling, this work presents geophysical-geological-structural models of this region. The integration of qualitative and semi-quantitative analysis, constrained by the geological data, formed the basis for the elaboration of models. The application of methods of anomalies enhancement (qualitative analysis) showed that the lineaments of Taxaquara Fault Zone and Itapirapua, Morro Agudo and Lancinha shear zones spread under the Parana Basin. This interpretation was validated by Euler solutions, which located sources with depth greater than 2,000 m, related to these structures. The gravity models, which were elaborated in distinct depth levels, indicate a crustal thinning from NW to SE, with different crustal thickness portions bounded by the shear zones.

Interpretação qualitativa e semiquantitativa dos dados aeromagnéticos sobre a Zona de Cisalhamento Lancinha, porção meridional do Cinturão Ribeira no estado do Paraná, sul do Brasil

The characterization of shear zones at the southern portion of the Ribeira Belt, PR, BR, as well as its recognition in depth is a major challenge. Despite the lack of subsurface information, the influence of such structures on the installation and evolution of the Parana Basin during the Phanerozoic is widely accepted. Therefore, in this paper, are applied methods of anomaly enhancement (qualitative analysis) and estimative of the sources depth (semiquantitative analysis), on the aeromagnetic coverage of the Lancinha Shear Zone area (LSZ) in the Parana state, in order to verify its spatial arrangement in subsurface. The processing resulted in the interpretation of magnetic-structural framework of the study area, which was validated by the depth estimative of the magnetic sources (Euler solutions). The results indicated the extension of the Lancinha, Morro Agudo and Itapirapua shear zones under the Parana Basin coverage.

Modelo gravimétrico-magnético do gráben de Paranaguá-PR, Brasil

We study the Paranagua Graben, which is part of the Cenozoic Rift System of southeastern Brazil. Specifically, it is considered a gravimetric-magnetic model of the top of the Precambrian basement under the Cenozoic sediments of the Parana state coastal plain. We aim to identify the main structures of the Paranagua Graben. We also evaluate the thickness of the sedimentary section and the Mesozoic basic intrusions in the basement. We use a regional geophysical survey that extends for more than 55 km of gravimetric profiles with 500 m of spacing between the stations and about 45 km of magnetic profiles with spacing of 25 m. The geophysical profiles were located between Paranagua Bay and the Sai-guacu river outlet, both in the context of the central region of the Ponta Grossa Arch (PGA). Data were collected along NE-SW acquisition lines, perpendicularly to the principal trend of the PGA. We present a 2-D geologic model using on gravity and magnetic data. We incorporate prior knowledge about the basement depth provided by boreholes. The identification of gravity high was related to a basement uplifting (Canoas structural high). Contiguous gravity lows had been interpreted as structural lows and called Albatroz and Shangri-la, whose maximum thickness of the sediments is 130 m. The magnetic model allowed to estimate the thicknesses of the basic dykes and to calculate an average crustal extension of 27% related to 45 km of the magnetic profiles.

Modelo gravimétrico-magnético do Gráben de Paranaguá-PR

This study presents a 2D gravimetric-magnetic model of the continental portion of the Paraná state coastal plain which is related with the Ponta Grossa Arch central region. Through simultaneous inversion of the gravimetric and magnetic data it was generated a model of the top of the basement underlying the sediments of this region. The model includes the density and magnetic susceptibility of the Cenozoic sediments, basement rocks and diabase dykes, and shows the variations of deep to the top of the basement, that reaches 148 meters in the deepest point. Using the thickness of the dykes calculated from this model it was possible estimate a crustal extension of 22% and a frequency about 2 dykes/km.