Methods used to identify magnetic anomalies produced by spreading seafloor in the Argentine continental margin between 35 ° S and 48 ° S, and to establish the relationship between the anomalies position and the topography of the top of the basement

ABRAHAM, D. A.; GHIDELA, M.; TASSONE A.; PATERLINI, M.; ANCAROLA, M.

Cancún

Conferencia; AGU meeting; 2013

AGU

This paper discusses some methods for better identification of the spreading seafloor magnetic anomalies in the region between 35 ° S and 48 ° S at the outer edge of the continental margin of Argentina.  In the area of ​​Rio de la Plata craton and Patagonia Argentina, there is an extensional volcanic passive margin. This segment of the Atlantic continental margin is characterized by the existence of seismic reflectors sequences that lean toward the sea (seaward dipping reflectors - SDRs). These sequences of seismic  reflectors located in the transitional-continental basement wedge, are presented in seismic profiles as an interference pattern interpreted as basalt flows intercalated with sedimentary layers, and its origin is related to volcanism occurred during the Early Cretaceous. The magnetic response of SDRs is in the area of ​​the magnetic anomaly G (Rabinowitz and LaBrecque, 1979). Magnetic alignments are highlighted on a map by superimposing total field anomaly semitransparent layer of curvature. This method allows a regional identification of the most prominent alignments. It is convenient to calculate the curvature in the direction perpendicular to the magnetic alignments.  The identification of seafloor spreading magnetic anomalies located in the eastern margin helps in the knowledge of the history of the Atlantic Ocean opening. M series magnetic alignments: M5n, M3n M0r (between 132 and 120 Ma) were identified in the analyzed area. The alignments orientation is approximately parallel to the general direction of the margin.  In order to improve the layout of the magnetic alignments we compared the magnetic response of adjacent prismatic bodies with magnetic anomalies measures. Prismatic bodies with remanent magnetization were modeled. Its width was associated with Gradstein et al. (2004) scale and the seafloor spreading velocity. This analysis corroborated quantitatively the age of the magnetic alignments.  The roughness of the top of the oceanic basement presents a contrast of amplitudes, in a wavelength range between about 4 km and 6 km, with the corresponding amplitudes in the area of ​​the transition crust. This contrast of amplitudes can be detected using spectral methods, especially short Fourier transform. The quantitative evaluation of the spectral energy density allowed the identification of wave numbers characterizing oceanic basement area and thus perform subsequent filtering of the signal with wavelengths found with the spectral method. The top of basement roughness were quantified using the root mean square (RMS), in sections of about 2 km, of residues between the depth of the basement top and first-degree polynomial that best fits in the sections mentioned.  The spreading seafloor magnetic alignments are on oceanic crust area identified by the point of view of the roughness analysis. The combined use of the methods that we have developed on the magnetic surveys in the study area, allowed us to improve the layout of the magnetic alignments and identify the transition between oceanic and continental crust.