Geofísica

The Araguaia Orogen, located in Central Brazil, represents an Ediacaran-Cambrian collisional orogen associated with the final assembly of West Gondwana. Two contrasting tectonic models have been proposed for the evolution of this orogen, involving different histories for the Amazonian palaeocontinent drift: (i) subduction of a large ocean and final collision of the Amazonian palaeocontinent with Gondwana between ~ 560 and 500 Ma and (ii) intracontinental orogeny after early amalgamation of the Amazonian palaeocontinent at ca. 620 Ma.

A multifractal methodology was utilized to analyze a set of seismic sequences distributed along the Pacific Ring of Fire, sourced from the National Earthquake Information Center (NEIC) catalog. The analysis employed the Multifractal Detrended Moving Average (MFDMA) analysis method to characterize the presence of intrinsic multifractality using different multifractal indicators.

Paleomagnetic data is collected from bulk samples, containing a mixture of stable and unstable magnetic particles. Recently, magnetic microscopy techniques have allowed the examination of individual magnetic grains. However, accurately determining the magnetic moments of these grains is difficult and time-consuming due to the inherent ambiguity of the data and the large number of grains in each image. Here we introduce a fast and semi-automated algorithm that estimates the position and magnetization of dipolar sources solely based on the magnetic microscopy data.

The kinematic analysis of magmatic structures is key evidence for the tectonic settings and deformation mechanisms related to the emplacement of intrusive bodies. The Dom Feliciano Belt (DFB), southernmost Brazil, registers voluminous post-collisional magmatism during the Neoproterozoic and the Arroio do Silva Pluton (ASP) is a diorite-monzonite-syenite body emplaced in this tectonic setting. The ASP structural investigation and magnetic fabric analysis showed the coexistence of flat-lying and steeply-dipping planar structures in most rock types.

The Tamengo Formation (Corumbá Group, midwest Brazil) is a carbonate-dominated succession of major importance to unravel the environmental and biological changes during the Ediacaran–Cambrian transition in Gondwana. Although it has been extensively studied in terms of sedimentology, isotope geochemistry, biostratigraphy, and geochronology, these studies are constrained to the Corumbá region.

A high electrical conductivity belt near the southeastern margin of the Amazonian craton, known as Paraguay-Araguaia Conductivity Anomaly (PACA), has been discovered and mapped over a distance of more than 1,000 km by a large array of magnetometer measurements. To precisely determine the location and structure of the conductive anomaly, we conducted a 200-km-long magnetotelluric (MT) profile with typical site spacing of 8 km over the northern part of PACA and crossing the Goiás magmatic arc and Araguaia belt in Central Brazil.

The origin of large igneous provinces (LIPs) is still an enigma but likely involves magma storage and pathways spread throughout the crust, requiring indirect methods for its study. Here, we present 3-D resistivity models derived from the inversion of broadband (∼0.0001–3000 s) magnetotelluric data with 9–13 km lateral spacing in the central Paraná Magmatic Province, an expressive Early Cretaceous LIP in South America.

The Rio Apa Terrane (RAT) is situated at the south end of the Amazonian Craton (AC) separated from it by the aulacogen Tucavaca belt. It encompasses basement rocks that evolved mainly during the Paleoproterozoic. Its relationship to the AC during Proterozoic is yet undefined, although geologic, geochronologic and isotopic evidence suggest it was close to the Ventuari-Tapajós and Rio Negro-Juruena Provinces at Paleoproterozoic and linked to southwestern AC at ca. 1320 Ma.

Anomalous paleomagnetic data have been found worldwide during the Ediacaran period, giving rise to several non-actualistic hypothesis. In order to get more information about this period, paleomagnetic, magnetic fabric and rock magnetic studies were carried out in the Avellaneda Formation (∼570–560 Ma) from two drill cores of the Alicia quarry in the Olavarría area of the Tandilia System, in the Río de la Plata craton (Argentina). Anisotropy of magnetic susceptibility studies indicate a pre-tectonic origin for the magnetic fabric of this Formation.

Airborne magnetics have found few applications in investigating basalt-trapped areas because anomaly interferences from deep and shallow sources prevent clear identification of subjacent dyke systems. The structural positioning of dykes is of major importance in basin studies due to their role as a heat source for maturing organic matter and plumbing capacity to feed intrusive bodies and surface lava flows. Aeromagnetic data in such a scenario can outline faults and the basin framework but faces difficulties in identifying the distribution of dykes seated at different depth levels.