Geofísica

This paper presents an overview of the present knowledge on the Paraná magmatism and the lithospheric structure under the Paraná Basin. The genesis and diversity of the flood basalt types are linked to the structure and tectonic processes that have affected the crust and upper mantle since the Western Gondwana amalgamation until subsequent rupture.

We examine some aspects of the tectonic evolution of Precambrian cratonic roots beneath South America based on lithospheric distribution of shear-wave velocities. We derive our model by inverting 26,984 fundamental mode Rayleigh wave group velocity dispersion curves, at periods of 9–180 s. We first regionalize our measurements and then invert the result for a 3D S-wave velocity model extending to 200 km depth.

Unrevealing the stratigraphy of volcanic systems is fundamental to understanding their eruptive history and requires a multiproxy approach for the accurate correlation and interpretation of deposits. We present new volcanological, ⁴⁰Ar/³⁹Ar ages and paleomagnetic data from the volcanic rocks of Trindade Island, located at ∼1.260 km from the Brazilian coast in the South Atlantic Ocean.

The Itareru tonalite is one of the Paleoproterozoic plutonic rock units that intruded the Serrinha block, an Archean-Paleoproterozoic crustal fragment of the S˜ ao Francisco Craton (Bahia, Brazil). It is characterized by a ca. 80 km long, NW-SE elongated leaf-shaped body, mainly comprised of tonalite-diorite to granodiorite rocks with numerous dioritic enclaves. Magnetic studies were performed on 26 sites of the Itareru pluton (including country rocks).

Contact thermal aureoles around mafic intrusions provide information about the emplacement and segregation of melts. The Garopaba-Silveira region is characterised by intrusions with large heat input responsible for the formation of a thermal aureole in the granitoids of the Paulo Lopes Suite (PLS), which extends along the coast to more distant locations in this region. Such melting processes are observed from meso-to microscale, along the granitoid-mafic dike interface and in areas as distant as 500 m from the mafic dikes.

In this study, we investigate the paleomagnetism of the basal Maieberg Formation (Namibia) cap carbonate sequence to elucidate its magnetic properties and paleolatitude of deposition, establish global correlations, and contribute to the understanding of Snowball Earth postglacial dynamics. Two distinct magnetization components, C1 and C2, were identified.

We present the first case of reservoir induced seismicity (RIS) ever reported in the Angola Craton, Laúca reservoir. Impoundment of the reservoir began in late 2017 and seismicity started in March 2018 shortly after the water level reached 86 m. Earthquakes continued to be recorded in the following years, with 287 events detected between March/2018 and April/2024. The largest event had magnitude 3.0 ML. The dam is 156 m tall, and the total reservoir volume is 5,044.85 Hm³. The reservoir area is monitored by two stations, LAUC and ZERO.

We document the arrival of seismic energy in the core shadow zone up to large distances beyond 150° more than 100 s prior to the core phases. Numerical simulations of the energy transport in an established heterogeneity model show that scattering throughout the entire mantle explains these observations. Diffraction at the core-mantle boundary is unlikely in our 1–2 Hz frequency band and is not required indicating misleading terminology with reference to P_diff for the scattered P∗P-energy.

The Tikhonov regularization parameter is a key parameter controlling the smoothness degree and oscillations of a regularized unknown solution. Usual methods to determine a proper parameter (L-curve or the discrepancy principle, for example) are not readily applicable to the evaluation of regularized derivatives, since this formulation does not make explicit a set of model parameters that are necessary to implement these methods.