Paleointensity data from volcanics of South America over the past of 10 Ma

• Grant number: 25/01094-6
• Support Opportunities: Scholarships in Brazil - Master
• Start date: March 01, 2025
• End date: January 31, 2027
• Field of knowledge: Physical Sciences and Mathematics - Geosciences - Geophysics
• Principal Investigator: Gelvam André Hartmann
• Grantee: Gustavo Soares da Silva
• Host Institution: Instituto de Geociências (IG). Universidade Estadual de Campinas (UNICAMP). Campinas , SP, Brazil
• Associated research grant: 22/03086-2 - Geomagnetic history of South America, AP.PNGP.PI

Abstract

Intensity variations of geomagnetic field have been observed at different time intervals, from years to millions of years. Investigations on regional and global scales can provide important information about the evolution of the Earth's magnetic field (EMF), and the operating conditions (low or high energy state) of the geodynamo. Long-period geomagnetic intensity variations reveal low values, which are related to the non-dipole field components, and seem to persist in certain regions of the globe at different timescales. Field reconstructions until the past of hundreds of thousand years indicated low intensity values in relation to the current field in regions of the African continent. This low intensity zone would be related to one of the large low-speed S-wave provinces (LLSVPs - abbreviation for Large Low Seismic shear wave Velocity Provinces). The African LLSVP is characterized by an extensive lower mantle region located under the African continent and the South Atlantic Ocean, which reflects thermal heterogeneity at the core-mantle boundary (CMB). This suggests that the African LLSVP would be a region of influence for the emergence of reverse flow of the geomagnetic field at CMB over short time periods, responsible for inducing geomagnetic polarity reversals on the scale of millions of years. In addition, the African LLSVP would be associated with the origin of the South Atlantic Magnetic Anomaly (SAA), which is historically characterized by the lowest values total field intensity and located between South America and the African continent. The challenge of understanding the behavior of the geomagnetic field, in terms of the intensity variations, is even greater for scales of millions and billions of years, due to the absence of a continuous and well-documented temporal record. In this project, we will characterize the geomagnetic field intensity variations over the last 10 Ma. It will carried out by the following: (i) contribute with new intensity data from volcanics of Argentina to the South American database; (ii) evaluate the behavior of geomagnetic field intensity by analyzing the distribution of VADMs; and (iii) investigate the contribution of non-dipole components to the mean field. To accomplish it, intensity data will be determined in rock volcanic samples from Argentina dated between 0-10 Ma. For determining the intensity variations, a detailed selection of paleointensity data will be performed, and combined with the new data, will allow a better understanding of the field variations in this timescale. Results from this project will help to understand the directional variations and the geometry of the field in South America, as well as for the global field intensity variations.