Paleomagnetic data of Trindade Island (Brazil) - Natalia Pasqualon - 2021 MagIC Workshop (1/20/21)
Channel: Magnetics Information Consortium (MagIC)
Date: 2021-01-27

"Paleomagnetic data of Trindade Island (Brazil): Preliminary Results" by Natalia Pasqualon, Instituto de Geociências, Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS, Brazil

Lightning poster talk presented at the virtual 2021 MagIC Workshop (https://earthref.org/events/MAGIC/2021/) - Rock and Paleomagnetism through Time and Space. Jan 19th-21st, 2021.

Abstract:
Pasqualon N.G.(1), Savian J.F.(1), Lima E.F.(1), Oliveira W.P.(2), Hartmann G.A.(2), Luz F.R.(1), Trindade R.I.F(3)
(1) Instituto de Geociências, Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS, Brazil - nati_pasqualon@yahoo.com.br
(2) Instituto de Geociências, Universidade Estadual de Campinas (Unicamp), Campinas, SP, Brazil.
(3) Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo (USP), São Paulo, SP, Brazil.
Keywords: South Atlantic Anomaly, Volcanic Island, Paleodirectional Data.

The present Earth’s magnetic field is characterized by anomalous low intensity values in the South Atlantic Ocean. The lowest field intensities are associated to the South Atlantic Anomaly (SAA), which has been recently investigated due to its major implications for core dynamics and core-mantle interaction (e.g., Hartmann and Pacca, 2009; Tarduno et al., 2015; Trindade et al., 2018; Shelby et al., 2020). Here we present preliminary paleomagnetic results of Trindade Island, which is a volcanic island located at 1.260 km from the Brazilian coast in the South Atlantic Ocean. The location of Trindade Island is ideal for testing the geomagnetic field behavior and the SAA evolution in a scale of millions to thousands of years (Fig. 1).

Volcanic activity started in Trindade Island at the mid-Pliocene, lasting until the Pleistocene (Cordani, 1970; Pires et al., 2016). The island is formed by lava flows, intrusions and pyroclastic rocks of strongly sodic alkaline, SiO2 undersaturated nature, divided by Almeida (1961) into five geological units: Trindade Complex (3.9-1.0 Ma, climax 3.9-2.5 Ma), Desejado Sequence (2.6-1.5 Ma), Morro Vermelho Formation (1.1-0.27 Ma), Valado Formation (no age) and Paredão Volcano (0.25±0.19 Ma).

Alternating field (AF) demagnetization was run in 17 sampling sites (504 oriented specimens), including phonolitic necks (7) and a melanephelinitic dyke (1) from Trindade Complex, and olivine-rich mel
anephelinitic aa flows from Morro Vermelho (4), Valado (3), and Paredão Volcano (2) formations. Here we present preliminary results of Trindade Complex sites, of which sublvolcanic bodies present good age determinations. Future steps of this study include precise dating of the youngest units and thermal demagnetization data acquisition of all sites.

Magnetic mineralogy was investigated through thermomagnetic cycles, isothermal remanent magnetization (IRM) curves, hysteresis loops and first order reversal curves (FORC) diagrams and its results are described in detail by Pasqualon et al. (2020). Principal component analysis (PCA) was conducted through Remasoft 3.0, and the lowest maximum angle deviation (MAD) values were accomplished when PCA was anchored to last point. Sites mean directions were calculated using at least 4 consecutive demagnetization steps (Fig. 2). From the 8 sampling locations of Trindade Complex, only 4 presented specimens with MAD ≤ 5°: TRGF-12, TRGF-16, TRGF-18 and TRGF-19.