Paleomagnetic study of Bahia Archean rocks

Author(s)

Caio Augusto Deiroz Amaral

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto Astronômico e Geofísico (IAG/SBD)
• Defense date: 2021-05-13

Examining board members

Ricardo Ivan Ferreira da Trindade; Augusto Ernesto Rapalini; Elder Yokoyama

• Advisor: Ricardo Ivan Ferreira da Trindade

Abstract

This study performed a characterization of the magnetic mineralogy, magnetic fabric and paleomagnetic direction in a set of undated mafic dikes (14.15 S, 40.72 W) and in an outcrop of Archean rhyolitic rocks (13.668ºS, 40.905ºW) in the interior of the state of Bahia, Brazil. The following laboratory procedures were performed: obtaining thermomagnetic curves ( T diagram), hysteresis loops, isothermal remanent magnetization (IRM) and first order reversal curves (FORC), definition of the anisotropy of magnetic susceptibility (AMS) and anisotropy of anhysteretic magnetic susceptibility (AAMS) and application of thermal and alternated magnetic fields demagnetization techniques. The main magnetic carrier in both sets of rocks is the pseudo-single domain to multi-domain magnetite, however the rocks also presented a large amount of paramagnetic minerals. The set of mafic dykes samples did not present satisfactory results for the AMS analysis and paleomagnetism direction characterization. The magnetic fabric of the rhyolites presented low values of magnetic susceptibility and anisotropy degree (P parameter). The outcrop region exhibited coherent eastward sub-vertical lava flow direction. The paleomagnetic characterization indicated only one secondary remanence direction (Dm = 40.52º, Im = 4.32º, 95 = 22.67º, K = 8.04) with a paleomagnetic pole located at 46.82ºN, 30.68ºE (dp = 11.38, dm = 22.72). (AU)

• FAPESP's process: 19/24450-1 - Paleomagnetism of the Archean rocks of the Gavião block
• Grantee: Caio Augusto Deiroz Amaral
• Support Opportunities: Scholarships in Brazil - Master