Paleomagnetism of Middle Proterozoic (1.01 to 1.08 Ga) mafic dykes in southeastern Bahia State—São Francisco Craton, Brazil

Abstract

Paleomagnetic results from profuse Middle-Late Proterozoic mafic dyke swarms in southeastern Bahia State (Sa˜o Francisco Craton) yield either an easterly direction with high upward inclination or a westerly direction with high downward inclination isolated during AF and/or thermal treatments. Thermal demagnetization behavior and thermochronologic and petrologic considerations indicate that these remanent components originated as primary TRM's. Four groups of directions were distinguished from dykes in spatially distinct areas: Ilheus normal polarity ( D = 60.0°; I = −68.8°; α 95 = 2.6° ; N = 17) , Olivença normal polarity ( D = 82.4°; I = −71.0°; α 95 = 5.1 ; N = 31), Itajúdo Coloˆnia ( D = 99.0; I = −71.9 ; α 95 = 5.9° ; N = 23) and Olivença reversed polarity ( D = 298.8°; I = 60.7°; α 95 = 6.4° ; N = 18), which yield paleomagnetic poles located at 100.4°E; 30.3°N ( I N ), 107.0°E; 16.1°N ( O N ), 111.0°E; 7.7°N ( IC) and 280.2°E; 17.0°N ( O R ), respectively. These poles define an APW path for the Sa˜o Francisco Craton between the time interval 1.01–1.08 Ga which is characterized by at least two polarity intervals.