Palaeomagnetism of the Permo-Triassic Araguainha impact structure (Central Brazil) and implications for Pangean reconstructions

Abstract

The configuration of the Pangea supercontinent has been a topic of intense debate for almost half a century, a controversy that stems from discrepancies between the geology-based Pangea-A and the palaeomagnetically based Pangea-B. Recent palaeomagnetic compilations aimed at resolving this controversy have identified the poor quality of palaeomagnetic data from Gondwana for Permian times as a major obstacle. Specifically, the vast majority of Gondwanan poles come from sedimentary rocks that are prone to biases from compaction or are poorly dated. Here, we present a new palaeomagnetic pole for cratonic South America based on impact melts from the 254.7 ± 2.5 Ma Araguainha impact structure (AIS). The granite basement, the impact-generated melt sheet and veins were sampled at 28 sites (169 specimens) and provided a reliable palaeomagnetic record similar to that of volcanic rocks. Alternating field and thermal demagnetization indicate a stable characteristic remanent magnetization carried by both magnetite and haematite. All sites but one show a single palaeomagnetic direction of normal polarity with a mean direction of Dec = 357.4°; Inc = -38.9°; N = 28; k = 62.35; α95 = 3.5°, yielding a palaeomagnetic pole (AIS) at Lat = -84.2; Lon = 326.6; K = 83.5; A95 = 3.6°; SB = 9.6°. The new pole provides a firm constraint on the position of Gondwana which is consistent with the Pangea A configuration. © The Authors 2014. Published by Oxford University Press on behalf of The Royal Astronomical Society.