THE PANGEA CONUNDRUM: IMPLICATIONS OF A NEW PALEOMAGNETIC POLE FROM THE PERMO-TRIASSIC ARAGUAINHA IMPACT STRUCTURE (CENTRAL BRAZIL)

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 paleomagneticallybased Pangea B. Recent paleomagnetic compilations aimed at resolving this controversy have identified the poor quality of paleomagnetic data from Gondwana for late 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 paleomagnetic pole for cratonic South America based on impactmelts from the 254.7 ± 2.5 Ma Araguainha impact structure, an unusual target for paleomagnetic studies. The impact-generated melt sheet and veins were sampled at 22 sites (137 samples) and provide a reliable paleomagnetic record, similar to that of volcanic rocks. Alternating field and thermal demagnetization indicate stable, usually univectorial magnetizations carried by both magnetite and hematite. All sites but one show a single paleomagnetic direction of normal polarity with a mean direction of Dec = 356.4°; Inc = -38.7°; N = 21; k = 91.1; α 95 = 3.3°, yielding a paleomagnetic pole (AIS) at Lat = -83.7; Lon = 340.1; K = 83.5; A 95 =3.5°; S B =8.3°. The new pole provides a firm constraint on the position of Gondwana within a Pangea A configuration.