Palaeomagnetism of the Silurian Lipeon formation, NW Argentina, and the Gondwana apparent polar wander path

A palaeomagnetic study was carried out on ferriferous beds of the Early Silurian Lipeon Formation in NW Argentina (WS"S, 69.9"W). Samples were collected at 19 sites in four different localities. Detailed thermal demagnetization has permitted the identification of three different magnetic components. All components are carried by haematite, as deduced from IRM curves and microscope analyses. Component A is interpreted to be of Recent origin, due to its coincidence with the geomagnetic dipole direction and its association with post-diagenetic platy haematite. Component B, with exclusive positive inclinations, was found in two out of four sampling localities. Its possible significance is discussed on the basis of an indeterminate result of the fold test and its correlation with the degree of deformation in the samples. The third isolated component ( C) was present in the other two localities. I t passed both fold and reversal tests and is clearly associated with oolitic haematite of early diagcnetic origin. A palaeomagnetic pole of possible Early Silurian age was computed on the basis of mean site directions of component C: 74.9"S, 213.X0E, A95 = 9.9", K = 47, N = 6. This new pole implies lower latitudes for Gondwana in the Silurian than were previously proposed and suggests a modification of the Gondwana APWP. A reversed polarity option for the Early-Middle Palaeozoic path is suggested as a possible alternative. Key words: Argentina, Gondwana, palaeomagnetism. Silurian