Magnetic fabrics and paleomagnetism of the El Nihuil Mafic unit, San Rafael Block, Mendoza, Argentina

Abstract

A reconnaissance magnetic fabric and paleomagnetic study was carried out on the El Nihuil mafic unit exposed in the San Rafael Block, Mendoza Province, Argentina. Sampling comprised eight sites on three different lithologies. While sites N1 and N2 corresponded to gneisses, N3 to N6 were located on dolerite outcrops. Sites N7 and N8 were situated on the Loma Alta gabbro, although site N8 corresponded to a dolerite intruding the gabbro. The magnetic fabric shows that the bulk susceptibility ranges from 4.9 × 10−4 SI to 1.7 × 10−2 SI, with the gabbro showing the lowest values and the dolerite the highest. Despite the different lithologies all sites showed a low anisotropy degree and an oblate fabric. Distribution of foliation planes shows a dominant NW trending describing an antiformal shape for the whole unit. Lineations were in most cases of low angle. Most samples showed well-defined but scattered remanence directions which indicate that no significant paleomagnetic data can be obtained from El Nihuil mafic unit.