Magnetic fabric and its significance in the Florianopolis dyke swarm, southern Brazil

Magnetic fabric was determined by applying the anisotropy from the low-held magnetic susceptibility (AMS) technique in 62 mafic dykes from the Mesozoic Florianopolis (Santa Catarina Island) dyke swarm, southern Brazil. These dykes cut the crystalline basement rocks, which are mainly Proterozoic. They are vertical or subvertical in dip and trend mainly NE, although NW-trending dykes are also found. Dykes are tholeiitic in composition and are geochemically similar to those from the Ponta Grossa swarm. Thicknesses vary from 0.3 to 60 m. Polished sections show that titanomagnetites carry the AMS in these dykes. Hysteresis parameters show that the magnetic minerals fall in the PSD range. Two types of magnetic fabric are recognized. Type I is characterized by K-1-K-2 parallel to the dyke wall, representing magma flow within the dykes; type II, with K-1-K-3 parallel to the dyke wall, was found in four dykes. Type I is found in 94 per cent of the dykes, and approximately 20 per cent of these have K-1 inclinations of less than 30 degrees, suggesting horizontal or subhorizontal flow. About 80 per cent have K-1 inclinations of greeter than 30 degrees due to inclined to vertical flow. The comparison of AMS studies from both the Florianopolis and the Ponta Grossa dykes suggests a source position closer to Santa Catarina Island than the Ponta Grossa arch.