ANISOTROPY OF MAGNETIC-SUSCEPTIBILITY IN THE PONTA-GROSSA DYKE SWARM (BRAZIL) AND ITS RELATIONSHIP WITH MAGMA FLOW DIRECTION

Measurements of anisotropy of magnetic susceptibility (AMS) in 95 mafic dykes (mainly tholeiites 10-200 m in width) from the Mesozoic Ponta Grossa swarm, Southern Brazil, revealed two main types of magnetic fabric. Type I fabric (plane K1-K2 parallel to the dyke plane) represents magma flow within the dykes, whereas Type II (plane K1-K3 parallel to the dyke plane) is compatible with a fabric pattern reflecting vertical compaction of the magma column. Fabric Type I dominates (51% of the dykes) within the swarm, whereas Type II (38% of the dykes) concentrates mainly in the western region where the dykes intrude sediments. Considering the dykes with Type I fabrics, it is concluded that 58% of the dykes were fed by horizontal or sub-horizontal (K1 inclinations less than 30-degrees) magmatic flow, and 42% were fed by inclined to vertical (K1 inclinations more than 30-degrees) magma flow. The latter are more frequent in the southeastern part of the swarm, suggesting a magma source close to this area, although there may have been other sources in other regions where dykes with inclined flow and distinct chemical characteristics are also found.