Magnetic fabrics in the Cabanas Granite (NE Brazil): interplay between emplacement and regional fabrics in a dextral transpressive regime

Abstract

The late Neoproterozoic Cabanas Granite, northeastern Brazil, is a tabular body that was emplaced south of the dextral East Pernambuco shear zone system. Anisotropy of magnetic susceptibility (AMS) measurements reveal that the Cabanas Granite has fabric patterns more complex than usually reported in plutons intruded in similar settings. Most structures have EW- to ENE-trending magnetic lineations consistent with the overall regional structural direction. In the north, these structures parallel the mylonitic fabric encountered in shear zones that bound or cross-cut the pluton. In the central and southern portions of the pluton, magnetic foliation trajectories, the overall banded disposition of the iso-susceptibility lines, and shape parameters of the AMS ellipsoids suggest that the Cabanas Granite was subjected to ENE-trending folding, along with its underlying and enclosing country rocks. It is concluded that emplacement took place during regional dextral transpression. A secondary, but well-developed, family of structures consists of N- to NW-plunging lineations, which is interpreted to represent the trace of the vertical conduits that fed the pluton. This study emphasizes the utility of the AMS to unravel both the internal structure of low anisotropy plutons and the interplay between emplacement and regional straining during magma crystallization.