Fabric reactivation: an example from the Hualapai Mountains, NW Arizona, USA

Foliation reactivation involves renewed movement on preexisting fabrics and can lead to difficulty in determining temporal and spatial relationships of fabrics to larger structures as well as correlation of fabrics to tectonic events. Porphyroblasts that contain internal fabrics allow for interpretation of the structural history of an area including the potential for foliation reactivation. In Boriana Canyon, Hualapai Mountains, NW Arizona, three vertical foliations (S2–S4) are preserved in the contact aureole of the 1.40 Ga Boriana granite. Foliation S2 strikes northeast and is parallel with regional foliation that formed post- or syn-1.68 Ga. Foliation S3 occurs throughout the canyon but is most prevalent in the contact aureole where, close to the pluton, it forms the main cleavage. Andalusite and garnet porphyroblasts overgrew S3 crenulations. Foliation S4 is parallel to the S2 regional fabric and, in some outcrops, deformation associated with S4 has decrenulated the S3 fabric although S3 is preserved in garnet and andalusite porphyroblasts. In these outcrops S4 is also axial planar to F2 folds. Recognition of fabric reactivation of this aureole allows for discrimination of foliation-forming episodes that are separated by ∼250 m.y. and a better understanding of the Proterozoic geologic history for this part of NW Arizona.