The role of conjugate crenulation cleavage in the development of 'millipede' microstructures

Millipede microstructures are described from Archean metaturbidites surroun ding the Back River volcanic complex, eastern Slave Structural Province. Th ey are locally developed within andalusite porphyroblasts that grew in resp onse to the intrusion of late syn-kinematic granitoids. The porphyroblasts acted as a mechanical heterogeneity and resulted in the nucleation of conju gate crenulations, which were then helicitically overgrown by the porphyrob lasts. This process produced the millipede morphology through a simple, con sistent mechanism. The model presented here for the development of milliped e microstructures represents an alternative to other models requiring compl ex deformation partitioning and restricted porphyroblast growth. (C) 2001 E lsevier Science Ltd. All rights reserved.