The role of conjugate crenulation cleavage in the development of ‘millipede’ microstructures

Millipede microstructures are described from Archean metaturbidites surrounding the Back River volcanic complex, eastern Slave Structural Province. They are locally developed within andalusite porphyroblasts that grew in response to the intrusion of late syn-kinematic granitoids. The porphyroblasts acted as a mechanical heterogeneity and resulted in the nucleation of conjugate crenulations, which were then helicitically overgrown by the porphyroblasts. This process produced the millipede morphology through a simple, consistent mechanism. The model presented here for the development of millipede microstructures represents an alternative to other models requiring complex deformation partitioning and restricted porphyroblast growth.