Syntectonic Growth of Porphyroblasts over Crenulation Cleavages - An Example from the Precambrian Rocks of the Lunavada Group, Gujarat

Porphyroblasts are known to overgrow crenulation cleavages syntectonicaIly in crenulated schists. However, the timing of growth of such porphyroblasts remains a problem. Whilst some researchers believe that porphyroblasts can syntectonically overgrow crenulation cleavages during the genesis of the crenulation cleavage, there are others who believe that porphyroblasts overgrow crenulation cleavages during an episode of deformation which post-dates the deformation which resulted in the formation of crenulation cleavage. In the present paper we present microstructural . evidence of syntectonic porphyroblasts overgrowing crenulation cleavages from the mica schists of the Lunavada Group of Precambrian rocks occurring in Gujarat. It is concluded that syntectonic porphyroblasts can grow over crenulation cleavages during the same episode of deformation which resulted in the genesis of the crenulation cleavage.