Fracture Analyses of the Early Cambrian Ambar Formation, at Ambar village, district Swabi Pakistan: in regional tectonic perspective

Abstract

An evaluation of fractures in the Early Cambrian Ambar Formation was conducted to ascertain the tectonic setup of the study area in regional tectonic context. It enables to understand large-scale tectonic dynamic processes that developed at the northwest Indo-Pakistan tectonic plate through time. Fracture analyses reveal that these rocks have been affected by at least two regional scale deformation events. Extension fractures of the Ambar Formation indicate the early history of tectonism, which pre-dates the Cenozoic Himalayan Orogeny. Microscopic study of the infilling secondary minerals and their internal structures in relation to fracture walls indicate that these fractures belong to Mode I extension fractures. Similarly the mechanism of crystal growth in en-echelon veins and the geometry of their arrays further support the extensional nature of these fractures. The remarkable resemblance among the trends of these extension fractures, normal faults in the south central Swat, Peshawar Basin and rift related intrusive bodies suggest that these fractures developed during the Late Paleozoic intra-continental rifting. Later deformation of these fractures and overall increase in fracture density in the rocks occurred during the Himalayan Orogeny.