Acid Front in Granitization

Abstract

DURING the course of field mapping a part of the khondalitic region near Salur (lat. 18° 36′ N., long. 83° 11′ E.) in the Vishakapatnam hill tracts, an interesting contact has been observed between a lens-like band of quartz-biotite-granulite (a member of the khondalites) and a porphyritic granite considered as intrusive¹ into the members of the khondalites in this region. The lens measures about 50 ft. in length, and 10 ft. in width, and appears at first sight as a caught-up xenolith amid the porphyritic granites. Careful examination at the contact shows a profound transfusion of quartzo-feldspathic material from the porphyritic granite into the lens along the whole of its length up to a distance of 2 ft. A typical specimen was collected from the contact, and though unfortunately broken into two pieces in the field, it has in no way affected the features exhibited before the mishap.