PALAEOMAGNETISM OF MAFIC DYKES OF CHITTOOR DISTRICT, ANDHRA PRADESH

摘要

Mafic dykes intrude the granite gneiss terrain of Eastern Dharwar Craton (east of Closepet Granite) in parts of Mahbubnagar, Anantapur, Chittoor districts of Andhra Pradesh. The dyke intrusion density varies from sparse to moderate (2 to 3 along a line km). The granitoid host rocks of the dykes also show variation in their composition,-granodiorite-adamellite-granite in Mahbubnagar, Anantapur areas, tonalite-trondhjemite-granodiorite in Chittoor area. Geochemical studies, coupled with dyke morphologies of the three areas indicated that the dykes are emplaced at higher crustal levels via brittle deformation in Mahbubnagar and Anantapur areas and at lower crustal levels via ductile deformation in Chittoor area (Sarma, 1996, 1997a & 1997b). Notwithstanding the differences in emplacement mechanisms, it is established that the dykes of all the three areas possess the same (or similar) magma source and have intruded contemporaneously within about the same time (Ca. 2200 Ma; Pandey et al, 1997). Migmatitic activity in the terrain predates the dyking event, and consequently the dykes are devoid of any granitic inclusions in them.