Petrology of the Anorthosite-Gabbro Mass at Kadavur, Madras, India

Abstract A small body of anorthosite with related gabbroic facies from the Archaean of Southern India is described. The mass is inferred to be a funnel shaped phacolithic pluton, emplaced in the crest of a steeply plunging major anticline of metasedimentary quartzite and quartz schists. The marginal rocks of the mass are gabbroic and foliated, while the core is largely made of massive anortho-sites occasionally showing flow structures. The chemistry and petrography of the rocks of this mass suggest their having resulted from differentiation in place of a gabbroic anorthosite intrusion. This occurrence is thought to be a unique example of the Adirondack type of anorthosite, and supports Buddington's hypothesis of evolution of anorthositic rocks from a gabbroic anorthosite magma.