Precambrian Research, 19 (1983) 301--315 301 Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands GENERAL GEOLOGY AND PETROLOGY OF SOME PRECAMBRIAN CRYSTALLINE ROCKS FROM THE VIJAYAN COMPLEX OF SRI LANKA KAPILA DAHANAYAKE and H.A.H. JAYASENA, Department of Geology, University of Peradeniya, Peradeniya (Sri Lanka) (Received January 29, 1982; revision accepted August 12, 1982) ABSTRACT Dahanayake, K. and Jayasena, H.A.H., 1983. General geology and petrology of some Precambrian crystalline rocks from the Vijayan Complex of Sri Lanka. Precambrian Res., 19: 301--315. Detailed field studies of the Precambrian Vijayan Complex terrain, Sri Lanka, reveal the occurrence of granites, gneisses and migmatites in association with calc-silicate gneisses, quartzites and dolerites. Microcline-rich granites and gneisses show both sharp and grada- tional contacts with the adjacent migmatites. Petrological observations favor a magmatic origin for the granites and gneisses. These bodies seem to have intruded into pre-existing metasedimentary rocks which were subsequently subjected to retrograde metamorphism under amphibolite facies conditions. INTRODUCTION Except for some coastal outliers of Miocene sediments and a few scattered Jurassic outcrops, the island of Sri Lanka consists dominantly of Precambrian crystalline rocks with imprints of varying degrees and ages of tectonism and metamorphism. Three major units of rocks can be recognized on the basis of lithology, structure and age (Cooray, 1978): (a) Highland Group, (b) South- western Group and (c) Vijayan Complex. The Highland Group of rocks, occurring extensively in the central highlands of Sri Lanka, comprises high-grade metamorphic rocks mostly of the hyper- sthene-granulite facies. They axe quartzites, marble, garnet--sillimanite gneis- ses, granulites associated with granites, migmatites, hornblende--biotite gneisses, charnockites and pegmatites. These rocks show remarkable consis- tency of strike with open and overturned folds giving rise to a series of anti- form and synform structures, and elongate basins and domes which form a north-plunging synclinorium in the center of the island (Vitanage, 1972). To- wards the north the synclinorium axis trends N--NE. The Southwestern Group, belonging to the cordierite-granulite facies, is characterized by cordierite-bearing gneisses, charnockites, relatively thin quartzites and calciphyres associated with granitic gneisses, augen gneisses, 0301-9268/83/0000--0000/$ 03.00 © 1983 Elsevier Scientific Publishing Company