About 90 % of the proterozoic basement of Sri Lanka is made up of high-grade metamorphic rocks and the rest is covered by cenozoic sedimentary rocks. On the basis of geochronological and petrological studies the subdivisions of the basement geology of Sri Lanka and introduced four lithological units.
# Highland Complex
# Vijayan Complex
# Wanni Complex
# Kadugannawa Complex
The NE-SW trending , granulite facies Highland Complex is composed charnokitic gneiss, biotite gneiss, qurtsites and marble, ect,. The amphibolite facies Vijayan Complex consists of granitoid gneiss, migmatites and metesedimentary rocks. The Wanni Complex is composed of metagranitoid, orthogneisses, charnokitic geniss and migmatites ect,.
The geomorphology of the Island is mainly controlled by the structures and tectonic activities of the high grade metamorphism. The strike ridges and valleys which are parallel the regional strike of the rock bands, are controlled by underlying rocks. But The valleys or topographic lows which are oblique to the regional strike direction is due to the zones of joints, fractures faults or lineaments. Differential weathering of individual rock types courses for the local morphological variations in the country.
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