Geo-vegetation Mapping and Soil Geochemical Characteristics of the Indikolapelessa Serpentinite Outcrop, Southern Sri Lanka

Abstract

The serpentinite blocks of Indikolapelessa, located along an identified litho-tectonic boundary between the Highland Complex (HC) and the Vijayan Complex (VC) of Sri Lanka, have undergone extensive lateralization with metal enrichment. Characteristic serpentinite vegetation with some endemic species was recognized in the soils and supergene deposits develop on serpentinite lithology. This type of geological and ecological relationship forms vegetation covers on serpentinite lithologies which are sharply demarcated from the surrounding metamorphic terrains. The aforesaid “geo-ecological phenomenon” can be used as a tool for geo-vegetation mapping in ultramafic terrains to trace the geological boundaries in landscapes where rock outcrops are virtually absent. We successfully applied the concept of geo-vegetation mapping in order to demarcate the boundary of underlain serpentinite rocks from surrounding non-serpentinite metamorphic rocks (e.g. granitic gneiss). The hypothesis was supported by the geochemical variations of soils/supergene deposits found at serpentinite and non-serpentinite sites, especially immobile elements and some trace elements. Based on whole rock chemistry and soil chemical data obtained, we suggest that the Indikolapelessa serpentinite outcrop, together with the other four serpentinite outcrops, is more likely to represent the Mg-rich mantle fragments at the time of overthrusting of the two crustal blocks of HC and VC during the Pan- African event.