The Livada torrent in Tinos Island (Cyclades, Aegean Sea), a fourth-order dendritic-type stream, has developed almost alongside the lithologic contact of granites (42% of drainage basin area) and schists (58%). The drainage network has not developed equally because of the differential permeability capacity and erosive susceptibility of the two rock types, the eastern part (schists) being more developed than the western (granitic) one. Within the study area, detailed coastal geomorphologic mapping, lithologic determination of fluvial and coastal pebbles and cobbles, and grain size distribution combined with mineralogical analysis of the sand fraction were performed. Chemical spheroidal weathering takes place through the joints of granite, forming tors and core stones. Tafoni are usually found closer to the coastline because of saltwater action. Near the shore, the coarse material (pebbles, cobbles) is almost exclusively composed of schists (90%) and only 10% of granite, as schists are highly and deeply fractured. The finer sandy material is composed mainly of quartz. Garnet, feldspar, magnetite, amphibole, biotite, and minerals of ophiolitic origin are minor constituents. Particle size analysis of fluvial and coastal sands between the 200–315-μm and 800–1000-μm grain size range showed a difference in percentage of quartz participation originating both from granite and schist. The predominance of grains of sand size rather than of boulders and cobbles of granitoid rocks in the stream sediments indicates that granitoid rocks disintegrate relatively faster than schists.
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Vol. 2010 • No. 261