Perlites and volcanic associations at Khao falamee, Amphoe Srabot, Changwat Lopburi

Abstract

Khao Falamee volcanics is situated in the central part of Lam Narai volcanic field which has been categorized as Late Tertiary alkali-calc-alkali volcanic. Perlites occur within a volcanic succession consisting of perlites, pumiceous perlites, pyroclastics, fine-grained perlites and devitrified perlites, respectively. Petrographic investigation shows that perlites are composed mainly of more than 70% silica-glass groundmass with microcrystalline lath-shaped feldspars and alkaline feldspar phenocrysts, biotite and iron oxides. Perlitic cracks are clearly observed in these rocks. Geochemical analyses show that majority of the studied perlites including pumiceous perlites, fine-grained perlites and devitrified perlites, similarly comprise major and minor oxides which contain about 70-79% SiO2, 0.2% TiO2, 10-13% Al2O3, 0.5-0.8% CaO, 0.2-0.6% MgO, 0.4-1 wt% FeOtotal, 4-6% K2O, 0.2-4% Na2O and 0.01-0.04% MnO. Consequently, Falamee perlites are mostly named as rhyolitic perlites. In addition, based on geochemical analyses, pyroclastic rocks associated with these perlites are also composed of rhyolitic components with a wider range which can be classified as dacitic and andesitic pyroclastic rocks.