Rock types characteristics of Prambanan and Sambisari Temples, Yogyakarta Province, Indonesia

Abstract

Many Hindu and Buddhist temples built in the 8 th to 10 th centuries are found in the Yogyakarta Province, Indonesia, including Prambanan and Sambisari temples. Based on petrographic and geochemical observations, both temples are built using basaltic to andesitic lavas and pumice breccias. The rock types are relatively similar to those the basaltic to andesitic lavas around the Quaternary age Merapi volcano, and the pumice breccia of the Tertiary age Semilir Formation in the Piyungan area situated at the south of the Prambanan temple. Selected rocks samples were analized using petrographic and X-ray fluorescence methods to identify minerals, textures and geochemical characteristics. Petrographic observations show that the rocks used to build Prambanan temple are hornblende-pyroxene andesite and pyroxene basalts, while the rocks of Sambisari temple consist of hornblende-pyroxene andesites and pumice breccias. Hornblende-pyroxene andesite is generally gray, showing porphyritic texture, 1-3 mm crystal size; phenocrysts are composed by plagioclase, hornblende, pyroxene, and opaque minerals set in groundmass of plagioclase microcrysts and volcanic glass. Pumice breccia, showing a light gray colour, moderate sorting, fragments, consist of andesite and pumice clasts in size range 2-6 cm, embedded in sandy to clay matrix. Most of the rocks are generally weathered or oxidized, which is reflected by the presence of secondary iron oxide. This is probably most of the basaltic to andesitic lavas used had a high vesicular texture, and that Yogyakarta has a tropical climate.