Perbedaan Karakteristik Kekar Tiang antara Lava Andesit dan Intrusi Andesit di Kecamatan Pule, Kabupaten Trenggalek, Jawa Timur, Indonesia

Abstract

The research area in Pule District, Trenggalek Regency, East Java, consists of the Arjosari Formation, Mandalika Formation, and Campurdarat Formation. The Mandalika and Arjosari Formations contain volcanic products closely associated with volcanic activity during the Late Oligocene to Early Miocene periods. This is attributed to the subduction of Java Island, which resulted in the widespread occurrence of volcanic rocks, such as andesite. One of the structures that developed extensively is columnar jointing. Columnar jointing is a morphological feature associated with the rapid cooling of rocks. Generally, columnar joints are associated with shallow intrusions and volcanic activity. The columnar joints at the study site are located in andesite with a different formation mechanism. In andesite lava lithology, columnar joints are surrounded by autoclastic breccia, while columnar joints in intrusions tend to narrow upward due to differences in temperature and pressure. Petrographic analysis showed that lava products tend to produce a trachytic texture, indicating a petrogenesis of lava flows with a porphyro-affinetic texture, while intrusions have larger crystal sizes with a unique texture not observed elsewhere. Meanwhile, based on paleoslope analysis, the direction of lava flow and the origin of the forming volcano can be estimated, unlike intrusions, which are dikes.