Geology, chronology, and temporal evolution of basaltic to dacitic magma system in Raung volcano, East Java, Indonesia

Abstract

Raung volcano, located within the Ijen UNESCO Global Geopark in East Java, poses a significant risk of volcanic hazard for nearby residents and visitors. Our study provides a framework to understand Raung long-term behavior and potential hazards by examining its stratigraphy, petrology, and temporal magma evolution. The erupted products of Raung vary from lava flow, pyroclastic density current (ignimbrite and block and ash flow), scoria fall, and pumice fall. Radiocarbon dating of charcoal samples within pyroclastic deposits and weathered sediments beneath tephra fall layers yield the age of 840 ± 30 BP to 370 ± 30 BP. It provides an important chronological marker that confirms the past VEI-4 to VEI-5 eruption around 1200 to 1600 CE. Petrological and geochemical data reveal that Raung magma composition ranges from basalt to dacite (48–64 wt% SiO₂) and can be classified into two distinct magma types. Type 1 magma has med-K series, low Rb/Nb, and no Eu anomaly. Type 2 magma has high-K series, high Rb/Nb, and negative Eu anomaly. Evidence of disequilibrium features (e.g., reverse zoning, sieve texture, resorption texture, orthopyroxene mantled by clinopyroxene) and mingling texture, along with geochemical features, indicate magma mixing and many episodes of mafic magma replenishment. While the current volcanic activity is dominated by andesitic Strombolian eruption, the characteristics of Raung eruptive products suggest that past major Plinian eruptions (VEI 4–5) had occurred in both andesitic and dacitic magmatic systems, with greater VEI associated with dacitic composition. The study of Raung temporal evolution documented various eruptive behaviors related to its wide range of magma composition, thus providing an essential database for hazard assessment and mitigation.