Temporal change of Barujari Volcano magmatic process: Inferred from petrological study of erupted products since AD 1944

Abstract

Abstract Barujari volcano is an active volcano located in Lombok Island Indonesia. The volcano is a part of post caldera stage of Rinjani volcano. The volcano shows strombolian to vulcanian type eruption and produces mainly lava with basaltic-andesitic composition (54-56 wt% SiO2). The volcano actively erupts several times during past 70 years. However, temporal change of its petrological characteristic has not been discussed. This paper discusses petrological changes in Barujari volcano erupted material through time from AD 1944 to 2015. Total 31 samples erupted from AD 1944, 1966, 1994, 2004, 2009, and 2015 are observed and analyzed with XRF method. Our study shows that most of samples can be classified into basaltic trachy-andesite with 53-56 wt% SiO2. All samples show nearly linear trend in harker diagram and shows no systematic change through time. However, AD 1966 shows curved trend and more silicic composition compared to other samples. We suggest that magma mixing with repeated injection of more mafic magma play an important role in producing most of basaltic-andesitic Barujari lava as suggested by linear trend of harker diagram and appearance of heterogeneity in groundmass. AD 1966 samples also contain evidence of magma mixing but curved trend does not suggest simple mixing processes. Appearance of olivine-poor samples in SiO2 rich AD 1966 samples might suggest more close system differentiation process that mixed with common Barujari products.