Geology, mineralogy and magma evolution of Gunung Slamet Volcano, Java, Indonesia

• Published in: Journal of Southeast Asian earth sciences Vol. 11; no. 2; pp. 135 - 164
• Main Authors: Vukadinovic, Danilo, Sutawidjaja, Igan
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.02.1995
• ISSN: 0743-9547; 1879-1832
• DOI: 10.1016/0743-9547(94)00043-E

Gunung Slamet, Central Java, is a large stratovolcano within the Sunda magmatic arc of Indonesia. The volcanic edifice includes products of two large overlapping Quaternary stratocones. Basaltic andesites and andesites, with rare basalts, dominate the western region of the complex, known as Slamet Tua (old); and basalts and basaltic andesites compose the eastern cone, called Slamet Muda (young). On the basis of stratigraphy, trace-element content, Zr Nb , Zr K and 87 Sr 86 Sr ratios, Slamet lavas can be broadly categorized as relating to high abundance magma (HAM) and low abundance magma (LAM) types. The Tua and Lebaksiu sequences generally comprise the LAM group, and are older, more salic and have higher 87 Sr 86 Sr ratios than those of HAM. LAM andesites contain some amphibole, but HAM andesites do not. Models involving randomized magma replenishment, tapping and fractionation (RTF) were developed to explain the geochemical features of both LAM and HAM rock groups. The salic lavas of the LAM suite can be generated if fractionation was dominant relative to replenishment and tapping in LAM magma chambers. Conversely, magma chambers with a high proportion of replenishment and tapping relative to fractionation can produce dominantly mafic lavas, such as those of the HAM suite. Concave-upward heavy-rare-earth element (HREE) patterns for LAM andesites are probably due to significant amphibole fractionation; HAM andesites display flat HREE patterns and do not require amphibole fractionation from parental basalts. The high TiO 2 contents of HAM basalts and basaltic andesites (relative to those of “average” arc rocks) are due to either suppressed crystallization—or minor accumulation—of Ti-magnetite, in conjunction with RTF processes.