The pre-eruptive magma plumbing system of the 2007–2008 dome-forming eruption of Kelut volcano, East Java, Indonesia

Jeffery, A. J.; Gertisser, R.; Troll, V. R.; Jolis, E. M.; Dahren, B.; Harris, C.; Tindle, A. G.; Preece, K.; O’Driscoll, B.; Humaida, H.; Chadwick, J. P.

Abstract

Abstract Kelut volcano, East Java, is an active volcanic
complex hosting a summit crater lake that has been the
source of some of Indonesia’s most destructive lahars. In
November 2007, an effusive eruption lasting approximately 7 months led to the formation of a 260-m-high and
400-m-wide lava dome that displaced most of the crater
lake. The 2007–2008 Kelut dome comprises crystal-rich
basaltic andesite with a texturally complex crystal cargo of
strongly zoned and in part resorbed plagioclase (An47–94),
orthopyroxene (En64–72, Fs24–32, Wo2–4), clinopyroxene
(En40–48, Fs14–19, Wo34–46), Ti-magnetite (Usp16–34) and
trace amounts of apatite, as well as ubiquitous glomerocrysts of varying magmatic mineral assemblages. In
addition, the notable occurrence of magmatic and crustal xenoliths (meta-basalts, amphibole-bearing cumulates, and
skarn-type calc-silicates and meta-volcaniclastic rocks) is a
distinct feature of the dome. New petrographical, whole
rock major and trace element data, mineral chemistry as
well as oxygen isotope data for both whole rocks and
minerals indicate a complex regime of magma-mixing,
decompression-driven resorption, degassing and crystallisation and crustal assimilation within the Kelut plumbing
system prior to extrusion of the dome. Detailed investigation of plagioclase textures alongside crystal size distribution analyses provide evidence for magma mixing as a
major pre-eruptive process that blends multiple crystal
cargoes together. Distinct magma storage zones are postulated, with a deeper zone at lower crustal levels or near
the crust-mantle boundary ([15 km depth), a second zone
at mid-crustal levels (*10 km depth) and several magma
storage zones distributed throughout the uppermost crust
(\10 km depth). Plagioclase-melt and amphibole
hygrometry indicate magmatic H2O contents ranging from
*8.1 to 8.6 wt.% in the lower crustal system to *1.5 to 3.3 wt.% in the mid to upper crust. Pyroxene and plagioclase d18O values range from 5.4 to 6.7 %, and 6.5 to
7.6 %, respectively. A single whole rock analysis of the
2007–2008 dome lava gave a d18O value of 7.6 %,
whereas meta-basaltic and calc-silicate xenoliths are
characterised by d18O values of 6.2 and 10.3 %, respectively. Magmatic d18O values calculated from individual
pyroxene and plagioclase analyses range from 5.7 to
7.0 %, and 6.2 to 7.4 %, respectively. This range in
O-isotopic compositions is explained by crystallisation of
pyroxenes in the lower to mid-crust, where crustal contamination is either absent or masked by assimilation of
material having similar d18O values to the ascending melts.
This population is mixed with isotopically distinct plagioclase and pyroxenes that crystallised from a more contaminated magma in the upper crustal system. Binary bulk
mixing models suggest that shallow-level, recycled volcaniclastic sedimentary rocks together with calc-silicates and/
or limestones are the most likely contaminants of the
2007–2008 Kelut magma, with the volcaniclastic sediments being dominant

Citation

Jeffery, A. J., Gertisser, R., Troll, V. R., Jolis, E. M., Dahren, B., Harris, C., …Chadwick, J. P. (2013). The pre-eruptive magma plumbing system of the 2007–2008 dome-forming eruption of Kelut volcano, East Java, Indonesia. Contributions to Mineralogy and Petrology, 166(1), 275-308. https://doi.org/10.1007/s00410-013-0875-4

• Journal Article Type: Article
• Acceptance Date: Mar 19, 2013
• Online Publication Date: Apr 17, 2013
• Publication Date: 2013-07
• Deposit Date: May 30, 2023
• Journal: Contributions to Mineralogy and Petrology
• Print ISSN: 0010-7999
• Electronic ISSN: 1432-0967
• Publisher: Springer Verlag
• Peer Reviewed: Peer Reviewed
• Volume: 166
• Issue: 1
• Pages: 275-308
• DOI: https://doi.org/10.1007/s00410-013-0875-4
• Keywords: Geochemistry and Petrology; Geophysics