Magma plumbing beneath Anak Krakatau volcano, Indonesia: evidence for multiple magma storage regions

Abstract

Understanding magma plumbing is essential for predicting the behaviour of explosive volcanoes. We investigate magma plumbing at the highly active Anak Krakatau volcano (Indonesia), situated on the rim of the 1883 Krakatau caldera by employing a suite of thermobarometric models. These include, clinopyroxene-melt thermobarometry, plagioclasemelt thermobarometry, clinopyroxene composition barometry and olivine-melt thermometry. Petrological studies have previously identified shallow magma storage in the region of 2-8 km beneath Krakatau, while existing seismic evidence points towards midto deep-crustal storage zone(s), at 9 and 22 km respectively. Our results show that clinopyroxene in Anak Krakatau lavas crystallized at a depth of 7-12 km, while plagioclase record both shallow crustal (3-7 km) and sub-Moho (23-28 km) levels of crystallisation. These magma storage regions coincide with well constrained major lithological boundaries in the crust, implying that magma ascent and storage at Anak Krakatau is strongly controlled by crustal properties. A tandem seismic tomography survey independently identified a separate upper crustal (< 7 km) and a lower to mid-crustal magma storage region (> 7 km). Both petrological and seismic methods are sensitive in detecting magma bodies in the crust, but suffer from various limitations. Combined geophysical and petrological surveys, in turn, offer increased potential for a comprehensive characterization of magma plumbing at active volcanic complexes.

Deposits, petrology and mechanism of the 2010–2013 eruption of Kizimen volcano in Kamchatka, Russia

“…Whether the hybridization domain remained spatially separated as individual magma pockets from the main dacitic magma chamber (Nakagawa et al 1999;Dahren et al 2012;Chadwick et al 2013), or in a density stratified magma chamber (Blake and Ivey 1986;Nakagawa et al 2011;Auer et al 2015), or both, is beyond the resolution of the seismic record or the amphibole thermobarometer. Overall, the effect of the recharge event was rather limited.…”

“…The erupted magmas are often two-pyroxene andesites (Auer et al 2015(Auer et al , 2016, which are characterized by relatively low viscosities and low water content (Kilgour et al 2013). Their magmatic systems are described as extensive mush columns within the crust rather than one discrete magma chamber (Dahren et al 2012). At the other end of the spectrum are relatively closed systems with long recurrence intervals that erupt highly evolved, hydrous magmas, such as amphibole-rich dacites (e.g.…”

Pre- and syn-eruptive degassing and crystallisation processes of the 2010 and 2006 eruptions of Merapi volcano, Indonesia

“…Therefore, a basaltic andesite bulk rock composition with ~55.5 wt% SiO 2 was used, which is representative of the composition of the 2010 and 2006 products and satisfies the equilibrium criteria. The model has a standard error of estimate (SEE) of ± 150 MPa and has recently yielded satisfactory results for similar Indonesian volcanic systems (Dahren et al 2012;Jeffery et al 2013). The second barometer is that of Putirka (2008), which is a recalibrated version of Nimis (1995) suitable for hydrous systems and based only upon the clinopyroxene composition.…”

Petrological record from young Ruapehu eruptions in the 4.5 ka Kiwikiwi Formation, Whangaehu Gorge, New Zealand

“…These aggregates are considered xenocrystic on account of their scarcity. Similarly, coexistence of a broad range of low-An# plagioclases with some extremely high X An plagioclase is not unusual (Dahren et al 2012) in that environment. Olivine, now only found as a rare relict phase, is assumed to have been a dominant phase during early magma diversification (Fig.…”