Highly explosive 2010 Merapi eruption: Evidence for shallow-level crustal assimilation and hybrid fluid

TLDR: The processes responsible for the highly explosive events at Merapi, Central Java, Indonesia have been investigated through a petrological, mineralogical and geochemical study of the first-stage tephra and pyroclastic flows sampled in October and November 2010, and second-stage ash sampled shortly after the 5-6th November 2010 paroxysmal subplinian eruption.

About: This article is published in Journal of Volcanology and Geothermal Research.The article was published on 2013-07-01 and is currently open access. It has received 56 citations till now. The article focuses on the topics: Basaltic andesite & Xenolith.

Figures

Figure 1 (1) and (1a) represents an example of the 2010 Merapi ash (M2010-1) sampling. (1b) – polished ash sample M2010-1 with olivine inclusion marked in red investigated by EDS mapping technique; (2) - M2010-GR sample investigated by EDS mapping technique; (3a) and (3b) - M2010K pyroclastic flow sample investigated by EDS mapping technique in two zones (T1 and T2, see Table 2); (4) and (4a) - M 2010 PF sample investigated by EDS technique. The sample numbers are according to the sample numeration given in Table 1. The data obtained with the EDS mapping “Feature” are summarized in Table 2.

Figure 6. (a) Cl contents and (b) bulk H2O+CO2 contents versus CaO/Al2O3 in glasses of melt inclusions (open circles) and glassy matrix (closed circles). Bulk H2O+CO2 contents in glasses are calculated bydifference method. The melt representing crustal assimilant is characterized by the highest Ca/Al (up to 1.2 wt% of CaO/Al2O3), low summary H2O+CO2 and low Cl contents. Volatile-richest K-rich melts are characterized by low Ca/Al.

Figure 7. Diagram demonstrating the ash leachate composition normalized to the bulk ash composition for analyzed elements. Positive peaks for Zn, Cu, Cd, Sb and Cl reflect the composition of magmatic fluid liberated during the paroxysmal subplinian eruption in 2010. Chemical data are given in Tables 3 and S6 of ESM.

Figure 2. The major and minor element composition of the Merapi 2010 volcanic samples compared to all available data on the Merapi volcanic rocks and calc-silicate xenoliths. The chemical data used here are obtained from MERAPIDATA (Borisova et al., 2011) which summarize the published and unpublished data of Berthommier (1990), Gertisser and Keller (2003a,b), Debaille et al. (2006), Camus et al., (2006) for the previous Merapi volcanic products; and Chadwick et al. (2007) for the 1998 Merapi calc-silicate xenoliths. The chemical data on the 2010 Merapi are given in Table 3.

Frequently asked questions

Q1. What contributions have the authors mentioned in the paper "Highly explosive 2010 merapi eruption: evidence for shallow-level crustal assimilation and hybrid fluid" ?

In this paper, the authors investigate the impact of shallow-level assimilation on the magma-fluid system producing the highly explosive 2010 eruption of Surono Merapi volcano, Central Java, Indonesia. 

Q2. How was the IRMS used to measure the yields of graphite?

Oxygen was converted to CO2 gas by reacting with graphite at high T (1450°C), the yields were measured, and CO2 was analyzed with the Isotope Ratio Mass Spectrometry (IRMS) in a dual inlet mode. 

Q3. What is the main source of the crustal assimilant?

Calc-silicate xenoliths such as those present in the 1998 and 2006 erupted products may represent the main source of the crustal assimilant, since the xenoliths are characterized by high δ 

Q4. What was the accelerating voltage for mineral profiling?

For spot analyses and mineral profiling the electron beam was set at an accelerating voltage of 15 kVand a current of 10 – 20 nA for minerals and 10 nA for glasses with a spot diameter on the sample of 2 µm. 

Q5. What was the method used for mineral profiling?

Major- and minor- element profiling of mineral phenocrysts was performed employing 1 to 10 micron steps between analytical spots/locations and the SAMX automation and wavelength-dispersive spectrometers. 

Q6. How long did the acquisition times for all elements in glasses be?

The acquisition times for all analysed elements in glasses and major elements in minerals were 10 s per element on the peak and 5 s per element on the background. 

Q7. What is the first hypothesis that can be proposed to produce plagioclases with An contents >?

The first hypothesis that can be proposed to produce plagioclases with An contents > 88 mol % is crystallization from a mafic melt (SiO2 < 56 wt%; Pichavant et al., 2002; Martel et al., 2006). 

Q8. What is the phenotype of the 2010 Merapi plagioclase?

The observed 18 O values in the early-stage plagioclase phenocrysts suggests that the 2010 Merapi plagioclase crystallized from a silicic melt contaminated by sedimentary crustal material. 

Q9. What is the composition of the late-stage ash samples?

Oxygen isotopic composition of the bulk late-stage ash samples (average δ 18 O is 6.5 ‰) is identical to the early-stage plagioclase composition. 

Q10. How many times did the ash powders and plagioclases get pretreated?

Ash powders and plagioclases were not pretreated overnight to prevent room-temperature reaction, but were pretreated in a series of small increments to reduce the blank to ~0.3 micromol level. 

Q11. how many phenocrysts are found in the ash samples?

The ash samples are quite homogeneous according to their mineral and glass proportions, showing more than 90 % (% refers to the surface percentage relative to the bulk surface of the investigated sample here and elsewhere in the text) of phenocryst fragments consisting of 55 to 60 % plagioclase (including anorthite), 3 to 5 % K-feldspar, 10 to 16 % clinopyroxene, 1 to 4 % orthopyroxene, 5 to 10 %of titanomagnetite, and < 1 % olivine, apatite, and SiO2 mineral phase. 

Q12. How many pg of Nd was used for the sample analyses?

The average blank corresponded to about 100 pg for Nd and was always negligible compared to the Nd mass used for the sample analyses. 

Q13. What is the bulk mass of the volcanic material erupted in 2010?

The estimated bulk mass of the volcanic material erupted in 2010 ranges from 6 × 10 10 to 1.2 × 10 11 kg (Surono et al., this volume).