Anastassia Y Borisova
email: anastassia.borisova@get.obs-mip.fr

Caroline Martel
email: cmartel@cnrs-orleans.fr

Sophie Gouy

Indyo Pratomo
email: indyopratomo@gmail.com

Sri Sumarti
email: martisumarti@yahoo.com

Jean-Paul Toutain
email: jean-paul.toutain@ird.fr

Ilya N Bindeman
email: bindeman@uoregon.ed

Jean-Philippe Metaxian
email: metaxian@univ-savoie.fr

HIGHLY EXPLOSIVE 2010 MERAPI ERUPTION: EVIDENCE FOR SHALLOW-LEVEL CRUSTAL ASSIMILATION AND HYBRID FLUID

Keywords: Merapi volcano, Indonesia, subplinian eruption, ash-leachate, magmatic fluid, decarbonation, limestone assimilation mechanism, CO 2 pressure

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 secondstage ash sampled shortly after the 5 -6 th November 2010 paroxysmal subplinian eruption.

Several chemical and physical parameters suggest that the magma assimilated calc-silicate xenoliths derived from the surrounding carbonate-bearing crust (Javanese limestone). The bulk volcanic samples have highly radiogenic 87 Sr/ 86 Sr (0.70571 -0.70598) ratios that approach the compositional field of material similar to the calc-silicate xenoliths. The 2010 plagioclase phenocrysts from the pyroclastic flow and tephra reveal anorthite cores (up to An 94-97 ) with low FeO contents (≤0.7 wt%), and 18 O enrichment (6.5 ‰ δ 18 O). The major and trace elements of the silicic glasses and phenocrysts (plagioclase, low-Al augite and titanomagnetite), the Sr-Nd-O isotopic compositions of the bulk samples and plagioclases erupted in 2010 can be explained by complete digestion of the 1998 calc-silicate xenoliths.

The bulk assimilation proceeded through mixing between a calcic melt ("crustal assimilant", CaO up to 10.5 wt%, CaO/Al 2 O 3 up to 1.2) and the deep source hydrous K-rich melt.

Similarly to the 1998 and 2006 calc-silicate xenolith composition, the 2010 crustal assimilant is enriched in Mn (MnO up to 0.5 wt%), Zn, V, Sc contents. In contrast, the hydrous K-rich melt is enriched in volatiles (Cl up to 0.37 wt%, bulk H 2 O+CO 2 up to 5 ± 1 wt%), Al 2 O 3 , TiO 2 and REE contents, consistent with their derivation from deep source. This hydrous Krich melt may have been saturated with an aqueous fluid at about 200 MPa, a pressure consistent with the level of the crustal assimilation. The estimated in this work 15 -40 wt% of calc-silicate material assimilated by the magma suggest liberation up to 2.1 Mt of additional CO 2 to the pre-eruptive basaltic andesite magma. Experimental leaching of the ash samples documents the release of an aqueous fluid enriched in Cl, Na, Ca, Cd, Sb and Zn during the paroxysmal subplinian eruption. The paroxysmal eruption may have been produced by saturating the pre-eruptive basaltic andesite magma with this hybrid aqueous carbonic NaCl-HCl-rich fluid due to bulk assimilation creating high partial pressure of CO 2 at shallow crustal conditions of about 200 MPa. In contrast, mildly explosive block-and-ash flows (typical Merapi-type) may result from incomplete (selective) assimilation of the carbonatebearing xenoliths and lower CO 2 partial pressure that may not lead to explosive degassing.

Introduction

Merapi volcano, Central Java, Indonesia is one of the most active volcanoes in the world and one of the most dangerous in Indonesia (3000 to 5000 fatalities since 1672; [START_REF] Simkin | Earth's volcanoes and eruptions: an overview[END_REF]. The recent activity of Merapi is characterized by (i) recurrent effusive growth of viscous lave domes that collapse to form concentrated pyroclastic density currents, referred to Merapi-type block-and-ash flows (Volcanic Explosivity Index, VEI 2, Schwarzkopf et al., 2005) and (ii) more exceptional explosive eruptions of subplinian type (VEI 3 -4) associated with column collapse into pumice-and-ash pyroclastic flows [START_REF] Voight | Deformation and seismic precursors to dome-collapse and fountain-collapse nuées ardentes at Merapi volcano[END_REF].

The explosive eruption of 2010 (VEI 4) and their earlier the VEI 3 -4 events (in 1931 and 1872, and several VEI 3 eruptions between 1822 and 1872, potentially marking a change in Merapi's activity towards a more explosive behavior (cf. Gertisser and Keller, 2003a,b). This major issue must be taken into account with respect to monitoring implications, hazard analysis, and early warning protocols. Hence, a detailed study of the physical and chemical processes leading to increased explosivity at Merapi is a prerequisite to better understand the mechanisms generating lava dome eruptions versus explosive volcanic events.

Recent investigations highlighted an important influence of subducted sedimentary material on trace element and Sr-Nd-Hf-Pb-O isotope compositions of the recent Merapi magmas (Gertisser and Keller, 2003a;[START_REF] Debaille | Multi-stage mixing in subduction zones: Application to Merapi volcano (Java island, Sunda arc)[END_REF]Handley et al., 2011), whereas detailed micro-analytical and experimental data reveal also significant effects of shallow-level assimilation with local Javanese sedimentary crust [START_REF] Chadwick | Carbonate assimilation at Merapi volcano, Java, Indonesia: Insights from crystal isotope stratigraphy[END_REF][START_REF] Deegan | Magma-carbonate interaction processes and associated CO 2 release at Merapi volcano, Indonesia: Insights from experimental petrology[END_REF]2011;Troll et al., 2012;Troll et al., this issue). Limestone assimilation can play a key role in producing highly explosive fluid-saturated magmas (e.g., [START_REF] Iacono-Marziano | Limestone assimilation by basaltic magmas: an experimental re-assessment and application to Italian volcanoes[END_REF][START_REF] Iacono-Marziano | Role of nonmantle CO 2 in the dynamics of volcano degassing: The Mount Vesuvius example[END_REF][START_REF] Freda | Magma-carbonate interaction: An experimental study on ultrapotassic rocks from Alban Hills (Central Italy)[END_REF][START_REF] Mollo | Carbonate assimilation in magmas: A reappraisal based on experimental petrology[END_REF][START_REF] Deegan | Magma-carbonate interaction processes and associated CO 2 release at Merapi volcano, Indonesia: Insights from experimental petrology[END_REF]Troll et al., this issue).

To investigate the impact of crustal assimilation on the magma-fluid system producing the highly explosive 2010 eruption of Merapi, we analyzed major, trace and volatile elements, as well as and Sr-Nd-Pb-O isotopes on bulk ash, tephra, pyroclastic flow products and their minerals and glasses, using state-of-the-art analytical methods. Based on the data, we propose a mechanism for crustal assimilation that preceded and triggered the 2010 Merapi paroxysmal subplinian eruption.

Materials and Methods

Ash, tephra and pyroclastic flow sampling

Solid tephra and blocks from pyroclastic flows (5 to 7 cm in diameter) have been sampled during the Merapi 2010 early-stage eruptions in 28/10/2010 -02/11/2010. Ash samples have been sampled on 09/11/2010 from different geographic locations on the Merapi slopes shortly after the paroxysmal stage of the subplinian eruption of 05-06/11/2010 (Table 1; Figure 1).

Energy dispersive spectroscopy (EDS) mapping and electron microprobe (EMP)

techniques EDS mapping and EMP analyses are performed at the GET laboratory in Toulouse (www.get.obs-mip.fr) and at ISTO (Institute des Sciences de la Terre d'Orléans) in Orléans.

In Toulouse, the ash, tephra and pyroclastic samples were polished and investigated using the scanning electron microscope JEOL JSM-6360 LV with EDS coupled with the automatic analyser of particles by the program "Esprit" working in the module "Feature". The main mineral phases (low-Al augite, plagioclase and titanomagnetite) and minor mineral phases (orthopyroxene and aluminous clinopyroxene, K-feldspar, mineral SiO 2 , olivine, Cl apatite) firstly identified by EDS technique in the samples have been confirmed thereafter by electron microprobe. Silicic matrix glasses were firstly analysed by electron microprobe and their contribution to the bulk samples was later re-examined among "unidentified phases" based on the EDS mapping.

Major-and minor-element compositions of glassy and microcrystalline matrix and melt inclusions as well as silicate, oxide and phosphate minerals were analysed in situ using a CAMECA SX-50 (GET, Toulouse), following the analytical procedures previously described in [START_REF] Borisova | Constraints on degassing of dacite magma and regime of the June 15, 1991, climactic eruption of Mount Pinatubo (Philippines): New data on melt and crystal inclusions in quartz[END_REF]2010;2012a,b). 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. For spot analyses and mineral profiling the electron beam was set at an accelerating voltage of 15 kV and a current of 10 -20 nA for minerals and 10 nA for glasses with a spot diameter on the sample of 2 µm. The following synthetic or natural standards were used: albite (Na), periclase (Mg), corundum (Al), sanidine (K), wollastonite (Si, Ca), pyrophanite (Mn, Ti), hematite (Fe), chromium oxide (Cr), nickel oxide (Ni), sphalerite (Zn), graftonite (P), tugtupite (Cl) and topaz (F). 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. The analytical uncertainties and detection limits for major elements in the main minerals and glasses were similar to well-known analytical procedure using reference materials previously described in [START_REF] Borisova | Constraints on degassing of dacite magma and regime of the June 15, 1991, climactic eruption of Mount Pinatubo (Philippines): New data on melt and crystal inclusions in quartz[END_REF]2010;2012a). Detection limits for Cl, F, P and S in silicate glasses at these conditions were 500 ppm, 700 ppm, 300 ppm and 500 ppm, respectively.

Apparent concentrations of elements (in particular, light ones) were corrected using the PAP data reduction method [START_REF] Pouchou | Quantitative analysis of homogeneous or stratified microvolumes applying the model "PAP[END_REF].

The microanalyses at the ISTO in Orléans were performed on blocks of the 2010 pyroclastic flows that have been mounted in epoxy resins and polished. The samples were first inspected using a scanning electron microscope JEOL JSM-6400. Major-element compositions of glasses (matrix and melt inclusions; Table S1 of ESM) and silicate minerals and Fe-Ti oxides were analysed by CAMECA SX-50 (ISTO-BRGM, Orléans), with the following conditions: accelerating voltage of 15 kV, a current beam of 10 nA, a counting time of 10 s on the peak and 5 s on the background. The spot size on the sample was 2 µm for the mineral phases and defocused to 8x8 µm for the glasses. The following synthetic or natural standards were used: albite (Si, Na), olivine (Mg), corundum (Al), orthoclase (K), andradite (Ca), synthetic oxide of MnTiO 3 (Mn, Ti) and magnetite (Fe). The analytical errors on the oxide analyses are 1 wt. % relative (%rel.) for SiO 2 and Al 2 O 3 , 2 %rel. for CaO, 3 %rel. for FeO, MgO, and TiO 2 , and 5 %rel. for MnO, Na 2 O and K 2 O.

Apparent volatile contents in the glasses (summary CO 2 + H 2 O) were estimated "bydifference" method using EMP data [START_REF] Devine | Comparison of microanalytical methods for estimating H 2 O contents of silicic volcanic glasses[END_REF]. The volatile content (assumed to be mainly water, see the part 4.4) is the difference to 100 wt% of the oxide EMP analyses, calibrated against hydrated standard glasses with well-known water contents (0.1, 4.4, and 6.4 wt% H 2 O, determined by Karl-Fischer titration; see [START_REF] Scaillet | The 15 June 1991 eruption of Mount Pinatubo. I. Phase equilibria and pre-erution P-T-f O2 -f H2O conditions of the dacite magma[END_REF][START_REF] Borisova | Constraints on degassing of dacite magma and regime of the June 15, 1991, climactic eruption of Mount Pinatubo (Philippines): New data on melt and crystal inclusions in quartz[END_REF].

In situ major and trace element analyses of mineral and glasses by LA-ICP-QMS (Hobart, Australia)

Major and trace elements in the matrix glasses and minerals of ash samples were analysed using laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-QMS) at Centre of Excellence in Ore Deposits (University of Tasmania in Hobart, Australia). The ash samples were analysed using a Resonetics Resolution M50 laser microprobe equipped with a Coherent 193 nm excimer laser, which is coupled to an Agilent 7500cs massspectrometer. Ablation was conducted in an atmosphere of pure He. Laser beam energy at the sample was set to ~ 3 J/cm 2 , laser beam diameter to 44 µm, and ablation rate to 10 Hz. Helium carrier gas was mixed with Ar carrier gas outside the ablation cell. The ICP-QMS was tuned to minimize production of oxide interferences (ThO + /Th + < 0.1%) and to enhance sensitivity in the middle to heavy mass range. Each analysis involved a 20 sec background acquisition (laser off), followed by 60 s of signal acquisition. The following masses have been measured: 7 Li, 11 B, 23 Na, 25 Mg, 27 Al, 29 Si, 39 K, 43 Ca, 45 Sc, 47 238 U with a dwell time of 0.015 sec on each mass. Data reduction was undertaken according to standard methods [START_REF] Longerich | Laser Ablation Inductively Coupled Plasma Mass Spectrometric Transient Signal Data Acquisition and Analyte Concentration Calculation[END_REF] using the "Sills" data reduction software [START_REF] Guillong | Sills: A MATLAB-based program for the reduction of laser ablation ICP-MS data of homogeneous materials and inclusions[END_REF] Internal standardization was performed assuming a total sum for all major element oxides of 99 wt%. Regular precision of the major and trace element analyses by the LA ICP MS is in the limit of 5 -10 %RSD (e.g., [START_REF] Guillong | Sills: A MATLAB-based program for the reduction of laser ablation ICP-MS data of homogeneous materials and inclusions[END_REF]. Limits of detection are listed below: SiO 2 (0.01 wt%), TiO 2 , Al 2 O 3 , FeO, MnO, MgO, CaO, Na 2 O, K 2 O (10 -3 -10 -5 wt%), B (1.2 -1.3 ppm), Li, Cr, Ni, Cu, Zn (~10 -1 ppm), Sc, V, Co, Rb, Sr, Zr, Nb, Sb, Cs, Ba, La, Nd, Sm, Gd, Dy (~10 -2 ppm), Y, Ce, Pr, Eu, Tb, Ho, Er, Tm, Yb, Lu, Ta, Th ,U (~10 -3 ppm).

Volatile, major, trace element and Sr-Nd-Pb measurement in the bulk samples

The bulk volatile concentrations of CO 2 and S were measured at SARM (Service [START_REF] Carignan | Routine analyses of trace elements in geological samples using flow injection and low pressure on-line liquid chromatography coupled to ICP-MS: A study of geochemical reference materials BR, DR-N, UB-N, AN-G and GH[END_REF] with ICP-OES IRIS Advantage ERS from Thermo Scientific and ICP-MS x7 of Thermo Scientific without pre-concentration of REE and U/Th.

For Sr-Nd-Pb isotope measurements, a special method (described below) developed in the SARM has been applied. Between 100 and 200 mg of very fine-grained powders (particle size <50 µm) were placed into 15 ml Savillex© beakers. A mixture of concentrated subboiled HNO 3 (4 ml) and ultrapure HF (1 ml) were added into the beakers. The solutions were heated at 115°C for 24 -48 h, then evaporated, re-filled with concentrated HCl and heated for 24 h until complete digestion of the powder samples was achieved. The sample was then split into two parts and dried for further purification of the elements.

For Pb chromatographic separation from the matrix, 1 ml of HBr (0.8M) was added to the aliquots. The chromatographic micro-column was then filled with AG1X8 resin. The matrix was eluted with HBr (0.8M) and lead recovered with HCl 6M following a method similar to that of Manhès (1980). Isotopic analysis has been performed on a MC-ICP-MS (Isoprobe from Micromass) using Tl (NIST 997) to correct for the instrumental mass bias. Tl and Pb isotope values used for the NIST 981 and NIST 977 in this work were those obtained earlier by [START_REF] Thirlwall | Multicollector ICP-MS analysis of Pb isotopes using a 207 Pb-204 Pb double spike demonstrates up to 400ppm/amu systematic errors in Tl-normalization[END_REF]. More analytical details on the applied method can be obtained in [START_REF] Cloquet | Atmospheric pollutant dispersion around an urban area using trace metal concentrations and Pb isootopic compositions in epiphytic lichens[END_REF]. The average blanks were always negligible compared to the Pb mass used for the sample analyses and was on average below 300 pg for Pb.

For Sr and Nd isolation, the samples were diluted with 2 ml of HNO 3 (2M) following the analytical protocol of [START_REF] Pin | Concominant separation of strontium and samarium-neodymium for isotopic analysis in silicate samples, based on specific extraction chromatography[END_REF]. An additional stage for further isolation of Nd from Sm was applied using Ln spec resin following the same chemistry as described by [START_REF] Pin | Sequential separation of light rare-earth elements, thorium and uranium by miniature extraction chromatography: Application to isotopic analyses of silicate rocks[END_REF]. Sr isotopes were measured with TIMS (Triton Plus from Thermo Electron) in the multicollection mode. Five Faraday cups were used in order to monitored Rb as well. Sr was loaded onto Re as filament. To correct for the instrumental mass bias, internal normalisation using 86 Sr/ 88 Sr (0.1194) ratio and exponential law were used. NBS 987 has been applied to control the method accuracy. The average blanks were always negligible compared to the Sr mass used for the sample analyses and was on average around 300 pg for Sr.

Nd isotopes were measured using MC-ICP-MS (Isoprobe from Micromass). To control the instrumental mass bias we used a constancy of the ratio 146 Nd/ 144 Nd (0.72190) [START_REF] Luais | Precise and accurate neodymium isotopic measurements by plasma-source mass spectrometry[END_REF] and exponential law. JMC Nd was applied to control the method accuracy.

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

Oxygen isotopic measurement of the bulk ash samples and plagioclase fractions

Oxygen isotopic measurements were performed on 1-2 mg of plagioclase crystal fractions and ash powders using laser fluorination technique at the University of Oregon [START_REF] Bindeman | Oxygen isotope heterogeneity and disequilibria of olivine crystals in large volume Holocene basalts from Iceland: Evidence for magmatic digestion and erosion of Pleistocene hyaloclastites[END_REF]. The samples were heated with an infrared laser (9.6 µm, CO 2 ) in the presence of purified BrF 5 to release oxygen. 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. The generated O 2 gas was purified in a series of cryogenic traps held at liquid nitrogen temperature, and then a mercury diffusion pump was used to remove any remaining traces of BrF 5 . Oxygen was converted to CO 2 gas by reacting with graphite at high T (1450°C), the yields were measured, and CO 2 was analyzed with the Isotope Ratio Mass Spectrometry (IRMS) in a dual inlet mode. Four to seven reference garnet (δ 18 O= 6.52‰, University of Oregon garnet from Gore Mt, NY, USA named as "UOG garnet") were analyzed together with the samples during each of seven analytical sessions. Day-to-day δ 18 O variability of standards ranged from 0.1 to 0.3‰ lighter than their reference values and the measurements of unknowns were adjusted accordingly.

The precision on standards is better than 0.1 ‰ of 1σ standard deviation.

Leaching experiment, ion chromatography and ICP-MS of the ash-leachates

Non-ground slightly wet ash samples have been frozen at -80° C for two reasons: (i) to avoid decomposition of possible biological material in the samples and (ii) to avoid complete loss of the volcanic fluid phase absorbed on the ash surface according to the ash leaching method revised by [START_REF] Witham | Volcanic ash-leachates: a review and recommendations for sampling methods[END_REF]. The following "freeze-dry" procedure was applied for 66 hours at GET laboratory. Two identical leaching experiments on every ash sample have been performed in distilled MQ water with solid to solution ratios ("SSR") from 1 / 24 to 1 / 18 for 28 hours following the recommendations of [START_REF] Witham | Volcanic ash-leachates: a review and recommendations for sampling methods[END_REF]. The ash-leachates were then centrifuged and filtered using 0.45 m filters. Fluor, Cl, Br, SO 4 , NO 3 , NO 2 and PO 4 ion concentrations were measured by ion chromatography, using an ICS -2000 Ion Chromatographic System with IonPac analytical column at GET. The analytical eluent was 30 mM KOH with the eluent source EGC-KOH II Cartridge. The analytical conditions were flow rate of 1 mL/min at 30°C, current of 100 mA and injection volume of 200 μL. The accuracy of the ion chromatographic method was controlled by the reference solution "CRM ION 915" (see [START_REF] Borisova | Processes controlling the 2010 Eyfjallajӧkull explosive eruption[END_REF].

The HR-ICP-MS (high resolution inductively coupled plasma mass spectrometry) technique used was Element XR for metal concentration measurements in the ash leachates at GET laboratory. Two elements, of known concentrations (In and Re) were used as internal standards. The accuracy of the HR-ICP-MS method was controlled by numerous ICP-MS Certified Reference Materials. Typical accuracy, blanks and detection limits are similar those of obtained by [START_REF] Borisova | Processes controlling the 2010 Eyfjallajӧkull explosive eruption[END_REF].

Results

Mineral and glass proportions

The results on phase proportions obtained by EDS mapping technique on the ash, tephra and pyroclastic flow samples are summarized in Table 2. 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 SiO 2 mineral phase. Heterogeneous matrix contains abundant bubbles and microphenocrysts (plagioclase, augite and titanomagnetite).

The consolidated tephra and pyroclastic flow samples show phenocryst contents between 26 and 65 % (depending on the sample zone) recalculated on a bubble-free basis and shows the following assemblage: 3 to 10 % plagioclase (including anorthite) up to 1700 µm size, up to 44 % orthopyroxene, 4 to 18 % clinopyroxene up to 1300 µm size, 2 to 27% titanomagnetite, < 1.5 % K-feldspar and apatite, and a single olivine and amphibole (in the pyroclastic flow samples).

Despite intensive searching, no Ca-rich metamorphic phases (e.g., wollastonite, diopside, grossular, etc.) that could have been provided from the calc-silicate xenoliths, as reported in the 1998 and 2006 products [START_REF] Chadwick | Carbonate assimilation at Merapi volcano, Java, Indonesia: Insights from crystal isotope stratigraphy[END_REF][START_REF] Deegan | Magma-carbonate interaction processes and associated CO 2 release at Merapi volcano, Indonesia: Insights from experimental petrology[END_REF], have been identified in the investigated 2010 samples (Table 2).

Bulk chemical composition (volatile, major and trace elements) of ashes, tephra and pyroclastic flow samples

The bulk 2010 ash sample chemistry summarized in Table 3 allows classifying them as basaltic andesite of the high-K series following the classification of [START_REF] Gertisser | Temporal variations in magma composition at Merapi volcano (Central Java, Indonesia): Magmatic cycles during the past 2000 years of explosive activity[END_REF]. The ash samples demonstrate major-and trace-element compositions typical for the Merapi volcanic series (Figures 2,3).

Chemical composition (volatile, major and trace elements) of glasses and minerals

The melt and multi-phase inclusions (from 10 to 80 µm size and consisting of pure glass or multiphase assemblage of glass with minerals, Figure 4c) from the early-stage pyroclastic flows have heterogeneous compositions (62 -71 wt% of SiO 2 refers to the majorand minor-element contents recalculated on the volatile-free basis here and elsewhere in the text) and variable Ca/Al ratios (CaO/Al 2 O 3 = 0.08 -1.2). The glassy melt inclusions range from Ca-poor (CaO/Al 2 O 3 = 0.08) and "calcic" (CaO/Al 2 O 3 = 1.2). The glassy melt inclusions from the late-stage ashes show variable SiO 2 contents (63 -73 wt%), CaO/Al 2 O 3 (0.07 -0.14) and MnO/Al 2 O 3 ratios (0.002 -0.017), with the SiO 2 -richest glasses (SiO 2 ≥ 70 wt%) being depleted in Al 2 O 3 (≤ 15.6 wt%) and CaO (≤ 1.2 wt%) relative to the "calcic" glasses (>5 wt% CaO, <13 wt% Al 2 O 3 , Tables 4 andS1 of ESM). Moreover, the variable Cl contents (0.06 -0.37 wt%) are not correlated with P (0.06 -0.39 wt%), indicating an insignificant influence of Cl-apatite crystallization on the volatile contents. Both Cl and K (3.1 -6.6 wt% K 2 O) demonstrate negative correlation with Ca contents and CaO/Al 2 O 3 ratios (0.07 -0.17; Figure 3). For example, high-K glass inclusions (analysis № 52: 6.6 wt%, 0.4 wt% of K 2 O and Cl, respectively, Table S1) are poor in CaO (1.4 wt%) at ~68 wt% SiO 2 , whereas some "calcic" glassy melt inclusions contain up to 10.5 wt% CaO and ~0.5 wt% MnO for SiO 2 contents of 62 -67 wt% (Table 4). (MnO up to 0.63 wt%) (Figure 3). The matrix glasses are characterized by high, but variable, contents of B (19.5 -61 ppm), Ba (703 -920 ppm), La (17 -41 ppm), Rb (70 -200 ppm), Th (9 -17 ppm), Sc (2.5 -15.6 ppm), Zn (50 -170 ppm) and V (15 -46 ppm, Figure 3) relative to adakitic rhyolitic glasses [START_REF] Borisova | Chemistry of silicic melts of the Mount Pinatubo, Philippines: Implications for oreforming potential of adakitic magmatism[END_REF]2008). Sr (140 -413 ppm) contents in the 2010 Merapi matrix glasses overlap those experimentally synthetized (370 -500 ppm, [START_REF] Deegan | Magma-carbonate interaction processes and associated CO 2 release at Merapi volcano, Indonesia: Insights from experimental petrology[END_REF] during calc-silicate xenolithmagma interaction runs. EMP profiling in plagioclase phenocrysts from the early-stage 2010 Merapi pyroclastic flow shows them to be strongly zoned, with cores up to 94 -97 mol% anorthite (An 94-97 ) and rims of An 45-50 (Figure 4a). The total range of plagioclase compositions in the 2010 samples overlap the compositional range reported for the previous eruptive events except for plagioclases richest in An and in FeO (Figure 4b). The plagioclase crystals in the late-stage ash samples are An 48-54 with 0.04 -0.06 wt% MgO, 0.4 -0.5 wt% FeO, and are strongly enriched in Sr (~1000 ppm) similarly to those of analyzed by [START_REF] Chadwick | Carbonate assimilation at Merapi volcano, Java, Indonesia: Insights from crystal isotope stratigraphy[END_REF]. S4 of ESM). The Fe-Ti oxides in the late-stage ash samples are titanomagnetites characterized by TiO 2 (12 -13 wt%), MgO (~2 wt%), MnO (~1 wt%), V (3000 -3300 ppm), Zn (1700 -2500 ppm), and Sc (19 -24 ppm) contents (Figure 3).

Minor mineral phases such as olivine, apatite, pargasitic amphibole, and SiO 2 mineral phases have been analyzed by different microprobe techniques (Table S5 of ESM). Olivines (Fo 44-66 ) have been found only in the ash samples and one crystal in the pyroclastic flow sample (Table 2). Apatites are ubiquitous and contain 53 -54 wt% CaO, 41 -42 wt% P 2 O 5 , and ~1 wt% Cl. Only one crystal of amphibole has been found in the block sample from the 2010 pyroclastic flows. The crystal does not show any reaction rim and has the chemical composition of pargasite (in wt%: 42 wt% of SiO 2 , 11 wt% of Al 2 O 3 , 11 wt% of CaO, 13 wt% of FeO, 13 wt% of MgO, Table S5). The ash samples also contain 0.2 -0.3% of a mineral of SiO 2 (97 -99 wt% of SiO 2 ) enriched in Al 2 O 3 (0.7 -3.3 wt%), Na 2 O (0.1 -0.7 wt%) and K 2 O (0.03 -0.3 wt%).

Sr-Nd-Pb-O isotopic composition of ash, tephra and pyroclastic flow samples

The bulk ash samples have 87 Sr/ 86 Sr ratios of 0.70571 -0.70575 and 143 Nd/ 144 Nd ratios of 0.51285 -0.51294 that plot on the high-87 Sr/ 86 Sr and low-143 Nd/ 144 Nd end of the Merapi Sr-Nd isotopic field (Figure 5). The 2010 87 Sr/ 86 Sr ratios in fact approach the Merapi calcsilicate xenolith field. Lead isotope ratios (Table 3) plot in the non-radiogenic side (low 206 Pb/ 204 Pb) of the Merapi rock field.

Oxygen isotope compositions of plagioclase phenocryst fractions from the 2010 earlystage pyroclastic flow samples are identical: 6.5‰ for both M2010K and M2010GR. The δ 18 O obtained for the 2010 Merapi plagioclases are comparably low values in the δ 18 O compositional range known for plagioclases of the Holocene Pyroclastic Series (δ 18 O = 6.5 -7, Figure 5c). Moreover, the δ 18 O obtained for the 2010 Merapi plagioclases plot within the common compositional range of δ 18 O measured in the Merapi whole rocks (Figure 5c).

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.

Chemistry of ash-leachates

The ash-leachates produced by leaching experiments demonstrate constant F/Cl ratios (0.05 ± 0.01) and Ca-Na-Zn-Cd-Sb-Cl enrichment relative to fluid-immobile high-field strength element (HFSE: Zr, Nb, Th, Ti) normalized to the host ash composition (Figure 7).

The complete compositions of the ash-leachates are given in Table S6 of ESM.

Discussion

Two time-constrained eruptive stages

Two main stages of eruptive activity can be distinguished based on the textural (Figure 1) and mineralogical characteristics (Table 2) of the time-constrained samples: that erupting as the early-stage tephra and pyroclastic flow and that erupting as the late-stage ashes. Rare crystals and their fragments of pure SiO 2 mineral phase, and olivine (Figure 1; Table S5 of ESM) are mostly identified in the late-stage ash samples, whereas single small fragment of olivine has been found in the early-stage pyroclastic flow sample (M2010GR, Table 2: 0.12% surface). The SiO 2 mineral phase (97 -99 wt% of SiO 2 ) enriched in Al, Na and K could be either magmatic cristobalite crystallized from a silica-rich melt [START_REF] Martel | Decompression experiments as an insight into ascent rates of silicic magmas[END_REF][START_REF] Martel | Eruption dynamics inferred from microlite crystallization experiments: Application to Plinian and dome-forming eruptions of Mt. Pelée (Martinique, Lesser Antilles)[END_REF] or metamorphic quartz issued from calc-silicate xenoliths [START_REF] Chadwick | Carbonate assimilation at Merapi volcano, Java, Indonesia: Insights from crystal isotope stratigraphy[END_REF]. Moreover, the Mn-rich olivines observed in the late-stage ash samples (Figure 1; MnO = 1.2 to 1.8 wt%) also occur among the Merapi volcanic samples and are typical magmatic phases for the Merapi volcano (Figure 4d). Similarly, one euhedral pargasite crystal (~11 wt% Al 2 O 3 ) found in the early-stage pyroclastic flows is a typical magmatic phase, since its composition (Table S5 of ESM) is compatible with crystallization from a basaltic andesite melt (53 wt. % SiO 2 ) at pressure ~200 MPa and temperature ~900°C [START_REF] Martel | Basaltinherited microlites in silicic magmas: evidence from Mt. Pelée[END_REF].

Evidences for sedimentary crustal assimilation

Sedimentary crustal assimilation is an important magmatic process for the generation of the 1998 and 2006 Merapi lavas (e.g., [START_REF] Chadwick | Carbonate assimilation at Merapi volcano, Java, Indonesia: Insights from crystal isotope stratigraphy[END_REF]. In particular, calc-silicate xenoliths produced by contact metamorphism of the Javanese limestone crust were present in the Merapi 1998 and 2006 erupted products [START_REF] Chadwick | Carbonate assimilation at Merapi volcano, Java, Indonesia: Insights from crystal isotope stratigraphy[END_REF]Troll et al., 2012;Troll et al., this issue). These xenoliths have characteristic skarn-type mineralogy dominated by wollastonite and diopside; with lesser amounts of anorthite, quartz, Fe-oxides; and rare tremolite, grossular, apatite, titanite, calcite, larnite, and other calcium-silicate and calcium oxide minerals [START_REF] Deegan | Magma-carbonate interaction processes and associated CO 2 release at Merapi volcano, Indonesia: Insights from experimental petrology[END_REF]Borisova, personal communication). Interestingly, and despite intensive EDS-mapping investigation, no calc-silicate xenoliths or typical phases they contain have been identified in the 2010 samples. Thus, we looked for evidence of possible pervasive crustal contamination in the 2010 products through EDS mapping, in situ microanalyses of the minerals and glasses and mineral profiling. The second line comes from the plagioclase analytical profiles, which are similar to those observed by [START_REF] Chadwick | Carbonate assimilation at Merapi volcano, Java, Indonesia: Insights from crystal isotope stratigraphy[END_REF] and [START_REF] Deegan | Magma-carbonate interaction processes and associated CO 2 release at Merapi volcano, Indonesia: Insights from experimental petrology[END_REF] in the 1998 Merapi lavas, i.e. plagioclase cores up to An 94-97 and more sodic rims typically around An 50 (Figure 4a). The first hypothesis that can be proposed to produce plagioclases with An contents > 88 mol % is crystallization from a mafic melt (SiO 2 < 56 wt%; [START_REF] Pichavant | Physical conditions, structure, and dynamics of a zoned magma chamber: Mount Pelée (Martinique, Lesser Antilles Arc)[END_REF][START_REF] Martel | Basaltinherited microlites in silicic magmas: evidence from Mt. Pelée[END_REF].

Yet, such plagioclases would have FeO contents around 1 wt %, either crystallized in a deep magma chamber (~400 MPa and ~1000°C; [START_REF] Pichavant | Physical conditions, structure, and dynamics of a zoned magma chamber: Mount Pelée (Martinique, Lesser Antilles Arc)[END_REF] or at shallower level (~200 MPa and ~900°C; [START_REF] Martel | Basaltinherited microlites in silicic magmas: evidence from Mt. Pelée[END_REF]. Such a plagioclase would also have low  18 O ratios. In contrast, the 2010 plagioclases have low FeO contents below 0.8 wt % (Figure 4a) and are enriched in 18 O (Figure 5c and discussion below). The 2010 Merapi phenocrysts (plagioclases and low-Al augites) were crystallized from silicic melts (SiO 2 ≥ 57 wt%; Tables 4,S1), which is inconsistent with the origin from a "classical" basaltic melt. Since the 2010 highly calcic plagioclases approach the plagioclase compositional field typical for the Merapi calc-silicate xenoliths (Figure 4b), a second possible origin could be the metamorphic calc-silicate xenoliths [START_REF] Chadwick | Carbonate assimilation at Merapi volcano, Java, Indonesia: Insights from crystal isotope stratigraphy[END_REF]), but we did not find residual xenoliths in the 2010 products.

Therefore, we propose that the highly calcic plagioclases crystallized from highly calcic melts firstly experimentally produced by [START_REF] Deegan | Magma-carbonate interaction processes and associated CO 2 release at Merapi volcano, Indonesia: Insights from experimental petrology[END_REF] and described in this work for the 2010 Merapi samples (see Table 4). The calcic melts represent the "crustal assimilant" possibly produced by complete dissolution and digestion of crustal xenoliths of 1998-type upon xenolithmagma interaction, as experimentally demonstrated by [START_REF] Deegan | Magma-carbonate interaction processes and associated CO 2 release at Merapi volcano, Indonesia: Insights from experimental petrology[END_REF].

Moreover, high quantity of clinopyroxene, and anorthite (≥90 mol% An) fragments in the 2010 ash samples (~40 to 50 % surface and 26 -28 % surface, respectively, Table 2) suggests abnormally Ca-enriched magma.

The third line of evidences for the early-stage crustal assimilation comes from the in situ measured compositions of the main phenocryst minerals (plagioclase, low-Al augite, titanomagnetite,) and matrix glasses. The matrix glasses are enriched in MnO (up to 0.4 wt%), Sr (up to ~380 ppm), Zn (up to ~170 ppm), V (up to ~160 ppm). The phenocrysts are characterized by enrichment in "vital elements" as Mn, Sr, Zn, V (Figure 3 and Tables S2 -S4 of ESM) which is typical signature of the 1998 calc-silicate xenoliths [START_REF] Chadwick | Carbonate assimilation at Merapi volcano, Java, Indonesia: Insights from crystal isotope stratigraphy[END_REF] and carbonate-bearing sediments [START_REF] Brugger | Manganese-rich assemblages in the Barrhorn Unit, Turtmanntal, Central Alps, Switzerland[END_REF][START_REF] Kamber | Transition metal abundancies in microbial carbonate: a pilot study based on in situ LA-ICP-MS analysis[END_REF]. The ash plagioclases are strongly enriched in Sr (typically at ~1000 ppm) at MgO = 0.04 -0.06 wt% and FeO = 0.4 -0.5 wt% at An 48 -54 , consistent with an assimilation and fractional crystallization process involving metamorphic crustal material. Finally, the observed values of 18 O in the early-stage plagioclase phenocrysts and the bulk-rock ash samples (δ 18 O Plag = 6.5 ‰; δ 18 O Ash = 5.6 -6.8 ‰) are lower than those characteristic for adakitic and related magmas for the 1991 Pinatubo eruption (δ 18 O Ash = 6.9 -7.3 ‰, [START_REF] Fournelle | Anhydrite-Bearing Pumices from the June 15, 1991, Eruption of Mount Pinatubo: Geochemistry, Mineralogy, and Petrology[END_REF], overlap those of basaltic andesites of the previous Merapi eruptions (Figure 5c) and are higher compared to typical mantle values (δ 18 O MORB =5.7 ‰).

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. 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 18 O ranging from 10 to 14 ‰ (Gertisser and Keller, 2003a;Troll et al., this issue).

These metamorphic xenoliths are derived from local upper Javanese crustal limestone which is characterized by yet higher δ 18 O, ranging from 18.9 to 24 ‰ (Troll et al., this issue).

Mechanism of crustal assimilation

The in situ analyzed mineral and glass compositions constrain the mechanism of crustal assimilation by the pre-eruptive magmatic system. Firstly, figure 3 andtable 4 demonstrate that the early-stage pyroclastic flow glasses and late-stage ash glasses of melt inclusions and matrix are heterogeneous in respect to CaO and Ca/Al, suggesting the existence of "calcic" melts representing a "crustal assimilant" at the 2010 pre-eruptive magma. High CaO and low Al 2 O 3 contents are known signatures of the 1998 calc-silicate xenoliths (Figures 2,3) and similar chemical signatures can be observed in "calcic" glassy melt inclusions trapped in low-Al augite (Al 2 O 3 Aug = 1.5 -1.6 wt%; This mixing process can also be observed in zonation of low-Al augite phenocryst (Al 2 O 3 Aug ≤ 3.3 wt%) which is oscillatory for Al, Ti, Na and Mn (Figure 4c). Positive peaks in Al, Ti and Na are associated with negative peaks in Mn in the augite phenocryst. These zones likely reflect crystallization from a batch of "pure" melt rich in alkalis, Al, Ti likely derived from a deep magmatic source rather than from sedimentary crust, i.e. less contaminated than the hybrid melts crystallizing most part of the augite phenocrystal. Moreover, the enrichment in Mn, Sr, Zn, V of the low-Al augites, as well as in the plagioclases, titanomagnetites (Figure 3; Tables S2 -S5 of ESM) and matrix glasses relative to adakitic rhyolitic melts (e.g., [START_REF] Borisova | Chemistry of silicic melts of the Mount Pinatubo, Philippines: Implications for oreforming potential of adakitic magmatism[END_REF]2008), suggest that these mineral phases were crystallized from the hybrid melt contaminated with material similar to the 1998 calc-silicate xenoliths.

On the basis of evidences, the overall analytical and microanalytical data support crustal assimilation process that proceeded through three major steps: (1) contact metamorphism of the Javanese limestone and formation of calc-silicate xenoliths of the 1998 type (not discussed here and broadly described by [START_REF] Chadwick | Carbonate assimilation at Merapi volcano, Java, Indonesia: Insights from crystal isotope stratigraphy[END_REF] for Merapi and by [START_REF] Fulignati | Skarn formation at the walls of the 79 AD magma chamber of Vesuvius (Italy): Mineralogical and isotopic constraints[END_REF] for Vesuvius); (2) bulk assimilation of the calc-silicate xenoliths through the complete digestion, melting/dissolution and formation of the "calcic" melt endmember representing the "crustal assimilant"; (3) effective binary chemical and physical mixing of the silicate and calcic melts that carry both signatures (i.e., magmatic and crustal)

and fractional crystallization of phenocrysts.

Because no information on kinetic parameters of the crustal assimilation is available (e.g., M a and r in DePaolo, 1981 or α in [START_REF] Russell | Volatile production possibilities during magmatic assimilation: heat and mass-balance constraints[END_REF] for coupled assimilationfractional crystallization), the pre-eruptive process of the 2010 Merapi magma assimilation can be described as an equation of binary mixing. We suggest the following equations:

C All Hybr = Average (C melt Hybr ; C cryst Hybr /D) = C melt Init × (1 -f) + C melt Ass × f (1),
where f is fraction (f = 0 -1) of "crustal assimilant" incorporated to the magma (hybrid melt + phenocrystals), C All Hybr is average concentration of an element in the bulk hybrid magmatic [START_REF] Borisova | Chemistry of silicic melts of the Mount Pinatubo, Philippines: Implications for oreforming potential of adakitic magmatism[END_REF]2008) and C melt Ass = 380 ppm (maximal measured Sr content in the 2010 Merapi matrix glasses), D is 5.0 (partitioning between plagioclase An 40-50 and silicic melt after [START_REF] Ren | Partitioning of Sr, Ba, Rb, Y, and LREE between plagioclase and peraluminous silicic magma[END_REF] and the equation ( 2), f is ~0.3.

Similarly, the pre-eruptive process of the 2010 Merapi magma assimilation can be constrained based on known Sr isotopic ratios in the bulk rocks and Sr concentrations in melts and crystals. For calculations, we adapted equation of binary mixing:

R melt Hybr = (f × C melt AssAll × R melt Ass + (1 -f) × C melt Init ×R melt Init ) / (f × C melt AssAll + (1 -f) × C melt Init ) (3),
where R melt Init is initial isotopic ratio in the melt before assimilation, R et al., 2007) and C melt AssAll varies from 286 to 386 ppm and D is 5.0 and the equation ( 4), f ranges from 0.15 to 0.40. These estimations suggest that the pre-eruptive Merapi magma has assimilated from 15 to 40 wt% of carbonate-bearing crustal material.

Fluid phase composition and hybrid origin

The volatile contents in the silicic glasses together with the ash-leachate compositions give us first information on the composition of the magmatic fluids liberated during the late stage subplinian eruption. The melt inclusions analyzed in the ash samples exhibit high Cl contents up to 0.37 wt% (analysis № 52, Table S1), suggesting that the K-rich melt approached saturation in H 2 O-Cl-bearing fluid or fluids (Cl = 0.6 -0.9 wt% at saturation with aqueous Cl-rich fluid at 200 MPa in silicic melt; [START_REF] Carroll | Solubilities of sulfur, noble gases, nitrogen, chlorine, and fluorine in magmas; In: Volatile in Magmas[END_REF]. The phenocrysthosted K-rich melt inclusions from the early-stage pyroclastic flows are enriched in volatiles (H 2 O+CO 2 regularly up to 5 ± 1 wt%, determined following the EMP by-difference method;

Figure 6), suggesting that the early-stage melts are close to be saturated with aqueous fluids at ~200 MPa (e.g., [START_REF] Burnham | Development of the Burnham model for prediction of H 2 O solubility in magmas[END_REF]. In contrast, calcic assimilant melts are depleted in volatiles (≤1.6 wt% of H 2 O+CO 2 contents) relatively to the K-rich inclusions (Figure 6). The derivation of the crustal assimilant melts from carbonate-bearing xenoliths suggests their enrichment in CO 2 (CO 3 2-

) rather than in H 2 O (OH -). Because no measurement of H 2 O/CO 2 in the investigated melt inclusions has been performed quantitatively, we suggest that the upper limit of CO 2 content in the calcic melt inclusions is 1.6 wt% content (Figure 6). For all samples, most of the matrix glasses have H 2 O+CO 2 contents ≤ 3.5 wt% (Figure 6, Table S1 of ESM), indicating progressive degassing during magma transport and subaerial emplacement.

The leaching experiments performed in this study on four ash samples (Table S6 of ESM) show constantly low F/Cl ratios (0.05 ± 0.01) and Na-Ca-Cl-Zn-Cd-Sb enrichment relative to fluid-immobile high field strength elements (HFSE: Zr, Nb, Th, Ti) (Figure 7), suggesting an aqueous Cl-rich fluid was liberated to the atmosphere during the subplinian eruption on 5-6 th November 2010. Low F/Cl ratios (<0.2) strongly support an eruption of nondegassed magma typical for initial stage of subplinian explosive events (e.g., [START_REF] Borisova | Processes controlling the 2010 Eyfjallajӧkull explosive eruption[END_REF]. High concentrations of Zn, Cd and Sb in the ash leachates may be achieved through the equilibration of an aqueous NaCl-HCl-rich fluid with a hydrous melt enriched in these elements. According to what is known on Zn, Cd and Sb complexation with Cl in NaCl-HClrich fluids, their K d fluid/melt should be significantly higher than 1 (Borisova et al., 2012 and references therein). According to the concept of the "geo-pH/Cl-meter" of [START_REF] Pokrovski | Antimony speciation in saline hydrothermal fluids: A combined X-ray absorption fine structure spectroscopy and solubility study[END_REF]2008), high HCl or an increased acidity into the aqueous phase results in formation of strong and volatile Sb-Cl ligands at the expense of Sb-OH complexes that are less stable under these conditions. This results in the preference of Sb for Cl in NaCl-HCl-rich fluids.

Moreover, the saturation of the 2010 Merapi magma with Cl-rich fluids enriched in Ca, Zn and Cd can be partially related to the inferred crustal assimilation. Indeed, Zn and Cd are known to be concentrated in oceanic carbonate-bearing sediments [START_REF] Heinrichs | Terrestrial geochemistry of Cd, Bi, Tl, Pb, Zn and Rb[END_REF].

These data provide an evidence for hybrid nature of the NaCl-HCl-rich magmatic fluids liberated during the paroxysmal eruption.

The above constrained fraction of the carbonate-bearing crustal material assimilated by magma is a basis for the following estimations of the amount of CO 2 liberated at the preeruptive conditions. The following simplified chemical equation of decarbonation can be used: CaCO 3 calc-silicate xenolith = CO 2 ↑ fluid + CaO melt (5).

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). This mass of the volcanic material erupted in 2010 can be suggested as the bulk mass of magma existed at the pre-eruptive conditions. Therefore, the fraction (f) of the assimilated crustal material (0.15 -0.40) estimated based on the equations ( 2) and ( 4), maximal contents of calcite in the calc-silicate xenoliths (5 to 10 wt% based on Borisova, personal communication) and chemical reaction (equation 5) gives 1.9 × 10 8 to 2.1 × 10 9 kg or 0.19 to 2.1 Mt of CO 2 which is equivalent from 0.3 to 3.5 wt% of an additional CO 2 in the magma (relative to the suggested mass 6 × 10 10 to 1.2 × 10 11 kg of the pre-eruptive magma). The upper estimate of CO 2 mass (2.1 Mt) is a factor of ~5 higher than the bulk mass of SO 2 (~0.44 Mt) liberated during the 2010 Merapi eruption (Surono et al., this volume).

This maximal estimate of the liberated CO 2 mass is also in accordance with the bulk CO 2 /SO 2 (7 -115 in mol%, Surono et al., this volume) corresponding to CO 2 /SO 2 (5 -80 in wt%) measured in fumaroles before the 2010 explosive events. Thus, the additional CO 2 liberated upon the decarbonation at the pre-eruptive magma chamber has resulted in increase in partial pressure of CO 2 (see Appendix A for at least 1.5 -10 MPa pressure of CO 2 liberated due to decarbonation depending on the suggested free volume) that was likely sufficient to trigger the explosive eruption in 2010.

Hypothesis for triggering highly explosive eruptions at Merapi

We propose that the paroxysmal eruption of 2010 may have resulted from the explosive degassing of a pre-eruptive magma saturated with hybrid aqueous fluids rich in NaCl-HCl and CO 2 (released due to decarbonation reaction). Such a state and maturation of the fluid phase were probably acquired because the 2010 magma completely digested an involved carbonate-bearing crust during bulk assimilation (terminology of [START_REF] Russell | Volatile production possibilities during magmatic assimilation: heat and mass-balance constraints[END_REF]. In contrast, the products erupted in 1998 and 2006 contain abundant metamorphic crustal xenoliths, suggesting incomplete assimilation (selective assimilation, terminology of [START_REF] Russell | Volatile production possibilities during magmatic assimilation: heat and mass-balance constraints[END_REF] of the carbonate-bearing crust and thus lower partial pressure of CO 2 not producing the necessary conditions of fluid saturation for explosive degassing.

In a more general perspective, we propose that the bifurcation between the classical mildly explosive eruptions at Merapi (i.e. block-and-ash flows of Merapi-type) and the paroxysmal events of subplinian type may result from the efficiency of the carbonate assimilation process by Merapi magma, with incomplete (selective) assimilation leading to less explosive events and complete (bulk) assimilation triggering highly explosive eruptions.

Compared to selective assimilation, bulk assimilation is the exception rather than norm [START_REF] Russell | Volatile production possibilities during magmatic assimilation: heat and mass-balance constraints[END_REF]. Such factors as kinetics of the magmacalc-silicate xenolith reaction, duration of the pre-eruptive period, volume of pre-eruptive magma and its physico-chemical properties and a contribution of basaltic end-member may potentially explain the reason of the complete (bulk) assimilation and highly explosive events. 3. Merapi volcanic products were obtained from database of MERAPIDATA, [START_REF] Borisova | MERAPIDATA": New Petrologic and Geochemical Database of the Merapi Volcano, Central Java, Indonesia[END_REF]. The database summarizes the published and unpublished data of [START_REF] Berthommier | Etude volcanologique du Merapi (Centre-Java). Téphrostratigraphie et chronologieproduits éruptifs[END_REF], Gertisser and Keller (2003a,b), [START_REF] Debaille | Multi-stage mixing in subduction zones: Application to Merapi volcano (Java island, Sunda arc)[END_REF]Camus et al. (2006) for the Merapi volcanic products; and [START_REF] Chadwick | Carbonate assimilation at Merapi volcano, Java, Indonesia: Insights from crystal isotope stratigraphy[END_REF] for the 1998 Merapi calc-silicate xenoliths. The chemical data on the 2010 Merapi are given in Tables 3 and4 and in Table S1 of ESM. [START_REF] Borisova | MERAPIDATA": New Petrologic and Geochemical Database of the Merapi Volcano, Central Java, Indonesia[END_REF] which summarize the published and unpublished data of [START_REF] Berthommier | Etude volcanologique du Merapi (Centre-Java). Téphrostratigraphie et chronologieproduits éruptifs[END_REF], Gertisser and Keller (2003a,b), [START_REF] Debaille | Multi-stage mixing in subduction zones: Application to Merapi volcano (Java island, Sunda arc)[END_REF], Camus et al., (2006) for the previous Merapi volcanic products; and [START_REF] Chadwick | Carbonate assimilation at Merapi volcano, Java, Indonesia: Insights from crystal isotope stratigraphy[END_REF] for the 1998 Merapi calc-silicate xenoliths.

Concluding remarks on the 2010

The chemical data on the 2010 Merapi are given in Table 3. [START_REF] Borisova | MERAPIDATA": New Petrologic and Geochemical Database of the Merapi Volcano, Central Java, Indonesia[END_REF]. The database summarizes the published and unpublished data of [START_REF] Berthommier | Etude volcanologique du Merapi (Centre-Java). Téphrostratigraphie et chronologieproduits éruptifs[END_REF], Gertisser and Keller (2003a,b), [START_REF] Debaille | Multi-stage mixing in subduction zones: Application to Merapi volcano (Java island, Sunda arc)[END_REF], Camus et al., (2006) for the Merapi volcanic products; and [START_REF] Chadwick | Carbonate assimilation at Merapi volcano, Java, Indonesia: Insights from crystal isotope stratigraphy[END_REF] for the 1998 Merapi calc-silicate xenoliths. The chemical data on the 2010 Merapi are given in Tables 3 and4 and in Table S1 of ESM. The Merapi 2010 plagioclase phenocryst composition compared to typical magmatic plagioclases and calcic plagioclases from the calc-silicate xenoliths. The plagioclase composition for the Merapi volcanic products were obtained from database of MERAPIDATA [START_REF] Borisova | MERAPIDATA": New Petrologic and Geochemical Database of the Merapi Volcano, Central Java, Indonesia[END_REF]. The database summarizes the published and unpublished data on plagioclases of [START_REF] Berthommier | Etude volcanologique du Merapi (Centre-Java). Téphrostratigraphie et chronologieproduits éruptifs[END_REF], Camus et al., (2006) [START_REF] Borisova | MERAPIDATA": New Petrologic and Geochemical Database of the Merapi Volcano, Central Java, Indonesia[END_REF] which summarize the published isotopic data of Gertisser and Keller (2003a), [START_REF] Debaille | Multi-stage mixing in subduction zones: Application to Merapi volcano (Java island, Sunda arc)[END_REF] for the previous Merapi volcanic products ;[START_REF] Chadwick | Carbonate assimilation at Merapi volcano, Java, Indonesia: Insights from crystal isotope stratigraphy[END_REF] for the 1998 Merapi calc-silicate xenoliths. The isotopic data on the 2010 Merapi are summarized in Table 3.

  d'Analyse des Roches et des Minéraux at Centre de Recherches Pétrographiques et Géochimiques (CRPG) in Vandoeuvre lès Nancy, France) by Leco SC 144DR through heating at 1400°C with oxygen flux and detected by IR. The bulk H 2 O concentrations were measured by Karl Ficher titration. The bulk major and trace elements were measured by ICP-OES (inductively coupled plasma atomic emission spectroscopy) and ICP-MS (inductively coupled plasma mass spectrometry) with method developed in SARM

  The matrix glasses are characterized by variable SiO 2 composition (57 -73 wt%), CaO/Al 2 O 3 (0.06 -0.48), MnO/Al 2 O 3 (0.001 -0.058) and K 2 O/Al 2 O 3 (0.11 -0.44) ratios; and negative correlation of CaO/Al 2 O 3 with K 2 O/Al 2 O 3 and positive correlation with MnO/Al 2 O 3

  These plagioclase phenocrysts contain LREE with typical concentrations of La (4 -7 ppm), Ce (6 -10 ppm), Nd (2 -4 ppm) and Rb (1 -4 ppm). The applied EDS mapping allows identifying two types of magmatic clinopyroxenes in the early-stage and late-stage samples: typical low-Al augites (Al 2 O 3 ≤ 5 wt%) and highpressure aluminous clinopyroxenes (Al 2 O 3 = 5 -8 wt%). EMP analyses of low-Al augite crystals from the early-stage pyroclastic flow samples demonstrate oscillatory zonings. An example shows two positive peaks of Ti, Na and Al associated with negative peaks of Mn (Figure 4c), whereas Mg-number = Mg/(Mg+Fe) is broadly constant for the whole phenocryst. The low-Al augite fragments in the late-stage ash samples are rich in MnO (0.4 -0.6 wt%), Al 2 O 3 (2.7 -3.4 wt%), Sc (~100 ppm), V (160 -200 ppm), Zn (80 -93 ppm), Co (35 -39 ppm), and Sr (37 -41 ppm) (Figure 3; Table

Figures 3

 3 Figures 3 and 5 demonstrate no geochemical difference (in trace element and Nd-Pb

  The first line of evidences is demonstrated on figure5(a) of the diagram of bulk-rock Sr isotope ratios versus SiO 2 contents in the Merapi pyroclastic flow and xenoliths. The radiogenic 87 Sr/ 86 Sr ratios in the 2010 samples are approaching those of the calc-silicate xenoliths. The extreme 87 Sr/ 86 Sr ratio in the 2010 bulk-rock Merapi pyroclastic flow sample (M2010 PF) is characterized by such radiogenic value as 0.706 which has never been observed yet in the pyroclastic flows of Merapi (Figure 5b).

  is bulk partition coefficient between the crystals and hybrid melt (D = C cryst /C melt ) and C melt Init is the elemental concentration in the initial melt before assimilation, C melt Ass is concentration of the element in the "ppm (average Sr contents in the 2010 Merapi matrix glasses, except for the maximal concentration) and bulk C cryst Hybr = 1063 ppm (average Sr contents in the 2010 Merapi plagioclases), C melt Init = 140 ppm (Sr content in a adakitic rhyolitic melt,

Merapi eruption 1 )

 1 Although calc-silicate metamorphic minerals or xenoliths have not been observed in the 2010 eruption products, a number of geochemical signatures underline efficient crustal assimilation process. There are: (i) the highest 87 Sr/ 86 Sr ratios among the known Merapi pyroclastic rocks, (ii) high-calcic cores of phenocrysts up to An 94-97 with low FeO contents of 0.4 -0.7 wt% and strong Sr enrichment up to ~1000 ppm at An 48-54 , (iii) enrichment in 18 O (δ 18 O around 6.5‰) of the bulk plagioclase phenocrysts, (iv) enrichment in Mn, Sr, Zn, V of the phenocrysts (plagioclases, low-Al augites, titanomagnetites), and (v) enrichment in Ca, Mn, Sr, Zn, V, Sc of silicic glasses in amounts comparable to the bulk 1998 calc-silicate xenoliths.2) We propose a process of crustal assimilation through three major steps: (1) contact metamorphism of Javanese limestone and formation of the 1998 and 2006 calc-silicate xenoliths (not investigated in this work); (2) bulk assimilation through complete melting/dissolution of the calc-silicate xenoliths and production of calcic melts representing the 2010 crustal assimilant; (3) effective chemical and physical binary mixing between hydrous K-Cl-rich silicic melts issued from a deep magmatic source and the 2010 crustal assimilant melts derived from the carbonated xenoliths, and fractional crystallization of phenocrysts at pre-eruptive pressures about 200 MPa.3) The magmatic fluid is Cl-Ca-Na-Zn-Cd-Sb-rich at the stage of the paroxysmal subplinian eruption. The saturation of the 2010 basaltic andesite magma with aqueous carbonic fluids is due to both high concentrations of NaCl and HCl in the aqueous fluid and likely CO 2 enrichment due to decarbonation of the crustal material. Such an enriched state of the magmatic fluid in CO 2 (≥1.5 MPa additional pressure in the magma chamber) may be reached by complete (bulk) assimilation of the surrounding carbonate-bearing crustal material that triggers this highly explosive event, (i.e. the paroxysmal subplinian eruption on 5-6 th November 2010), whereas the classical mildly explosive eruptions atMerapi (i.e. in 1998 and 2006) may have resulted from incomplete (selective) assimilation and immature saturation state of the fluid phase.

FIGURE CAPTIONS Figure 1

 CAPTIONS1 FIGURE CAPTIONS

Figure 2 .

 2 Figure 2. Plots showing the major-and minor-element composition of the Merapi 2010

Figure 3 .

 3 Figure 3. Log-log plots of the major (wt%) and trace element contents (ppm) versus

Figure 4

 4 Figure 4 (a). BSE image of a plagioclase phenocryst from pyroclastic flow (M 2010 PF) and

Figure 4 (

 4 Figure 4(b). FeO (wt%) versus An (mol%) contents in the Merapi 2010 plagioclase

Figure 4 (

 4 Figure 4 (c). BSE image of low-Al augite phenocryst from pyroclastic flow (M 2010 PF) and

Figure 4

 4 Figure 4(d). MnO (wt%) versus Fo contents (mol%) in the Merapi 2010 olivines compared to

Figure 7 .

 7 Figure 7. Diagram demonstrating the ash leachate composition normalized to the bulk ash

Figure 1

 1 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 Table2); (4) and (4a) -M 2010 PF sample investigated by EDS technique. The sample numbers are according to the sample numeration given in Table1. The data obtained with the EDS mapping "Feature" are summarized in Table2.

Figure 2 .

 2 Figure2. 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[START_REF] Borisova | MERAPIDATA": New Petrologic and Geochemical Database of the Merapi Volcano, Central Java, Indonesia[END_REF] which summarize the published and unpublished data of[START_REF] Berthommier | Etude volcanologique du Merapi (Centre-Java). Téphrostratigraphie et chronologieproduits éruptifs[END_REF],Gertisser and Keller (2003a,b),[START_REF] Debaille | Multi-stage mixing in subduction zones: Application to Merapi volcano (Java island, Sunda arc)[END_REF],Camus et al., (2006) for the previous Merapi volcanic products;[START_REF] Chadwick | Carbonate assimilation at Merapi volcano, Java, Indonesia: Insights from crystal isotope stratigraphy[END_REF] for the 1998 Merapi calc-silicate xenoliths. The chemical data on the 2010 Merapi are given in Table3.

Figure 3 .

 3 Figure 3. The major (wt%) and trace element contents (ppm) versus CaO/Al 2 O 3 ratio in the 2010 glass inclusions, matrix glasses and phenocrysts compared to the 2010 Merapi bulk volcanic rocks and the 1998 crustal xenoliths. The chemical data on the Merapi were obtained from database of MERAPIDATA,[START_REF] Borisova | MERAPIDATA": New Petrologic and Geochemical Database of the Merapi Volcano, Central Java, Indonesia[END_REF]. The database summarizes the published and unpublished data of[START_REF] Berthommier | Etude volcanologique du Merapi (Centre-Java). Téphrostratigraphie et chronologieproduits éruptifs[END_REF],Gertisser and Keller (2003a,b),[START_REF] Debaille | Multi-stage mixing in subduction zones: Application to Merapi volcano (Java island, Sunda arc)[END_REF],Camus et al., (2006) for the Merapi volcanic products; and[START_REF] Chadwick | Carbonate assimilation at Merapi volcano, Java, Indonesia: Insights from crystal isotope stratigraphy[END_REF] for the 1998 Merapi calc-silicate xenoliths. The chemical data on the 2010 Merapi are given in Tables3 and 4and in TableS1of ESM.

Figure 4 (

 4 Figure 4 (a). Pyroclastic flow (M 2010 PF) plagioclase phenocryst profiling from A to B points demonstrating extremely enriched in An core (An 94 ). The high-An core is chemical signature of assimilation of sedimentary crustal material (see text). Symmetric chemical zonation in An is spectacular. Fe contents demonstrate oscillatory zonation.

Figure 4 (

 4 Figure 4 (c). Pyroclastic flow (M 2010 PF) augite phenocryst profiling from A to B points demonstrating oscillatory zonation for trace Al, Ti, Na and Mn. The high-Al -Ti and -Na zones depleted in Mn are marked. The high-Al -Ti and -Na zones indicate crystallization from trachyte melts enriched in alkalis and Al. Numerous inclusions in this crystal have been excluded from the phenocryst zonation. The chemical data on the 2010 Merapi pyroxenes are given in Table S4 of ESM.

Figure 7 .

 7 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.

  Ti, 51 V, 53 Cr, 55 Mn, 57 Fe, 59 Co, 60 Ni, 65 Cu, 66 Zn, 75 As, 85 Rb, 88 Sr, 89 Y, 90 Zr, 93 Nb, 121 Sb, 133 Cs, 137 Ba, 139 La, 140 Ce, 141 Pr, 146 Nd, 147 Sm, 153 Eu, 157 Gd, 159 Tb, 163 Dy, 165 Ho, 166 Er, 169 Tm, 172 Yb, 175 Lu, 178 Hf, 181 Ta, 208 Pb, 232 Th,

Table 4

 4 source (analysis № 52, Table4), whereas high Ca and Mn contents are signatures of crustal assimilant melts derived from calc-silicate xenoliths. Positive correlations of CaO/Al 2 O 3 with MnO/Al 2 O 3 , in turn, in silicic glasses argue in favor of the binary mixing with the crustal assimilant enriched in Ca and Mn.

	), suggesting their

the melt inclusions and glassy matrix (Figure

3

), suggesting two different sources of Ca and K in silicic melts. Indeed, high K contents are signatures of hydrous (Cl-rich) silicic melts issued from deep magmatic

Table 2

 2

	); (4) and (4a) -

.

  Table S5 of ESM. Plots of the 87 Sr/ 86 Sr versus (a) SiO 2 in the Merapi bulk rocks; (b) versus 143 Nd/ 144 Nd; (c) δ 18 O in plagioclases and bulk rocks versus SiO 2 wt% contents in the host Merapi rocks. The 2010 Merapi products are characterized by highest 87 Sr/ 86 Sr ratios approaching those of the calc-silicate xenoliths. The isotopic data used here are obtained from Figure 6. Plots of the (a) Cl contents (wt%) and (b) apparent H 2 O+CO 2 contents (wt%) versus CaO/Al 2 O 3 in glasses of melt inclusions (open circles) and glassy matrix (closed circles).

	Apparent H 2 O+CO 2 contents in glasses are calculated by-difference method. The melt
	representing crustal assimilant is characterized by the highest Ca/Al (up to 1.2 of CaO/Al 2 O 3 ),
	low summed H 2 O+CO 2 and low Cl contents. Volatile-richest K-rich melts are characterized
	by low Ca/Al.
	Figure 5. MERAPIDATA (Borisova et al., 2011) which summarize the published isotopic data of
	Gertisser and Keller (2003a), Debaille et al. (2006) for the previous Merapi volcanic products;

and

[START_REF] Chadwick | Carbonate assimilation at Merapi volcano, Java, Indonesia: Insights from crystal isotope stratigraphy[END_REF]

for the 1998 Merapi calc-silicate xenoliths. The isotopic data on the 2010 Merapi are summarized in Table

3

Table 2 )

 2 ; (4) and (4a) -M 2010 PF sample investigated by EDS technique. The sample numbers are according to the sample numeration given in Table1. The data obtained with the EDS mapping "Feature" are summarized in Table2.

  for the previous Merapi volcanic products; and Chadwick et al. (2007) for the 1998 Merapi calcsilicate xenoliths. The chemical data on the 2010 Merapi plagioclases are given inTable S2 of ESM.

  Table S4 of ESM. Figure 5. 87 Sr/ 86 Sr versus (a) SiO 2 in the Merapi bulk rocks; (b) versus 143 Nd/ 144 Nd; (c) δ 18 O in plagioclases and bulk rocks versus SiO 2 wt% in the host Merapi rocks. The 2010 Merapi products are characterized by highest 87 Sr/ 86 Sr ratios approaching those of the calc-silicate xenoliths. The isotopic data used here are obtained from MERAPIDATA

	0.709	(a)					87 Sr/ 86 Sr
	0.708					-2010 volcanic samples -Merapi volcanic rocks
						-Merapi calc-silicate xenoliths
	0.707
	0.706
	30 0.705	40	50	60	70	80	90	100
				SiO 2 wt%
	0.7060
		(b)
							87	Sr/ 86	Sr
	0.7055
	0.7050
	0.51265		0.51270		0.51275		0.51280
				143 Nd / 144 Nd
	9
		(c)						 18	O
						-2010 plagioclases
	8					-Merapi volcanic rocks
						-Merapi plagioclases
	7
	6
	5
	30	40	50	60	70	80	90	100
				SiO 2 wt%

Acknowledgements

Authors thank V. Troll, J. Webster, an anonymous reviewer for numerous suggestions improving the article and editors J.W. Neuberg and Ph. Jousset for the editorial handling. C.M. greatly thanks Ida Di Carlo for help with the SEM and EMP analyses. J.K. Russell and B.R. Edwards are thanked by A.Y.B. for fruitful discussion on the kinetics of crustal assimilation. M. Guillong and L. Danyshevsky are thanked by A.Y.B., for performing LA-ICP-MS analyses at Tasmania University (Hobart, Australia). F. Candaudap, J-F Mena and S. Mounic are thanked by A.Y.B. for performing HR-ICP-MS analyses, for the preparation of polished sections and for performing ion chromatographic methods, respectively. This work was supported by OMP (VELI, CNAP, 2011-2012) for A.Y.B. A.Y.B. is also partially supported by RFBR (number 10-05-00254).

Appendix A. Calculations of additional pressure of CO 2 liberated due to decarbonation of crustal xenoliths

To calculate pressure of the additional CO 2 liberated during decarbonation reaction, we applied the ideal gas equation:

where P is pressure, V is free volume, R is gas constant (Boltzmann's constant), n is moles, T is temperature (K). Applying the following parameters to the equation A.1: free volume (V) equals to the suggested magma chamber volume from 0.03 to 0.06 km 3 (Surono et al., this volume, equal to 3 × 10 13 -6 × 10 13 cm 3 ), n from 4.3 × 10 9 to 4.8 × 10 10 moles (corresponding to the calculated mass of CO 2 1.9 × 10 8 to 2.1 × 10 9 kg = 1.9 × 10 11 to 2.1 × 10 12 g divided by molar mass of CO 2 = 44.01 g mol -1 ); R = 8.314 cm 3 MPa K -1 mol -1 , temperature T = 1000 -1200 °C = 1273.16 -1473.16 K (obtained at 200 MPa according to [START_REF] Wells | Pyroxene thermometry in simple and complex systems[END_REF], pressure P varies from 1.5 to 10 MPa. These estimates are, however, minimal, because they depend strongly from the assumed free volume (V) in the equation (A.1). The Merapi 2010 olivine composition compared to the typical Merapi olivines. The olivine composition for the Merapi volcanic products were obtained from database of MERAPIDATA [START_REF] Borisova | MERAPIDATA": New Petrologic and Geochemical Database of the Merapi Volcano, Central Java, Indonesia[END_REF]. The database summarizes the published and unpublished data on olivines of [START_REF] Berthommier | Etude volcanologique du Merapi (Centre-Java). Téphrostratigraphie et chronologieproduits éruptifs[END_REF], Camus et al., (2006) for the previous Merapi volcanic products. The olivine data on the 2010 Merapi products are given in Table S5 of ESM.