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Konradsreuth, Germany

Chadwick J.P.,VU University Amsterdam | Chadwick J.P.,Trinity College Dublin | Troll V.R.,Uppsala University | Waight T.E.,Copenhagen University | And 3 more authors.
Contributions to Mineralogy and Petrology | Year: 2013

Recent basaltic-andesite lavas from Merapi volcano contain abundant and varied igneous inclusions suggesting a complex sub-volcanic magmatic system for Merapi volcano. In order to better understand the processes occurring beneath Merapi, we have studied this suite of inclusions by petrography, geochemistry and geobarometric calculations. The inclusions may be classified into four main suites: (1) highly crystalline basaltic-andesite inclusions, (2) co-magmatic enclaves, (3) plutonic crystalline inclusions and (4) amphibole megacrysts. Highly crystalline basaltic-andesite inclusions and co-magmatic enclaves typically display liquid-liquid relationships with their host rocks, indicating mixing and mingling of distinct magmas. Co-magmatic enclaves are basaltic in composition and occasionally display chilled margins, whereas highly crystalline basaltic-andesite inclusions usually lack chilling. Plutonic inclusions have variable grain sizes and occasionally possess crystal layering with a spectrum of compositions spanning from gabbro to diorite. Plagioclase, pyroxene and amphibole are the dominant phases present in both the inclusions and the host lavas. Mineral compositions of the inclusions largely overlap with compositions of minerals in recent and historic basaltic-andesites and the enclaves they contain, indicating a cognate or 'antelithic' nature for most of the plutonic inclusions. Many of the plutonic inclusions plot together with the host basaltic-andesites along fractional crystallisation trends from parental basalt to andesite compositions. Results for mineral geobarometry on the inclusions suggest a crystallisation history for the plutonic inclusions and the recent and historic Merapi magmas that spans the full depth of the crust, indicating a multi-chamber magma system with high amounts of semi-molten crystalline mush. There, crystallisation, crystal accumulation, magma mixing and mafic recharge take place. Comparison of the barometric results with whole rock Sr, Nd, and Pb isotope data for the inclusions suggests input of crustal material as magma ascends from depth, with a significant late addition of sedimentary material from the uppermost crust. The type of multi-chamber plumbing system envisaged contains large portions of crystal mush and provides ample opportunity to recycle the magmatic crystalline roots as well as interact with the surrounding host lithologies. © 2012 Springer-Verlag. Source


Troll V.R.,Uppsala University | Deegan F.M.,Uppsala University | Jolis E.M.,Uppsala University | Budd D.A.,Uppsala University | And 2 more authors.
Geografiska Annaler, Series A: Physical Geography | Year: 2015

Merapi volcano is among the most hazardous volcanoes on the planet. Ancient Javanese folklore describes Merapi's activity as the interaction between the Spirit Kings that inhabit the volcano and the Queen of the South Sea, who resides at Parangtritis beach, 50km SSE of Merapi. The royal palace in Yogyakarta is located half-way along the hypothetical line between Merapi and Parangtritis (the Merapi-Kraton-South Sea axis) to bring balance between these mystical forces. In 2006 and 2010, Merapi erupted explosively and on both occasions, earthquakes shook the region and the eruptions grew more violent in response. These earthquakes appear to influence the sub-volcanic magma supply of Merapi and a positive feedback loop has recently been postulated between the volcano and local earthquake patterns. The 2006 earthquakes clustered along the Opak River fault to the south of the volcano, which trends NE-SW, and reaches the southern sea at Parangtritis beach, the fabled residence of the Queen of the South Sea. Our interpretation of the Merapi-Kraton-South Sea axis is that local folklore was used by ancient people to describe and rationalize the complex interplay between geological processes. We suggest that Merapi displayed volcano-earthquake interaction many times in the past, and not only during its most recent eruptive cycle. Although now shrouded in mystery, these oral traditions can be thought of as an ancient hazard mitigation tool, which makes them likely useful in helping to foster effective dialogues with a variety of target parties and interest groups around the volcano's slopes. © 2015 Swedish Society for Anthropology and Geography. Source


Troll V.R.,Uppsala University | Deegan F.M.,Uppsala University | Deegan F.M.,Swedish Museum of Natural History | Jolis E.M.,Uppsala University | And 8 more authors.
Journal of Volcanology and Geothermal Research | Year: 2013

Indonesian volcano Merapi is one of the most hazardous volcanoes on the planet and is characterised by periods of active dome growth and intermittent explosive events. Merapi currently degasses continuously through high temperature fumaroles and erupts basaltic-andesite dome lavas and associated block-and-ash-flows that carry a large range of magmatic, coarsely crystalline plutonic, and meta-sedimentary inclusions. These inclusions are useful in order to evaluate magmatic processes that act within Merapi's plumbing system, and to help an assessment of which phenomena could trigger explosive eruptions. With the aid of petrological, textural, and oxygen isotope analysis we record a range of processes during crustal magma storage and transport, including mafic recharge, magma mixing, crystal fractionation, and country rock assimilation. Notably, abundant calc-silicate inclusions (true xenoliths) and elevated δ18O values in feldspar phenocrysts from 1994, 1998, 2006, and 2010 Merapi lavas suggest addition of limestone and calc-silicate materials to the Merapi magmas. Together with high δ13C values in fumarole gas, crustal additions to mantle and slab-derived magma and volatile sources are likely a steady state process at Merapi. This late crustal input could well represent an eruption trigger due to sudden over-pressurisation of the shallowest parts of the magma storage system independently of magmatic recharge and crystal fractionation. Limited seismic precursors may be associated with this type of eruption trigger, offering a potential explanation for the sometimes erratic behaviour of Merapi during volcanic crises. © 2013 Elsevier Ltd.V. Source


Troll V.R.,Uppsala University | Chadwick J.P.,Trinity College Dublin | Jolis E.M.,Uppsala University | Deegan F.M.,Swedish Museum of Natural History | And 4 more authors.
Geology Today | Year: 2013

High-temperature gas in volcanic island arcs is widely considered to originate predominantly from the mantle wedge and from subducted sediments of the down-going slab. Over the decade (1994-2005) prior to the 2006 eruption of Merapi volcano, summit fumarole CO2 gas δ13C ratios are relatively constant at -4.1 ± 0.3‰. In contrast, CO2 samples taken during the 2006 eruption and after the May 26th 2006 Yogyakarta earthquake (M6.4) show a dramatic increase in carbon isotope ratios to -2.4 ± 0.2‰. Directly following the earthquake (hypocentre depth 10-15 km), a 3-5-fold increase in eruptive intensity was observed. The elevated carbon isotope gas data and the mid-crustal depth of the earthquake source are consistent with crustal volatile components having been added during the 2006 events, most probably by the thick local limestone basement beneath Merapi. This 'extra' crustal gas likely played an important role in modifying the 2006 eruptive behaviour at Merapi and it appears that crustal volatiles are able to intensify and maintain eruptions independently of traditional magmatic recharge and fractionation processes. © 2013 Blackwell Publishing Ltd, The Geologists' Association & The Geological Society of London. Source


Troll V.R.,Uppsala University | Hilton D.R.,University of California at San Diego | Jolis E.M.,Uppsala University | Chadwick J.P.,Trinity College Dublin | And 5 more authors.
Geophysical Research Letters | Year: 2012

High-temperature volcanic gas is widely considered to originate from ascending, mantle-derived magma. In volcanic arc systems, crustal inputs to magmatic gases mainly occur via subducted sediments in the mantle source region. Our data from Merapi volcano, Indonesia imply, however, that during the April-October 2006 eruption significant quantities of CO2 were added from shallow crustal sources. We show that prior to the 2006 events, summit fumarole gas δ13C(CO2) is virtually constant (δ13C1994-2005 =-4.1 0.3‰), but during the 2006 eruption and after the shallow Yogyakarta earthquake of late May, 2006 (M6.4; hypocentres at 10-15 km depth), carbon isotope ratios increased to-2.4 0.2‰. This rise in δ13C is consistent with considerable addition of crustal CO2 and coincided with an increase in eruptive intensity by a factor of 3 to 5. We postulate that this shallow crustal volatile input supplemented the mantle-derived volatile flux at Merapi, intensifying and sustaining the 2006 eruption. Late-stage volatile additions from crustal contamination may thus provide a trigger for explosive eruptions independently of conventional magmatic processes. Copyright 2012 by the American Geophysical Union. Source

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