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| Titel |
Insights into Magmatic Degassing at Merapi Volcano, Indonesia from Uranium-Series Disequilibria in Recently Erupted Volcanic Rocks |
| VerfasserIn |
Heather Handley, Mark Reagan, Ralf Gertisser, Katie Preece, Kim Berlo, Jenni Barclay, Richard Herd |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250138746
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| Publikation (Nr.) |
 EGU/EGU2017-1862.pdf |
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| Zusammenfassung |
| We present new uranium-series isotopic data for the volcanic products of the 2006 and 2010
eruptions at Merapi to investigate magmatic degassing and the driving forces behind the
recent unusual explosive behavior in 2010. The 2006 and 2010 Merapi whole-rock samples
and plagioclase separates have U excesses ((238U/230Th) activity ratios > 1) and
excess Ra ((226Ra//230Th) > 1) with no significant difference between the 2006 and
2010 whole-rock samples. Two samples, one from 2006 and one from 2010 have
apparent (228Ra/232Th) values in excess of secular equilibrium, suggesting that the
process causing the 226Ra enrichments over 230Th (possibly the interaction of
magma with carbonate material in the crust) might have continued to shortly before
eruption at least for some magmas. The 2010 Merapi rocks were variably degassed of
210Po upon eruption, showing no systematic temporal evolution. The variation
observed in (210Pb/226Ra)0 for the 2006 and 2010 eruptions is comparable to the full
range of ratios measured in the time period from 1981 to 1995, previously reported
for the volcano. The 2006 and 2010 samples are largely characterised by 210Pb
deficits ((210Pb/226Ra)0 < 1), though four of the samples lie within error of secular
equilibrium. The observed variability in (210Pb/226Ra)0 is attributed to variations in
magmatic source depth as well as potential variable speed of ascent. The range of 210Pb
deficits observed in the 2006 Merapi samples imply approximately 2-4 years of
degassing prior to eruption. In the main 2010 dome-building phase, the three samples
analysed show small 210Pb deficits to a small 210Pb excess and lie within error of
secular equilibrium. This likely represents the arrival of fast moving magma that
did not stall and degas for any significant amount of time since its last stagnation
point. The higher (210Pb/226Ra)0 in samples erupted between 1 to 4 Nov 2010,
compared to 2006, supports the previous model that periods of magmatic recharge are
linked to rapid dome extrusion and, ultimately, more explosive eruptions at Merapi
and the low/zero initial Po activities in these samples suggest that open-system
degassing must have occurred very shortly (weeks to months) before eruption. |
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