A Multi-Component Geochemical Study of Short-Term Melt and Volatile Evolution in the Kamchatka Volcanic Arc
Abstract
New major and trace element measurements, coupled with high-precision Pb isotope data and a suite of U-series isotope data for four Kamchatkan volcanoes show that within each volcano, magmas derived by different processes are closely juxtaposed in space and time, while retaining their chemical identity. In this study, we focus on sampling eruptive products from Klyuchevskoy, Bezymianny, Shiveluch, and Karymsky volcanoes because of their range of compositions and eruptive styles. We analyze samples erupted over decades to investigate the short-term evolution of magmatic systems. U-series and Pb isotopes are used to infer differences in magma genesis processes and sources. These data are supported by trace element variations to investigate secondary processing of magmas in the crust. U-series data from the Kamchatka volcanic arc record both U-excesses and U-deficits manifested in products from a volcanic center over a period of 50 years (Dosseto et al. 2003, Turner et al. 1998, 2007). The complexity of U-series data over short timescales highlights the dynamic evolution of melts in arc settings and warrants further investigation. At Karymsky volcano, we record both U- and Th-excesses within a short one-year period of eruptive activity. This behavior is present in Karymsky eruptive products from both 1996 and 2008. Bezymianny data for eruptions from 1956 to 2007 show Th-excesses, which are contemporaneous with samples preserving U-excesses (reported by Turner et al. 2007). High-precision Pb isotope data show variation within volcanic centers. Shiveluch magmas become more radiogenic in the 1980 dome and less radiogenic in the 2001 dome. Klyuchevskoy lava flows trend toward more radiogenic between 1946 and 2007. Bezymianny data show a long-term evolution to less radiogenic Pb isotopes between the evolution of Pre-Bezymianny and modern Bezymianny and fluctuate in composition between 1956 and present-day juvenile erupted products. Karymsky is the only center in this study that shows no change in Pb-isotope values despite the wide variability in U-series isotopic data measured in the same samples. Pb-isotope and U-series isotope variations suggest magmas generated by different processes erupt nearly simultaneously from a single edifice. We also investigated (210Pb)/(226Ra) disequilibria at Bezymianny and Shiveluch volcanoes to trace volatile fluxing at the magma chamber level. Periodic large explosions and dome growth and collapse characterize the eruptive behavior of these volcanoes. Shallow processing and loss of volatiles over the period of 2005 to 2007 is observed at Bezymianny and Shiveluch volcanoes where both systems record a shift from equilibrium values of (210Pb)/(226Ra) to deficits as high as 15% and 8% at Bezymianny and Shiveluch respectively. At Bezymianny volcano, this is consistent with an observed long-term shift to more mafic compositions from 1956 to 2007 (pers. comm. Pavel Izbekov).
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.V51A1648K
- Keywords:
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- 1036 GEOCHEMISTRY / Magma chamber processes;
- 1040 GEOCHEMISTRY / Radiogenic isotope geochemistry;
- 1065 GEOCHEMISTRY / Major and trace element geochemistry;
- 8413 VOLCANOLOGY / Subduction zone processes