Variations of glass composition in the Holocene tephra of Shiveluch volcano (Kamchatka): applications for magmatic history and tephrochronology

• Main Authors: Ponomareva, V., Portnyagin, Maxim, Blaauw, M., Pevzner, M., Kyle, P. R.
• Format: Conference Object
• Language: unknown
• Published: 2011
• Subjects: Kamchatka
• Online Access: https://oceanrep.geomar.de/id/eprint/13406/; http://agu-fm11.abstractcentral.com/s1aplanner/com.scholarone.s1aplanner.s1aplanner/S1APlanner.html?&CONFIG_ID=2224&USER_ID=1593989&ROLE_ID=11362&ROLE_TYPE_ID=10&PERSON2ROLE_ID=15483859&WORKFLOW_ID=17&CURRENT_PAGE=BROWSE_THE_PROGRAM&ALLOW_EDIT_INSTRUCTION

The dominantly andesitic Shiveluch volcano (Kamchatka) is a highly explosive eruptive center with a magma discharge of ~36 Mt/year, an order of magnitude higher than that typical of island arc volcanoes. Frequent ash plumes from Shiveluch pose hazards to local towns and to dozens of daily airflights. Numerous Shiveluch tephras, once fingerprinted, can serve as excellent markers for dating Holocene deposits and landforms at a distance of ~350 km. Based on bulk rock analyses, Shiveluch tephra was considered to have a uniformly andesitic composition, with the exception of two basaltic cinders (Ponomareva et al., 2007). As a next step to understanding the evolution of Shiveluch melts, we have performed EMP analyses of glass from 117 pumice and cinder lapilli representing proximal tephras of 73 Holocene eruptions. All the analyses were obtained in IFM-GEOMAR (Kiel, Germany) at the JEOL JXA 8200 microprobe using a single analytical protocol (15 keV accelerating voltage, 6 nA current, and 5 micron beam size). To raise the tephrochronological potential of Shiveluch tephras we combined 101 C14 dates and 73 tephras from Shiveluch as well as 74 dates for marker tephra layers into a single Bayesian framework taking into account the stratigraphical ordering within and between the sites. This approach has allowed us to enhance the reliability and precision of the estimated calibrated ages for the eruptions. As a result we have a new database of ~1400 high-quality glass analyses from proximal Shiveluch tephra of known age, which serves as a basis for understanding temporal patterns in the eruptive activity and geochemical variations of magma, and provides a reference for correlations with distal tephras. Shiveluch glasses are predominantly silicic (SiO2=57-80 wt%) and belong to the medium- and high-K series. Most of the tephras have homogeneous glass compositions while few are variable with ≤10% SiO2 range. Andesitic (57-66% SiO2) glasses split into medium-K and high-K fields while more silicic glass all belongs to a medium-K ...