Large-magnitude Pauzhetka caldera-forming eruption in Kamchatka: Astrochronologic age, composition and tephra dispersal.

Ponomareva, Vera, Bubenshchikova, Natalia, Portnyagin, Maxim, Zelenin, Egor, Derkachev, Alexander, Gorbarenko, Sergey, Garbe-Schönberg, Dieter and Bindeman, Ilya (2018) Large-magnitude Pauzhetka caldera-forming eruption in Kamchatka: Astrochronologic age, composition and tephra dispersal. Journal of Volcanology and Geothermal Research, 366 . pp. 1-12. DOI 10.1016/j.jvolgeores.2018.10.006.

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Abstract

Highlights

• First identification of distal tephra from the Pauzhetka caldera offshore Kamchatka.
• Geochemical correlation of Pauzhetka proximal altered ignimbrite to distal tephra.
• Pauzhetka caldera-forming eruption has an astrochronologic age of 421.2 ± 6.6 ka.
• The eruption had DRE volume of 150–170 km3 and magnitude of 7.60–7.65.
• Pauzhetka tephra marks Termination V in the NW Pacific and Okhotsk Sea sediments.

Correlation of individual tephra layers over large areas permits the assessment of eruption magnitude and synchronization of disparate sedimentary archives. The middle Pleistocene Pauzhetka caldera with a diameter of ~30 km is one of the largest in Kamchatka. Distal tephra from the caldera-forming eruption has, however, never been found, hampering precise estimates of the eruption volume and magnitude. In this paper, we report first geochemical identification of distal tephra from the Pauzhetka caldera in the Northwest (NW) Pacific and Okhotsk Sea sediments recovered by ODP 145 cores 881B, 882A and 884B, and IMAGES cores MD01-2415 and MD01-2416. Distal tephras are rhyolites of narrow compositional range allowing their reliable identification among the studied marine cores using major and trace element data. Geochemical correlation of the distal tephra to the proximal strongly welded and altered ignimbrite was performed based on immobile trace elements determined in situ by laser ablation ICP-MS. Based on this case study, we propose that a number of trace elements (U, Th, Nb, Ta, Zr, Hf, Ti, REE, Y and Sc) are immobile during on-shore alteration of welded tuffs and can be used for correlation of pristine glass and altered rock groundmass allowing direct identification of volcanic source of distal tephra. Our new data on the spatial dispersal of the airborne Pauzhetka tephra in the NW Pacific sediments defines its minimum dense rock equivalent (DRE) volume of ~46 km3. Together with the exposed volcanic material around the caldera, the total DRE volume is estimated at 150–170 km3 (3.8–4.4 × 105 Mt) corresponding to the eruption magnitude of 7.60–7.65. Stratigraphic position of the Pauzhetka tephra in the studied cores at transition between marine isotope stage 12 and 11c (Termination V) yields a precise astrochronologic age of 421.2 ± 6.6 ka (weighted mean ± 2σ), which is 27 ka younger than the published average 39Ar/40Ar dates on plagioclase from the proximal ignimbrite. Due to the characteristic composition and precise age, the Pauzhetka tephra may serve as a regional marker for Termination V in the NW Pacific and Okhotsk Sea sediments. A multidisciplinary approach adopted in this study is useful for identification and precise dating of the past explosive eruptions in Kamchatka and other volcanic arcs.

Document Type: Article
Keywords: Tephra, NW Pacific, Kamchatka, Caldera, Glacieal termination
Research affiliation: OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS Magmatic and Hydrothermal Systems
Kiel University
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/j.jvolgeores.2018.10.006
ISSN: 0377-0273
Date Deposited: 16 Oct 2018 08:27
Last Modified: 17 Jan 2019 13:34
URI: http://oceanrep.geomar.de/id/eprint/44497

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