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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Large-magnitude Pauzhetka caldera-forming eruption in Kamchatka: Astrochronologic age, composition and tephra dispersal
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Large-magnitude Pauzhetka caldera-forming eruption in Kamchatka: Astrochronologic age, composition and tephra dispersal

机译：堪察加火山爆发的大爆发波兹奇卡破火山口：天文年龄，成分和特非拉散布

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摘要

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 similar to 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 similar to 46 km(3). Together with the exposed volcanic material around the caldera, the total DRE volume is estimated at 150-170 km(3 )(3.8-4.4 x 10(5)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 +/- 2 sigma), which is 27 ka younger than the published average Ar-39/Ar-40 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. (C) 2018 Elsevier B.V. All rights reserved.
机译：大面积上各个提弗拉层的相关性允许评估喷发量和不同沉积档案的同步性。直径约30公里的中更新世Pauzhetka破火山口是堪察加最大的火山之一。然而，从未发现破火山口形成的远侧红斑狼疮，这妨碍了对火山爆发数量和强度的精确估计。在本文中，我们首次报道了由ODP 145岩心881B，882A和884B以及IMAGES岩心MD01-2415和MD01-2416回收的西北（NW）太平洋和鄂霍次克海沉积物中的波扎特卡火山口的远端特非拉的地球化学特征。远距离特弗拉斯是流纹岩，其组成范围较窄，因此可以利用主要和微量元素数据在所研究的海洋岩心中进行可靠的识别。根据激光烧蚀ICP-MS在原位测定的固定微量元素，进行了远端球体与近端强焊接和改变的火成岩的地球化学相关性。根据此案例研究，我们建议在焊接凝灰岩的陆上蚀变过程中，许多痕量元素（U，Th，Nb，Ta，Zr，Hf，Ti，REE，Y和Sc）是不动的，可用于原始玻璃与改变后的岩石地基的相关性，可以直接识别远端特非拉火山的来源。我们关于西北太平洋沉积物中机载Pauzhetka tephra的空间散布的新数据定义了其最小密实岩石当量（DRE）量，大约为46 km（3）。连同火山口周围裸露的火山物质一起，DRE的总体积估计为150-170 km（3）（3.8-4.4 x 10（5）Mt​​），对应于7.60-7.65的喷发度。在海洋同位素第12阶段和第11c阶段（终点V）过渡期间，被研究岩心中的Pauzhetka tephra的地层位置产生了精确的天文年龄，即421.2 +/- 6.6 ka（加权平均值+/- 2 sigma），年轻了27 ka。比已发表的平均Ar-39 / Ar-40日期来自近端火成岩的斜长石。由于特有的成分和准确的年龄，因此，Pauzhetka tephra可能成为西北太平洋和鄂霍次克海沉积物中V终止的区域标志。在这项研究中采用的多学科方法对于识别和精确确定堪察加半岛和其他火山弧中过去的爆发喷发是有用的。 （C）2018 Elsevier B.V.保留所有权利。

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