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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Explosive eruptive activity and temporal magmatic changes at Yotei Volcano during the last 50,000 years, southwest Hokkaido, Japan
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Explosive eruptive activity and temporal magmatic changes at Yotei Volcano during the last 50,000 years, southwest Hokkaido, Japan

机译：日本北海道西南部近5万年来火山爆发的爆发活动和时间岩浆变化

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摘要

To understand the eruptive history, structure, and magmatic evolution of Yotei Volcano, southwest Hokkaido, Japan, we investigated the geology and petrology of tephras located around the base of the volcano. We identified 43 tephra units interbedded with soils (in descending stratigraphic order, tephras Y1-Y43), and four widespread regional tephras. Ten radiocarbon ages were obtained from soils beneath the Yotei tephras. On the basis of petrologic differences and, the stratigraphic positions of thick layers of volcanic ash soil, indicative of volcanic stratigraphic gaps, the Yotei tephras are divided into four groups (in ascending stratigraphic order): Yotei tephra groups I,II-1,II-2, and II-3. We calculated the age of each eruptive deposit based on the soil accumulation rate, and estimated the volume of each eruption using isopach maps or the correlation between eruption volume and the maximum thickness at similar to 10 km from the summit crater. The results regarding eruptive activity and the rate of explosive eruptions indicate four eruptive stages at Yotei Volcano over the list 50,000 years. Stage I eruptions produced Yotei tephra group I between ca. 54 cal. ka BP and up to at least ca. 46 cal. ka BP, at relatively high average eruption rates of 0.07 km(3) dense-rock equivalent (DRE)/ky. After a pause in activity of ca. 8000 years, Stage II-1 to II-2 eruptions produced Yotei tephra groups II-1 and II-2 from ca. 38 to ca. 21 cal. ka BP at high average eruption rates (0.10 km(3) DRE/ky), after a pause in activity of 2000-3000 years. Finally, after another pause in activity of 4000-5000 years, Stage II-3 eruptions produced Yotei tephra group II-3 from ca. 16.5 cal. ka BP until the present day, at low average eruption rates (0.009 km(3) DRE/ky). Whole-rock geochemical compositions vary within each tephra group over the entire eruption history. For example, group I and II-3 tephras contain the lowest and highest abundances, respectively, of K2O, P2O5, and Zr. Group II-1 has the highest abundances of Zr and Y. These trends indicate that the explosive activity was controlled by an evolving magma system. An understanding of these temporal changes in the chemical composition of the magma will enable future correlations of tephras with volcanic edifices, thereby revealing the full eruptive history and structure of Yotei Volcano, and constraining the timing of geological events in the region. (C) 2016 Elsevier B.V. All rights reserved.
机译：为了了解日本北海道西南部Yotei火山的喷发历史，构造和岩浆演化，我们调查了位于火山底部的特非拉斯的地质和岩石学。我们确定了43个与土壤互层的地弗拉单位（按地层降序排列，特弗拉斯Y1-Y43）和四个分布广泛的区域性特弗拉斯。从特提斯火山底下的土壤中获得了十个放射性碳年龄。根据岩石学差异以及火山灰土壤厚层的地层位置（指示火山岩地层间隙），将特提斯火山分成四组（按地层升序排列）：特提斯火山I，II-1，II组-2和II-3。我们根据土壤积累速率计算了每个喷发矿床的年龄，并使用等值线图估算了每次喷发的量，或者估算了喷发量与距山顶火山口约10 km处的最大厚度之间的相关性。有关喷发活动和喷发速率的结果表明，在列表50,000年中，Yotei火山有四个喷发阶段。第一阶段的喷发产生了约特之间的Itete tephra。 54卡路里ka BP，至少约ca。 46卡路里ka BP，处于相对较高的平均喷发率，为0.07 km（3）致密岩当量（DRE）/ ky。暂停活动后约大约8000年，II-1至II-2期的爆发从约公元前期产生了Yotei tephra组II-1和II-2。 38至21卡路里在2000-3000年的活动暂停后，ka BP处于高平均喷发率（0.10 km（3）DRE / ky）。最终，在4000-5000年的活动又一次停顿之后，II-3期的爆发从约莫桑比克造就了Yotei tephra组II-3。 16.5卡路里ka BP直到今天，平均喷发率较低（0.009 km（3）DRE / ky）。在整个喷发历史中，每个特非拉组内的整个岩石地球化学组成各不相同。例如，第I组和第II-3种特弗拉斯分别含有最低和最高的K2O，P2O5和Zr丰度。 II-1组具有最高的Zr和Y丰度。这些趋势表明，爆炸活动受不断演化的岩浆系统控制。对这些岩浆化学成分的时间变化的了解将使特弗拉斯与火山岩的未来联系成为可能，从而揭示了Yotei火山的完整喷发历史和结构，并限制了该地区地质事件的发生时间。 （C）2016 Elsevier B.V.保留所有权利。

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