Distal record of multi-sourced tephra in Onepoto Basin, Auckland, New Zealand: implications for volcanic chronology, frequency and hazards
Distal record of multi-sourced tephra in Onepoto Basin, Auckland, New Zealand: implications for volcanic chronology, frequency and hazards
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新西兰奥克兰 Onepoto 盆地多源火山灰的远程记录：对火山年代、频率和危害的影响
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发表时间：
2002
期刊：
影响因子：
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通讯作者：
J. Hoverd
中科院分区：
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作者：
P. Shane;J. Hoverd
抽象。我们已经记录了80火山灰床从公元前。9.5~>50 ka，含于新西兰奥克兰火山爆发坑Onepoto盆地连续沉积的古湖沉积物中。已知的远源（距离喷口>190 km）火山灰来源包括流纹岩陶波火山中心（4）和奥卡泰纳火山中心（14），以及安山质塔拉纳基火山（40）和汤加里罗火山中心（3）。该记录提供了四个新的事件之间的CA证据。50和28 ka（Mangaone亚群），表明Okataina比以前已知的更活跃。火山灰记录也大大扩展了已知的其他Mangaone亚群火山灰的北方分布。10流纹岩火山喷发前的Rotoehu喷发（>约。50 ka），和一些化学上不同的后50 ka的韵律。其中一些较老的火山点是由大规模事件产生的;然而，它们的来源仍然不确定。还鉴定了来自当地玄武质奥克兰火山岩场（AVF）的8个火山碎屑。沉积速率的插值使我们能够估计塔拉纳基火山在27.5-9.5 ka期间的12次大爆发的时间。此外，还有28个较老的事件得到确认。火山灰的成分为粗面质至流纹岩。所有样品都具有高K2 O含量（> 3wt%），并且没有时间趋势。这与近端熔岩记录相反，该记录显示K2 O随时间增加的趋势。结合Onepoto火山喷发记录和Pukaki火山口的记录，15个AVF玄武岩坠落事件被限制在：34.6，30.9，29.6，29.6，25.7，25.2，24.2，23.8，19.4，19.4，15.8和14.5 ka，以及3个50 ka前的事件。这为AVF提供了一些最佳的年龄限制，也是危险复发计算的唯一可靠数据。可以估计远端和本地坠落事件的最小事件频率，并证明奥克兰市地区经常受到许多火山灰坠落的影响。
Abstract. We have documented 80 tephra beds dating from ca. 9.5 to >50 ka, contained within continuously deposited palaeolake sediments from Onepoto Basin, a volcanic explosion crater in Auckland, New Zealand. The known sources for distal (>190 km from vent) tephra include the rhyolitic Taupo Volcanic Centre (4) and Okataina Volcanic Centre (14), and the andesitic Taranaki volcano (40) and Tongariro Volcanic Centre (3). The record provides evidence for four new events between ca. 50 and 28 ka (Mangaone Subgroup) suggesting Okataina was more active than previously known. The tephra record also greatly extends the known northern dispersal of other Mangaone Subgroup tephra. Ten rhyolitic tephra pre-date the Rotoehu eruption (>ca. 50 ka), and some are chemically dissimilar to post-50 ka rhyolites. Some of these older tephra were produced by large-magnitude events; however, their source remains uncertain. Eight tephra from the local basaltic Auckland Volcanic Field (AVF) are also identified. Interpolation of sedimentation rates allow us to estimate the timing of 12 major explosive eruptions from Taranaki volcano in the 27.5–9.5-ka period. In addition, 28 older events are recognised. The tephra are trachytic to rhyolitic in composition. All have high K2O contents (>3 wt%), and there are no temporal trends. This contrasts with the proximal lava record that shows a trend of increasing K2O with time. By combining the Onepoto tephra record with that of the previously documented Pukaki crater, 15 AVF basaltic fall events are constrained at: 34.6, 30.9, 29.6, 29.6, 25.7, 25.2, 24.2, 23.8, 19.4, 19.4, 15.8 and 14.5 ka, and three pre-50 ka events. This provides some of the best age constraints for the AVF, and the only reliable data for hazard recurrence calculations. The minimum event frequency of both distal and local fall events can be estimated, and demonstrates the Auckland City region is frequently impacted by ash fall from many volcanoes.