Tools and techniques for developing tephra stratigraphies in lake cores: A case study from the basaltic Auckland Volcanic Field, New Zealand
Tools and techniques for developing tephra stratigraphies in lake cores: A case study from the basaltic Auckland Volcanic Field, New Zealand
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开发湖心火山灰地层的工具和技术：新西兰奥克兰玄武岩火山场的案例研究
DOI：
10.1016/j.quascirev.2015.06.014
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发表时间：
2015
影响因子：
4
通讯作者：
H. Neil
中科院分区：
文献类型：
--
作者：
J. Hopkins;M. Millet;C. Timm;C. Wilson;G. Leonard;J. Palin;H. Neil
火山地区的概率灾害预测依赖于对喷发记录（可能来自近端和远端火山）的理解和重建。火山灰地层学通常被用作重建工具，通过将火山灰沉积物相互关联来创建地层框架，该框架可用于评估喷发历史的震级-频率关系。当应用于广泛分布的流纹岩矿床时，火山灰的识别和对比是成功的;然而，玄武质火山灰的识别和对比是有问题的。在这里，使用tefras从六个maars在新西兰的奥克兰火山场（AVF）的岩心，我们展示了如何X射线密度扫描加上磁化率分析可以用来准确和可靠地识别玄武玻璃碎片轴承层在湖相沉积物，当结合的主要和微量元素的tefras签名，可以用来区分主要的改造层。在可靠地识别出岩心内的原生玄武岩层与改造玄武岩层之后，我们详细介绍了一种基于地层学和地球化学指纹的跨岩心对比的改进方法。我们提出的主要和微量元素数据的个人玻璃碎片从57个单独的玄武岩层内确定的核心。我们的研究结果表明，在主要元素组成（SiO2，CaO，Al 2 O3，FeO，MgO）没有提供明确的相关性，微量元素（例如La、Gd、Yb、Zr、Nb、Nd）和微量元素比率（例如[La/Yb]N、[Gd/Yb]N、[Zr/Yb]N）成功地改善了AVF玄武质火山灰层位之间的成分差异，从而允许重建AVF的改善的喷发史。
Probabilistic hazard forecasting for a volcanic region relies on understanding and reconstructing the eruptive record (derived potentially from proximal as well as distal volcanoes). Tephrostratigraphy is commonly used as a reconstructive tool by cross-correlating tephra deposits to create a stratigraphic framework that can be used to assess magnitude–frequency relationships for eruptive histories. When applied to widespread rhyolitic deposits, tephra identifications and correlations have been successful; however, the identification and correlation of basaltic tephras are more problematic. Here, using tephras in drill cores from six maars in the Auckland Volcanic Field (AVF), New Zealand, we show how X-ray density scanning coupled with magnetic susceptibility analysis can be used to accurately and reliably identify basaltic glass shard-bearing horizons in lacustrine sediments and which, when combined with the major and trace element signatures of the tephras, can be used to distinguish primary from reworked layers. After reliably identifying primary vs. reworked basaltic horizons within the cores, we detail an improved method for cross-core correlation based on stratigraphy and geochemical fingerprinting. We present major and trace element data for individual glass shards from 57 separate basaltic horizons identified within the cores. Our results suggest that in cases where major element compositions (SiO2, CaO, Al2O3, FeO, MgO) do not provide unambiguous correlations, trace elements (e.g. La, Gd, Yb, Zr, Nb, Nd) and trace element ratios (e.g. [La/Yb]N, [Gd/Yb]N, [Zr/Yb]N) are successful in improving the compositional distinction between the AVF basaltic tephra horizons, thereby allowing an improved eruptive history of the AVF to be reconstructed.