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首页> 外文期刊>Journal of Volcanology and Geothermal Research2012V243-244NOCT,15 >Volcanic glass as a proxy for Cenozoic elevation and climate in the Cascade Mountains, Oregon, USA
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Volcanic glass as a proxy for Cenozoic elevation and climate in the Cascade Mountains, Oregon, USA

机译：火山玻璃替代美国俄勒冈州喀斯喀特山脉的新生代海拔和气候

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After deposition, volcanic glass hydrates with ambient water, recording the average hydrogen isotope ratio (delta D or delta H-2) of local meteoric water during the hydration period. Previous researchers have used ancient glass delta D values to reconstruct paleotopography and paleoclimate, while others have questioned the long-term reliability of the proxy as a recorder of ancient meteoric water. In this study, we sampled volcanic glasses ranging in age similar to 33 Ma to <50 ka from tuffs on the leeward (east) side of the Oregon Cascade Mountains. Our results strongly suggest that volcanic glass acquires and preserves SD values that are proportional to the stable isotopic composition of environmental water at the time of ash deposition based on 1) a 20 parts per thousand difference in delta D values between samples of different ages (similar to 8 Ma apart) from the same locality, 2) preservation of stable isotopic compositions consistent with lacustrine and non-lacustrine depositional environments in coeval samples, and 3) substantial differences between SD values of ancient volcanic glass (>1 Ma) and local meteoric water (converted to glass delta D values) throughout the study area.We propose a paleoenvironmental interpretation of volcanic glass results that resolves previously published isotopic data and agrees well with the petrologic, structural, and stratigraphic record. Namely, the Oregon Cascades have been a significant topographic barrier since at least the mid-Miocene, and likely as far back as the Oligocene. Since reaching a topographic maximum during the eruption of Columbia River flood basalts in the mid-Miocene, surface elevations in Oregon have decreased, while the northern Cascades in Washington continue to rise. Published by Elsevier B.V.
机译：沉积后，火山玻璃与环境水合，记录水化期间局部陨石水的平均氢同位素比率（δD或δH-2）。以前的研究人员曾使用古代玻璃三角洲D值来重建古地形和古气候，而其他人则质疑该代理作为古代陨石记录仪的长期可靠性。在这项研究中，我们从俄勒冈喀斯喀特山脉背风（东）侧的凝灰岩中取样了年龄在33 Ma至<50 ka左右的火山玻璃。我们的研究结果强烈表明，火山灰玻璃获得并保留与灰分沉积时环境水的稳定同位素组成成比例的SD值，其依据是：1）不同年龄的样品之间的D值差异千分之二十（相似）距同一地点相距8 Ma），2）保留与同期样本中湖相和非湖相沉积环境一致的稳定同位素组成，以及3）古火山玻璃（> 1 Ma）与局部陨石的SD值之间存在实质性差异整个研究区域内的水（转换为玻璃δD值）。我们提出了对火山玻璃结果的古环境解释，该解析可以解析以前发表的同位素数据，并与岩石学，结构和地层记录相吻合。就是说，至少从中新世中期开始，俄勒冈级联一直是重要的地形屏障，并且可能早在渐新世。自中新世中期哥伦比亚河洪水玄武岩喷发达到最高峰以来，俄勒冈州的地表海拔下降了，而华盛顿北部的小瀑布则继续上升。由Elsevier B.V.发布

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