Rb-Sr Chronometry of Magma Differentiation

最近发表的一项关于前火山岩的同位素研究 玻璃山，长谷，已经表明， 流纹质岩浆的分异作用可由Rb-Sr （一）以“以德为先”为原则，以“以德为先”为原则。 Ar ages）。 此外，这些差异很难解释 除非流纹岩岩浆持续存在于 在稳定的，分层的区域长时间的室内， 105至106年的数量级，之间的质量转移可以忽略不计 不同的层次。 这种长期居留的情况是 大大超过了最近的估计， 已发表的高级别核反应堆寿命的热模型 岩浆房。 这个项目是为了扩展这项研究 对矿物玻璃Rb-Sr系统学的综合研究 玻璃山流纹岩的40 Ar-39 Ar年龄及其发育 类似的研究在其他年轻的星系。 附加 已经选择的火山中心是科索（加州）， 矿物山，双峰和蜂巢山（犹他州），路易斯安那州 Primavera（墨西哥火山带）和Naivasha（肯尼亚）。 这些 选择特定的火山中心是因为它们包含 原始的流纹岩玻璃，成分从 具有高Rb/Sr比的偏铝到高过碱性，以及 已经在实地关系方面得到了很好的描述， 年龄、化学和岩相学。

A recently published isotopic study of the precaldera rhyolites of Glass Mountain, Long Valley, has shown that the timing of differentiation of rhyolitic magma can be determined from Rb-Sr dating and resolved from the age of eruption (as determined by K- Ar ages). Furthermore, the differences are difficult to explain unless the rhyolitic magmas persisted in the upper reaches of the chamber in stable, stratified zones for long periods, of the order of 105 to 106 years, with negligible mass transfer between the different layers. Such protracted residence periods are considerably in excess of the estimates implied by recently published thermal modelling of the longevity of high-level silicic magma chambers. This project is to extend this research to a comprehensive study of the mineral-glass Rb-Sr systematics and 40Ar-39Ar ages of the Glass mountain rhyolites and to develop similar research on other young silicic systems. The additional volcanic centers which have been selected are Coso (California), Mineral Mountains, Twin Peaks and Honeycomb Hills (Utah), La Primavera (Mexican Volcanic Belt) and Naivasha (Kenya). These particular volcanic centers were chosen because they contain pristine rhyolitic glasses ranging in composition from metaluminous to highly peralkaline with high Rb/Sr ratios, and have already been well characterized in terms of field relations, age, chemistry and petrography.