Rb-Sr Chronometry of Magma Differentiation

岩浆分异的铷-锶计时

• 批准号: 9004133
• 负责人: Alexander Halliday
• 金额: $ 13.22万
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1990
• 资助国家: 美国
• 起止时间: 1990-06-01 至 1992-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9004133&HistoricalAwards=false
• 关键词: Rb; Sr; Chronometry; Magma; Differentiation

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.

最近发表的一项关于长谷玻璃山前破火山口流纹岩的同位素研究表明，流纹岩岩浆分化的时间可以通过Rb-Sr测年确定，并通过喷发年龄（通过K- Ar年龄确定）来解决。此外，这种差异很难解释，除非流纹岩岩浆在岩室的上游以稳定的分层带长期存在，大约105至106年，不同层之间的质量传递可以忽略不计。如此漫长的停留期大大超过了最近发表的高硅岩浆库寿命热模拟所暗示的估计。本项目拟将此研究扩展到玻璃山流纹岩矿物玻璃Rb-Sr系统和40Ar-39Ar年龄的综合研究，并开展其他年轻硅质体系的类似研究。被选中的其他火山中心是科索（加利福尼亚州），矿泉山，双峰和蜂窝山（犹他州），La Primavera（墨西哥火山带）和奈瓦沙（肯尼亚）。选择这些特殊的火山中心，是因为它们含有原始流纹岩玻璃，其成分从铝质到高过碱性，具有高Rb/Sr比，并且在场关系、年龄、化学和岩石学方面已经有了很好的特征。