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Determination of the depth of rhyolitic magma chambers in the Snake River Plain province, USA,: an experimental calibration

美国蛇河平原省流纹岩浆房深度的测定：实验校准

基本信息

批准号：
235224487
负责人：
Professor Dr. Francois Holtz, Ph.D.
金额：
--
依托单位：
Institut für Mineralogie
依托单位国家：
德国
项目类别：
Infrastructure Priority Programmes
财政年份：
2013
资助国家：
德国
起止时间：
2012-12-31 至 2015-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/235224487?language=en
关键词：
Determination depth rhyolitic magma chambers

项目摘要

The investigation of high-silica rhyolitic rocks collected in the recent ICDP drilling from the Snake River Plain (SRP) volcanic province (western United States) as well as rocks from the adjacent rhyolitic complexes offers a unique opportunity to track the evolution of magma storage conditions in time and space in the Yellowstone hotspot intracontinental volcanic province. The application of various geothermometers which can be used to determine pre-eruptive temperatures show a general trend indicating a general decrease of temperature over the last 16 Ma. However, the depth (or pressure) of the magma chambers is difficult to constrain and remains mainly unknown because the mineral assemblage in the rhyolitic systems is not suitable for geobarometry. As an alternative to mineral compositions, the silica content of rhyolitic melts can be used to constrain pressure, provided that the silicate melts have cotectic compositions (melts coexisting with quartz and feldspar), which is the case for most SRP rhyolites. From studies in synthetic systems, it is well known that the silica content of cotectic melts decreases with increasing pressure and that it may be used as barometer in pressure ranges of ~ 1000 to 50 MPa. However, the evolution of silica content with pressure is not calibrated for natural systems containing up to 2 wt% CaO and 4 wt% FeO. In this study, we plan to determine the role of pressure on the silica content of cotectic melts compositions relevant for SRP compositions. Preliminary results show that the effect of CaO (or Anorthite content) on the position has been underestimated. The experimental data are crucial to interpret the natural glass compositions (matrix glass and glass inclusions) analyzed in the ICDP core samples and are used to extract quantitative information on the depth of magma storage prior to eruption. The dataset obtained from various eruptive events (samples from ICDP drillings and other SRP rhyolites) will be used to check if there is an evolution of the depth of magma storage over the lifetime of the Yellowstone hotspot in the last 16 Ma and if there is a correlation between the pre-eruptive pressure, the volume of erupted material, the temperature (or differentiation level) and the water activity of magmas. This study is conducted in cooperation with other U.S. groups who are in charge of the analysis of ICDP rhyolitic samples. It is emphasized that the experimental database obtained in this project can also be applied to other case studies (high silica rhyolites, A-type granites).

调查收集的高硅流纹岩岩石在最近的ICDP钻井从蛇河平原（SRP）火山省（美国西部），以及岩石从邻近的流纹岩杂岩提供了一个独特的机会，以跟踪岩浆储存条件的演变在黄石热点陆内火山省的时间和空间。可用于确定喷发前温度的各种地质温度计的应用表明，在过去16 Ma中，温度普遍下降。然而，岩浆房的深度（或压力）是难以约束的，主要是未知的，因为流纹质系统中的矿物组合是不适合的地质压力。作为矿物成分的替代，流纹质熔体中的二氧化硅含量可以用来限制压力，前提是硅酸盐熔体具有石英成分（熔体与石英和长石共存），这是大多数SRP流纹质的情况。从合成系统的研究中，众所周知，钴熔体中的二氧化硅含量随着压力的增加而减少，并且它可以在~ 1000至50 MPa的压力范围内用作气压计。然而，二氧化硅含量与压力的演变是没有校准的天然系统含有高达2重量%的CaO和4重量%的FeO。在这项研究中，我们计划确定的作用，压力的二氧化硅含量的钴熔体组成相关的SRP组合物。初步结果表明，CaO（或钙长石含量）对位置的影响被低估了。实验数据是至关重要的解释天然玻璃成分（基质玻璃和玻璃夹杂物）分析的ICDP核心样品，并用于提取定量信息的岩浆存储深度喷发前。从各种喷发事件中获得的数据集（来自ICDP钻探和其他SRP韵律的样本）将用于检查在过去16 Ma中黄石热点的生命周期内岩浆储存深度是否有演变，以及喷发前压力、喷发物质体积、温度（或分异水平）和岩浆水活动之间是否存在相关性。这项研究是与负责分析ICDP流纹岩样品的其他美国小组合作进行的。强调本项目所获得的实验数据库也可应用于其他实例研究（高硅流纹岩、A型花岗岩）。