Timescales of quartz crystallization and the longevity of the Bishop giant magma body.
Timescales of quartz crystallization and the longevity of the Bishop giant magma body.
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DOI：
10.1371/journal.pone.0037492
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发表时间：
2012
期刊：
影响因子：
3.7
通讯作者：
Rivers ML
中科院分区：
文献类型：
--
作者：
Gualda GA;Pamukcu AS;Ghiorso MS;Anderson AT Jr;Sutton SR;Rivers ML
超级爆发在几天内将大量（100 s-1000 s km 3）的岩浆猛烈地转移到地表，并证明了深处存在巨大的岩浆池。这些巨型岩浆体的寿命具有重大的科学和社会意义。对整个岩石、玻璃、长石和锆石晶体的放射性测量数据表明，毕晓普凝灰岩巨型岩浆体在大约76万年前爆发并形成了长谷破火山口（加州），寿命很长（> 10万年），而且进化相当缓慢。在这项工作中，我们提出了四条证据来限制Bishop岩浆体结晶的时间尺度：（1）基于Ti分布的扩散弛豫的石英停留时间，（2）基于熔融包裹体的刻面动力学的石英停留时间，（3）使用石英+长石晶体尺寸分布导出的石英和长石结晶时间，（4）基于热力学和热流模型的冷却和结晶时间尺度。我们所有的估计都表明，石英结晶的时间尺度小于10，000年，更典型的是在喷发前500- 3，000年内。我们的结论是，大体积，晶体贫岩浆体是短暂的功能，一旦建立，千年的时间尺度上演变。我们还认为，锆石晶体，而不是记录结晶的时间尺度的一个大池的结晶贫岩浆，记录延长的时间段所需的成熟的地壳和建立这些巨大的岩浆体。
Supereruptions violently transfer huge amounts (100 s–1000 s km3) of magma to the surface in a matter of days and testify to the existence of giant pools of magma at depth. The longevity of these giant magma bodies is of significant scientific and societal interest. Radiometric data on whole rocks, glasses, feldspar and zircon crystals have been used to suggest that the Bishop Tuff giant magma body, which erupted ∼760,000 years ago and created the Long Valley caldera (California), was long-lived (>100,000 years) and evolved rather slowly. In this work, we present four lines of evidence to constrain the timescales of crystallization of the Bishop magma body: (1) quartz residence times based on diffusional relaxation of Ti profiles, (2) quartz residence times based on the kinetics of faceting of melt inclusions, (3) quartz and feldspar crystallization times derived using quartz+feldspar crystal size distributions, and (4) timescales of cooling and crystallization based on thermodynamic and heat flow modeling. All of our estimates suggest quartz crystallization on timescales of <10,000 years, more typically within 500–3,000 years before eruption. We conclude that large-volume, crystal-poor magma bodies are ephemeral features that, once established, evolve on millennial timescales. We also suggest that zircon crystals, rather than recording the timescales of crystallization of a large pool of crystal-poor magma, record the extended periods of time necessary for maturation of the crust and establishment of these giant magma bodies.
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