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Residence time of magma within the magma chamber

岩浆在岩浆室内的停留时间

基本信息

批准号：
13640478
负责人：
SHIMOBAYASHI Norimasa
金额：
$ 2.3万
依托单位：
Kyoto University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13640478/
关键词：
magma chamber volcanic rock pigeonite plagioclase microstructure residence time 噴火予知平均滞在時間

项目摘要

For the purpose of specifying the phenocrysts which were crystallized within the magma chamber before its eruption, we have been managing to observe and analyze a number of specimens from many volcanic localities, for example, Usu Miyake-jima, Sakura-jima, Funagata, and Takadate volcanoes and so on. The criteria are as follows, (1) the rock contains pigeonite phenocrysts, (2) the phenocrysts are surrounded by the overgrown rims, (3) the compositions of these overgrown rims and grains in groundmass are almost similar, and (4) the growth temperature of the core parts of these phenocrysts can be estimated with such as a pyroxene geothermometry. Unfortunately, however, no specimens but one can be found satisfying all of these criteria - the only one exceptional specimen is a tholeiitic basalt from the Kurohana area in Funagata volcano.This sample has already been studied by us (Miyake & Shimobayashi, 2000), and we inferred that the phenocrysts of pyroxene and plagioclase crystallized at above 1200℃ in the magma chamber and that they were kept in the chamber less than half a year, which was determined on a basis of the coarsening kinetics of pigeonite-augite intergrowth. Another study (Yoshimura, private communication) using the same sample that we used, on the other hand the residence time in the chamber is estimated as 50-560 years based on a theory of crystal size distribution (CSD). In the present study, we minutely examined these two significantly different durations and considered that the latter duration (50-560 years) could be shortened to the value, which is not so largely inconsistent with ours. Consequently, we suggest that the CSD theory is very useful to estimate the residence time in the chamber even if the crystal growth rate in the chamber can be properly determined.

为了确定岩浆房喷发前结晶的斑晶，我们对宇须三宅岛、樱岛、船形、高手等火山区的大量样品进行了观察和分析，其标准如下：（1）岩石中含有鸽子岩斑晶;（2）斑晶被过生长的边缘所包围，（3）这些过生长的边缘与基质中的颗粒成分几乎相似，（4）这些斑晶的核心部分的生长温度可以用辉石地质测温法等来估算。然而不幸的是，除了一个样本之外，没有找到满足所有这些标准的样本-唯一一个特殊的样本是来自船形火山黑花地区的拉斑玄武岩。我们已经研究了这个样本（Miyake & Shimobayashi，2000年），推测辉石和斜长石斑晶是在岩浆房中1200℃以上结晶形成的，根据褐帘石-普通辉石共生粗化动力学，确定了该粗化速率。另一项研究（Yoshimura，私人交流）使用了我们使用的相同样品，另一方面，根据晶体尺寸分布（CSD）理论，在腔室中的停留时间估计为50-560年。在本研究中，我们仔细地检查了这两个显著不同的持续时间，并认为后者的持续时间（50-560年）可以缩短到与我们的值并不太不一致的值。因此，我们建议，CSD理论是非常有用的估计在室内的停留时间，即使在室内的晶体生长速率可以适当地确定。