Optimal depth of subvolcanic magma chamber growth controlled by volatiles and crust rheology
Optimal depth of subvolcanic magma chamber growth controlled by volatiles and crust rheology
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DOI：
10.1038/s41561-019-0415-6
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发表时间：
2019-09-01
影响因子：
18.3
通讯作者：
Bachmann, Olivier
中科院分区：
文献类型：
--
作者：
Huber, Christian;Townsend, Meredith;Bachmann, Olivier
岩浆房的储存压力影响火山喷发的方式、频率和规模。中性浮力或流变转变通常被认为是控制岩浆聚集和形成这种腔室的原因。然而，富含挥发分的岩浆的密度通常低于周围地壳的密度，并且地壳的流变学本身并不能定义岩浆房周围脆-韧性转变的深度。然而，从地球物理反演或岩石学方法推断的典型储存压力似乎在所有构造环境和地壳成分中聚集在2 +/- 0.5 kbar左右。在这里，我们使用热机械模拟表明，存储压力是由挥发性出溶和地壳流变学。在压力小于或接近1.5千巴，地质现实的水含量，腔室体积和补给率，存在的出溶岩浆挥发相阻碍腔室的增长，因为喷发量通常大于补给饲料系统在休眠期间。当压力大于rsim2.5千巴时，长寿命岩浆区的地壳粘性足够低，足以抑制大多数喷发。可持续的可喷发岩浆储层只能在2 +/- 0.5千巴左右的相对狭窄的压力范围内形成，在此范围内，出溶挥发物的数量促进增长，而地壳的高粘度促进喷发所需的超压。
Storage pressures of magma chambers influence the style, frequency and magnitude of volcanic eruptions. Neutral buoyancy or rheological transitions are commonly assumed to control where magmas accumulate and form such chambers. However, the density of volatile-rich silicic magmas is typically lower than that of the surrounding crust, and the rheology of the crust alone does not define the depth of the brittle-ductile transition around a magma chamber. Yet, typical storage pressures inferred from geophysical inversions or petrological methods seem to cluster around 2 +/- 0.5 kbar in all tectonic settings and crustal compositions. Here, we use thermomechanical modelling to show that storage pressure is controlled by volatile exsolution and crustal rheology. At pressures less than or similar to 1.5 kbar, and for geologically realistic water contents, chamber volumes and recharge rates, the presence of an exsolved magmatic volatile phase hinders chamber growth because eruptive volumes are typically larger than recharges feeding the system during periods of dormancy. At pressures > rsim2.5 kbar, the viscosity of the crust in long-lived magmatic provinces is sufficiently low to inhibit most eruptions. Sustainable eruptible magma reservoirs are able to develop only within a relatively narrow range of pressures around 2 +/- 0.5 kbar, where the amount of exsolved volatiles fosters growth while the high viscosity of the crust promotes the necessary overpressurization for eruption.