Thermal Budgets of Magma Storage Constrained by Diffusion Chronometry: the Cerro Galán Ignimbrite
Thermal Budgets of Magma Storage Constrained by Diffusion Chronometry: the Cerro Galán Ignimbrite
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受扩散计时限制的岩浆储存热收支：Cerro Galán Ignimbrite
DOI：
10.1093/petrology/egac048
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发表时间：
2022
影响因子：
3.9
通讯作者：
de Silva, Shanaka
中科院分区：
文献类型：
--
作者：
Lubbers, Jordan;Kent, Adam J;de Silva, Shanaka
长期的热化学条件下，大量的岩浆储存在地壳中是不可或缺的，我们的时间，频率和强度的火山爆发的理解，并提供了重要的背景下解释火山监测数据。然而，尽管如此，个别岩浆系统可能表现出一系列的时间-温度路径或热历史，这是许多复杂的，在某些情况下，竞争过程的结果。这种复杂性导致了对地壳内岩浆长期热演化的不完全理解。火山学团体最近感兴趣的是大量的流变学可喷发的岩浆在喷发之前存在于地壳内的时间长度。在这里，我们使用扩散测年法，微量元素和热力学建模相结合，量化的长期热演化的2.08马，630 km 3塞罗加兰火山灰岩（CGI）在阿根廷西北部，在最近的地质记录中最大的火山爆发之一。我们发现，斜长石中Mg和Sr的扩散表明，喷发的岩浆物质仅在维持大量可喷发岩浆储存所需的温度（约750°C）或以上的温度下度过了数十年至数百年。计算斜长石平衡组合物揭示了一系列的液体，控制整体分馏斜长石+黑云母+透长石，虽然高分辨率的微量元素断面记录的分馏途径的多样性。总的来说，我们认为，有令人信服的证据表明，从CGI岩浆系统喷发的岩浆花了大部分的上地壳居住在一个基本上不可喷发的状态，并迅速再动员前不久爆发。
The long-term thermochemical conditions at which large bodies of silicic magma are stored in the crust is integral to our understanding of the timing, frequency, and intensity of volcanic eruptions and provides important context for interpreting volcano monitoring data. Despite this, however, individual magmatic systems may exhibit a range of time–temperature paths, or thermal histories, that are the result of many complex and, in some cases, competing processes. This complexity contributes to an incomplete understanding of the long-term thermal evolution of magma stored within the Earth’s crust. Of recent interest to the volcanology community is the length of time large volumes of rheologically eruptible and geophysically detectable magma exist within the crust prior to their eruption. Here we use a combination of diffusion chronometry, trace element, and thermodynamic modeling to quantify the long-term thermal evolution of the 2.08 Ma, 630 km3Cerro Galán Ignimbrite (CGI) in NW Argentina; one of the largest explosive volcanic eruptions in the recent geologic record. We find that diffusion of both Mg and Sr in plagioclase indicate that erupted magmatic material only spent decades to centuries at or above temperatures (~750°C) required to maintain significant volumes of stored eruptible magma. Calculated plagioclase equilibrium compositions reveal an array of liquids that is controlled overall by fractionation of plagioclase + biotite + sanidine, although high-resolution trace element transects record a diversity of fractionation pathways. Overall, we suggest that there is compelling evidence that the magma erupted from the CGI magmatic system spent most of its upper crustal residence in a largely uneruptible state and was rapidly remobilized shortly before eruption.