Collaborative Research: Investigating the Processes and Timescales of Andesite Differentiation: A Comprehensive Petrological and Geochemical Study of Arenal Volcano, Costa Rica

合作研究：安山岩分异过程和时间尺度的研究：哥斯达黎加阿雷纳尔火山的岩石学和地球化学综合研究[a] -0207185；耳朵- 0207287;耳朵- 0207761;耳朵- 0207316 -π:吉尔;里根;Tepley;哥斯达黎加的GardnerArenal火山是一个极好的自然实验室，在这里可以测试关于岩浆过程的分化机制和时间尺度及其与火山爆发的关系的具体假设。我们的目标是开展多管齐下的岩石学和地球化学调查，以利用现有的数据和模型。阿雷纳尔火山正在进行的喷发经历了复杂的喷发行为变化，一个关键的问题是这些变化是否与不同的岩浆储存条件有关，比如不同的深度和初始挥发性含量，或者不同的脱气方式和速率。我们将通过几种技术来研究这个重要的问题。我们试图确定脱气的时间尺度，脱气岩浆的停留时间和上升速率，以及脱气诱导斜长石结晶的时间尺度。我们将测量铀衰变系列中的短寿命核素，以约束岩浆过程的时间尺度，并测量整个岩石的长寿命同位素组成，以及Sr的矿物分离物和单个矿物，以确定在分化过程中是否有同位素不同成分参与的证据。最后，我们将测量一套主要和微量元素浓度，以评估Arenal熔岩组成的长期变化。这些测试的数据将有助于回答以下问题：分化速率是否取决于结晶的深度和程度，以及脱气的程度和特征；在安山岩近乎稳定的喷发过程中，晶体和岩浆的停留时间是否短至数天至数月；喷发内岩浆成分的变化是由分离结晶加补给或同化的开放系统过程引起的，还是两者兼而有之；喷发类型是否与脱气历史和岩浆停留时间有关。

Collaborative Research: Investigating the processes and timescales of andesite differentiation: a comprehensive petrological and geochemical study of Arenal Volcano, Costa RicaEAR-0207185; EAR-0207287; EAR-0207761; EAR-0207316PIs: Gill; Reagan; Tepley; GardnerArenal Volcano in Costa Rica is an excellent natural laboratory in which to test specific hypotheses regarding differentiation mechanisms and the timescales of magmatic processes and their relationship to eruptions. Our objective is to undertake a multi-pronged petrological and geochemical investigation to take advantage of existing data and models. The on-going eruption of Arenal volcano has undergone complex changes in eruptive behavior, and a crucial question is whether those changes relate to different magma storage conditions, such as varying depths and hence initial volatile contents, or to different degassing styles and rates. We will investigate this important issue through several techniques. We seek to determine the timescales of degassing, the residence times and ascent rate of degassed magmas, and the timescales of degassing-induced plagioclase crystallization. We will measure short-lived nuclides within the uranium decay series to constrain the timescales of magmatic processes as well as measure the long-lived isotopic compositions of whole rocks, and mineral separates and individual minerals in the case of Sr, to determine whether there is evidence for involvement of isotopically distinct components during differentiation processes. Lastly, we will measure a suite of major- and trace-element concentrations to evaluate the secular change in Arenal lava composition.The data from these tests will help answer questions such as whether rates of differentiation depend on the depth and degree of crystallization and on the extent and character of degassing; whether crystal and magma residence times can be as short as days to months during near steady-state eruptions of andesite; whether within-eruption changes of magma composition are caused by open-system processes of fractional crystallization plus recharge or assimilation or both; and whether eruption styles are related to degassing history and magma residence time.