Collaborative research: Andean Plutonic Perspectives on Generation, Storage, and Eruption of Rhyolite

合作研究：安第斯深成流纹岩生成、储存和喷发的观点

• 批准号: 1650265
• 负责人: John Cottle
• 金额: $ 8.64万
• 依托单位: University of California-Santa Barbara
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-01-15 至 2020-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1650265&HistoricalAwards=false
• 关键词: Collaborative; research; Andean; Plutonic; Perspectives

Large-scale, caldera-forming volcanic eruptions, for example those characteristic of Yellowstone National Park, owe their explosivity and widespread impact to the composition of molten rock called magma that fuels their plumbing systems. Yet, the generation of such magma plumbing systems, and how the erupted volcanic rock rhyolite is related to the unerupted magma that crystallizes at depth to form plutons of rock called granite that makes up the continental crust which we live on, remains unknown and highly controversial among earth scientists. Our study focuses on the formation of a plutonic body of granite in the southern Andes in Chile that preserves a record of processes required to generate large quantities of potentially explosive volcanic rhyolite. We will map spatially distinct rock types, measure their compositions, and determine the compositions of the constituent minerals that comprise this very young, and exceptionally well-exposed pluton. A multidisciplinary approach using modern geochemical methods, geochronology, and numerical modeling will then be used to interpret the processes, timescales, and thermal history of magma that are preserved in this pluton. We aim to bring the discipline of igneous petrology one step closer to a universal model of magma dynamics that incorporates both the plutonic and volcanic realms.High silica granites are hypothesized to form via crystal-melt fractionation in the shallow crust yet, the resulting crystal residues are rarely identified and can be difficult to distinguish from plutons whose compositions plot along liquid lines of descent. Bulk rock compositional mass balance in the late Miocene Risco Bayo-Huemul plutonic complex in the Southern Andes of Chile suggests that lithological differences reflect crystal concentration in response to melt extraction. We aim to combine field observations with U-Pb petrochronology of zircon and titanite, 40Ar/39Ar thermochronology, compositional and isotopic measurements of whole rocks and minerals within the plutonic complex, and thermal modeling to: (1) establish the rates and mechanisms of emplacement, (2) identify individual magma batches and assess any interaction between them, (3) determine the timescales of crystallization and cooling of individual magma batches and system-wide, (4) establish petrogenetic relationships between the Risco Bayo and Huemul plutons including subdomains within each, and (5) evaluate whether eruptible rhyolitic melt may have formed within this system. This young plutonic complex preserves a detailed record of a process commonly associated with the formation of rhyolite that has propelled large silicic eruptions during the past million years within the adjacent Andean subduction zone.

大规模的、形成破火山口的火山爆发，例如黄石国家公园的那些特征，其爆炸性和广泛的影响都归功于一种叫做岩浆的熔岩成分，它为它们的管道系统提供燃料。然而，这种岩浆管道系统的产生，以及喷发的火山岩流纹岩与未喷发的岩浆之间的关系，这些岩浆在深处结晶，形成称为花岗岩的岩石，构成了我们赖以生存的大陆地壳，这些岩石在地球科学家中仍然是未知的，而且存在很大的争议。我们的研究重点是智利安第斯山脉南部花岗岩深成体的形成，它保存了产生大量潜在爆炸性火山流纹岩所需的过程记录。我们将绘制空间上不同的岩石类型，测量它们的成分，并确定构成这颗非常年轻、异常暴露的岩体的组成矿物的成分。使用现代地球化学方法、地质年代学和数值模拟的多学科方法将用于解释保存在该岩体中的岩浆的过程、时间尺度和热历史。我们的目标是使火成岩岩石学学科更接近于岩浆动力学的通用模型，该模型包含了深部和火山领域。高硅花岗岩被认为是在地壳浅层通过结晶熔融分馏作用形成的，然而，由此产生的晶体残留物很少被识别出来，并且很难与成分沿着液体下降线绘制的岩体区分开来。智利南安第斯山脉晚中新世Risco Bayo-Huemul深部杂岩的整体岩石成分质量平衡表明，岩性差异反映了熔体萃取作用下晶体浓度的变化。我们的目标是将野外观测与锆石和钛矿的U-Pb岩石年代学、40Ar/39Ar热年代学、深部杂岩体内整个岩石和矿物的组成和同位素测量以及热模拟相结合，以达到：(1)确定侵位速率和机制；(2)确定单个岩浆批次并评估它们之间的相互作用；(3)确定单个岩浆批次和系统范围内结晶和冷却的时间尺度；(4)建立Risco Bayo和Huemul岩体之间的成岩关系，包括各自的子域；(5)评估该系统内是否形成了可喷发的流纹岩熔体。这个年轻的深成复合体保存了一个过程的详细记录，这个过程通常与流纹岩的形成有关，流纹岩在过去的几百万年里推动了邻近的安第斯俯冲带内的大规模硅喷发。

项目成果

Complementary crystal accumulation and rhyolite melt segregation in a late Miocene Andean pluton

• DOI: 10.1130/g39167.1
• 发表时间: 2017-09
• 期刊: Geology
• 影响因子: 5.8
• 作者: A. Schaen;J. Cottle;B. Singer;C. B. Keller;N. Garibaldi;B. Schoene