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.

大规模的火山喷发，例如黄石国家公园的特征，其爆炸性和广泛的影响归因于称为岩浆的熔岩成分，为管道系统提供燃料。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如何相关，后者在深处结晶形成称为花岗岩的深成体，构成了我们赖以生存的大陆地壳，在地球科学家中仍然未知，并且存在很大争议。我们的研究重点是智利安第斯山脉南部深成花岗岩体的形成，该花岗岩体保存了产生大量潜在爆炸性火山流纹岩所需过程的记录。 我们将绘制空间上不同的岩石类型图，测量它们的成分，并确定构成这个非常年轻且暴露得非常好的岩体的矿物组成。然后，将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来解释该岩体中保存的岩浆的过程、时间尺度和热历史。 我们的目标是使火成岩石学学科更接近于包含深成岩和火山领域的岩浆动力学通用模型。人们假设高硅花岗岩是通过浅地壳中的晶体熔融分馏而形成的，但所产生的晶体残留物很少被识别，并且很难与成分沿液体下降线绘制的深成体区分开来。智利安第斯山脉南部中新世晚期 Risco Bayo-Huemul 深成杂岩体的块体岩石成分质量平衡表明，岩性差异反映了熔体提取引起的晶体浓度。我们的目标是将现场观测与锆石和钛矿的 U-Pb 岩石年代学、40Ar/39Ar 热年代学、深成杂岩内整个岩石和矿物的成分和同位素测量以及热建模相结合，以：(1) 建立侵位速率和机制，(2) 识别单个岩浆批次并评估它们之间的任何相互作用，(3) 确定结晶的时间尺度 以及单个岩浆批次和整个系统范围的冷却，（4）建立 Risco Bayo 和 Huemul 岩体之间的成岩关系，包括每个岩体中的子域，以及（5）评估该系统内是否可能形成可喷发的流纹岩熔体。这个年轻的深成杂岩体保存了通常与流纹岩形成相关的过程的详细记录，流纹岩在过去的数百万年里在邻近的安第斯俯冲带内推动了大规模的硅质喷发。

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