Magma Residence and Recharge in Thick Continental Crust: Volcan Maipo, Andean Southern Volcanic Zone

厚厚的大陆地壳中的岩浆居住和补给：安第斯山脉南部火山带迈波火山

• 批准号: 0911430
• 负责人: Maureen Feineman
• 金额: $ 26.05万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-08-01 至 2013-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0911430&HistoricalAwards=false
• 关键词: Magma; Residence; Recharge; Thick; Continental

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The proposed project seeks to determine the nature of continental crust involvement in the generation of a suite of lavas erupted over the past ~86 thousand years at Volcán Maipo, one of the northernmost volcanoes of the Southern Volcanic Zone (SVZ) of the Andes. Five of the six worst volcanic disasters that have occurred since 1600 AD have occurred at subduction zones, including the 1985 eruption of Nevado del Ruiz in the Northern Andes that claimed the lives of 25,000 people. Recent volcanic activity in the Andean SZV includes eruptions at both Llaima and Chaitén in Chile. The eruption of Chaitén after ten thousand years of dormancy necessitated the evacuation of more than 4,000 people, reminding us that we must be mindful of volcanic processes in the Andes at al times. Volcán Maipo is located within 150 km of the populous cities of Santiago del Chile and Mendoza, Argentina, and the ash from an ancient eruption of this volcanic system underlies the modern city of Santiago. The volcano itself lies within a popular national park, and less than 10 km from an international gas pipeline. The combination of high population density, threat to public utilities, and historic volcanic activity make study of this volcano acutely pertinent. Understanding the role of continental crust in modifying the composition and transport of magma at subduction zones will provide information that may be of use in understanding the hazards posed by the Cascades volcanoes, which currently threaten major metropolitan areas of the American Northwest including Seattle and Portland. The proposed study will support a PhD student for 3 years, helping to prepare a new generation of American scientists. The study also supports collaboration between an early-career female US scientist and a senior female Argentine scientist.It is generally understood that magmas are generated at subduction zones by fluid-fluxed melting of the mantle wedge to generate Mg-rich basalts and basaltic andesites. However, the bulk of the lavas erupted at subduction zones are evolved andesites to dacites. The proposed work will test the hypothesis that the bulk of chemical differentiation occurs in a lower crustal hot zone, followed by some degree of continued differentiation through repeated cycles of magma recharge in an upper crustal magma chamber prior to eruption. The specific hypotheses to be addressed are: 1) Differentiation from mantle-derived basaltic magma to fractionated basaltic andesite occurs in the lowermost crust; 2) Continuous differentiation from basaltic andesite to dacite proceeds in the deep crustal hot zone by fractional crystallization of garnet and plagioclase; 3) Magma crystallizes in the shallow crustal chamber through multiple episodes of recharge by fresh magma from the lower crustal system until the time of eruption. Whole rock major element, trace element, and isotopic data for a suite of rocks ranging from basaltic andesites to dacites will help to address hypotheses (1) and (2), and in situ analysis of major element, trace element, and Sr isotope zonation in plagioclase phenocrysts will help to address hypothesis (3), while also helping to determine the relative amounts of differentiation taking place in the shallow crustal magma chamber and the deep crustal hot zone.

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。拟议的项目旨在确定大陆地壳参与形成一套熔岩的性质，这些熔岩在过去约8.6万年间在迈波火山喷发，迈波火山是安第斯山脉南部火山区（SVZ）最北端的火山之一。 自公元1600年以来发生的六次最严重的火山灾害中有五次发生在俯冲带，包括1985年北方安第斯山脉的Nevado del Ruiz火山爆发，造成25，000人死亡。 安第斯SZV最近的火山活动包括智利的Llaima和Chaitén的火山爆发。 柴滕火山在沉寂了一万年之后爆发，迫使4 000多人撤离，这提醒我们必须时刻注意安第斯山脉的火山活动。马伊波火山位于人口众多的智利圣地亚哥和阿根廷门多萨市的150公里范围内，该火山系统古代喷发的火山灰构成了现代城市圣地亚哥的基础。 火山本身位于一个受欢迎的国家公园内，距离国际天然气管道不到10公里。 高人口密度、对公共设施的威胁和历史上的火山活动的结合使得对这座火山的研究变得非常重要。 了解大陆地壳在改变俯冲带岩浆的成分和运输方面的作用，将提供可能有助于了解喀斯喀特火山造成的危害的信息，喀斯喀特火山目前威胁着美国西北部的主要大都市地区，包括西雅图和波特兰。 这项研究将支持一名博士生3年，帮助培养新一代的美国科学家。 该研究还支持了一位美国早期女科学家和一位阿根廷资深女科学家之间的合作。一般认为，岩浆是在俯冲带通过地幔楔的流体熔融产生的，从而产生富镁玄武岩和玄武安山岩。 然而，在俯冲带喷发的大部分熔岩是演化的安山岩到英安岩。拟议的工作将检验这样一种假设，即大部分化学分异发生在下地壳热区，然后在喷发前通过上地壳岩浆房中岩浆补给的重复循环，在一定程度上继续分异。 提出的具体假设是：（1）幔源玄武岩浆向分离玄武安山岩的分异作用发生在地壳最低层，（2）玄武安山岩向英安岩的连续分异作用发生在地壳深部热带，主要是通过石榴子石和斜长石的分离结晶作用进行的;（3）岩浆在地壳浅室中结晶，是通过下地壳系统新鲜岩浆的多次补给而形成的。 从玄武安山岩到英安岩的一系列岩石的全岩主量元素、微量元素和同位素数据将有助于解决假说（1）和（2），斜长石斑晶中主量元素、微量元素和Sr同位素分带的原位分析将有助于解决假说（3），同时也有助于确定在地壳浅部岩浆房和地壳深部热区中发生的分异的相对量。