MARGINS: Collaborative Research: Origins of Local Variations in Subduction-Related Fluids: Evidence from Olivine-Hosted Melt Inclusions from the Central American Subduction Zone

边缘：合作研究：俯冲相关流体局部变化的起源：中美洲俯冲带橄榄石熔融包裹体的证据

• 批准号: 0742460
• 负责人: Kurt Roggensack
• 金额: $ 7.58万
• 依托单位: Arizona State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-03-01 至 2011-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0742460&HistoricalAwards=false
• 关键词: MARGINS; Collaborative; Research; Origins; Local

One of the most important processes that occurs at subduction zones is the fluid-mediated transfer of material from subducting lithosphere into overlying mantle. The sources of fluid for this important mass transfer remain controversial. Along the Central American subduction zone erupted basaltic magmas display systematic geochemical variations along the volcanic front which have been linked to changes in intensity and the agents of slab-to-wedge mass transfer (e.g., Eiler et al., 2006). In the Nicaraguan portion of the Central American subduction zone there are also local (i.e., intravolcano) geochemical variations in basaltic magmatism that can rival the much-ballyhooed along-arc differences (e.g., Patino et al., 2000). These local variations in the chemistry of erupted basalts have also been linked to variations in fluid transfer from the subducting Cocos plate (Patino et al., 2000; Walker et al., 2001). They may also reflect local variability in melt generation and/or mantle wedge depletion (Carr et al., 1990; Feigenson and Carr, 1993; Reagan et al., 1994; Walker et al., 2007). We propose to critically evaluate the origin of the local geochemical variations in Nicaragua through major, volatile and trace element analyses of olivine-hosted melt inclusions in basaltic tephras.Intellectual Merit. A full major, volatile and trace element characterization of the melt inclusion population in Nicaraguan basaltic tephras will allow us to determine the range in primitive compositions feeding Nicaraguan volcanoes. We can then test whether the range in primitive compositions is caused by local variations in fluid input from the subducting Cocos plate; in the melting history of the mantle wedge; or in the melting dynamics in the mantle wedge. The volatile and trace element contents of the melt inclusions will also permit further characterization of the slab signals imprinted on Nicaraguan magmas and, when combined with existing whole-rock data, help us to identify the fluid bearers of these slab signals, a question that remains unresolved both on local and regional scales. Better constraints on the variety of slab-related fluids contributing to magmatism are integral to identifying which tectonic parameters (slab dip, slab hydration, crustal thickness) are most instrumental in creating an environment conducive to maximizing heterogeneity in erupted magma compositions in Nicaragua (e.g., Abers et al., 2003; Ranero et al., 2003) and along other subduction zones. The volatile element analyses of the melt inclusions will include the determinations of H2O, CO2, Cl and S. This will allow us to evaluate all of the magmatic processes that can affect the volatile concentrations of magmas (e.g. Hauri, 2002; Wade et al., 2006). Thus, we will be able to determine the degassing histories of magmas at individual volcanoes, which exerts a critical control on the explosivity of eruption (Roggensack et al., 1997; Cervantes and Wallace, 2003b; Spilliaert et al., 2006).Broader Impacts. The proposed project will provide continued support for programs at both Northern Illinois University and Arizona State University involving research experience for undergraduate students, particularly female students. In addition, it will permit continued transfer of scientific knowledge to Central American colleagues to help enhance community-level understanding about the workings of active and dormant volcanoes. For instance, knowledge of the degassing and eruptive processes learned from melt inclusions will provide important information on potential volcanic hazards.

在俯冲带发生的最重要的过程之一是流体介导的物质从俯冲岩石圈转移到上覆地幔。这一重要传质的流体来源仍有争议。沿着中美洲俯冲带喷发的玄武质岩浆沿着火山前缘显示出系统的地球化学变化，这与强度变化和板楔质量转移的因素有关（例如，Eiler等人，2006年）。在中美洲俯冲带的巴拿马部分，也有当地的（即，火山内）玄武岩岩浆活动的地球化学变化，可以与大肆宣传的沿弧差异（例如，Patino等人，2000）。喷发玄武岩的化学性质的这些局部变化也与来自俯冲科科斯板块的流体转移的变化有关（Patino等人，2000;步行者等人，2001年）。它们也可能反映了熔体生成和/或地幔楔消耗的局部变化（卡尔等人，1990; Feigenson和卡尔，1993; Reagan等人，1994年;步行者等人，2007年）。我们建议批判性地评估在尼加拉瓜通过主要的，挥发性和微量元素分析的橄榄石托管熔融包裹体在玄武质火山岩的本地地球化学变化的起源。一个完整的主要的，挥发性和微量元素的特性的熔体包裹体人口在Xuanuan玄武质火山岩将使我们能够确定的范围内的原始成分喂养Xuanuan火山。然后，我们可以测试是否在原始成分的范围是由当地的变化所造成的流体输入从俯冲科科斯板块，在熔融历史的地幔楔，或在熔融动力学的地幔楔。熔融包裹体的挥发性和微量元素含量也将允许进一步表征印在岩浆上的板片信号，并与现有的全岩数据相结合时，帮助我们确定这些板片信号的流体载体，这是一个在局部和区域尺度上仍未解决的问题。更好地限制有助于岩浆活动的板片相关流体的多样性，对于确定哪些构造参数（板片倾角、板片水合作用、地壳厚度）最有助于创造有利于最大化尼加拉瓜喷发岩浆成分异质性的环境（例如，Abers等人，2003; Ranero等人，2003）和沿着其他俯冲带。熔融包裹体挥发分分析包括H_2O、CO_2、Cl和S的测定。这将使我们能够评估所有可能影响岩浆挥发性浓度的岩浆过程（例如，Hauri，2002年; Wade等人，2006年）。因此，我们将能够确定个别火山岩浆的脱气历史，这对喷发的爆炸性起到关键的控制作用（Roggensack等人，1997年;塞万提斯和华莱士，2003年b; Spilliaert等人，2006).更广泛的影响。拟议的项目将继续支持北方伊利诺斯大学和亚利桑那州立大学的方案，这些方案涉及本科生，特别是女生的研究经验。此外，它将使科学知识能够继续转让给中美洲的同事，以帮助加强社区一级对活火山和休眠火山的运作的了解。例如，从熔融包裹体中了解到的脱气和喷发过程的知识将提供关于潜在火山灾害的重要信息。