Collaborative Research: Fluid Transport and Fluid-Rock Interactions Preserved in Two Serpentinite Melanges in the Guatemala Suture Zone

合作研究：危地马拉缝合带两个蛇纹岩混杂岩中保存的流体传输和流体-岩石相互作用

• 批准号: 1119456
• 负责人: Hannes Brueckner
• 金额: $ 4.84万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-07-01 至 2016-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1119456&HistoricalAwards=false
• 关键词: Collaborative; Research; Fluid; Transport; Rock

Subduction channel fluids are responsible for modification of metamorphic blocks, crystallization of vein rocks, serpentinization of the overlying mantle wedge and ultimately the flux melting that spawns arc volcanism. We propose to extend our studies of the serpentinite mélanges of the Guatemala Suture Zone (GSZ) to elucidate this record of mass transport by fluid as recorded in the rocks. The GSZ encompasses two serpentinite mélanges that preserve the elements described above. One system on the south side of the Motagua fault records very cold and wet conditions within the subduction channel, represented by lawsonite eclogite blocks formed at ~2.6 GPa and 450-500ºC. The other system north of the fault represents somewhat warmer but still wet conditions preserved in epidote-eclogite blocks, with peak metamorphism at 500-600°C and ~ 2 GPa. Both mélanges carry fragments of vein systems that formed within the overlying serpentinizing mantle peridotites; these include jadeitite, omphacitite, albitite, and mica-dominant rocks that contain a strong signature of fluids from altered oceanic crust and subducted sediment. Detailed petrologic and geochemical characterization of representative rocks is proposed for major, minor, and trace-element geochemistry and Sr-Nd isotopic systematics for this research, with a focus on B, Li, Be concentrations and isotopes. Textures, mineralogy, and chemical composition will be utilized to sort between processes that occurred during subduction as opposed to later exhumation. Intellectual Merit: Subduction is a fundamental process on Earth that recycles surface matter into the interior mantle and contributes to growth of continental crust. However, details of fluid-mediated mass transport and alteration in subduction zones are poorly understood and require further resolution. Careful study of preserved subduction zones, where both fluid precipitates and hydrated mantle wedge rocks are preserved, will contribute important insights on this issue. It is proposed to build upon results of a previously NSF-funded project by detailed chemical analysis of minerals in rocks preserved in serpentinite mélanges in the GSZ with the following objectives: (1) Characterize the mantle wedge protolith by study of the relict phases; (2) Analyze serpentinite minerals for major, minor and trace elements with particular attention to B, Li, and Be (and isotopic signatures) and textural settings to assess fluid modification of protolith and distinction between changes produced during subduction versus during exhumation; (3) Analyze minerals from vein rocks (e.g., jadeitite, omphacitite, mica-rock, etc.) with the same approach to determine the solute load of fluids traversing the subduction channel and entering the mantle wedge, as well as the relative timing based on textures and mineral assemblages. Using fluid-mineral partition coefficients we will estimate fluid composition entering the mantle wedge. (4) Utilize Sr-Nd isotopic data to assess sources of lithologic components (e.g., mantle vs. recycled continental or sedimentary sources). The proposed research will enhance understanding of fluid transport from subduction channels to the mantle wedge. Broader Impacts: These include the collaboration of researchers at universities and museums, involvement of students and scientists in many countries, including those in Central America, support of teacher training and geological training in Guatemala, links with archaeological studies on Caribbean-area jade, connections among research groups, and extensive outreach to both the media and the public via interviews, articles and Museum web-sites aimed both at student education and dissemination of our activities, results, and data.

俯冲通道流体负责变质块体的改造，脉岩的结晶，上覆地幔楔的蛇纹石化，并最终产生弧火山作用的通量熔融。我们建议扩大我们的研究的蛇纹岩混杂岩的危地马拉缝合带（GSZ），以阐明这种记录的质量运输流体记录在岩石中。地面稳定区包括两个蛇纹岩混杂岩，保存了上述元素。Motagua断层南侧的一个系统记录了俯冲通道内非常寒冷和潮湿的条件，以在约2.6 GPa和450-500ºC下形成的硬柱石榴辉岩块为代表。断层以北的另一个系统代表了在绿帘石-榴辉岩块中保存的稍微温暖但仍然潮湿的条件，在500-600°C和~ 2 GPa时达到变质作用的峰值。这两种混杂岩都携带着在上覆的蛇纹地幔橄榄岩中形成的矿脉系统的碎片;这些包括硬玉岩、绿辉石岩、钠长石岩和云母为主的岩石，这些岩石含有来自蚀变洋壳和俯冲沉积物的强烈流体特征。详细的岩石学和地球化学表征的代表性岩石提出的主要，次要和微量元素地球化学和Sr-Nd同位素系统的研究，重点是B，Li，Be的浓度和同位素。纹理，矿物学和化学成分将被用来在俯冲过程中发生的过程之间进行分类，而不是后来的折返。智力优势：俯冲是地球上一个基本的过程，它将地表物质注入地幔内部，并促进大陆地壳的生长。然而，流体介导的质量传输和俯冲带的蚀变的细节知之甚少，需要进一步解决。仔细研究保存俯冲带，流体沉淀物和水化地幔楔岩保存，将有助于对这个问题的重要见解。建议在国家科学基金会资助的一个项目的基础上，通过对保存在地下安全区蛇纹混杂岩中的岩石中的矿物进行详细的化学分析，实现以下目标：（1）通过研究残留相来表征地幔楔原岩;（2）分析蛇纹岩矿物的主要、次要和微量元素，特别注意B、Li，和Be（和同位素特征）和结构设置，以评估原岩的流体改性和俯冲期间与折返期间产生的变化之间的区别;（3）分析来自脉岩的矿物（例如，硬玉岩、绿辉石岩、云母岩等）用同样的方法来确定穿过俯冲通道进入地幔楔的流体的溶质负荷，以及基于结构和矿物组合的相对时间。利用流体-矿物分配系数，我们将估计进入地幔楔的流体成分。(4)利用Sr-Nd同位素数据评估岩性成分的来源（例如，地幔与再循环大陆或沉积源）。这项研究将加深对俯冲通道向地幔楔的流体输送的理解。更广泛的影响：其中包括大学和博物馆研究人员的合作，包括中美洲国家在内的许多国家的学生和科学家的参与，支持危地马拉的教师培训和地质培训，与加勒比地区玉器考古研究的联系，研究小组之间的联系，以及通过采访向媒体和公众进行广泛宣传，文章和博物馆网站，旨在学生教育和传播我们的活动，结果和数据。