RUI: Subduction Zone Flight Recorders: Integrating P-T-t-f Histories of Subduction and Exhumation of Eclogite through Microanalysis of Garnet and its Inclusions

RUI：俯冲带飞行记录仪：通过石榴石及其包裹体的微分析，整合榴辉岩俯冲和折返的 P-T-t-f 历史

• 批准号: 1249778
• 负责人: F. Zeb Page
• 金额: $ 17.48万
• 依托单位: Oberlin College
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-03-01 至 2018-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1249778&HistoricalAwards=false
• 关键词: RUI; Subduction; Zone; Flight; Recorders

The recycling of oceanic crust into the mantle through subduction is ultimately responsible for the formation of the Earth's continental crust through arc magmatism. The origin of these magmatic processes is thought to be the melting of mantle rocks under volcanic arcs triggered by the release of fluids from the subducting oceanic slab. The composition of the fluids ultimately responsible for this magmatism is the subject of much research, including the study of the metamorphic byproducts of subduction that are occasionally returned to the surface. These garnet-bearing metamorphic rocks (eclogite) are the only samples of material that have been subducted to great depth, but are available for study. Although eclogite can preserve a record of fluids from subduction zones, it is difficult to determine whether the fluid record preserved in these rocks comes from deep in the subduction zone, or is a result of their exhumation. The research funded by this grant will tie the record of fluids preserved in the oxygen isotope composition of garnets that grew during subduction with the pressure and temperature conditions recorded by the chemical composition of the garnets, generating an integrated tectonic and fluid record for these rocks.Chemically zoned garnets and mineral inclusions entrapped during their growth have been shown to preserve pressure and temperature information from both the subduction of ocean crust and exhumation of eclogite. Slow intragranular diffusion of oxygen in garnet suggests that these garnets will preserve the δ18O of fluids in equilibrium with the garnet along these paths as well. New advances in ion microprobe technique now allow the δ18O of garnet to be measured in situ with high precision. By integrating in situ δ18O analysis of garnet with existing and new quantitative prograde and retrograde P-T-fO2 information and texturally guided geochronology, this study will generate the first detailed P-T-t-f paths for eclogite and related rocks formed in subduction zones. These histories will allow samples of eclogite to serve as probes into the tectonic and fluid conditions of the fore-arc and subduction channel environment of fossil subduction zones. The integrated nature of these data will tie information on fluids directly to the tectonic evolution of these rocks, and allow them to be used to test a number of hypotheses regarding the nature and timing of the fluid record preserved by exhumed subduction-zone metamorphic rocks. Comparison of data sets between rocks with sedimentary and igneous protoliths found in mélange zones and in coherent fault bounded blocks will offer insight into the timing of their juxtaposition, and will allow existing geochemical studies to be tied to a common tectonic and thermal framework.

海洋地壳通过俯冲作用再循环到地幔中，最终导致了通过弧岩浆作用形成地球大陆地壳。这些岩浆过程的起源被认为是由俯冲洋板释放出的流体引发的火山弧下地幔岩石的熔化。最终导致这种岩浆作用的流体成分是许多研究的主题，包括对偶尔返回地表的俯冲变质副产品的研究。这些含石榴石的变质岩（榴辉岩）是唯一已俯冲到很深但可用于研究的物质样本。虽然榴辉岩可以保存俯冲带的流体记录，但很难确定这些岩石中保存的流体记录是来自俯冲带深处，还是俯冲带折返的结果。这项拨款资助的研究将把俯冲过程中生长的石榴石氧同位素成分中保存的流体记录与石榴石化学成分记录的压力和温度条件联系起来，为这些岩石生成一个完整的构造和流体记录。化学分区的石榴石和在其生长过程中捕获的矿物包裹体已被证明可以保存来自洋壳俯冲和折返的压力和温度信息。 榴辉岩。石榴石中氧的缓慢晶内扩散表明，这些石榴石也将沿着这些路径保持流体的 18O 与石榴石保持平衡。离子微探针技术的新进展现在可以高精度地原位测量石榴石的 18O。通过将石榴石的原位 18O 分析与现有和新的定量顺行和逆行 P-T-fO2 信息以及结构引导的地质年代学相结合，这项研究将为俯冲带中形成的榴辉岩和相关岩石生成第一个详细的 P-T-t-f 路径。 这些历史将使榴辉岩样本能够作为对化石俯冲带弧前和俯冲水道环境的构造和流体条件的探针。这些数据的综合性质将把流体信息直接与这些岩石的构造演化联系起来，并允许它们被用来检验一些关于挖出的俯冲带变质岩所保存的流体记录的性质和时间的假设。对在混杂岩带和连贯断层边界块中发现的沉积岩和火成岩原岩的岩石之间的数据集进行比较，将有助于深入了解它们并置的时间，并使现有的地球化学研究能够与共同的构造和热框架联系起来。