Collaborative Research: Testing for Rapid Pulses of Crustal-scale Heat and Mass Transfer by Fluids in Metamorphic "Hot Spots", New Hampshire, USA

合作研究：测试美国新罕布什尔州变质“热点”中流体的地壳尺度传热传质快速脉冲

• 批准号: 0948308
• 负责人: Ethan Baxter
• 金额: $ 17.88万
• 依托单位: Trustees of Boston University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-08-01 至 2015-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0948308&HistoricalAwards=false
• 关键词: Collaborative; Research; Testing; Rapid; Pulses

Intellectual Merit. This project addresses the role of H-O-C fluids in heat transfer associated with formation of a Paleozoic belt of metamorphic 'hot spots' exposed in a north-south transect across New Hampshire (NH). At each of these localities, steep gradients in metamorphic temperature and rock geochemistry are centered on syn-metamorphic quartz±graphite vein networks. Chamberlain and Rumble (1988) proposed the hypothesis that these features represent zones where large quantities of hot fluids ascended through fracture networks during Acadian regional metamorphism. On the other hand, numerical modeling studies have shown that typical regional metamorphic devolatilization is unlikely to transport sufficient heat to strongly perturb regional geotherms. It would appear that hot spots can only be produced if the fluid fluxes are enormous and the timescales of flow are extremely short, but it is unknown if such fluxes and timescales are realistic. A multidisciplinary approach is proposed to test this hypothesis. Field work will focus on well-exposed hot spot localities near Bristol and Nelson, NH. The hypothesis must pass five crucial tests. (1) Fluid fluxes must have been large. Time-integrated fluid fluxes through veins will be estimated by quantifying chemical and isotopic (O, H) mass transfer in the vein networks. (2) Fluid flow must have been in a direction of decreasing temperature. The nature and extent of chemical and isotopic metasomatism will determine the direction of fluid flow, and elucidate fluid sources and pathways. (3) Timescales of flow must have been short (10^6 yrs). The absolute timing of hot spot formation will be determined using Sm/Nd dating of garnet in metamorphic rocks, and U/Pb dating of monazite and zircons in metamorphic rocks and any magmatic dikes in the field areas. Furthermore, chemical diffusion profiles in calcite, apatite, and garnet will be used to constrain timescales of peak heating. (4) The timing of peak thermal conditions must have been nearly synchronous across isograds (test via Sm/Nd and U/Pb dating). (5) Metamorphic pressures must have been roughly constant across isograds at the present level of exposure. Thermobarometry will be done to determine peak conditions, regional T/P gradients, and P-T-t paths. Knowledge of the time-integrated fluid fluxes and timescales of flow will allow estimation of the actual fluid fluxes through the hot spots as well as gradients in the fluxes across the field areas. This information, together with the P-T-t history, age(s) of fluid flow, and field relations, will provide the initial and boundary conditions needed for modeling of fluid flow (2-dimensional) and its effect on regional thermal structure. If the hypothesis fails then other alternatives will be investigated, including magmatism and upwelling of lower crustal gneiss domes. The Ague lab will take primary responsibility for thermobarometry, mass transfer analysis, and diffusion and flow modeling; the Baxter lab for Sm/Nd garnet dating; and the Chamberlain lab for stable isotope and U/Pb work. Broader Impacts. Large fluid fluxes poentially transport mass as well as heat. Therefore, if correct, the hypothesis of fluid-driven heating would bear on problems of societal relevance including ore metal transport and the transfer of greenhouse gases out of metamorphic belts. Human resources will be developed because Ph.D. graduate student and undergraduate involvement is critical. PIs and students will take part in field work and, in Years 2 and 3, coordinate "group meetings" at international conferences. All of the PIs have advised women students and are committed to diversity, including the involvement of underrepresented minority groups in science. Ague spearheaded development of the new Hall of Minerals, Earth, and Space (HoMES) at the Yale Peabody Museum, allowing integration of new research results into Earth science displays viewed by over 150,000 visitors annually. A large fraction of these visitors are schoolchildren, many of whom live in the urban centers of New Haven, Bridgeport, and other Connecticut cities. Moreover, Ague has separate NSF funding to develop educational programs based on the new Hall for area schoolteachers. Baxter will incorporate the field area into his annual "RoBOT: Rocks Beneath Our Toes" outreach program as a part of his Fall mineralogy class. The program engages Boston area high school students and BU undergraduates.

智力价值 该项目探讨了 H-O-C 流体在与新罕布什尔州 (NH) 南北横断面中暴露的古生代变质“热点”带的形成相关的作用。变质温度和岩石地球化学以同变质石英±石墨脉网络为中心，Chamberlain 和 Rumble (1988) 提出了这些特征代表区域的假设。另一方面，数值模拟研究表明，典型的区域变质挥发分不可能输送足够的热量来扰乱区域地温。如果流体通量巨大且流动时间尺度极短，则会产生这种情况，但尚不清楚这种通量和时间尺度是否现实，提出了一种多学科方法来检验这一假设。新罕布什尔州布里斯托尔和尼尔森附近暴露的热点地区。该假设必须通过五个关键检验（1）通过量化化学和同位素（O、H）的流体通量必须很大。 (2) 流体流动必须沿着温度降低的方向进行。化学和同位素交代作用的性质和程度将决定流体流动的方向，并阐明流体的来源和方向。 (3) 流动的时间尺度一定很短（10^6 年），热点形成的绝对时间将通过变质岩中石榴石的 Sm/Nd 测年以及变质岩中独居石和锆石的 U/Pb 测年来确定。此外，方解石、磷灰石和石榴石中的化学扩散剖面将用于限制峰值加热的时间尺度。各等梯度的峰值热条件必须几乎同步（通过 Sm/Nd 和 U/Pb 测年进行测试）。 (5) 在当前的暴露水平下，等梯度的变质压力必须大致恒定，以确定峰值条件。 、区域 T/P 梯度和 P-T-t 路径的时间积分流体通量和流动时间尺度的知识将允许估计通过热点的实际流体通量以及梯度。该信息与 P-T-t 历史、流体流动年龄和场关系一起，将提供流体流动（二维）及其影响建模所需的初始条件和边界条件。如果该假设失败，则将研究其他替代方案，包括下地壳片麻岩穹顶的岩浆作用和上升流，Ague 实验室将主要负责热压测量、传质分析以及扩散和流动建模； Sm/Nd 石榴石测年；以及张伯伦实验室的稳定同位素和 U/Pb 工作。因此，如果流体驱动加热的假设正确，那么大流体通量可能会带来问题。社会相关性包括矿石金属运输和温室气体从变质带的转移，因为博士研究生和本科生的参与至关重要，并且，在第二年和第三年，协调国际会议上的“小组会议” 所有 PI 都为女学生提供了建议，并致力于多元化，包括让代表性不足的少数群体参与科学领域的建设。 ，和空间（HoMES）在耶鲁皮博迪博物馆，允许将新的研究成果整合到地球科学展览中，每年有超过 150,000 名参观者观看这些参观者中的很大一部分是学童，其中许多人住在里面。此外，阿格还获得国家科学基金会的单独资助，为地区学校教师开发基于新大厅的教育项目，巴克斯特将把该领域纳入他的年度“机器人：我们脚趾下的岩石”。 “外展计划是他秋季矿物学课程的一部分。该计划吸引了波士顿地区的高中生和波士顿大学的本科生。