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

智力优势。 本项目研究了H-O-C流体在热传递中的作用，该热传递与在横跨新罕布什尔州（NH）的南北向断面中暴露的古生代变质"热点"带的形成有关。在这些地方，变质温度和岩石地球化学的陡峭梯度集中在同变质石英±石墨脉网络。Chamberlain和Rumble（1988年）提出了这样的假设，即这些特征代表了在西印度群岛区域变质作用期间大量热流体通过断裂网络上升的区域。另一方面，数值模拟研究表明，典型的区域变质脱挥发分作用不太可能输送足够的热量来强烈扰动区域地热。似乎只有在流体流量巨大且流动的时间尺度极短的情况下才能产生热点，但这种流量和时间尺度是否现实尚不清楚。一个多学科的方法提出来测试这一假设。实地工作将集中在布里斯托和纳尔逊，新罕布什尔州附近暴露的热点地区。这个假设必须通过五个关键的检验。(1)流体流量一定很大。通过静脉的时间积分流体通量将通过量化静脉网络中的化学和同位素（O，H）质量传递来估计。(2)流体流动一定是沿着温度下降的方向。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，并阐明流体来源和通道。(3)流动的时间尺度必须很短（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、变质岩中独居石和锆石的U/Pb测年以及现场区域的任何岩浆岩脉来确定。此外，方解石，磷灰石和石榴石中的化学扩散曲线将用于限制峰值加热的时间尺度。(4)热条件峰值的时间在各等梯度线上几乎是同步的（通过Sm/Nd和U/Pb测年进行测试）。(5)在目前的暴露水平上，变质压力在各等梯度线上一定是大致恒定的。将进行热压测定，以确定峰值条件、局部T/P梯度和P-T-t路径。时间积分的流体通量和流动的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跨场区域的通量的梯度。这些信息与P-T-t历史、流体流动的年龄和场关系一起，将提供流体流动（二维）建模及其对区域热结构的影响所需的初始和边界条件。如果假设失败，那么将调查其他替代方案，包括岩浆作用和下地壳片麻岩穹丘的上涌。Ague实验室将主要负责热压法、质量传递分析以及扩散和流动建模;巴克斯特实验室负责Sm/Nd石榴石测年;张伯伦实验室负责稳定同位素和U/Pb工作。 大的流体通量在传递热量的同时也传递质量。因此，如果正确的话，流体驱动加热的假设将对社会相关问题产生影响，包括矿石金属的运输和变质带温室气体的转移。人力资源将得到开发，因为博士学位。研究生和本科生的参与至关重要。PI和学生将参加实地工作，并在第二年和第三年，在国际会议上协调“小组会议”。所有的PI都为女学生提供咨询，并致力于多样性，包括代表性不足的少数群体参与科学。Ague率先在耶鲁皮博迪博物馆开发了新的矿物，地球和太空大厅（HoMES），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名游客观看。这些游客中有很大一部分是学童，其中许多人住在纽黑文、布里奇波特和康涅狄格州其他城市的市中心。此外，Ague有单独的NSF资金，以开发基于新大厅的地区教师教育计划。巴克斯特将把实地纳入他的年度"机器人：我们脚趾下的岩石"推广计划，作为他秋季矿物学课程的一部分。该计划吸引波士顿地区的高中生和BU本科生。

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.