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: 0948102
• 负责人: C. Page Chamberlain
• 金额: $ 8.84万
• 依托单位: Stanford 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 2014-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0948102&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.

智力上的功绩。该项目致力于H-O-C流体在与新汉普郡(NH)南北断面上暴露的古生代变质‘热点’带的形成相关的热传递中的作用。在这些地区，变质温度和岩石地球化学的陡峭梯度都集中在同变质石英±石墨脉网络上。张伯伦和朗布尔(1988)提出的假设是，这些特征代表了在阿卡迪亚区域变质过程中，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，典型的区域变质去挥发作用不太可能输送足够的热量来强烈扰动区域地热。看来，只有当流体通量巨大而流动的时间尺度非常短时，才能产生热点，但这种通量和时间尺度是否真实还不得而知。提出了一种多学科的方法来检验这一假设。实地工作将集中在布里斯托尔和纳尔逊附近暴露良好的热点地区。这一假设必须通过五个关键测试。(1)流体流量必须很大。通过量化静脉网络中的化学和同位素(O，H)传质来估计流经静脉的时间积分流体流量。(2)流体流动方向一定是降温的。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路径。(3)流动的时间尺度必须很短(10^6年)。利用变质岩中石榴石的Sm/ND定年和变质岩中独居石和锆石的U/Pb定年，以及野外岩浆岩脉中的独居石和锆石的U/Pb定年，将确定热点形成的绝对时间。此外，方解石、磷灰石和石榴石中的化学扩散曲线将被用来限制峰值加热的时间尺度。(4)峰值热条件的时间必须在等射线之间几乎同步(通过Sm/ND和U/Pb测年进行测试)。(5)在目前的暴露水平下，变质压力必须在等轴线上大致恒定。将进行温度气压测量以确定峰值条件、区域T/P梯度和P-T-T-T路径。了解时间积分的流体通量和流动的时间尺度将能够估计通过热点的实际流体通量以及跨油田区域的通量中的梯度。这些信息与P-T-t历史、流体流动年龄(S)和场关系一起，将为流体流动(二维)模拟及其对区域热结构的影响提供所需的初始条件和边界条件。如果假设失败，那么将研究其他替代方案，包括岩浆作用和下地壳片麻岩穹顶的上涌。阿格实验室将主要负责温压测量、传质分析以及扩散和流动模拟；巴克斯特实验室将负责Sm/Nd石榴石测年；张伯伦实验室将负责稳定同位素和U/Pb工作。更广泛的影响。大流量的流体既能输送质量，又能输送热量。因此，如果流体驱动加热的假设是正确的，那么它将与社会相关的问题有关，包括矿石金属的运输和温室气体从变质带转移出去。人力资源将得到开发，因为博士研究生和本科生的参与至关重要。PIS和学生将参加实地工作，并在2年级和3年级协调国际会议上的“小组会议”。所有的私人投资机构都为女学生提供建议，并致力于多样性，包括让代表性不足的少数群体参与科学。阿格带头开发了耶鲁大学皮博迪博物馆新的矿物、地球和空间(房屋)展厅，允许将新的研究成果整合到地球科学展示中，每年有超过15万名参观者观看。这些游客中有很大一部分是小学生，他们中的许多人生活在纽黑文、布里奇波特和其他康涅狄格州城市的市中心。此外，阿格还有单独的NSF资金，用于在新的地区学校教师大厅的基础上发展教育项目。巴克斯特将把这片区域纳入他每年一度的“机器人：脚趾下的岩石”推广项目，作为秋季矿物学课程的一部分。该项目吸引了波士顿地区的高中生和波士顿大学的本科生。