Collaborative Research: Probing the Effect of Volatiles and Temperature on Thermal Diffusivity: Implications for Upper Mantle and Lithospheric Processes

合作研究：探讨挥发物和温度对热扩散率的影响：对上地幔和岩石圈过程的影响

• 批准号: 0711020
• 负责人: Anne Hofmeister
• 金额: $ 19.92万
• 依托单位: Washington University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-01-01 至 2011-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0711020&HistoricalAwards=false
• 关键词: Collaborative; Research; Probing; Effect; Volatiles

Movement of heat within Earths outer layers is largely governed by the vibrational component of thermal diffusivity (D) and how this depends on structure, composition and temperature. Recent transfer of the accurate (±2%) laser-flash analysis (LFA) technique from engineering to Earth science has shown that methods previously applied to Earth materials systematically underdetermined D by ~15 to 100%, underestimated anisotropy in D, and gave incorrect dD/dT. New LFA data on garnet, olivine, quartz, and two glasses show that hydration lowers D and the closely related property, lattice thermal conductivity klat for these phases. If this effect is universal, then significant depression of klat should occur in wet regions of the upper mantle. If this is the case, hydration will promote heat retention and magma generation in the mantle wedge and under mid-ocean ridges, and provides positive feedback for hydrolytic weakening and mantle heterogeneities. To test if this relationship is general, accurate measurements of the dependence of D on T and volatile content are proposed for relevant minerals, rocks, and melts. These new data will be made available for use in thermal models. The PI's efforts will immediately improve understanding of the flow of heat on a microscopic basis (i.e., the results pertain directly to physical behavior of solids) and in the long run will improve our understanding of conductive heat flow in the crust and upper mantle (i.e. the data are needed for various applications in Earth science). Broader impacts include relevance to materials science, and training of undergrad and graduate students in a state-of-the-art technology. The investigators will present results at conferences and public lectures, which combines student training with outreach. Public speaking helps the female PI to serve as a role model. The PI may provide inspiration to young women as her career was impeded for a decade due to child-raising, but her productivity has rebounded.Experimental details are as follows: The effect of volatiles and T on D will be quantified through LFA measurements from ~25ºC up to melting or ~2000ºC of an appropriately diverse suite of samples: major upper mantle minerals and rocks, and re-melted lavas and synthetic analog melts. Oriented single-crystals will be studied. Liquids will be characterized by gathering data above the glass transition temperature. Volatile concentration, speciation, and dehydration rates will be characterized using IR spectroscopy (for OH, H2O, CO2, also Fe2+ content) and microprobe analyses (for F and Fe total). Using synthetics allows isolation of chemical effects.Suites of appropriate rocks (mantle xenoliths, basalts, andesites) and mineral samples are available. These three suites, minerals, and the glasses provide sub-projects suitable for research by students ranging from undergraduate to PhD level. The team will focus on isolating the effects of volatiles, and on quantifying the temperature dependence and structural effects because in the upper mantle, pressure effects on D are low and predictable. The effect of grain-size will be discerned by comparing mineral to rock data.

地球外层的热量运动在很大程度上受热扩散率(D)的振动分量的支配，而这又如何取决于结构、成分和温度。最近，精确（±2%）激光闪光分析（LFA）技术从工程学转移到地球科学，表明以前应用于地球材料的方法系统地低估了D的15%至100%，低估了D的各向异性，并给出了不正确的dD/dT。石榴石、橄榄石、石英和两种玻璃的LFA数据表明，水化降低了这些相的D和与之密切相关的晶格导热系数klat。如果这种影响是普遍的，那么明显的克拉特凹陷应该发生在上地幔的湿润区域。如果是这样，水合作用将促进地幔楔和洋中脊下的热保存和岩浆生成，并对水解减弱和地幔非均质性提供正反馈。为了测试这种关系是否普遍，建议对相关矿物、岩石和熔体进行D对T和挥发物含量依赖的精确测量。这些新数据将用于热模型。PI的努力将立即提高对微观基础上的热流的理解（即，结果直接与固体的物理行为有关），从长远来看，将提高我们对地壳和上地幔传导热流的理解（即，地球科学中的各种应用都需要这些数据）。更广泛的影响包括与材料科学相关，以及对本科生和研究生的最新技术培训。调查人员将在会议和公开讲座上展示结果，这将学生培训与外展活动相结合。公开演讲有助于女性PI成为榜样。由于抚养孩子，她的事业受到了10年的阻碍，因此PI可能会给年轻女性带来灵感，但她的生产力已经反弹。实验细节如下：挥发物和T对D的影响将通过LFA测量来量化，从~25ºC到熔融或~2000ºC，适当多样化的样品：主要上地幔矿物和岩石，再熔融熔岩和合成模拟熔体。取向单晶将被研究。液体将通过收集高于玻璃化转变温度的数据来表征。挥发性浓度，形态和脱水速率将使用红外光谱（OH, H2O, CO2，以及Fe2+含量）和微探针分析（F和Fe总量）进行表征。使用合成材料可以隔离化学效应。合适的岩石（地幔捕虏体、玄武岩、安山岩）和矿物样品可供选择。这三个套房，矿物和玻璃提供了适合本科生到博士水平的学生研究的子项目。该团队将专注于分离挥发物的影响，并量化温度依赖性和结构效应，因为在上地幔中，压力对D的影响很低，而且是可预测的。粒度的影响将通过比较矿物和岩石的数据来辨别。