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

地球外层内的热量移动在很大程度上受热扩散率(D)的振动分量以及这如何取决于结构、成分和温度的影响。最近，精确的(±2%)激光闪光分析(LFA)技术从工程学到地球科学的转移表明，以前应用于地球材料的方法系统地低估了约15%到100%的D，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、石英和两种玻璃的新LFA数据表明，水合作用降低了D和这些相的密切相关性质，晶格热导率Klat。如果这种影响是普遍的，那么Klat的显著低压应该发生在上地幔的潮湿地区。如果是这样的话，水化作用将促进地幔楔体和大洋中脊下的热保持和岩浆生成，并为水解性减弱和地幔的不均质性提供正反馈。为了测试这一关系是否具有一般性，建议对相关矿物、岩石和熔体的D与T和挥发分含量的依赖关系进行精确测量。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)，并从长远来看，将提高我们对地壳和上地幔中传导热流的理解(即，这些数据是地球科学中各种应用所需的)。更广泛的影响包括与材料科学的相关性，以及对本科生和研究生进行最先进技术的培训。调查人员将在会议和公开讲座上展示结果，这些会议和公开讲座将学生培训与外联相结合。公开演讲有助于女性PI成为榜样。PI可能会给年轻女性提供灵感，因为她的职业生涯因养育孩子而受阻了十年，但她的生产力已经回升。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，范围从~25℃到熔化或~2000℃，样品包括主要的上地幔矿物和岩石，以及重熔的熔岩和合成的模拟熔体。将对取向单晶进行研究。液体的特征是在玻璃化转变温度以上收集数据。挥发分浓度、形态和脱水速率将使用红外光谱(对于OH、H2O、CO2以及Fe2+含量)和微探针分析(对于F和Fe总量)来表征。使用合成物可以隔离化学效应。可以获得合适的岩石(地幔包体、玄武岩、安山岩)和矿物样品的套装。这三个套间、矿物和眼镜提供了适合从本科生到博士水平的学生进行研究的子项目。该团队将专注于分离挥发物的影响，并量化温度相关性和结构影响，因为在上地幔，压力对D的影响很小，而且是可以预测的。颗粒大小的影响将通过比较矿物和岩石数据来辨别。

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.