SGER - Genesis and Diagenesis of an Enigmatic Precambrian Carbonate cement: an Investigation using Microanalytical and Experimental Techniques

智力优势：磨牙（MT）是一种神秘的碳酸盐织物，其特征是各种形状的空隙填充着均匀、等量的微晶石。迄今为止，研究主要集中在对孔隙形成机制的解读和对MT在时间和空间上的分布的描绘上。然而，MT保存与MT微晶石的沉淀密切相关，对此我们知之甚少。MT微晶石由均匀、均匀、非互锁的晶体组成，在阴极发光（CL）下表现为暗发光、亚球形核（直径5-7 m）和发光过度生长。在中元古代和新元古代早期（1600-750 Ma），有利于降水的条件普遍存在，其中MT微晶石占90%的单个层和5-25%的保存碳酸盐（体积相当于古生代骨骼颗粒）。本研究的目的是研究一种不寻常的，但具有体积意义的碳酸盐微晶石，称为磨牙（MT）微晶石，它广泛存在于中元古代和新元古代早期，表明碳酸盐降水与海洋环境的大范围地球化学演化之间存在联系。本研究将解决以下三个问题：(1)这种不寻常的碳酸盐微晶石的成核和生长机制是什么？(2)该微晶石的原始矿物学是否如先前所提出的那样是钒矾石？(3)这种不寻常的碳酸盐形态能告诉我们关于元古代海洋系统组成的什么信息？不幸的是，小晶体尺寸限制了许多传统技术在进一步研究微晶石起源中的应用。我提出了一种多学科方法，其中高分辨率CL和SEM成像将用于定义形态端元，重建晶体尺寸分布，并解释成核和生长机制；激光拉曼光谱将用于记录晶格结构，以帮助约束矿物学变化；结合高分辨率SIMS微量元素成像、拉曼光谱和晶体生长实验，将用于约束初始流体组成和沉淀条件。最终，破译MT微晶石的成因将有助于确定形成的化学环境，并有助于理解地球长期化学变化对沉积的影响。生物圈。更广泛的影响:该项目旨在通过扩大田纳西大学碳酸盐基础研究的广度，增加本科生的研究机会，让学生直接参与科学探究的过程，鼓励本科生在研究生和教师的帮助和指导下进行科学活动，促进发现和理解，同时促进教学、培训和学习。并鼓励学生参加区域和国家会议。目前，我有3名学生排队参加这个项目[1名硕士（男）和2名学士（女）；其中2名非传统学生在成家后重返学校。该项目还将加强UT的研究和教育基础设施，支持扩大多用户设施的使用，并在大学内部（地质-化学）和橡树岭国家实验室建立跨学科合作。最后，该项目旨在通过与西乔治亚州立大学（非博士）持续的研究和设备合作，扩大代表性不足群体的参与。授予机构。这种合作提高了学生对地球科学机会的认识，并加强了UT。吸引新研究生的能力。

PROJECT SUMMARY Intellectual Merit: Molar-tooth (MT) is an enigmatic carbonate fabric marked by variously shaped voids filled with a uniform, equant microspar. To date, research has focused largely on deciphering mechanisms of void formation and delineating MT distribution in time and space. MT preservation, however, is intimately linked to precipitation of MT microspar, about which we know little. MT microspar consists of uniform, equant, non-interlocking crystals that under cathodoluminescence (CL) show dully-luminescent, subspherical cores (5-7 m diameter) and luminescent overgrowths. Conditions favoring precipitation were common in the Mesoproterozoic and early Neoproterozoic (1600-750 Ma), where MT microspar comprises 90% of individual beds and 5-25% of preserved carbonate (volumetrically equivalent to Paleozoic skeletal grains). The objective of this project is to investigate an unusual, yet volumetrically significant, morphology of carbonate, termed molar-tooth (MT) microspar, whose widespread occurrence in the Mesoproterozoic and early Neoproterozoic suggests linkages between carbonate precipitation and the broad-scale geochemical evolution of marine environments. This proposal will address three questions: (1) What are the nucleation and growth mechanisms of this unusual carbonate microspar? (2) Was vaterite the original mineralogy of this microspar, as has been previously proposed? and (3) What can this unusual carbonate morphology tell us about the composition of Proterozoic marine systems? Unfortunately, small crystal sizes inhibit use of many traditional techniques in further examining microspar origins. I propose a multidisciplinary approach wherein high-resolution CL and SEM imaging will be used to define morphologic endmembers, reconstruct crystal size distributions, and interpret nucleation and growth mechanisms; laser-Raman spectroscopy will be used to document lattice structure to help constrain mineralogical change; and combined high-resolution SIMS trace element imaging, Raman spectroscopy, and crystal growth experiments will be used to constrain initial fluid compositions and precipitation conditions. Ultimately, deciphering the genesis of MT microspar will help identify chemical environments of formation and will aid in understanding the sedimentary impact of long-term chemical changes in the Earth.s biosphere. Broader Impacts: This project aims to advance discovery and understanding while promoting teaching, training, and learning by expanding the breadth of carbonate-based research at the University of Tennessee, adding research opportunities for undergraduate students, involving students directly in the process of scientific inquiry, encouraging scientific activity in which undergraduates will assist and be mentored by graduate students and faculty, and encouraging student participation in regional and national meetings. Currently, I have 3 students lined up for this project [1 M.S. (male) and 2 B.S. (female); 2 of them non-traditional students returning to school after starting families]. This project will also enhance the research and education infrastructure at the UT by supporting initiatives to expand use of multi-user facilities and establish interdisciplinary collaboration within the University (Geology-Chemistry) and with Oak Ridge National Labs. Finally, the project aims to broaden participation of under-represented groups through continued research- and equipment-based collaboration with the State University of West Georgia, a non-Ph.D. granting institution. Such collaboration raises student awareness of opportunities in the Earth Sciences and strengthens UT.s ability to attract new graduate students.