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

项目概要智力优点：臼齿（MT）是一种神秘的碳酸盐岩组构，其特征是各种形状的空隙填充有均匀的等长微晶石。迄今为止，研究主要集中在解释空洞的形成机制和描绘MT的时空分布。然而，MT保存与MT微晶石沉淀密切相关，我们对此知之甚少。MT微晶石由均匀的、等长的、非联锁的晶体组成，在阴极发光（CL）下显示暗发光的、亚球形核（直径5-7 m）和发光的过度生长。有利于沉淀的条件在中元古代和新元古代早期（1600-750 Ma）很常见，其中MT微晶石包括90%的个体层和5-25%的保存碳酸盐（体积相当于古生代骨骼颗粒）。该项目的目的是调查一种不寻常的，但体积显着，碳酸盐的形态，称为臼齿（MT）微晶石，其广泛存在于中元古代和新元古代早期的碳酸盐沉淀和海洋环境的大规模地球化学演化之间的联系。本研究提出三个问题：（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)球文石是这种微晶石的原始矿物学吗？（3）这种不寻常的碳酸盐形态能告诉我们元古宙海洋系统的组成是什么？ 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来源。我提出了一个多学科的方法，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，以帮助限制矿物学变化;以及结合高分辨率西姆斯痕量元素成像，拉曼光谱，晶体生长实验将用于限制初始流体成分和沉淀条件。最终，破译MT微晶石的成因将有助于确定形成的化学环境，并有助于了解地球生物圈长期化学变化的沉积影响。 更广泛的影响： 该项目旨在推进发现和理解，同时促进教学，培训和学习，通过扩大田纳西大学碳酸盐基研究的广度，为本科生增加研究机会，让学生直接参与科学探究过程，鼓励本科生协助研究生和教师指导的科学活动，并鼓励学生参加区域和国家会议。目前，我有3名学生正在排队参加这个项目[1硕士（男）和2个学士学位。（女）;其中2人是在成家后返回学校的非传统学生]。该项目还将通过支持扩大多用户设施的使用并在大学内（地质化学）和橡树岭国家实验室建立跨学科合作的举措，加强UT的研究和教育基础设施。最后，该项目旨在通过继续与西格鲁吉亚州立大学（一所非博士学位学校）开展以研究和设备为基础的合作，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.