RUI: Raman Spectroscopy and Stable Isotope Investigations of Graphite in Marble

碳是一种独特的元素，构成了我们所知的生命的化学基础。当生物死亡时，它们的遗体通常会被氧化或消耗，从而在地球的大气圈、水圈和生物圈中循环。 在适当的条件下，一些有机质被捕获在沉积盆地中，从而在地壳和地幔中循环。 这种含碳材料具有许多显著的后果，例如包括煤、石油和天然气的沉积物。 但是，除了具有重要经济意义的化石燃料积累之外，地壳岩石中分散的小块有机物质的命运可以告诉我们许多关于古代沉积环境、生命历史和地壳环境中的地球化学过程的信息。 该项目将研究最终将沉积物中的含碳物质转化为矿物石墨的物理和化学过程。 这种转化称为石墨化，涉及碳的重组和其他元素的损失，并在变质过程中对热，压力和变形作出反应。 随着对这一过程认识的提高，我们将有能力利用碳质物质更好地约束地质事件的温度-压力-变形历史，并可能认识到原始沉积在古沉积物中的有机质的差异。本研究的目的是阐明变质温度与碳质物质（CM）和石墨的结构状态之间的关系，并将CM向石墨的转化与石墨和方解石之间的碳同位素交换相关联。 该项目将使用激光拉曼光谱来表征低品位到高品位大理石中的CM和石墨的结晶度，并首次与温度相关的方解石-石墨同位素分馏进行比较。 将严格评估拉曼分析技术和结果的再现性、样品内变异性、跨露头变异性、制备方法和退变质作用。 方解石和石墨之间的碳稳定同位素分馏是温度依赖性和有用的地质温度计在中角闪岩麻粒岩相大理石，然而，在较低温度的岩石中观察到的同位素分馏不同意理论上预期的分馏。 通过对不同粒级的石墨进行同位素研究和激光拉曼分析，将石墨粗化与同位素交换联系起来，揭示石墨中是否存在同位素分带。 将石墨的结构状态与碳同位素交换的程度进行比较，将有助于我们更好地理解同位素交换过程，并可能为揭示中低温岩石的热历史提供新的工具。

Carbon is a unique element, forming the chemical basis for life as we know it. When living things die, their remains are often oxidized or consumed and thereby recycled in the earth's atmosphere, hydrosphere, and biosphere. Under appropriate conditions, some organic matter is trapped in accumulating sedimentary basins, and thus, cycled through the earth's crust and mantle. This carbonaceous material has many significant consequences, such as comprising deposits of coal, petroleum and natural gas. But aside from economically important accumulations of fossil fuels, the fate of small, dispersed bits of organic matter in rocks of the earth's crust can tell us much about ancient sedimentary environments, the history of life, and geochemical processes that operate in crustal environments. This project will investigate the physical and chemical processes that ultimately convert carbonaceous material in sediment into the mineral graphite. This conversion, known as graphitization, involves reorganization of the carbon and loss of other elements, and occurs in response to heat, pressure and deformation during metamorphism. As our understanding of this process improves, so will our ability to use carbonaceous material to better constrain the temperature-pressure-deformation history of geological events, and also to possibly recognize differences in the organic matter originally deposited in ancient sediments.The objectives of this research are to clarify the relationship between metamorphic temperature and the structural state of carbonaceous material (CM) and graphite, and to correlate the conversion of CM to graphite with the exchange of carbon isotopes between graphite and calcite. This project will use laser Raman spectroscopy to characterize the crystallinity of CM and graphite in low- to high-grade marble and compare that for the first time with temperature dependent calcite-graphite isotopic fractionations. Raman analytical techniques and results will be critically evaluated for reproducibility, within-sample variability, across-outcrop variability, preparation methods, and retrograde metamorphism. The fractionation of stable isotopes of carbon between calcite and graphite is temperature dependent and useful as a geothermometer in middle amphibolite to granulite facies marble, however, the isotopic fractionations observed in lower temperature rocks do not agree with theoretically expected fractionations. Different size fractions of CM will be studied isotopically and by laser Raman to relate graphite coarsening with isotopic exchange, and will reveal whether or not prograde isotopic zoning exists in graphite. Comparing the structural state of graphite with the extent of the carbon isotope exchange will help us better understand the isotopic exchange processes and may lead to new tools for unraveling the thermal history of moderate- to low-temperature rocks.