Testing the Slushball Earth Model for the Paleoproterozoic Glacaiations in Uniquely 18-O Depleted Rocks from Karelia, Russia

这个项目是由最近在俄罗斯卡累利阿Belomorian带的古元古代变质岩中发现的极端氧（-26 / mil）和氢（-233 / mil）同位素耗竭引发的，这是迄今为止世界上发现的最低值。该项目要求供资，以扩大一项初步研究，证明这些枯竭的比率存在于一个大的地理区域（200多公里长，几十公里宽）。目前有待验证的假设是，这些岩石的低同位素值是通过24亿年前存在于裂谷带的高温水岩相互作用而继承下来的。氧和氢的稳定同位素组成小于0 / mil（相对于同位素标准SMOW）只存在于经历瑞利蒸发-降水循环的大气水中，这种负同位素值是极地冰的特征。目前的古地理和古地磁模型表明，卡累利阿在整个古元古代都位于赤道附近，如此低的同位素比率与它们形成于古元古代第一次已知的冰期的解释一致。为了通过蒸汽蒸馏实现这种同位素消耗，水/海洋的液体储存库必须保持不冻结状态。这个所谓的“泥球地球”模型与更普遍接受的雪球地球模型形成对比，雪球地球模型认为地球表面没有未冻的水。对泥球地球的气候稳定性和反照率效应进行了讨论和质疑。目前的气候模式显示，如果高纬度地区2/3的地表被冻结，失控效应将导致一个坚硬的雪球地球。如果卡累利阿岩石的这种耗尽的稳定同位素组成可以被证明是广泛的，它可能表明在冰期期间，水文气象水循环一定在运作，从而作为泥球地球气候模式稳定性的第一个物质证据。该项目的范围将包括对异常衰竭区进行进一步的表征和同位素绘制，结合原位同位素和地质年代学方法确定氧同位素衰竭的时间，以及对样品进行实地和微量元素调查以确定其原岩，并与Fennoscandia的低变质等级、早古元古代Sariolian和Sumian沉积序列进行地质年代学和地球化学对比。该提案将探索在大气氧气上升之前或期间发生的极端气候条件和原始生命形式的多样化。该项目将促进国际合作，吸引和支持传统上在地球科学领域代表性不足的学生，让本科生和社区学院的学生参与研究，并让他们接触科学和国际合作，并支持俄勒冈大学稳定同位素实验室的分析基础设施。

This project is triggered by the recent discovery of extreme oxygen (-26 per mil) and hydrogen (-233 per mil) isotope depletion for Paleoproterozoic metamorphic rocks in the Belomorian Belt in Karelia, Russia that represent the world's lowest values found so far. This project requests funding to extend a preliminary study that demonstrates that these depleted ratios are present in a large geographical area (over 200 km long and several tens of kilometers wide). The current hypothesis to be tested is that these rocks inherited their low isotopic values through high-temperature water-rock interaction in rift zone that existed 2.4 billion years ago. Oxygen and hydrogen stable isotope compositions of less than 0 per mil (relative to the isotopic standard SMOW) exist only in meteoric water that went through the Rayleigh evaporation-precipitation cycle, and such negative isotopic values are characteristic of ice from polar regions. Current paleogeographic and paleomagnetic models suggest that Karelia was located near the equator throughout the Paleoproterozoic, and such low isotopic ratios are consistent with an interpretation that they formed during the first known panglacial episode in the Paleoproterozoic. In order to achieve such isotopic depletion through vapor distillation a liquid reservoir of water/oceans must remain unfrozen. This so-called 'Slushball Earth' model contrasts with the more commonly accepted Snowball Earth model where no unfrozen water remains on the surface of the planet. The climate stability and the albedo effects of a Slushball Earth have been discussed and questioned. Current climate models suggest that if 2/3 of the high latitude surface is frozen, the runaway effect will lead to a hard Snowball Earth outcome. If this depleted stable isotope composition of the Karelian rocks can be shown to be extensive, it may signify that the hydrologic meteoric water cycle must be in operation during the panglacial episodes, thus serving as the first material evidence of the stability of the Slushball Earth climate model. The scope of this project will include further characterization and isotopic mapping of the anomalously depleted area, determination of the time of oxygen isotope depletion via combination of in situ isotopic and geochronologic methods, as well as field and trace element investigation of samples to identify their protolith, and geochronologic and geochemical correlation with the lower metamorphic grade, early Paleoproterozoic Sariolian, and Sumian sedimentary sequences in the Fennoscandia. The proposal will explore extreme climate condition happening just before or during the rise of atmospheric oxygen and diversification of primitive life forms. This project will promote international collaboration, involve and support students traditionally underrepresented in geosciences, involve undergraduate and community college students in research and expose them to science and international collaboration, and support the analytical infrastructure of the stable isotope lab at the University of Oregon.