Collaborative Research: Mass Independent Fractionation of Sulfur Isotopes, Re-Os Dating of Sedimentary Pyrite, and the Composition of the Late Archean Atmosphere

合作研究：硫同位素的质量独立分馏、沉积黄铁矿的铼锇测年以及晚太古代大气的组成

• 批准号: 0309197
• 负责人: Holly Stein
• 金额: $ 15万
• 依托单位: Colorado State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-08-01 至 2006-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0309197&HistoricalAwards=false
• 关键词: Collaborative; Research; Mass; Independent; Fractionation

ABSTRACTThe discovery of mass independent fraction (MIF) of the sulfur isotopes in pre-2.45 Ga sulfides and sulfates opened a new window on the chemical evolution of the atmosphere-ocean system. At present, the MIF data for sulfur in Archean sediments are few and contradictory. We propose to undertake a thorough study of the MIF of sulfur in pyrite for three pairs of highly carbonaceous sedimentary rock units deposited between 2.7 and 2.5 Ga in Western Australia, South Africa, and Canada. Pyrite will be selected for this study on the basis of textural, chemical, and isotopic evidence indicative of a syngenetic or diagenetic origin. Pyrite in each of the six rock units will be dated by the Re-Os method. Preliminary data show that it is possible to determine the age of 2.3 Ga sedimentary pyrites with a precision of 1 m.y. Initial 187Os/ 188Os ratios inferred from the pyrite isochrons will provide information on secular variations in the Os isotopic composition of seawater, which probably reflects changes in oxidative weathering and transport of Os from the continents. The dating of Archean sedimentary pyrite can therefore yield important information regarding Os cycling.The MIF measurements will be made on the MAT 253 mass spectrometer at the Geophysical Laboratory in Washington, D.C, using laser fluorination and continuous flow inlet technology. The Re-Os dating will be done at the AIRIE laboratory at Colorado State University (CSU) using Carius tube dissolution and negative thermal ionization mass spectrometry. Sample preparation, microscopy and trace element analyses will be done at Harvard University.We expect that our data will demonstrate to what extent local conditions determined the MIF of the sulfur isotopes in these rock units, to what extent global differences were important, and to what extent global differences reflected changes in the composition of the atmosphere during the last 200 Ma of the Archean.Broader Impacts CriterionThe project will promote training and learning through involvement of students at all levels (postdoctoral, graduate, undergraduate, and high school) with at least the younger students drawn from underrepresented groups. All will be engaged in application of state-of-the-art techniques, and will be encouraged to present their findings at professional meetings. New collaborations are established through this project between Harvard University and CSU, among researchers on three continents, and across geologic sub-disciplines. Dissemination of results will reach beyond immediate research communities, as the Harvard group reports to NASA through participation on the Astrobiology Team, and the AIRIE Program at CSU is based on international collaboration, and transfers new techniques and concepts quickly to applications of direct use in mineral exploration.

前驱2.45Ga硫化物和硫酸盐中硫同位素质量独立分数(MIF)的发现为研究大气-海洋系统的化学演化开辟了新的窗口。目前，太古宙沉积物中硫的MIF数据很少，而且相互矛盾。我们建议对西澳大利亚、南非和加拿大三个沉积于2.7~2.5Ga之间的高碳质沉积岩单元的黄铁矿中硫的MIF进行深入的研究。根据同生或成岩成因的结构、化学和同位素证据，黄铁矿将被选作本次研究的基础。六个岩石单元中的黄铁矿将用Re-Os法测定年龄。初步数据表明，确定2.3Ga沉积黄铁矿的年龄是可能的，其精度为1m.y。根据黄铁矿等时线推断的187Os/188Os初始比值将提供海水中Os同位素组成的长期变化信息，这可能反映了来自大陆的Os的氧化风化和迁移的变化。因此，太古宙沉积黄铁矿的测年可以提供有关Os循环的重要信息。MIF测量将在华盛顿特区地球物理实验室的MAT 253质谱仪上进行，使用激光氟化和连续流动进样技术。Re-Os测年将在科罗拉多州立大学(CSU)的AIRIE实验室使用Carius管溶解和负热电离质谱仪进行。样品制备、显微镜和微量元素分析将在哈佛大学进行。我们预计我们的数据将在多大程度上决定这些岩石单元中硫同位素的MIF，全球差异在多大程度上是重要的，以及全球差异在多大程度上反映了太古宙最后200 Ma期间大气成分的变化。广泛影响准则该项目将通过各级学生(博士后、研究生、本科生和高中学生)的参与促进培训和学习，至少有来自代表性不足群体的年轻学生。所有人都将致力于应用最先进的技术，并将被鼓励在专业会议上展示他们的发现。通过这个项目，哈佛大学和CSU之间、三大洲的研究人员之间以及地质子学科之间建立了新的合作关系。成果的传播将超越直接的研究社区，因为哈佛小组通过参与天体生物学团队向NASA报告，CSU的AIRIE计划基于国际合作，并迅速将新技术和概念转移到直接用于矿产勘探的应用中。