Investigation of magnesium isotope fractionation during basalt weathering

玄武岩风化过程中镁同位素分馏的研究

• 批准号: 0922070
• 负责人: Louis Derry
• 金额: --
• 依托单位: Cornell University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-09-01 至 2013-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0922070&HistoricalAwards=false
• 关键词: Investigation; magnesium; isotope; fractionation; during

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). We propose a study of magnesium isotope variations produced by weathering processes and biogeochemical cycling in the surface environment of Hawaii. Recent work has demonstrated Mg isotopic variations among fresh rocks, soils, stream, spring and ground waters in silicatehosted watersheds, and between natural carbonates and water. Other recent experimental work has demonstrated Mg isotope fractionation during uptake by higher plants. However, the magnitudes, mechanisms, and even direction of Mg isotopic fractionation in the surface environment remain poorly constrained. We hypothesize that weathering related fractionation is a function of the type of secondary minerals produced. We will utilize a series of climate gradient sites at two locations in the Hawaiian Islands where significant changes in secondary mineral assemblages arise because of climatic variation. While all sites have similar basalt substrate lithology, dominant secondary minerals range from Mg-carbonates and halloysite at the dry Kohala sites, to allophane at wetter sites. In the SE Koolau Range, smectite gives way to halloysite and kaolinite with increasing rainfall. We will analyze rocks, soils and soil extracts, rain, stream and ground waters, and leaf tissues from these sites, to characterize 26Mg variations during basalt alteration and biogeochemical cycling. We will also synthesize clay minerals and measure 26Mg on reactant and product phases, to better constrain mineralogical controls on Mg isotope fractionation. The project will be carried out in close collaboration with Dr. Nathalie Vigier of the CRPG, Nancy, France, who has developed protocols for 26Mg analysis in these kinds of samples. Scientific merit: This project will provide critical data for understanding the mechanisms of Mg isotope fractionation in the surface environment, and so develop the use of this new tool to trace sources and pathways of Mg in weathering and biogeochemical processes. The cycle of Mg is closely linked to the cycles of carbon and silicon at multiple times scales, and is of first order importance. The project will be transformative in that it will enable the use of 26Mg as a new and powerful quantitative tool in studying biogeochemical cycles.Broader impacts: Previous studies of tracer systems at our sites in Hawaii have had substantial impact in the scientific community because of the value of Hawaii as a natural laboratory and model system, and we expect this to be similar. Secondly, we will develop a strong international collaboration with a promising young French researcher and her students, who are funded independently to work with us. We also will gain access for our students to state of the art MCICP- MS instrumentation not available in the US. US graduate students will visit French laboratories, and French students will visit our labs and Hawaiian field sites. Third, this project will interface closely with Cornell?s undergraduate field program in Hawaii. Students will interact with project researchers and work on aspects of this project while in Hawaii. We will sponsor at least two senior thesis projects associated with the project.

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。我们提出了一个镁同位素变化的研究所产生的风化过程和地球化学循环在夏威夷的表面环境。最近的工作表明，镁同位素之间的新鲜岩石，土壤，溪流，泉水和地下沃茨在硅酸盐托管流域，天然碳酸盐和水。其他最近的实验工作表明镁同位素分馏过程中吸收的高等植物。然而，在地表环境中镁同位素分馏的幅度，机制，甚至方向仍然缺乏约束。我们假设风化相关的分馏是一个功能的类型次生矿物产生。我们将利用一系列的气候梯度网站在两个地点在夏威夷群岛的次生矿物组合出现显着变化，因为气候变化。虽然所有网站有类似的玄武岩基底岩性，占主导地位的次生矿物范围从镁碳酸盐和埃洛石在干燥的Kohala网站，水铝英石在潮湿的网站。在东南部的库劳山脉，随着降雨量的增加，蒙皂石让位于埃洛石和高岭石。我们将分析岩石，土壤和土壤提取物，雨水，溪流和地下沃茨，以及这些网站的叶组织，以表征26镁变化玄武岩蚀变和地球化学循环。我们还将合成粘土矿物，并测量反应物和产物相的26 Mg，以更好地约束Mg同位素分馏的矿物学控制。该项目将与法国南希CRPG的Nathalie Vigier博士密切合作进行，他已经制定了这些样品中26 Mg分析的协议。科学价值：该项目将为了解地表环境中Mg同位素分馏机制提供关键数据，并开发使用这一新工具来追踪风化和地球化学过程中Mg的来源和途径。Mg的循环在多个时间尺度上与碳和硅的循环密切相关，并且具有一级重要性。该项目将是变革性的，因为它将使使用26镁作为一个新的和强大的定量工具，在研究地球化学cycles.Broader影响：以前的研究在我们的网站在夏威夷的示踪剂系统在科学界产生了重大影响，因为夏威夷作为一个自然的实验室和模型系统的价值，我们希望这是类似的。第二，我们将与一位有前途的法国年轻研究人员及其学生开展强有力的国际合作，他们独立获得资助与我们合作。我们还将为我们的学生获得最先进的MCICP- MS仪器在美国不可用。美国研究生将参观法国实验室，法国学生将参观我们的实验室和夏威夷实地考察。第三，这个项目将与康奈尔大学密切合作？在夏威夷的本科实习项目。学生们将与项目研究人员互动，并在夏威夷从事该项目的各个方面。我们将赞助至少两个与该项目相关的高级论文项目。