Intracrystalline Boron Isotope Fractionation in Illite/Smectite: A Potential Geothermometer and Paleo-Fluid indicator r

伊利石/蒙脱石中的晶内硼同位素分馏：潜在的地温计和古流体指示剂

• 批准号: 0229583
• 负责人: Lynda Williams
• 金额: --
• 依托单位: Arizona State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-01-01 至 2007-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0229583&HistoricalAwards=false
• 关键词: Intracrystalline; Boron; Isotope; Fractionation; Illite

Intra-crystalline Boron Isotope Fractionation in Illite/SmectiteBoron is found in two different crystallographic sites of the 2:1 clay minerals illite/smectite. Boron is present in the interlayers of these clay minerals and also substitutes in the tetrahedral layers. Our pilot study (NSF SGER #0108852) developed a technique to analyze the boron isotopic ratio in these two sites, and we found that in natural samples the difference in the B-isotope ratios between each crystallographic site can be as high as 40. The present work is to study the factors that affect intra-crystalline B isotope variations. These results have the potential to provide a major advance in our understanding of clay mineral diagenesis and may also be a useful low temperature geothermometer. The research combines two different approaches: the synthesis of illite/smectite under carefully controlled conditions of temperature, pressure, and fluid composition and the analysis of natural samples from well-characterized localities.Our experimental work will react a variety of smectites to illite in the presence of fluids with different aqueous d11B starting compositions. In order to test the B selectivity for tetrahedral sites, we will examine beidellite and montmorillonite compositions and di- and tri-octahedral clays to determine the effect of octahedral cation exchange relative to tetrahedral cation exchange on the d11Bint compositions. Isotope equilibration of I/S phases can be tested in experimental samples by changing the fluid d11B during reaction progress.It is critical to compare the experimental work to natural I/S undergoing illitization in different hydrothermal regimes. The mechanisms of illitization may be different for closed (mudstone or bentonite) versus open (sandstone or geothermal) systems. We need to test the dependence of the intracrystalline d11B variations in different thermal regimes and varying the fluid/rock ratio. To do this we propose to study samples from a bentonite (closed system), a rapidly buried shale versus slowly buried mudstones and geothermal samples from 180-400C (open system). The geothermal system holds the most promise for finding fluids and natural I/S in equilibrium.The combined experiments and analysis of natural samples will allow us to assess the role of fluid composition, mineral composition, temperature, temperature gradient, and fluid/rock ratios on the composition of B in the interlayers and tetrahedral layers of I/S. This new research will produce important information relating to the illitization process and may prove the potential for a novel low-temperature geothermometer.

在2：1粘土矿物Illite/entectite的两个不同的晶体学位点发现，在伊利特/蒙蒂特堡的晶体内同位素分馏。这些粘土矿物的层中存在硼，也存在于四面体层中的替代物。我们的试点研究（NSF SGER＃0108852）开发了一种分析这两个地点的硼同位素比率的技术，我们发现，在自然样品中，每个晶体学位点之间的B-同位素比率的差异可以高达40。目前的工作是研究影响内晶型Brysstalline b iSotope variatiations的因素。这些结果有可能在我们对粘土矿物质成岩作用的理解方面提供重大进展，并且也可能是有用的低温地球计。该研究结合了两种不同的方法：在仔细控制的温度，压力和流体组成条件下，伊利石/蒙蒂特的合成以及来自特征良好的地方的天然样品的分析。我们的实验性工作将在具有不同水性D11b的流体的情况下对各种晶状体作出反应，以对伊利特做出反应。为了测试四面体位点的B选择性，我们将检查贝德莱特和蒙脱石组成以及二甲状腺面体粘土，以确定相对于四面体阳离子交换对D11BINT组成的八面体阳离子交换的影响。可以通过在反应进度期间改变流体D11B来测试I/S相的同位素平衡。将实验工作与不同热液状态下的自然I/S进行了虚拟化至关重要。对于封闭的（泥岩或膨润土）而言，私密的机制可能不同于开放（砂岩或地热）系统。我们需要测试不同热疗法中晶体内D11b变化的依赖性，并改变流体/岩石比。为此，我们建议研究膨润土（封闭系统）的样品，迅速掩埋的页岩与缓慢掩埋的泥岩和180-400C的地热样品（开放系统）。地热系统是在平衡中找到液体和天然I/S的最有希望的人。对天然样品的合并实验和分析将使我们能够评估流体组成，矿物质组成，温度梯度，温度梯度以及流体/岩石比率对B组组成的室内层和I/S层中B组成的作用。这项新研究将产生与文明过程有关的重要信息，并可能证明具有新型低温地热计的潜力。