Collaborative Research: Halogen and chlorine isotope behavior during metamorphism of metapelitic rocks

合作研究：变质岩变质作用过程中的卤素和氯同位素行为

• 批准号: 2321368
• 负责人: Jaime Barnes
• 金额: $ 6.53万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-09-01 至 2025-08-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2321368&HistoricalAwards=false
• 关键词: Collaborative; Research; Halogen; chlorine; isotope

Volatile elements are elements that volatilize (turn into a gas or vapor) at low temperatures. Examples of such elements include H, C, O, N, and many others. They are critically important in generating habitable conditions on Earth and in how they influence Earth’s dynamics -- particularly their rock-weakening effects. Despite their importance, we do not have a good understanding of how volatile elements are distributed between different portions of the Earth (e.g., atmosphere/ocean, crust, mantle), nor how this distribution may have changed over Earth history. Halogen elements (F, Cl, Br, I) are volatile elements that have been used to trace volatile cycling between Earth’s surface and its interior. Recent work has shown that the upper continental crust has a distinctive halogen concentration signature that was likely generated by near-surface weathering of rocks. This signature is similar to that seen in the upper mantle, potentially implicating recycling of weathered upper crustal rocks into the mantle. However, it is also possible that the signature is generated by volatile-element loss accompanying recrystallization of the sediments at the higher pressures and temperatures found in Earth’s interior (metamorphism). This project will quantify how halogens and chlorine isotopes behave during metamorphic dehydration of sedimentary rocks that started out as mud at Earth’s surface. Such rocks have high concentrations of water and other volatile elements that systematically decline as the rock is metamorphosed at higher and higher temperatures. These data will inform our understanding of how halogens (and, by implication volatile elements) are re-distributed within Earth. The project will support the research of a first-generation PhD student as well as two undergraduate researchers from groups historically excluded from Earth Science.Recent work showed that the upper continental crust is depleted in halogens relative to lithophile elements of similar incompatibility during mantle melting, which is likely due to volcanic degassing and perhaps some amount of chemical weathering at the time of crust formation. Interestingly, the crystalline upper continental crust has relative halogen abundances that are similar to those seen in upper mantle rocks and may suggest a role for UCC recycling in controlling mantle halogen budgets. A better understanding of halogen, including Cl isotope, behavior during metamorphism will allow determination of the degree that mantle halogen signatures are influenced by terrigenous sedimentary rock recycling. This project will fund a PhD researcher who will determine how halogen elements (F, Cl, Br, I) and chlorine isotopes behave during metamorphic dehydration of terrigenous sedimentary rocks. The researchers will analyze complete halogen concentrations (F, Cl, Br, I) in four well-characterized suites of metapelites: British Caledonian mudrocks; metapelites from the contact aureole of the Onawa pluton, Maine; Otago schists, New Zealand; and metapelites from the Ivrea Zone, Italy. These metapelites experienced sub-greenschist facies to granulite facies metamorphic conditions and will allow the researchers to determine if and when halogens are fractionated from one another during metamorphic dehydration reactions. Accompanying chlorine isotope and total organic carbon contents of the same rocks will allow them to evaluate the degree to which organic matter influences halogen abundances in metapelites and how metamorphism may change these signatures.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

挥发性元素是在低温下挥发（转化为气体或蒸气）的元素。此类元素的示例包括H，C，O，N和许多其他元素。它们对于在地球上产生可居住的条件以及如何影响地球动态（尤其是其岩石效果）至关重要。尽管它们的重要性，但我们对挥发性元件的分布方式没有很好的了解（例如，大气/海洋，外壳，地幔），也不了解这种分布在地球历史上如何改变。卤素元素（F，CL，BR，I）是挥发性元素，用于追踪地球表面与其内部之间的挥发性循环。最近的工作表明，上大陆壳具有独特的卤素浓度特征，可能是由岩石的近地表风化产生的。该签名类似于上地幔中看到的签名，可能是将风化的上层岩石融入地幔中的隐含回收。但是，签名也可能是通过挥发性元素损失而产生的，涉及在地球内部发现的较高压力和温度下重结晶（变质）。该项目将量化卤素和氯同位素在沉积岩石的变质脱水过程中的表现，这些岩石最初是地球表面的泥浆。这样的岩石具有高浓度的水和其他挥发性元素，由于岩石在较高的温度下变态而有系统地降低。这些数据将使我们对卤素（以及对挥发性元素的意义）如何在地球内重新分布。该项目将支持第一代博士学位学生的研究以及两名来自地球科学排除的群体的本科研究人员。骨骼的工作表明，相对于在甲板融化过程中相似不相容性的岩质元素，卤素中的上大陆壳被耗尽，这可能是由于在化学作品和化学量的造成的，这可能是由于在化学效果和化学量所致。有趣的是，晶体上大陆壳具有相对的卤素丰度，与上地幔岩石中看到的相似，并且可能暗示UCC回收在控制地幔卤素预算中起作用。对卤素的更好理解，包括CL同位素，变质过程中的行为将允许确定地幔卤素特征受到陆质沉积岩石回收影响的程度。该项目将资助博士研究人员，该博士研究人员将确定卤素元素（F，CL，BR，I）和氯同位素在陆质沉积岩的变质脱水过程中的表现。研究人员将在四个特征良好的Metapelites套件中分析完整的卤素浓度（F，Cl，Br，I）：英国喀里多尼亚式泥石岩；来自缅因州Onawa Pluton的Aureole的Metapelites；奥塔哥片岩，新西兰；和来自意大利伊夫里亚地区的代叶岩。这些Metapelites经历了颗粒状设施的变质器条件，将使研究人员能够在变质脱水反应期间确定和何时将卤素彼此分馏。伴随的氯同位素和同一岩石的总有机碳含量将使他们能够评估有机物影响到MetapeLites中的卤素滥用的程度，以及变质化可能如何改变这些签名。该奖项反映了NSF的法规任务，并认为通过基金会的知识优点和更广泛的criteria cripitia criperia criperia criperia criperia criperia criperia criperia criperia criperia criperia criperia均被视为珍贵。