Melt-Rock and Fluid-Rock Reaction in the Petrogenesis of Archean Subcontinental Mantle

太古代次陆幔岩石成因中的熔岩和流体岩石反应

• 批准号: 0310330
• 负责人: David Bell
• 金额: $ 10.28万
• 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: 2003-08-01 至 2005-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0310330&HistoricalAwards=false
• 关键词: Melt; Rock; Fluid; Reaction; Petrogenesis

EAR-0310330BellArchean subcontinental mantle is commonly enriched in Si with respect to other regions of the upper mantle and is also the virtually exclusive source of natural diamond. It has been proposed that both these phenomena are the result of metasomatism, yet the nature and origins of the metasomatic agents and the details of their reaction with the mantle lithosphere remain poorly understood. The proposed research will attempt to quantify the chemical and mineralogical reactions accompanying the deposition of Si and C into Archean mantle peridotite and constrain the compositions, origin and timing of the metasomatic fluids.The specific objectives of this work are to determine the spatial variations in chemical composition of veined harzburgites and to characterize the mineralogy, texture and chemical features of carbonaceous harzburgite xenoliths. These results will be used to calculate the stoichiometry of chemical reactions producing enstatite-rich veins in subcalcic garnet harzburgite, to assess the petrologic context of carbon deposition in refractory harzburgite, and to test the hypotheses that the two processes are genetically related and responsible for metasomatism on a craton-wide scale. The problem will be approached by the analysis of mantle xenolith samples from the Bultfontein kimberlite, Kimberley, South Africa. These include refractory harzburgites selected for their lack of evidence of Mesozoic overprinting and unusual veined examples interpreted as persuasive textural evidence for fluid reaction. Mineral major and trace element compositions will be determined by EMP and LA-ICP-MS analysis and bulk compositions calculated from chemical maps of large thin sections. Compositions of added components will be determined by digital spatial analysis of chemical maps of veined samples. Mineralogical evidence for carbonate will be examined using EMP, SEM, XRD and TEM. Abundance and distribution of diamond in subcalcic garnet harzburgite will be evaluated by X-ray tomography. A young age for diamond-forming metasomatism will be tested by examining garnet for trace element heterogeneity. Protolith ages will be constrained using Re-Os isotope analysis and source of metasomatizing fluids by mineral trace element, and Sr and Nd isotope compositions. Quantifying metasomatic effects allows a clearer window into the history of Archean mantle and an increased understanding of petrogenesis that is the key to continent stabilization in the early Earth. It is anticipated that the results of this study will have important implications for the Archean craton formation and evolution, mechanisms of volatile and trace element storage and transport in the mantle, and the evolution of the global carbon cycle.

与上地幔其他区域相比，贝尔太古代陆下地幔普遍富集Si，也是天然金刚石的唯一来源。 有人提出，这两种现象是交代作用的结果，但交代剂的性质和起源以及它们与地幔岩石圈反应的细节仍然知之甚少。 该研究将试图量化硅和碳沉积到太古代地幔橄榄岩中的化学和矿物学反应，并限制交代流体的成分、来源和时间，这项工作的具体目标是确定脉状方辉橄榄岩化学成分的空间变化，并表征碳质方辉橄榄岩捕虏体的矿物学、结构和化学特征。 这些结果将被用来计算化学反应的化学计量产生顽火辉石丰富的静脉在亚钙石榴石辉橄榄岩，评估碳沉积在耐火辉橄榄岩的岩石学背景下，并测试的假设，这两个过程是遗传相关的，并负责交代在一个广泛的规模。 这个问题将通过对南非金伯利布尔方丹金伯利岩地幔捕虏体样品的分析来解决。 这些包括耐火方辉橄榄岩选择他们缺乏证据的中生代叠印和不寻常的脉的例子解释为有说服力的纹理证据的流体反应。矿物主要和微量元素的组成将通过EMP和LA-ICP-MS分析确定，并从大薄片的化学图计算整体组成。 通过脉状样品化学图谱的数字空间分析确定添加成分的组成。 碳酸盐的矿物学证据将使用EMP、SEM、XRD和TEM进行检查。本文用X射线层析法评价了亚钙榴辉岩中金刚石的产状和分布。 一个年轻的年龄钻石形成交代将测试通过检查石榴石的微量元素的异质性。用Re-Os同位素分析确定原岩年龄，用矿物微量元素和Sr、Nd同位素组成确定交代流体的来源。 量化交代作用可以更清楚地了解太古代地幔的历史，并增加对岩石成因的理解，这是早期地球大陆稳定的关键。 研究结果对太古代克拉通的形成与演化、地幔中挥发性元素和微量元素的储存与迁移机制以及全球碳循环的演化具有重要意义。