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.

EAR-0310330贝尔结构次大套相对于上地幔的其他区域通常富含Si，并且实际上也是自然钻石的独特来源。 已经提出，这两种现象都是交代主义的结果​​，但是分子剂的性质和起源以及它们与地幔岩石圈反应的细节仍然很少了解。 拟议的研究将试图量化Si和C沉积到大天堂底甲铁矿中的化学和矿物学反应，并限制分类液体的组成，起源和时间。这项工作的具体目的是确定Harzburgites和Harzburgite和化学特征的化学成分的空间变化。 这些结果将用于计算化学反应的化学计量法在亚钙化石榴石Harzburgite中产生富含Enstatite的静脉，以评估难治性Harzburgite中碳沉积的岩石学背景，并测试两个过程在基因上相关的假设是在遗传上相关的，并且负责在craton-scapon-scaperismissismissismismissismissismismississismismissismisp。 该问题将通过分析南非金伯利Bultfontein Kimberlite的地幔异种石样品的分析。 其中包括因缺乏中生代过度打印和异常的脉络示例而被选出的难治性的哈尔兹堡人，被解释为流体反应的有说服力的质地证据。矿物主要和痕量元素组成将通过EMP和LA-ICP-MS分析以及根据大薄切片的化学图计算出的大量组成来确定。 添加组件的组成将通过对脉络样品的化学图的数字空间分析来确定。 将使用EMP，SEM，XRD和TEM检查碳酸盐的矿物学证据。 X射线层析成像将评估钻石在亚钙石榴石哈尔茨堡石中的丰度和分布。 将通过检查石榴石是否有痕量元素异质性来测试钻石形成的化生年龄的年龄。原石年龄将使用Re-OS同位素分析和通过矿物质痕量元素和SR和ND同位素组成来限制流体的源。 量化的化学效应可以使更清晰的窗口进入大将幔的历史，并增加对石化的理解，这是地球早期大陆稳定的关键。 可以预料，这项研究的结果将对大将克拉顿的形成和进化，地幔中的挥发性和微量元素存储和运输的机制以及全球碳循环的演变具有重要意义。