Oxidation state of the lithospheric mantle beneath Somerset Island, Rae Craton, Canada as a function of depth and its relation to metasomatism

加拿大雷伊克拉通萨默塞特岛下方岩石圈地幔的氧化状态与深度的关系及其与交代作用的关系

• 批准号: 393808454
• 负责人: Professor Dr. Alan Butler Woodland
• 金额: --
• 依托单位: Department of Earth and Atmospheric Sciences
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/393808454?language=en
• 关键词: Oxidation; state; lithospheric; mantle; beneath

The oxidation state of the Earths mantle, expressed as oxygen fugacity (fO2), is a fundamental parameter along with pressure and temperature that influences many geochemical and geophysical processes. For example, knowing how mantle fO2 varies both laterally and vertically is important for understanding global volatile cycles and the physical stability of mantle-crust domains, such as long-lived cratonic masses. Archean-age cratonic mantle is often observed to be stratified in terms of mineralogy and geochemical fertility, which reflects its compositional and tectonic evolution before, during and after cratonisation. Vertical variations in oxidation state can also be correlated with this stratification, although overprinting by metasomatic activity is often observed. In this way, oxidation through metasomatism can cause diamond to become locally unstable. Such variations have been well documented for the Slave craton (NW Canada), but no redox data are currently available for the neighboring Rae cratonic block that lies directly to the east and collided with the Slave 1.97 Ga ago. The aim of this study is to determine the oxidation state of the mantle lithosphere beneath the Rae craton, establishing a redox profile with depth. A suite of peridotite xenoliths from Somerset Island will be investigated. Fe3+/Fetot in garnet will be determined by Mössbauer spectroscopy and combined with major element analyses of garnet, olivine, orthopyroxene and clinopyroxene to compute fO2. Trace element concentrations of garnet and clinopyroxene will also be measured to check for possible metasomatic interactions. Results will be used to assess volatile speciation at depth and the potential for diamond stability/instability. In addition, results will be compared with published data for the neighboring Slave craton, to reveal differences in the evolution of the two cratonic blocks.

地幔的氧化态，用氧逸度（fO 2）表示，是影响地球化学和地球物理过程的一个基本参数，沿着压力和温度。例如，了解地幔fO 2在横向和垂直方向上的变化对于理解全球挥发性循环和幔壳域的物理稳定性（如长寿的地幔质量）非常重要。太古代地幔在矿物学和地球化学丰度方面具有明显的分层性，反映了地幔在变质作用前、变质作用中和变质作用后的成分和构造演化。氧化态的垂直变化也与这种分层有关，尽管经常观察到交代活动的叠印。通过这种方式，通过交代作用的氧化可以导致金刚石变得局部不稳定。这样的变化已经很好地记录了奴隶克拉通（加拿大西北部），但没有氧化还原数据，目前可用于邻近的雷克拉通块，直接位于东部，并与奴隶碰撞1.97 Ga前。本研究的目的是确定Rae克拉通下的地幔岩石圈的氧化状态，建立一个氧化还原剖面与深度。研究了萨默塞特岛的一套橄榄岩捕虏体。利用穆斯堡尔谱学测定石榴石中的Fe 3 +/Fetot，并结合石榴石、橄榄石、斜方辉石和单斜辉石的主量元素分析计算fO 2。还将测量石榴石和单斜辉石的微量元素浓度，以检查可能的交代作用。研究结果将用于评估深层挥发性物质形态以及钻石稳定性/不稳定性的可能性。此外，结果将与相邻的奴隶克拉通公布的数据进行比较，以揭示两个板块的演化差异。