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

地幔的氧化状态，用氧逸度(FO2)表示，是一个与压力和温度一起影响许多地球化学和地球物理过程的基本参数。例如，了解地幔fO2在横向和垂直方向上的变化对于了解全球挥发循环和地幔-壳域的物理稳定性非常重要，例如长期存在的克拉通质量块。太古宙克拉通地幔在矿物学和地球化学丰度方面经常被观察到是分层的，这反映了其在克拉通形成之前、期间和之后的成分和构造演化。氧化状态的垂直变化也可以与这种分层相关，尽管经常观察到交代活动造成的叠印。在这种情况下，通过交代作用进行的氧化会导致钻石在局部变得不稳定。这种变化在Slave Craton(加拿大西北部)已经有了很好的记录，但目前还没有关于邻近的Rae克拉通地块的氧化还原数据，该地块位于正东，并在1.97 Ga前与Slave 1.97 Ga相撞。这项研究的目的是确定Rae克拉通之下地幔岩石圈的氧化状态，建立随深度变化的氧化还原剖面。将对萨默塞特岛的一套橄榄岩包体进行调查。用穆斯堡尔光谱仪测定石榴石中的Fe3+/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fO2。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。结果将用于评估深层的挥发性形态和钻石稳定/不稳定的可能性。此外，结果将与邻近的奴隶克拉通的公开数据进行比较，以揭示这两个克拉通地块演化的差异。

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.