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

地球地幔的氧化状态，表示为氧逸度（fO2），是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如何在横向和纵向上变化，对于理解全球挥发循环和地幔-地壳域（如长寿命的克拉通块体）的物理稳定性非常重要。太古宙克拉通地幔在矿物学和地球化学肥力方面经常被观察到分层，反映了克拉通化之前、期间和之后的成分和构造演化。氧化态的垂直变化也可以与这种分层相关联，尽管经常观察到由交代活动引起的套印。通过这种方式，通过交代作用的氧化会导致钻石局部不稳定。这种变化已经在奴拉通（加拿大西北部）中得到了很好的记录，但目前还没有关于邻近的Rae克拉通块体的氧化还原数据，该克拉通块体直接位于东部，并在1.97 Ga以前与奴拉通碰撞。本研究的目的是确定Rae克拉通下地幔岩石圈的氧化状态，建立一个随深度的氧化还原剖面。将对萨默塞特岛的一套橄榄岩捕虏体进行研究。石榴石中的Fe3+/Fetot将通过Mössbauer光谱测定，并结合石榴石、橄榄石、正辉石和斜辉石的主要元素分析来计算fO2。还将测量石榴石和斜辉石的微量元素浓度，以检查可能的交代相互作用。结果将用于评估深度的挥发性形态和钻石稳定性/不稳定性的潜力。此外，研究结果将与邻近的奴隶克拉通的已发表数据进行比较，以揭示两个克拉通块体的演化差异。

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.