Widespread Layered Pyroxenites in the Earth's Mantle

地幔主要由橄榄岩组成，橄榄岩是镁和铁硅酸盐岩石，通常含有5%至10%的体积非均质性。这些非均质性在组成上可能变化很大，但富含辉石岩的岩石，特别是韦氏岩（在硅酸盐晶体结构中含有额外的钙、钠和铝的岩石）似乎是与地球上出土的橄榄岩相关的主要非均质性类型。年代的表面。到目前为止，还没有研究解释这种非均质性为何以及如何在地幔岩石中如此普遍。重要的是，这可能表明一个普遍存在的过程正在显著地改变地幔及其衍生熔岩的组成。将进行一项多学科研究，其中将结合现场观测、地球化学和岩石物理分析从两个地点选定的韦氏岩：Lherz地块（FR）和Josephine橄榄岩（美国），这两个地点被认为分别代表次大陆和次弧地幔。痕量元素和主要元素的变化将被测量和建模，以便约束导致地幔非均质性形成的过程。此外，通过测量矿物晶格偏好取向的小尺度变化，将限制韦氏体就位的地球动力学条件。这项研究的结果将使广泛的科学家群体受益，因为它的多学科方法可以调和地幔地球化学家、流变学实验家和地球物理学家感兴趣的观测结果。地幔约占地球体积的80%，位于地壳下方，深度约为30公里至2900公里。地球的大部分热和化学变化是由地幔控制的，地幔在局部融化，并引起了地球表面可见的大部分火山活动。为了更好地预测火山灾害，限制什么类型的物质在深处融化是至关重要的，因为熔岩的成分会影响火山喷发的爆炸性。为了回答这个问题，地幔的组成应该得到很好的约束。地幔岩石在地球上的暴露？S表面是罕见的，但我们可以获得访问，我们发现其组成的许多方面仍然不确定。我们知道，地球的地幔在组成上是不均匀的，它含有非均质性，然而，这些非均质性的性质和分布却很少受到限制。例如，可能有地壳物质的斑点，在地球深处通过板块构造循环。该项目将重点关注这些异质性形成的基本过程。

The Earth's mantle is primarily composed of peridotites, which are magnesium and iron silicate rocks that often contain 5 to 10% heterogeneities by volume. These heterogeneities can be very variable in composition but pyroxene-rich rocks, and in particular websterites (those that have additional calcium, sodium and aluminum in the silicate crystal structure) appear to be the dominant type of heterogeneity associated with peridotites exhumed at the Earth?s surface. No study has so far explained why and how this type of heterogeneity is so widespread in mantle rocks. Importantly, it might be an indication that a ubiquitous process is significantly modifying the composition of the mantle and its derived lavas. A multidisciplinary study will be conducted, which will combine field observations, geochemical and petrophysical analyses of selected websterites from two locations: the Lherz Massif (FR) and the Josephine Peridotite (USA), that are believed to represent subcontinental and subarc mantle, respectively. Trace and major element variations will be measured and modeled in order to constrain the process(es) responsible for the formation of heterogeneities in the mantle. Additionally geodynamical conditions of emplacement of the websterites will be constrained by measuring small-scale variations of lattice-preferred orientations of minerals. The results of this study will benefit a broad community of scientists due to its multidisciplinary approach that can reconcile observations of interest for mantle geochemists, rheology experimentalists and geophysicists.The mantle represents about 80% of the volume of our planet, lying underneath the crust between approximately 30 km and 2900 km depth. A large part of the thermal and chemical variations of the Earth is controlled by the mantle, which locally melts and gives rise to most of the volcanic activity visible at the surface of the planet. In order to better predict volcanic hazards, it is fundamental to constrain what type of material is melting at depth, because the composition of the lava affects the explosivity of volcanic eruptions. In order to answer this question, the composition of the mantle should be well constrained. Exposures of mantle rock at the Earth?s surface are rare but where we can obtain access, we find that many aspects of its composition remain uncertain. We know that the Earth's mantle is not uniform in composition and that it contains heterogeneities, however the nature and the distribution of these heterogeneities are poorly constrained. For instance, there could be blobs of crustal material, recycled in the deep Earth by plate tectonics. This project will focus on the fundamental processes responsible for the formation of these heterogeneities.