The Fingerprint of Water in Mantle Melting

知识的优点。本项目旨在研究水和含水熔体在约瑟芬橄榄岩（俄勒冈州西南部）融化过程中的作用。该体由辉橄榄岩（5%斜辉石）和辉石（5%斜辉石）岩石组成，解释为地幔熔融的残留物：首先在干燥条件下的海洋脊上产生了局部的websterite分层，然后在潮湿的含水熔融环境中使残留物达到了深海橄榄岩套中所没有的极端消耗。这表现在其矿物组成范围广泛，既包括来自洋中脊的深海橄榄岩，也包括被认为形成于超俯冲带环境的蛇绿岩橄榄岩。第二阶段的熔融是由于下沉的海洋岩石圈板块将水和/或含水熔体引入地幔楔体，从而降低了地幔的熔点，使其远远超出了限制海洋脊下熔融的Cpx-out阶段边界。山脊岩浆活动可以归因于几乎干燥的地幔的绝热上涌和熔融，而弧相关的火山活动则涉及将挥发物和含水熔体引入地幔，从而引起含水（或“通量”）重熔。在与弧有关的岩浆的形成过程中，板块成因和地幔楔块组分的相对作用一直争论不休。大多数研究通过反演弧相关熔岩的同位素和微量元素组成来限制岩浆过程。这种方法受到熔体生成过程的复杂性的阻碍，这可能涉及到迁移熔体与上覆地幔之间的相互作用，以及通过弧壳的运输和与弧壳的相互作用。约瑟芬橄榄岩提供了直接研究和限制水和含水熔体是如何被引入、相互作用和通过亚弧地幔运输的机会，以及这是如何影响熔体化学的。提出了一项综合主微量元素全岩和矿物研究，以记录约瑟芬橄榄岩地块的组成如何受到挥发物和含水熔体的影响，以及这种影响是局部的还是普遍的。更广泛的影响：该项目直接关系到了解挥发物在与弧相关的岩浆活动中的作用——由于弧火山活动的爆炸性，这是一个广泛关注和重大社会影响的主题。此外，该项目还将资助一名博士生。

Intellectual Merits. This project seeks to study the role of water and hydrous melt in melting of the Josephine Peridotite (SW Oregon). This body comprises lherzolite (5% clinopyroxene) and harzburgite (5% clinopyroxene) rocks interpreted to the residue of mantle melting: first at an ocean ridge under dry conditions that produced local websterite layering, and then in a wet hydrous melting environment that drove the residue to extreme depletions not seen in abyssal peridotite suites. This is expressed by a wide range in mineral composition spanning that for both abyssal peridotites from mid-ocean ridges, and for ophiolite peridotites believed formed in supra-subduction zone environments. A second stage of melting is attributed to introduction of water and/or hydrous melt from a down-going ocean lithosphere slab into the mantle wedge - lowering the mantle melting point and allowing it to proceed well beyond the Cpx-out phase boundary that limits melting beneath ocean ridges. Whereas ridge magmatism can be attributed to adiabatic upwelling and melting of nearly dry mantle, arc-related volcanism involves introduction of volatiles and hydrous melts into the mantle that induce hydrous (or 'flux') remelting. The relative contribution of the slab-derived and mantle wedge components in the production of arc-related magmas has been long debated. Most studies constrain magmatic processes by inverting isotopic and trace element compositions of arc-related lavas. This approach is hindered by the complexity of the melt generation process, that may involve as yet poorly understood interactions between migrating melts and the overlying mantle, as well as transport through and interaction with arc crust. The Josephine Peridotite offers the opportunity to directly study and constrain how water and hydrous melts are introduced into, interact with and are transported through the subarc mantle - and how this effects melt chemistry. A combined major and trace element whole rock and mineral study is proposed to document how the composition of the Josephine Peridotite massif was influenced by the introduction of volatiles and hydrous melt, and whether this is a local or pervasive influence.Broader Impacts: This project relates directly to the goal of understanding the role of volatiles in arc-related magmatism - a subject of broad interest and significant societal impact due to the explosive nature of arc volcanism. In addition, the project will support a Ph.D. student.