Generation of Subduction-Zone Magmas from Melange Diapirs

在地球上，海洋板块不断地沿着沿着具有破坏性的板块边缘被拖入地幔。这个过程被称为“俯冲”，它是板块构造的基本表现之一。俯冲带是地球表面和内部之间物质的主要运输机制。对俯冲带化学循环的理解为我们提供了工具，使我们能够更好地了解造山和岩浆过程，这些过程有助于关键元素的全球循环，形成宝贵的自然资源，如贱金属矿石，以及俯冲带的日常危害，如地震，海啸和火山。据设想，从俯冲洋板块排出的流体迁移到热的上覆地幔，在那里它们引发熔融和岩浆的产生，导致形成地球周围沿着俯冲带无处不在的火山链。这些已建立的模型可以解释在俯冲带火山中发现的许多岩浆成分。然而，在俯冲带火山中观察到的一些岩浆类型不能用传统的模型来解释，需要一个不同于正常地幔的源区。通过计算机模拟、野外工作和地球化学研究，已经出现了关于物质输运的新模型。这些新模型表明，俯冲洋壳和上覆地幔的岩石混合，导致俯冲板块正上方形成厚厚的混合岩石层。这些混合岩层，即所谓的“混杂岩”，预计将迅速上升到上覆的热地幔楔中，在那里它们开始产生大量的熔体。在这个项目中，研究人员Marschall，Gaetani和Cruz-Uribe将通过在实验室中进行高压实验，首次研究在地幔中普遍存在的压力-温度条件下天然混合岩产生的熔体的组成。这些实验中产生的熔体和矿物将通过现代微观分析方法进行表征，这些方法能够非常灵敏地确定材料的化学成分，并且规模非常小。这些成分将与俯冲带火山喷发的熔岩进行比较。这项研究的结果可能有助于解释与传统模型相比更大范围的火山岩成分的形成，它有助于我们理解地球上最活跃的火山活动形成的深层化学和机械过程。对楔状底辟中混杂岩熔融形成弧岩浆的研究将对整个固体--因此，这项工作的结果将引起广大科学家的兴趣。这包括对沿着俯冲带岩浆生成感兴趣的岩石学家和地球化学家，以及对俯冲带的机械过程和热状态感兴趣的岩石学家和数值模拟师。

On planet Earth, oceanic plates are constantly dragged down into the mantle along destructive plate margins. This process is called "subduction" and it is one of the fundamental manifestations of plate tectonics. Subduction zones function as the primary transport mechanism for materials between the surface and interior of the Earth. An understanding of chemical cycling in subduction zones provides us with the tools to better understand the mountain-building and magmatic processes that contribute to the global cycles of critical elements, the formation of valuable natural resources, such as base-metal ores, and daily hazards of subduction zones, such as earthquakes, tsunamis and volcanoes.Traditionally, it is envisaged that fluids expelled from the subducting oceanic plate migrate into the hot overlying mantle, where they trigger melting and the generation of magmas that lead to the formation of the volcanic chains that are ubiquitous along subduction zones around the planet. These established models can explain a number of magma compositions found in subduction-zone volcanoes. However, some magma types observed in subduction-zone volcanoes cannot be explained by that traditional model and require a source region that is different from the normal mantle. New models on material transport have emerged from computer modeling, fieldwork and geochemical studies. These new models suggest that mixing between rocks derived from subducting oceanic crust and the overlying mantle leads to the formation of thick layers of mixed rocks directly above the subducting plate. These mixed-rock layers, so-called "mélanges", are predicted to buoyantly rise into the overlying hot mantle wedge, where they start to produce significant amounts of melt. In this project, researchers Marschall, Gaetani and Cruz-Uribe will investigate for the first time the composition of melts produced from natural mélange rocks under the pressure-temperature conditions prevailing in the mantle by performing high pressure experiments in the laboratory. The melts and minerals produced in these experiments will be characterized by modern micro-analytical methods that are capable of determining the chemical composition of the material very sensitively and at a very small scale. The compositions will be compared to those of lavas erupted from subduction-zone volcanoes. Results from this study may help to explain the formation of a larger range of composition of volcanic rocks compared to the traditional model, and it help us to understand the chemical and mechanical processes operating at depth that lead to the formation of the most vigorous volcanism on the planet.This study of the formation of arc magmas by mélange melting in wedge diapirs will have important consequences for the entire solid-Earth science community and thus, the results of this work will be of interest to a broad range of scientists. This includes petrologists and geochemists who are interested in the generation of magmas along subduction zones, as well as geophysicists and numerical modelers with an interest in the mechanical processes and the thermal state of subduction zones.