Collaborative Research: Volatile Recycling and Magma Genesis in a Hot, Dry Subduction Zone: A Case Study of the Cascade Arc

俯冲带在控制地壳、水圈和大气与更深地幔之间的化学循环方面发挥着重要作用。在这些环境中，挥发性元素（H，C，F，Cl，S等）介导质量转移和元素循环，并强烈影响导致俯冲带环境中岩浆生成，运输和喷发的过程。为了探讨挥发性元素的分布和作用及其对单一俯冲系统中物质传递和熔融的影响，本研究将对加州、俄勒冈州和华盛顿喀斯喀特弧原始岩浆熔融包裹体中的常量、微量和挥发性元素进行系统研究。其目的是确定火山爆发前的挥发性浓度和氧逸度条件下发现的不同原始岩浆类型的喀斯喀特弧，并利用这些数据来检查组成板楔和地幔楔派生组件沿着和跨越弧，并测试目前的模型熔融和岩浆成因的俯冲带。虽然喀斯喀特俯冲带被认为是一个端元“干热”俯冲带，但挥发分在元素循环和岩浆成因中的作用仍不清楚。现有的研究和我们的初步数据表明，水的含量各不相同，一些原始的喀斯喀特岩浆是相当“湿”的-H2O高达4至7重量%。将采取两种取样策略，首先是研究俄勒冈州中部小瀑布（纬度）沿沿着东西交叉弧的熔岩。~43-45度）。俄勒冈州高喀斯喀特地区的特点是镁铁质岩浆近期喷发量最高，并包含弧中发现的所有主要原生岩浆类型（HAOT、OIB类、CAB和钾玄岩）。这项工作将与其他熔岩的工作相结合，从选定的充分研究的位置沿着弧。总的来说，这种方法将允许用于确定在喀斯喀特弧内产生的不同岩浆类型的挥发性成分，并提供关于弧上和沿着弧的挥发性丰度变化的见解。

Subduction zones play a major role in governing chemical cycling between the Earth's crust, hydrosphere and atmosphere and the deeper mantle. In these environments volatile elements (H, C, F, Cl, S and others) mediate mass transfer and elemental cycling, and also strongly influence the processes that lead to the generation, transport and eruption of magmas within subduction zone environments. To investigate the distribution and role of volatile elements and their effect on mass transfer and melting in single subduction system, this study will involve a systematic study of major, trace and volatile elements trapped in melt inclusions from primitive magmas in the Cascade arc in California, Oregon and Washington. The aims are to determine pre-eruptive volatile concentrations and oxygen fugacity conditions for the different primitive magma types found in the Cascade arc, and to use this data to examine the composition of slab- and mantle-wedge derived components along and across the arc, and to test current models for melting and magma genesis in subduction zones. Although the Cascade subduction zone is recognized as an endmember "hot and dry" subduction zone, the role of volatiles in element cycling and magma genesis remains unclear. Existing studies and our preliminary data show that water contents vary and that some primitive Cascade magmas are quite "wet" - with H2O up to 4 to 7 wt.%. Two sampling strategies will be pursued, firstly involving study of lavas from along an east-west cross-arc traverse in the Central Oregon Cascades (Lat. ~43-45 degrees). The Oregon High Cascades region is characterized by the highest recent erupted volumes of mafic magma and contains all major primary magma types found in the arc (HAOT, OIB-like, CAB, and shoshonite). This work will be combined with work on other lavas from selected well-studied locations along the arc. Overall this approach will allow use to identify the volatile composition of the range of different magma types produced within the Cascade arc, and provide insight on the variations in volatile abundances across and along the arc.