Towards Mass Balancing Arc Magmatic fluxes - Insights from the Central Mexican Volcanic Belt

对物质平衡弧岩浆通量的认识——来自墨西哥中部火山带的见解知识价值：认识到弧中的板块再循环是理解固体地球化学循环的一个根本性突破。然而，量化板块通量的大小是一项复杂的任务，需要了解弧岩浆的岩石成因，特别是其高平均SiO2 （50- 65% wt%）的原因，这使得它们在全球范围内与洋中脊和板内环境中产生的岩浆不同。本项目的目的是研究高硅安山岩和英安岩(=？墨西哥中部火山带（MVB）中地幔与地壳来源的硅岩浆？同一时期玄武岩和安山岩MVB岩浆中存在高地幔型3He/4He （=7-8 Ra）平衡橄榄石，表明高sio2熔体可能是地幔成因。对Malinche、Popocateptl和Nevada de Toluca的第四纪复合火山和同时期Chichinautzin火山场的硅质单成因火山的硅质火山岩进行了研究，以验证这一观点。将在大块岩石和斑晶中测量综合的主微量元素和同位素数据（包括Sr-Nd-Pb-Hf同位素），以评估地壳和地幔对这些岩石形成的贡献，特别是硅岩浆是否主要是(i)地壳部分熔体，还是（ii）由反应性硅流体渗透的亚弧地幔产生的熔体和俯冲板块的部分熔体。硅质岩浆的地壳起源将强调地壳内加工和再循环的重要性，以牺牲从板块中再循环的地壳通量为代价。然而，确认在MVB中部存在更广泛的玄武岩-英英质初始地幔熔体，对于弧岩浆成因模式、弧和大陆地壳生长模式、弧-沟连通性模式以及弧通量对更广泛的地球化学旋回的总体影响具有变革潜力。更广泛的影响：该项目促进了两位女科学家（残疾的斯特劳布和博尔格）的职业生涯。本科生和研究生的参与将有助于培养下一代。拉蒙特大学和俄勒冈州立大学的美国科学家与墨西哥、台湾和苏格兰的国际同事之间的科学互动将得到进一步加强。拟议的项目引起了更广泛科学界的兴趣，因为它解决了地质危机倡议和2013年后国际海洋发现计划（IODP）新科学计划的前沿问题。

Towards mass balancing arc magmatic fluxes - insights from the central Mexican Volcanic Belt Intellectual Merit: A fundamental breakthrough in understanding the solid Earth geochemical cycle was the recognition of slab recycling in arcs. Quantifying the magnitude of the slab flux, however, is a complex task that requires understanding the petrogenesis of arc magmas, and in particular the causes of their high average SiO2 (50-65 wt%) by which they differ globally from magmas produced at mid-ocean ridges and intraplate settings. The purpose of this project is to investigate the provenance of high-Si andesites and dacites (=?silicic magmas?) in the central Mexican Volcanic Belt (MVB) from mantle vs. crustal sources. The presence of equilibrium olivines with high, mantle-type 3He/4He (=7-8 Ra) in coeval basaltic and andesitic MVB magmas suggests the possibility that the high-SiO2 melts may have a mantle origin. Studies of silicic volcanic rocks from Quaternary composite volcanoes Malinche,Popocateptl and Nevada de Toluca and from coeval silicic monogenetic volcanoes of The interjacent Sierra Chichinautzin Volcanic Field are proposed to test this idea. Comprehensive major and trace element and isotopic data (incl. Sr-Nd-Pb-Hf isotopes) will be measured in bulk rocks and phenocrysts to evaluate crust vs. mantle contributions to formation of these rocks, and specifically whether or not the silicic magmas are principally(i) crustal partial melts, vs. (ii) melts generated in a subarc mantle infiltrated by reactive silicic fluids and partial melts from the subducting slab. A crustal origin of the silicic magmas would emphasize the importance of intracrustal processing and recycling at the expense of the recycled crustal flux from slab. Confirming the existence of broader spectrum of basaltic to dacitic initial mantle melts in the central MVB, however, has transformative potential as to models of arc magma genesis, arc and continental crustal growth, arc-trench connectivity and hence the overall impact of arc fluxes on the broader geochemical cycles. Broader Impacts: The project furthers the careers of two female scientists (Straub, with a disability, and Bolge). Participation of undergraduate and graduate students will contribute to the training of the next generation. Scientific interaction between US scientists at Lamont and the Oregon State University and international colleagues in Mexico, Taiwan and Scotland will be furthered. The project proposed is of interest to the broader science community, as it addresses questions on the forefront of the GeoPRISMS Initiative and of the New Science Plan of the post-2013 International Ocean Discovery Program (IODP).