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

迈向物质平衡的弧状岩浆通量--来自墨西哥中部火山带的洞察知识价值：在理解固体地球地球化学循环方面的一项根本性突破是认识到弧状板块的再循环。然而，量化板岩通量的大小是一项复杂的任务，需要了解弧形岩浆的岩石成因，特别是其高平均二氧化硅(50-65wt%)的原因，因为它们在全球范围内不同于大洋中脊和板内背景产生的岩浆。该项目的目的是调查高硅安山岩和英安岩(=？硅质岩浆？)的来源。在墨西哥中部火山带(MVB)，来自地幔与地壳来源。在同时代的玄武岩和安山质MVB岩浆中，平衡橄榄石的存在表明高SiO_2熔体可能来自地幔。对第四纪复合火山马林切、波波卡特特尔和内华达德托卢卡的硅质火山岩以及其间奇奇诺津山脉火山田同时代硅质单生火山的研究被提出以验证这一观点。全面的常量和微量元素及同位素数据(包括将在块状岩石和斑晶中测量锶-钕-铅-氢同位素)，以评估地壳和地幔对这些岩石形成的贡献，特别是硅质岩浆是否主要是(I)地壳部分熔体，还是(Ii)由反应硅质流体渗入的弧下地幔中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壳内处理和再循环的重要性，但代价是从板岩中再循环的地壳通量。然而，证实MVB中部存在更广泛的玄武岩-英安岩初始地幔熔体，对于弧岩浆成因、弧和大陆地壳生长、弧沟连通性以及弧通量对更广泛的地球化学循环的整体影响等模式具有转化潜力。更广泛的影响：该项目进一步促进了两位女科学家(残疾的施特劳布和博尔格)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的科学界的兴趣，因为它解决了地球空间信息系统倡议和2013年后国际海洋发现计划(IODP)的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).