Collaborative Research: Resolving Mantle, Crustal and Slab Fluxes to Arc Magmatism in Central America Using Geothermal Fluids and Volcanic Rocks

该方案旨在通过量化俯冲板块、地幔楔和上覆地壳对整个弧收支的贡献，为中美洲俯冲带产生一个不稳定的物质平衡。之所以选择中美洲弧，是因为它具有一些独特的特征，可以在火山产出的系统变化与俯冲参数的变化之间建立明确的联系，特别是板块倾角、沉积物供应和地壳厚度。我们的方法是结合二氧化碳和氦的测量（同位素和相对丰度），从而可以识别和定量评估岩浆输出的各种贡献者。尽管是一种强大的技术，但任何通量估计的准确性都受到岩浆脱气对所得CO2/3He比率的影响的不确定性以及对弧磁作用中潜在端元成分的同位素和丰度特征的假设的限制。通过分析和比较沿中美洲弧线和横跨中美洲弧线的地热流体与基性矿物中的CO2-He关系，我们的目标是探索这些限制的程度，并评估有可能克服任何困难的方法。此外，我们将通过结合COSPEC和气体化学研究得出当前的CO2通量。这为推导N2和H2O的绝对通量提供了进一步的可能性，也为确定它们在俯冲带工厂中的来源提供了可能。

Hilton/Walker/FischerEAR-0003628/0003664/0003668 This proposal is aimed at producing a volatile mass balance for the Central American subduction zone by quantifying the contributions from the subducting slab, mantle wedge and overlying crust to the overall arc budget. The Central American arc was chosen because it possess a number of unique features which allow explicit linkages to be forged between systematic variations in volcanic output and variations in subduction parameters, specifically slab dip, sediment supply and crustal thickness. Our approach is to couple CO2 and helium measurements (isotopes and relative abundances) which allows for identification and quantitative assessment of the various contributors to the magmatic output. Although a powerful technique, the accuracy of any flux estimates is limited by uncertainties in the effects of magmatic degassing on resultant CO2/3He ratios and on assumptions on the isotopic and abundance characteristics assigned to potential endmember compositions involved in arc magmagenesis. By analyzing and comparing the CO2-He relationships in geothermal fluids with mafic minerals both along and across the Central America arc, we aim to explore the extent of these limitations and to assess approaches with the potential to circumvent any difficulties. Additionally, we will derive present-day CO2 fluxes through combined COSPEC and gas chemistry studies. This offers the further possibility of deriving absolute fluxes for N2 and H2O and for also constraining their provenance in the subduction zone factory.