Collaborative Research: Integrated He-CO2-N2 Isotope and Petrologic Study of Volatiles Cycling via the New Zealand Subduction System

地球会聚边缘的挥发性物质（如水（H2O）、二氧化碳（CO2）和分子氮（N2））循环的知识对于理解流体在与地球板块构造相关的各种过程中的作用至关重要。为了充分评估与人类有关的（“人为”）过程对地表环境（大气、海洋和生物圈）的影响，我们必须了解在所有时间尺度上造成环境变化的自然（非人为）过程。没有比大气中二氧化碳的积累及其对全球平均表面温度和无数其他相关过程（海洋表面水温变化、海洋环流、极地冰融化等）的可能影响更好的例子了。了解这些过程的前提是定量评估的质量平衡的挥发物进入俯冲带与部分返回到表面的弧前，火山前，或弧后的地方，与比例输送到更深的地球（深度大于150公里，在地幔）。直接返回地表的挥发物与俯冲到更深地幔的挥发物的通量估计存在巨大的不确定性，并且阻止了对地球内部和外部水库之间关键挥发物的长期和短期循环历史的评估。研究小组将研究井中挥发物的循环，新西兰北岛俯冲系统的特征，输入和输出通量的特定挥发物（CO2，N2和惰性气体，如He和Ar）可以很好地约束。拟议的研究区是希库朗吉边缘、轴向山脉、陶波火山带和豪拉基裂谷带的组合，包括一个弧前-火山前-弧后剖面，对希库朗吉海沟沉积和海洋岩石圈输入与北岛各种构造体系中通过岩浆、地热和地下水活动输出的这些关键挥发物之间的质量平衡进行了重要测试。挥发性输入特征将使用ODP站点1124、DSDP站点317和即将到来的IODP腿的沉积物岩心进行限制，而输出挥发性特征和通量将通过在整个北岛战略位置的约100个站点的广泛岸上采样来提供。该方法将得到利用Perple_X和其他软件对板状挥发物释放进行热力学模拟以及输入沉积物/基底的复合剖面的支持。总之，在新西兰俯冲带结合岩石学-地球化学-地热方法提供了诱人的前景，为通过俯冲系统的关键挥发物的再循环效率问题提供了良好的约束解决方案，并更清楚地了解了基本过程（例如，板组成、P-T状态、板耦合和上层板结构）参与控制俯冲挥发物释放/保留性质。

Knowledge of the cycling of volatiles such as water (H2O), carbon dioxide (CO2), and molecular N (N2) at Earth's convergent margins is fundamental to understanding the role of fluids in a variety of processes related to plate tectonics on Earth. In order to fully assess the impacts of human-related ("anthropogenic") processes on our surface environment (atmosphere, oceans, and biosphere), we must understand the natural (non-anthropogenic) processes contributing to environmental change, at all time scales. There is no better example of this need than that relating to the buildup of CO2 in the atmosphere and its likely effect on global mean surface temperature and the myriad other related processes (change in ocean surface water temperature, ocean circulation, polar ice melting, etc.). Understanding these processes is predicated on a quantitative assessment of the mass balance of volatiles entering subduction zones versus the fraction returned to the surface in fore-arc, volcanic front, or back-arc localities, versus the proportion transported into the deeper Earth (to depths greater than 150 km, in the mantle). Huge uncertainties on flux estimates of volatiles returned directly to the surface versus those subducted to the deeper mantle remain, and prevent assessments of both long- and short-term cycling histories of key volatiles between Earth's interior and external reservoirs.In this study, the research team will investigate the cycling of volatiles in the well-characterized New Zealand North Island subduction system where input and output fluxes of specific volatiles (CO2, N2, and noble gases such as He and Ar) can be well constrained. The proposed study area, a combination of the Hikurangi Margin, Axial Ranges, Taupo Volcanic Zone and Hauraki Rift Zone, comprises a forearc-volcanic front-backarc profile providing a crucial test of the mass balance of these key volatiles between sedimentary and oceanic lithosphere inputs at the Hikurangi Trench to output via magmatic, geothermal and groundwater activity in various tectonic regimes of the North Island. The volatile input characteristics will be constrained using sediment cores from ODP Site 1124, DSDP Site 317, and an upcoming IODP leg, whereas output volatile characteristics and fluxes will be provided by extensive on-shore sampling of ~100 sites at strategically-placed localities throughout the North Island. The approach will be underpinned by thermodynamic modeling of slab volatile release utilizing Perple_X and other software and composite profiles of incoming sediment/basement. Taken together, the combination of combined petrologic-geochemical-geothermal approaches at the NZ subduction zone offers the tantalizing prospect of providing well-constrained solutions to the question of recycling efficiencies for key volatiles through subduction systems, and a clearer understanding of fundamental processes (e.g., slab composition, P-T regime, plate-coupling and upper plate structure) involved in controlling subducted volatile release/retention properties.