Quantification of Metamorphic Devolatilization in the Subduction Factory Focus Sites: Implications to Fluid Fluxes, Seismicity, and Volatile Recycling

由于许多进入俯冲带的含水海相沉积物缺乏二氧化碳（即缺乏碳酸盐矿物），因此在俯冲时脱水将占主导地位。在这笔资金的支持下，PIs将利用来自伊豆-博宁-马里亚纳和哥斯达黎加-尼加拉瓜的ODP钻探地点的各种限制条件，计算无二氧化碳含水海洋沉积物的主要岩性类型的俯冲带脱挥发：红粘土、热液（含铁）粘土、浊浊岩和混合岩性，即与粘土或火山灰混合的辐射虫/硅藻泥。由于上大洋地壳蚀变玄武岩的碳酸盐含量随着年龄的增长而增加，因此PIs将比较侏罗纪地壳俯冲带（如马里亚纳）和晚新生代地壳俯冲带（如哥斯达黎加）海洋变质玄武岩的变质脱挥发作用，并将量化各种含挥发物组合的相对贡献，并评估挥发物释放的深度分布。提出的研究的一个主要目标是量化进入这些俯冲带的岩性的变质脱挥发作用，并将结果与与每个俯冲带相关的地震震源和火山活动的分布进行比较。

Because many hydrous marine sediments entering subduction zones lack CO2 (i.e., lack carbonate minerals), dehydration would be dominant over decarbonation upon subduction. Under this funding, the PIs will compute subduction zone devolatilization for the major lithologic types of CO2-free hydrous marine sediments: red clays, hydrothermal (ferruginous) clays, turbidites, and mixed lithologies, i.e., radiolaria/diatom oozes mixed with clays or volcanic ash, using a variety of constraints from ODP drill sites off the Izu-Bonin- Marianas and Costa Rica-Nicaragua. Because the carbonate content of altered basalts in the upper oceanic crust increases with age, the PIs will compare metamorphic devolatilization of oceanic metabasalts in subduction zones with Jurassic crust (e.g., Marianas) with those subducting late Cenozoic crust (e.g., Costa Rica), and will quantify the relative contributions of the various volatile-bearing assemblages and assess the depth distribution of volatile release. A primary goal of the proposed research is to quantify metamorphic devolatilization for the lithologies entering these subduction zones and to compare the results with the distribution of earthquake hypocenters and volcanic activity associated with each subduction zone.