Volatiles in the Central American Volcanic Arc: Constraints on Subduction Processes From I-129, C, N and Noble Gas Determinations

9902919大洋地壳的俯冲和板块会聚边界的沉积物引起了各种地质作用，包括新大陆地壳的堆积，火山弧系统的发展和矿床的形成。 虽然人们对俯冲过程的大致轮廓达成了一致意见，但对沉积物再循环的程度、火山系统中流体的来源以及这些地点的大陆地壳、海洋地壳和地幔之间的相互作用等重要问题却知之甚少。 为了解决这些问题，我们计划使用同位素系统研究火山流体，碘-129携带时间信号，分配到流体相，并与海洋沉积物有很强的关联。 这些测定将与在相同环境下的气体系统学调查相联系，特别是He、N2、CO2和CH 4浓度和同位素特征。 这些系统的组合提供了一个强有力的工具，以确定类型和年龄的源地层的火山流体。 本研究选择的背景是中美洲火山弧南部，这是一个经过充分研究的活跃俯冲带的例子。 我们计划将研究重点放在三个火山中心，分别位于哥斯达黎加、尼加拉瓜和萨尔瓦多萨尔瓦多，样本主要取自地热威尔斯井和相关的温泉和火山口。 本次调查的目的是确定这些环境中沉积物再循环的量、存在的沉积物的年龄以及大陆地壳、海洋地壳和地幔的影响 火山流体的影响 这些结果将为与大陆地壳形成、洋壳和沉积物的再循环以及活弧火山作用的机制有关的主要过程提供重要信息。

9902919FehnThe subduction of oceanic crust and sediments at convergent plate boundaries gives rise to a variety of geologic processes including the accumulation of new continental crust, the development of volcanic arc systems and the formation of ore deposits. Although agreement exists on the general outline of the subduction process, important questions such as the extent of sediment recycling, the origin of fluids in volcanic systems and the interaction between continental crust, oceanic crust and mantle at these locations are only poorly understood. In order to address these questions, we plan to study volcanic fluids using an isotopic systems, iodine-129, which carries a time signal, partitions into the fluid phase and has a strong association with marine sediments. These determinations will be linked to an investigation of the gas systematics in the same settings, in particular of He, N2, CO2 and CH4 concentrations and isotopic characteristics. The combination of these systems provides a powerful tool to determine type and age of source formations for volcanic fluids. The setting chosen for this study is the southern Central American Volcanic Arc, a well studied and accessible example of an active subduction zone. We plan to focus the study on three volcanic centers, one each in Costa Rica, Nicaragua and El Salvador, with samples taken predominantly from geothermal wells and associated hot springs and fumaroles. The goal of this investigation is to determine the amount of sediment recycling in these settings, the age of the sediments present, and the influence of continental crust, oceanic crust and mantle on volcanic fluids. The results will give important information on principal processes associated with the formation of continental crust, the recycling of oceanic crust and sediments and the mechanics of active arc volcanism.