MARGINS: The Slab Component in Central America: Isotopic Evidence For Both Hydrous and Silicic Fluxes in Nicaragua

9905167 Carr边缘计划的俯冲工厂计划致力于了解火山弧系统中的通量。具体目标包括发现控制岩浆产生的因素。我们的工作将通过澄清中美洲板条通量的性质来解决这一目标。我们最近在中美洲熔岩中发现了不寻常的微量元素系统。数据最好的解释是两个端元之间的混合，因此至少有两个焊剂需要识别。沉淀物部分俯冲在中美洲之下，也有两个末端成员：下部碳酸盐软泥和上半洋泥浆。这些岩性具有非常不同的微量元素特征，总的来说，沉积物的化学特征与熔岩中看到的两个端元相匹配。我们确定这两个地球化学端元的起源是俯冲沉积物，但沉积物是如何成为引发熔融和火山作用的助熔剂的？它们是以含水流体还是熔融的形式进入地幔？我们提出的项目可以通过使用非常精确的同位素测量来回答后一个问题的一半。中美洲熔岩的锶-钕同位素数据定义了一个阵列，显然包括在微量元素数据中看到的相同端元。一旦有足够的数据可用，更精确的同位素数据有可能严重限制解释。中美洲的同位素混合线的几何形状是这样的，来自上层半深海沉积物的通量可以是熔体，但不能是含水流体。为了确定这一点，我们计划扩大数据集，目前数据集太稀疏，我们无法将其作为确定的结论

9905167CarrThe Subduction Factory Initiative of the MARGINS Program strives to understand fluxes through volcanic arc systems. Specific goals include uncovering what regulates the production of magma. Our work will address this goal by clarifying the nature of the slab fluxes in Central America. We recently discovered unusual trace element systematics in lavas from Central America. The data are best explained by mixing between two end-members, thus there are at least two fluxes to identify. The sediment section, subducting beneath Central America, also has two end-members; a lower carbonate ooze and an upper hemipelagic mud. These lithologies have hugely different trace element signatures and, in general, the chemical signatures of the sediments match up with the two end-members seen in the lavas. We identify the origin of the two geochemical end-members as the subducted sediments, but how do sediments become fluxing agents that trigger melting and volcanism? Do they move into the mantle as hydrous fluids or as melts? Our proposed project can answer half of the latter question by employing very precise isotopic measurements. The Sr-Nd isotopic data for Central American lavas define an array apparently involving the same end members seen in the trace element data. The far more precise isotopic data have the potential to severely restrict interpretations once sufficient data are available. The geometry of the isotopic mixing lines for Central America is such that a flux from the upper, hemipelagic sediments can be a melt but can not be a hydrous fluid. To establish this, we plan to expand the data set, which at present is too sparse to allow us to state this as a firm conclusion