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

9905167 Carr MARGINS计划的俯冲工厂倡议致力于了解通过火山弧系统的通量。 具体目标包括揭示是什么调节岩浆的产生。 我们的工作将通过澄清中美洲板块通量的性质来实现这一目标。 我们最近在中美洲的熔岩中发现了不寻常的微量元素系统学。数据最好解释为两个端元之间的混合，因此至少有两个通量要识别。 沉积物部分，俯冲到中美洲之下，也有两个端员：一个较低的碳酸盐软泥和上半远洋泥。 这些岩性具有非常不同的微量元素特征，一般来说，沉积物的化学特征与熔岩中看到的两个端元相匹配。 我们确定的两个地球化学的端员的俯冲沉积物的起源，但沉积物如何成为触发熔融和火山作用的助熔剂？ 它们是以含水流体的形式还是以熔体的形式进入地幔的？ 我们提出的项目可以通过采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Sr-Nd同位素数据定义了一个阵列，显然涉及相同的端成员中看到的微量元素数据。 一旦有足够的数据，更为精确的同位素数据有可能严重限制解释。中美洲同位素混合线的几何形状是这样的，从上层，半远洋沉积物的通量可以是熔体，但不能是含水流体。为了证实这一点，我们计划扩大数据集，目前数据集太少，无法让我们将其作为一个确定的结论

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