The Effects of Incipient Weathering on Trace Element Distributions in Arc-Related Lavas From SE Guatemala, CA

9909493 patinogeochemical弧状熔岩构成通常是用来推断源组成和变化程度的融化的岩浆。这些研究假设熔岩的原始成分在暴露于地表期间被保存了下来。然而，有证据表明，早期风化作用能够改变火成岩的化学特征。例如，在危地马拉东南部，相当年轻的样品（约0.5至2毫克）已经发展出改变的REE剖面，即使在手工标本或薄片中没有明确的改变证据。为了了解不同蚀变阶段火山岩的“初级”地球化学成分是如何变化的，我们建议对火山熔岩的矿物和岩石化学成分沿风化剖面的变化进行详细的研究。我们将重点探索危地马拉东南部弧熔岩风化剖面的地球化学变化，特别关注风化的早期阶段。风化剖面上的成分变化将通过鉴定次生矿物相和确定微量元素迁移率来重建样品的风化历史。样品中地球化学成分的变化也将用于制定一种标准，以识别因早期蚀变而发生改变的岩石，从而提高中美洲和其他弧的熔岩岩石成因模型的准确性。

9909493PatinoGeochemical composition of arc lavas is frequently used to infer changes in the source composition and degree of melting of the magmas. These studies have assumed that the original composition of the lavas has been preserved during their exposure at the surface. However, there is evidence that incipient weathering is capable of modifying the chemical characteristics of igneous rocks. For example, in southeast Guatemala, rather young samples (about 0.5 to 2 my) have developed altered REE profiles, even thought there is no clear evidence of alteration either in hand specimen or thin section. We propose to carry out a detailed study of the changes in mineral and rock chemical composition along weathering profiles of arc lavas in order to comprehend how the "primary" geochemical composition of the lavas changes during the different stages of alteration. We will focus on exploring the geochemical variations in weathering profiles of arc lavas in southeast Guatemala, with particular attention given to the early stages of weathering. The compositional variations along the weathering profiles will be used to reconstruct the weathering history of the samples by identifying the secondary mineral phases, and determining trace element mobility. The variations in the geochemical composition of the samples will also be used to develop a criteria to identify rocks that have been modified by incipient alteration, thus improving the accuracy of petrogenetic models for lavas from Central America, and other arcs.