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

弧状熔岩的地球化学成分经常被用来推断岩浆的来源成分和熔融程度的变化。这些研究假设熔岩的原始成分在暴露在地表期间被保存下来。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2My)已经形成了改变的REE剖面，尽管在手部样品或薄片中都没有明显的改变证据。我们建议对弧状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，以了解熔岩的“主要”地球化学成分在不同的蚀变阶段是如何变化的。我们将重点探索危地马拉东南部弧状熔岩风化剖面中的地球化学变化，并特别注意风化的早期阶段。风化剖面上的成分变化将通过识别次生矿物相和测定微量元素活动性来重建样品的风化历史。样品的地球化学成分的变化还将被用来制定一种标准，以识别已被早期蚀变改造的岩石，从而提高中美洲熔岩和其他弧形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.