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

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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.