Lithology, mineralogy, and chemical weathering of volcanic rocks from Panama

Chemical weathering of silica rocks is the only know mechanism on a long-term geologic time scale (100s of million of years and longer) for sequestration of carbon dioxide. Lithologic and mineralogical analysis of rocks provides understanding of which minerals may be weathering preferentially, and thus what ratio of ions are released into the environment and sequestering the carbon. Collision of the Caribbean plate and the Cocos plate and the associated subduction causes melting of crustal layers and andesitic/dacitic volcanism. Rock samples were collected in summer 2006 and spring 2007 from several andesitic-dacitic volcanic centers located in the western part of the country. Previous research has shown that basalts are generally absent from the volcanic centers with basaltic andesites and andesites predominating. Collection was performed as part of a larger project which included water and sediment collection and stream gauging. Previous studes on volcanic centers in the region revealed ags from 17.5 Ma to 300 yr B.P. with the majority of dates focused between 12-7MA and around 1.3+1 Ma. Volcanism appears to have been significantly reduced between 6 and 1 MA, with increased activity from 2 Ma to present. Petrologic thin sections were prepared by cutting samples with a diamond blade saw into small bocks which were then processed into this sections. I will then analyze them underneath a microscope to determine the minerals present and their relative proportions. I will also perform X-ray fluorescence analysis of crushed samples to determine bulk chemical analysis. Mineralogical assemblages of these rock samples show relationships between the volcanic centers along with individual magma chamber evolution. Mineralogical assemblages and chemical content will reveal which minerals are lickely to weather fastest and will be used in association with geochemical analyses of stream water sample and associated weathering studies to determine the extent and rates of chemical weathering taking place. Results are expected to show that the silicate minerals of these andesitic-dacitic volcanic rocks of Panama are rapidly weathering and sequestering significant amounts of atmospheric carbon dioxide