TWO DECADES OF CENTAM

CENTAM (Carr and Rose, 1987) presented a database of Central American volcanic rocks in a volume celebrating the 75th birthday of Richard E. Stoiber, who instigated wide ranging volcanological studies in Central America. Carr and Rose were fluent in computing, both had worked on a teletype in Stoiber's office. By 1986 huge amounts of data (360 kb) could be copied onto a floppy. Rose suggested CENTAM and Carr created the disk. Three motivations created this project. First, it was a sneaky way to get the data on Central American volcanoes into the published literature; editors wanted just a few representative examples. Furthermore, many MS theses from Dartmouth, Michigan Tech. and Rutgers were unpublished. Second, NSF paid so the results should be publicly available. Third, we wanted to be in the forefront of the computer revolution that was making it easy to share data.

CENTAM attracted users with special analytical facilities, so its depth grew as Carr and Rose provided samples to: Columbia, Rice, DTM, Washington Univ., New Mexico, Caltec, Boston College, Northern Illinois, Kansas, Iowa, GEOMAR. Thus, CENTAM became comprehensive, a description of an entire margin, providing a new perspective for arc study. We discovered regional variations that helped make Central America a choice of the NSF Margins Subduction Factory.

One result was the discovery of geographic variations in elemental and isotopic ratios (e.g. Ba/La, 10Be/9Be, U/Th) that trace material from the subducted plate. These tracers reach maxima in Nicaragua and decrease outward. The flux of slab-derived elements, Ba and U, is constant along the margin. The variation occurs in La, 9Be, Th etc, which change with melting. The regional pattern is a correlation between the tracers and the degree of melting. The tectonic factor that mimics this is dip of the subducted slab. A reasonable explanation is for areas of steeper dip to focus the constant slab flux into smaller volumes of mantle wedge leading to higher degrees of melting and higher ratios for Ba/La, U/Th etc.