San Pedro Pellado Volcanic Complex by Davidson, Ferguson, Colucci, and Dungan

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Subsequent research focusing more solely on the San Pedro Pellado Volcanic Complex by Davidson, Ferguson, Colucci, and Dungan (1988) provides evidence that some degree of crustal assimilation has had an impact on the evolution of magmas in the volcanic complex. The evidence for this is the high δ^18O observed in fresh non-glassy rock units. Taylor and Sheppard (1986) argue that the differences in characteristics among rock units of the complex cannot be explained by the closed system fractionalization of an unaltered mantle melt. The concentrations of the oxygen isotopes suggest that the magmas that formed these igneous rocks have undergone some contamination with a crustal component containing a higher concentration of 18O (Davidson et al., 1988). The occasional presence of granitic xenoliths in the lavas and tuffs, such as the Pellado unit, are also indicative of some level of crustal contamination. These xenoliths are enriched in large ion lithophiles and have similar concentrations of REE as the underlying basement material and are therefore believed to be pieces of the underlying basement of the volcanic complex (Davidson et al., 1988). For the granites to be included into the melts as they rise through the crustal material indicates there is some degree of interaction between melts and crustal material. In addition to alteration by crustal contamination, the magmas of the San Pedro Pellado Complex were also likely subject to alteration by magma mixing (Davidson et

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