New Mexico Geological Society Annual Spring Meeting — Abstracts

Whole rocks and phenocrysts from the 33.4 ka El Calderon basalt flow of the Zuni-Bandera volcanic field in west central New Mexico are used to distinguish between melting of heterogeneous mantle sources and mixing of a single asthenospheric magma with variable amounts of felsic crust during ascent. The Zuni-Bandera volcanic field is located along the Jemez lineament, an 800km long suture zone that is defined by a series of young volcanic field stretching from Springerville, Arizona, to Raton, New Mexico. El Calderon basalts have OIB like trace element signatures, and whole rock Sr isotopes show little variation, ranging from 0.70472±7 to 0.70479±10 (Peters et al., 2007).

While whole rock major element variations require only ~2% fractionation of olivine, trace element enrichments suggest a reduction in magma volume of up to 40%. Whole rock trace element results discount fractionation as the only process affecting the El Calderon magma and are consistent with mixing of two compositional end member magmas. Variations of major elements of melt inclusions correspond with crystal fractionation of olivine, while trace element variations are consistent with two-component mixing.

References:

1. Peters, T.J., Menzies, M., Thirlwall, M., Kyle, P.R., 2008, Zuni-Bandera volcanism, Rio Grande, USA – Melt formation in garnet- and spinel - facies mantle straddling the asthenosphere - lithosphere boundry. Lithos 102, p. 295-315.