PETROGENESIS OF THE RATON-CLAYTON VOLCANIC FIELD, NORTHEASTERN NEW MEXICO

The Raton-Clayton volcanic field (RCVF) is located on the east flank of the Rio Grande Rift at the northeastern end of the Jemez Lineament. Magmatism in the RCVF from ~10 to < 0.1 Ma produced abundant basalt, trachybasalt, basaltic andesite and feldspathoidal mafic rocks. Scattered dacite to rhyolite domes and one trachyandesitic stratovolcano (Sierra Grande) are also present. Two pyroxene geothermometry after Lindsley (1983) suggests temperature ranges of 1100 to 930^oC for trachyandesite and 985 to 940^oC for dacite. These magmas evolved through open system processes as evinced by reverse chemical zonation of pyroxene phenocrysts in trachyandesite and abundant xenocrystic quartz and plagioclase with sodic cores and calcic rims in Capulin basalts (<100 Ka). All rock types possess elevated LILE and depleted HFSE (e.g. high Ba and low Nb) compositions similar to modern subduction-related magmas, in spite of their rift association. This subduction geochemical signature would have to have been inherited from previous episodes of subduction, which altered the compositions of source rocks in lithospheric mantle and crust. Ba/La vs. Nb/La plots also support the hypothesis for a subduction modified continental lithospheric source. This origin is consistent with published εNd values of +1 to +1.4 for mafic feldspathoidal rocks of the Raton-Clayton volcanic field (Phelps et al., 1983).