Ireteba pluton, Eldorado Mountains, Nevada: Late, deep-source, peraluminous magmatism in the Cordilleran interior

The Ireteba pluton is a similar to66 Ma biotite +/- muscovite +/- garnet granite emplaced at the eastern edge of the Cordilleran plutonic belt in southeastern Nevada. In common with other Cordilleran peraluminous granites, its mineralogy, major element chemistry, isotopic composition, and abundant Proterozoic zircon inheritance document crustal origin. Distinctive trace element chemistry, field relations, and inherited components further constrain its genesis. High Sr concentrations, low heavy rare earth elements, and absence of negative Eu anomalies indicate that the Ireteba magma was extracted from a residue relatively rich in garnet and poor in feldspar; rounded quartz is probably a resorbed, high-P liquidus phase or restite. The granite shares with adakites (slab-derived arc magmas) and Archean granitoids the Sr-rare earth element signature of deep-source origin. Nd-Sr isotopic compositions indicate a dominantly crustal origin for the granite, but it is less mature than the underlying ancient Mojave crust. The granite is apparently a hybrid derived primarily from the ancient crust but with a less mature component as well: either Jurassic igneous rock, as suggested by sparse 150-170 Ma zircon cores, or juvenile mafic magma, as implied by abundant synplutonic mafic rocks, or both. Influx of basaltic magma during the waning stages of Cordilleran convergence may have triggered melting in the deep, thickened crust, with basaltic magmas being trapped beneath the less dense crustal melts. Like other relatively young peraluminous granites of the Cordilleran Interior, including the Idaho-Bitterroot batholith, the Ireteba pluton may reflect changing conditions during the waning stages of plutonism.