Alkaline hybrid mafic magmas of the Yampa area, NW Colorado, and their relationship to the Yellowstone mantle plume and lithospheric mantle domains

摘要: The Yampa volcanic field (late Miocene) consists of about 70 outcrops monogenetic cinder cones, lavas, dykes, necks and hydrovolcanic pyroclastic deposits is situated in the most northerly part Rio Grande rift. Contemporaneous extension this rift was small, but there geological geophysical evidence that, by late Miocene, area underlain hot asthenosphere convected Yellowstone mantle plume. rocks are mafic chemically diverse, including basanites, alkali basalts, potassic trachybasalts, hawaiites shoshonites. About half bear xenocryst suite feldspar, pyroxene, Fe−Ti oxide, amphibole, biotite. There a tendency for xenocryst-free to be mafic, interpreted indicate that xenocrysts cognate, represent cumulate material from fractional crystallization magmas deep crustal magma chambers. elemental isotopic (Nd Sr) variations can modelled mixing variable proportions partial melts local lithospheric with an OIB end-member formed melting asthenosphere. appears have composition typical Northern Hemisphere OIB, particular plume-derived basanites Loihi seamount, Hawaii. at been derived