Geochemistry of mafic lavas in the early Rio Grande Rift, Yarmony Mountain, Colorado, U.S.A.

Mafic lavas (high-K basalts and shoshonites) erupted 21–24 Ma ago (early Miocene) near State Bridge, NW Colorado, and now exposed on Yarmony Mountain, were related to the initial phase of extension in the northernmost section of the Rio Grande Rift. The volcanism was of small volume, consisting of eleven flows on Yarmony Mountain, although much more voluminous contemporaneous lavas occur 50 km to the west. All eleven flows have been analysed …