Petrology, Geochemistry, and Genesis of High-Al Tonalite and Trondhjemites of the Cornucopia Stock, Blue Mountains, Northeastern Oregon

of Wallowa terrane crust, as the Blue Mountains terrane assemblage The Cornucopia stock, in the Blue Mountains of northeastern collided with the continental margin during Early Cretaceous time. Oregon, is a small composite intrusion comprising five distinct Results of this study suggest that deformation and crustal melting intrusive units: a hornblende biotite tonalite, a biotite trondhjemite, associated with this accretion event were not strictly limited to the and three cordierite-bearing two-mica trondhjemites. The stock suture zone. was emplaced at shallow levels (<2 kbar) in island arc-related metasedimentary and metavolcanic rocks of the Wallowa terrane. The age of the intrusion is 116·8±1·2 Ma determined by Ar/ Ar incremental heating of biotite. These ages and volume constraints imply coeval emplacement of the tonalitic and trondhjemitic magmas.