EMPLACEMENT AND DEFORMATION HISTORY OF THE WESTERN MARGIN OF THE IDAHO BATHOLITH NEAR MCCALL, IDAHO - INFLUENCE OF A MAJOR TERRANE BOUNDARY

Cretaceous plutons of the western margin of the Idaho batholith were e mplaced along and to the west of the major terrane boundary separating middle Proterozoic and Paleozoic continental rocks from mostly Mesozo ic accreted oceanic-arc terranes of the Blue Mountain Province. This b oundary is marked by a change in the lithology of pendants and inclusi ons within the batholith. Plutons form two newly named complexes of ig neous and metamorphosed igneous rocks. The Hazard Creek Complex, empla ced west of the boundary between the oceanic arc and the continental m argin, consists primarily of a series of variably deformed and metamor phosed quartz diorite to trondhjemite plutons. The Little Goose Creek Complex, which intruded the boundary between the oceanic arc and the c ontinental margin, is primarily porphyritic granodiorite to granite or thogneiss. A preliminary U-Pb age of 111 Ma for this porphyritic ortho gneiss is a minimum age for the formation of the oceanic-arc-continent boundary. The plutonic rocks were deformed both during and after empl acement in response to east-west compressive stresses. Cretaceous defo rmation was localized along the boundary between the accreted terranes and the continental margin and is interpreted to have occurred after the formation of this boundary. The major deformation of the Hazard Cr eek Complex occurred during its emplacement. The dominant fabric in th e Little Goose Creek Complex is due to subsolidus ductile deformation. The localization of two deformation events along the pre-existing bou ndary between the accreted terranes and the continental margin suggest s that a terrane boundary may form a long-lasting, crustal flaw.