Ca. Manduca et al., EMPLACEMENT AND DEFORMATION HISTORY OF THE WESTERN MARGIN OF THE IDAHO BATHOLITH NEAR MCCALL, IDAHO - INFLUENCE OF A MAJOR TERRANE BOUNDARY, Geological Society of America bulletin, 105(6), 1993, pp. 749-765
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.