Mesozoic terrane accretion and formation of the Idaho batholith

Abstract:

The Mesozoic suturing of the Blue Mountains province to North America was accompanied by a complex history of magmatism that ultimately culminated in the formation of the Idaho batholith. The oceanic terranes of the Blue Mountains were most likely assembled offshore in the Late Jurassic and accreted to North America in the Early Cretaceous, probably south of their current latitude. Suturing was followed by a renewal of subduction outboard of the Blue Mountains, leading to tonalitic and trondhjemitic magmatism in the eastern portion of the province from about 130 to 110 Ma. Additional compositionally diverse magmatism within the suture occurred from about 110 to 100 Ma and included the reworking of crustal material from both sides of the suture. This resulting mid-Cretaceous intrusive suite was collapsed by dextral transpressional deformation from ~102 to 92 Ma, leading to the formation of the western Idaho shear zone and transporting the Blue Mountains to their present latitude. During the later stages of WISZ deformation, continental arc magmatism migrated east of the WISZ and produced the early metaluminous phases of the Idaho batholith. By 90 Ma, a large metaluminous continental arc connecting to the Sierra Nevada in the south and Coast Mountains in the north existed in Idaho, but subsequent crustal thickening on the continental side of the WISZ led to pervasive crustal melting in two pulses between ~83 and 54 Ma, which obliterated much of the earlier magmatic history of the batholith. Further magmatism occurred in the Eocene in response to changing plate boundary conditions and onset of extension.