Structure, depositional age, and magmatism in the Sawtooth metamorphic complex, Idaho: Implications for cordilleran tectonics in the northern U.S.A

U-Pb ages of detrital zircons from Sawtooth metamorphic complex (SMC) metapsammites yield age-spectra consisting of 1.87-1.67 Ga, 1.49-1.33 Ga, and 1.22- 1.02 Ga zircons for one group, and 2.79-2.65 Ga and 1.99-1.76 Ga zircons for the other group. These age-spectra are similar to those from some Cambrian and Middle Ordovician shelf strata of the U.S. Cordillera. These similarities and the presence of Cambrian detrital zircons suggest that the depositional age for the former group is Cambrian; Middle Ordovician strata provide a good match for the detrital zircon data of the latter group. These data indicate that Lower Paleozoic shelf strata of the Cordilleran passive margin were not removed from Idaho batholith region by strike-slip faulting.;Geologic mapping across the SMC reveals alternating contraction- and shear-dominated domains. The contraction-dominated domains are north-south striking and comprise shallowly to steeply plunging upright folds and associated thrust faults. The shear-dominated domains are characterized by north-south striking, subvertical foliations and subhorizontal lineations. Pervasive kinematic indicators show a dextral sense of shearing. The structures across the two domains are compatible and kinematically linked, indicating they are broadly synchronous. Dating of syntectonic intrusives indicates that the SMC transpressional deformation occurred between ~91-87 and ~80 Ma, and had ended by ~73 Ma. The SMC transpressional zone is kinematically compatible and was coeval with deformation of the western Idaho shear zone, suggesting that they were parts of a regional transpressional system and that crustal deformation inboard of the continental margin contributed to northward orogen-parallel translation of accreted terranes during the Late Cretaceous.;Zircon U-Pb ages and Hf isotopes of igneous rocks reveal four phases of magmatism in the SMC (~120 Ma, ~97-96 Ma, ~91-87 Ma, ~84-73 Ma). The sources and differentiation history of the magmas varied between these phases according to trace element compositions. Zircon Lu-Hf and whole-rock Sm-Nd isotopic data suggest that (1) the younger undeformed granitoids are more evolved and perhaps had Paleoproterozoic and Neoarchean sources, (2) the older magmatically foliated granitoids are less evolved and possibly had Mesoproterozoic (or younger) sources, and (3) the earliest phases (gabbro/mylonitic granitoids) are least evolved, possibly had a juvenile mantle source.