| Metamorphic core complexes in the Sevier hinterland record how a thick orogen formed and later
collapsed. In the Albion-Raft River-Grouse Creek metamorphic core complex of southern Idaho
and northern Utah, the Basin-Elba fault, preserved in the footwall of the core complex, has been
interpreted as an important structure for regional Mesozoic crustal thickening. In the northern
Albion Range, limited detailed geologic mapping and age control have left the ages of
metasedimentary rocks and shear zone kinematics across important structures poorly defined,
creating uncertainty in the Mesozoic tectonic history of the area. Detailed 1:12,000-scale geologic
mapping and structural analysis in the northern Albion Range identify the Basin-Elba fault as a
low-angle normal fault, with top-to-the-NW shear fabrics recorded throughout structural levels
beneath the core complex detachment. Lithostratigraphic correlations paired with U-Pb detrital
zircon geochronology of metasedimentary rocks in the hanging wall of the Basin-Elba fault
confirm an overturned, continuous section of late Neoproterozoic to early Cambrian rift-topassive-
margin strata. A maximum depositional age of 482.4 ± 14.4 Ma in the footwall of the
Basin-Elba fault suggests that Upper Cambrian–Ordovician carbonates and quartzites are a
continuation of the overturned limb of a regional fold nappe. Thus, the structurally lower
Mahogany Peaks fault is interpreted to record a Mesozoic thrust history that formed a regional fold nappe, with later Cenozoic extensional reactivation overprinting earlier fabrics and producing topto-
the-NW normal displacement during core complex development.
Key Words: Cordilleran hinterland, Basin-Elba Fault, Albion Range, Fold nappe, Extension |