ZIGZAG GEOMETRY OF NEOPROTEROZOIC-EARLY PALEOZOIC CORDILLERAN RIFT MARGIN: IMPLICATIONS FOR MINERAL DEPOSITS, CANADA TO NEVADA
The U.S. Cordilleran margin formed as northwest-striking rift segments offset by northeast-striking transform or transfer zones, including the St. Maries-Moyie transform, Washington-Idaho upper-plate rift, Snake River transfer, southeast Idaho-Utah-Nevada (Great Basin) lower-plate rift, and Mina transfer. This U.S. margin had similar geometries to those interpreted for the Canadian margin, such that the Cordilleran rift and passive margin had a zigzag geometry of reentrants and promontories. It is paralleled by salients and recesses in younger thrust belts and by segmentation of younger extensional domains where transform-transfer zones localized subsequent deformation.
Sediment-hosted ore deposits also follow the rift margin: Cambrian–Early Ordovician and Devonian extension-related sedimentary exhalative (SEDEX) Zn-Pb-Ag ± Au and barite ore deposits in continental-slope rocks and Late Devonian–Mississippian and Mesozoic Mississippi Valley type (MVT) Zn-Pb deposits in continental-shelf rocks during structural reactivation. Distribution of the sediment-hosted deposits was controlled by polarity, kinematics, basin depth, and internal structure of each rift or transcurrent segment. Locally, discrete mineral belts parallel internal structures such as rotated crustal blocks at depth that produced sedimentary subbasins and caused hydrothermal-fluid conduits. Where overprinted by Mesozoic and Cenozoic deformation and magmatism, igneous rock-related, epigenetic ore deposits prevail.