Geometry of the Neoproterozoic and Paleozoic rift margin of western Laurentia: Implications for mineral deposit settings

Abstract

The U.S. and Canadian Cordilleran miogeocline evolved during several phases of Cryogenian-Devonian intracontinental rifting that formed the western margin of Laurentia. Recent fi eld and dating studies across central Idaho and northern Nevada result in identifi cation of two segments of the rift margin. Resulting interpretations of rift geometry in the northern U.S. Cordillera are compatible with interpretations of northweststriking asymmetric extensional segments subdivided by northeast-striking transform and transfer segments. The new interpretation permits integration of miogeoclinal segments along the length of the western North American Cordillera. For the U.S. Cordillera, miogeoclinal segments include the St. Mary-Moyie transform, eastern Washingtoneastern Idaho upper-plate margin, Snake River transfer, Nevada-Utah lower-plate margin, and Mina transfer. The rift is orthogonal to most older basement domains, but the location of the transform-transfer zones suggests control of them by basement domain boundaries. The zigzag geometry of reentrants and promontories along the rift is paralleled by salients and recesses in younger thrust belts and by segmentation of younger extensional domains. Likewise, transform-transfer zones localized subsequent transcurrent structures and igneous activity. Sediment-hosted mineral deposits trace the same zigzag geometry along the margin. Sedimentary exhalative (sedex) Zn-Pb-Ag ± Au and barite mineral deposits formed in continental-slope rocks during the Late Devonian-Mississippian and to a lesser degree, during the Cambrian-Early Ordovician. Such deposits formed during episodes of renewed extension along miogeoclinal segments. Carbonate-hosted Mississippi Valleytype (MVT) Zn-Pb deposits formed in structurally reactivated continental shelf rocks during the Late Devonian-Mississippian and Mesozoic due to reactivation of preexisting structures. The distribution and abundance of sedex and MVT deposits are controlled by the polarity and kinematics of the rift segment. Locally, discrete mineral belts parallel secondary structures such as rotated crustal blocks at depth that produced sedimentary subbasins and conduits for hydrothermal fl uids. Where the miogeocline was overprinted by Mesozoic and Cenozoic deformation and magmatism, igneous rock-related mineral deposits are common.

Regional crustal-scale structures as conduits for deep geothermal upflow

“…Concurrent hydrothermal fluid flow and ore deposition along the Getchell, Crescent Valley-Independence and Alligator Ridge mineral trends (Fig. 3) is also interpreted to have been controlled by preexisting, possibly Proterozoic, crustal structures, though the age and nature of the structures remain more ambiguous (Cline et al, 2005;John et al, 2003;Lund, 2008).…”

“…The western edge of the Laurentian craton was originally defined by the Sr = 0.706 line (Kistler, 1990;Oldow, 1992), but more recent lead and strontium isotopic studies (Crafford and Grauch, 2002;Grauch et al, 2003;Wooden et al, 1998) and sedimentary facies studies (Lund, 2008) have delineated the edge of the craton with a higher degree of detail (Fig. 3).…”

“…3). Though the north-northwest striking late Proterozoic rift segments are orthogonal to pre-existing structures, transform/transfer zones may reactivate even older inferred northeast-striking Paleo-to Mesoproterozoic basement structures (Lund, 2008).…”

“…The western Cordillera of North America underwent continental-scale rifting in the late-Proterozoic and has undergone nearly continuous, collisional, extensional and strike-slip deformation since the Devonian (Dalziel, 1997;Dickinson, 2006;Lund, 2008 and references therein). These deformational events have generated a series of crustal-and lithospheric-scale structures of varying character and age throughout the Great Basin.…”

Geology, Mantle Tomography, and Inclination Corrected Paleogeographic Trajectories Support Westward Subduction During Cretaceous Orogenesis in the North American Cordillera

“…Some workers (Lund 2008;Dehler et al 2010;Balgord et al 2013) suggest that Neoproterozoic rocks of the Windermere Supergroup and its equivalents are rift rocks, but evaporites are unreported, volcanic rocks are very sparse, and overall the rocks are 100-200 Myr older than passive margin subsidence of the North American margin (Bond and Kominz 1984). The lack of such rocks along the entire length of the Cordillera suggests that the rift rocks, along with outer riseslope sedimentary rocks, which are also missing from North America, were not simply displaced by strike-slip faults, but instead torn from the margin during slab failure -a feature readily accounted for in the westerly subduction model, in which North America was attached to a westerly subducting slab, but difficult to reconcile in easterly dipping models (Hildebrand and Bowring 1999;Hildebrand 2009Hildebrand , 2013.…”