Revised exhumation history of the Wind River Range, WY, and implications for Laramide tectonics

Abstract

A reanalysis of apatite fission track (AFT) thermochronology coupled with thermal‐kinetic modeling of samples from the Wind River Range document Late Cretaceous to early Eocene episodic cooling and exhumation of one of the largest basement‐cored ranges in the western United States. Three vertical transects taken at different latitudes along the length of the 145 km Wind River Range reveal that exhumation is uniform along strike suggesting steady displacement along the Wind River Fault, and significant exhumation and relief in the Wind River Range by the early Eocene. Thermal modeling of AFT ages, lengths, and compositional proxies document rapid exhumation from ~65 to 50 Ma. This rapid exhumation episode matches a period of accelerated subsidence in the adjacent Green River and Wind River basins. At ~50 Ma, exhumation dramatically slowed by an order of magnitude coincident with decreasing subsidence in the adjacent basins. No signal of Oligocene cooling is apparent in either AFT cooling ages or thermal modeling suggesting that a possible later phase of reactivation of structures and uplift, as previously suggested, was limited to less than approximately 1 km of exhumation.

Early Inception of the Laramide Orogeny in Southwestern Montana and Northern Wyoming: Implications for Models of Flat‐Slab Subduction

“…Previous studies of uplift, basin subsidence, and erosional histories of the Laramide in Wyoming indicate mostly early Cenozoic ages (e.g., Peyton et al, ; Stevens et al, ); these relatively young ages may represent thermal processes related to westward roll‐back of the subducting slab (Fan & Carrapa, ) or accretion of Shatsky conjugate depleted mantle lithosphere beneath Wyoming and the associated upper crustal deformation and subsequent removal (Humphreys et al, ; Stevens et al, ). Westward to southwestward migration of magmatism in the mid‐Cenozoic is consistent with the history of the stress field (Bird, ) and can be explained by westward migration of the Farallon plate hingeline and falling away of the slab (referred to as slab rollback ; Best et al, ; Coney & Reynolds, ; Constenius, ; Dickinson & Snyder, ).…”

“…However, the Laramide uplifts of Montana present some difficulties for recent geodynamic models that project a narrow zone of shallow flat-slab subduction from the Mojave Desert region into central Wyoming along a northnortheastward trajectory (e.g., Axen et al, 2018;Jones et al, 2011;. Refined models might include the effects of a spatially less restricted Shatsky conjugate moving along a trajectory more eastward than northward; a zone of somewhat deeper, but still flat, subducting Farallon lithosphere to the north of the zone of shallowest subduction (e.g., Saleeby, 2003); and a cratonic lithospheric root that extends farther north below the Archean crust of western Journal of Geophysical Research: Solid Earth may represent thermal processes related to westward roll-back of the subducting slab (Fan & Carrapa, 2014) or accretion of Shatsky conjugate depleted mantle lithosphere beneath Wyoming and the associated upper crustal deformation and subsequent removal (Humphreys et al, 2015;Stevens et al, 2016). Westward to southwestward migration of magmatism in the mid-Cenozoic is consistent with the history of the stress field (Bird, 2002) and can be explained by westward migration of the Farallon plate hingeline and falling away of the slab (referred to as slab rollback; Best et al, 2009;Coney & Reynolds, 1977;Constenius, 1996;Dickinson & Snyder, 1978).…”

“…Interestingly, no significant cooling is recorded by AFT between ca. 60 and 50 Ma, which is the main timing of cooling recorded by AFT in the Wind River Range in Wyoming (Stevens et al, ).…”

“…Exhumation of the Wind River Range occurred between ca. 60 and 50 Ma (Fan & Carrapa, 2014;Stevens et al, 2016). Apatite fission track (AFT) and (U-Th[-Sm])/He thermochronology have been applied to Precambrian basement samples of the Beartooth Range (Cerveny & Steidtmann, 1993;Omar et al, 1994;Peyton et al, 2012; this study) and the Bighorn Range (Crowley et al, 2002;Peyton et al, 2012), revealing a complex Cretaceous to early Cenozoic cooling history.…”

Along-strike continuity of structure, stratigraphy, and kinematic history in the Himalayan thrust belt: The view from Northeastern India

“…The AFT ages are similar to AFT ages reported by Grujic et al [] from Bhutan but significantly older than ages reported by Adlakha et al []. We note that Adlakha et al [] used a slow etching protocol for AFT, which has been shown to produce unreliable ages [e.g., Murrell et al ., ; Stevens et al ., ].…”