1995/01/01 by Peter G. DeCelles, Gautam Mitra · 5 citations
Earth and Planetary Sciences · #Geological and Geochemical Analysis #earthquake and tectonic studies #Geological formations and processes
paper · doi:10.1130/0016-7606(1995)107<0454:hotsow>2.3.co;2
Research Article| April 01, 1995 History of the Sevier orogenic wedge in terms of critical taper models, northeast Utah and southwest Wyoming Peter G. DeCelles; Peter G. DeCelles 1Department of Geosciences, University of Arizona, Tucson, Arizona 85721 Search for other works by this author on: GSW Google Scholar Gautam Mitra Gautam Mitra 2Department of Earth and Environmental Sciences, University of Rochester, Rochester, New York 14627 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1995) 107 (4): 454–462. https://doi.org/10.1130/0016-7606(1995)107<0454:HOTSOW>2.3.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Peter G. DeCelles, Gautam Mitra; History of the Sevier orogenic wedge in terms of critical taper models, northeast Utah and southwest Wyoming. GSA Bulletin 1995;; 107 (4): 454–462. doi: https://doi.org/10.1130/0016-7606(1995)107<0454:HOTSOW>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Problems with applying critical taper models to ancient orogenic wedges are overcome in the Late Cretaceous–late Paleocene Sevier orogenic wedge in Utah and Wyoming by a symptomatic approach in which wedge behavior is inferred from the time-space distribution of thrust faulting, erosion, and synorogenic sediment accumulation in association with the orogenic wedge. In turn, the causes of wedge behavior are interpreted in terms of features that are known about the Sevier wedge, such as the locations of major décollements and the lithologic constituents of major thrust sheets. From Coniacian through late Paleocene time (∼35 m.y.), basement and cover rocks in the Sevier wedge were shortened by ∼100 km in three major and one minor events. An overall eastward progression of thrusting was punctuated by several episodes of out-of-sequence and hinterland vergent thrusting.Over the long term, wedge taper was controlled by internal wedge strength, initial taper, and changes in the durability of the upper surface of the wedge and its internal lithostratigraphy. Critical taper was maintained by the offsetting effects of basement duplexing in the rear of the wedge and forward imbrication at the front of the wedge. While the basal décollement was mainly in basement rocks, the wedge was highly tapered and thrust spacing was relatively close (∼15 km). Beginning ca. 75 Ma, the basal décollement ramped upward and eastward into weak Cambrian shale and Jurassic salt, thrust spacing increased to 25–45 km, and wedge taper decreased drastically. The highly tapered rear part of the wedge carried strong basement rocks above moderately weak mylonitic and cataclastic décollements, whereas the frontal, lower-taper part of the wedge carried sedimentary rocks above extremely weak (salt and shale) décollements. Through time, internal strength of the wedge decreased as it incorporated an increasing proportion of sedimentary rocks; the thrust belt was able to advance eastward in spite of its decreasing internal strength and decreasing taper because the basal décollement of the wedge also became weaker through time, both by strain softening (beneath the rear of the wedge) and by propagating along extremely weak rocks (beneath the front of the wedge).Provenance data from associated synorogenic conglomerates indicate that the durability of the upper surface of the wedge probably increased over the long-term history of the Sevier wedge, as an increasing proportion of the erosional surface became occupied by resistant Precambrian quartzite and basement rocks. This would have had the effect of decreasing the rate of erosion through time and maintaining a steeper surface slope, which would have helped the wedge to remain at critical to supercritical taper.The Sevier wedge also exhibits several shorter-term (<10 m.y.), three-part cycles of behavior in terms of deformation, erosion, and sedimentation. The wedge (1) began each cycle in a critical state and imbricated internally and forward, (2) became supercritical and slid forward >10 km, and (3) was subjected to regional erosion (marked by major unconformities) that ultimately caught up with tectonic thickening and caused the wedge to stall. This cyclicity is attributed to the need for wedges to become supercritical before they can propagate forward over large distances and a lag-time between wedge thickening (and uplift) and wedge erosion. Erosion eventually catches up to the rate of uplift, the wedge stalls, and the locus of deformation shifts to the rear of the wedge in order to rebuild taper. This analysis suggests that orogenic wedges continually deform and "find a way" to maintain taper sufficient to allow forward propagation as long as a sufficient push from the rear exists. The actual taper value may change substantially through time as lithostratigraphy, internal strength, upper surface durability, and presence/absence of weak potential stress guides conspire to maintain a critical taper. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.