Three new articles by NBMG research geologist Sean Long and co-authors (including NBMG’s Chris Henry and John Muntean), two focusing on the Eureka area, and one regional study across eastern Nevada, have recently been published in the journals Geosphere and Geology. PDFs of these papers, and accompanying maps and plates, are available for download at www.seanpatricklong.com/publications.html
Long, S.P., Henry, C.D., Muntean, J.L., Edmondo, G.P., and Cassel, E.J., 2014, Early Cretaceous construction of a structural culmination, Eureka, Nevada, U.S.A.: implications for out-of-sequence deformation in the Sevier hinterland: Geosphere, v. 10, p. 564-584, doi:10.1130/GES00997.1.
Abstract: Documenting the timing relationships between deformation in the frontal and distal parts of mountain belts is fundamental for understanding the dynamics of how they are constructed. In this study, we present a new geometric and timing model for deformation in the distal part of the Mesozoic Cordilleran mountain belt in central Nevada. The model is based on new geologic mapping, cross-sections that illustrate the modern and pre-deformed geometry, new age dates from volcanic and sedimentary rocks, and assessment of regional field relationships. Our results reveal that Cretaceous deformation was taking place in the distal part of the mountain belt in Nevada at the same time as deformation in the frontal part in Utah. We use this new timing relationship, along with the predictions of models for the dynamic behavior of the construction of mountain belts, to propose that this deformation in Nevada and Utah was genetically-linked.
Long, S.P., 2015, An upper-crustal fold province in the hinterland of the Sevier orogenic belt, eastern Nevada, U.S.A.: a Cordilleran Valley and Ridge in the Basin and Range: Geosphere (published online 2-17-15), v. 11, doi:10.1130/GES01102.1.
Abstract: In Nevada, Tertiary extension of the crust has obscured the geological records of older deformation events, including the Mesozoic construction of the Cordilleran mountain belt. In this study, a paleo-geologic map of eastern Nevada, showing the ages and distributions of rocks that were at the surface at about 30 million years ago, illustrates the style and geometry of deformation associated with Cordilleran mountain building. The map reveals a region of folds in eastern Nevada that are similar in scale to those in the Valley and Ridge province of the Appalachian mountains. The folds are interpreted to have formed during the Cretaceous period, as a result of eastward translation above a deep detachment surface that projects westward from the Sevier fold-and-thrust belt in Utah. These observations are synthesized with studies of other structural provinces of Nevada and western Utah, to propose a model for deformation during Cordilleran mountain building.
Long, S.P., Thomson, S.N., Reiners, P.W., and Di Fiori, R.V., 2015, Synorogenic extension localized by upper-crustal thickening: an example from the Late Cretaceous Nevadaplano: Geology (published online 2-27-15), v. 43, doi:10.1130/G36431.1.
Abstract: Mountain belts such as the Himalayas, Andes, and North American Cordillera are formed from contractional deformation that shortens and thickens continental crust. However, in several mountain belts, extensional deformation that thins and stretches the crust has been documented to occur simultaneously with contractional deformation. At present, we do not fully understand the factors that control the location of extension during mountain building. In this paper, an example of extension during mountain building is documented in the North American Cordilleran mountain belt in Nevada, where an arch-shaped fold that developed from contractional deformation was later extended by faults. Motion on these faults brought rocks that were buried to 6-8 km depths to near the surface, resulting in significant cooling. The timing and rates of this cooling are calculated, using four different techniques that give ages for cooling through a total temperature range of 220˚C to 60˚C. The timing of cooling, and therefore the timing of extensional faulting, was between 75 and 60 million years ago, which is synchronous with contractional mountain building in this region of Nevada. This study demonstrates that sites of local crustal thickening can focus the location of extension during mountain building.