Control of Mechanical Stratigraphy on Brittle Deformation Style, Northern Snake Range, Nevada
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Date
2019-12
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The Ohio State University
Abstract
Bourne (2003) presents a theoretical, layered-elastic model by which fractures can form as a result of mechanical stratigraphy, yet the ability of this model to explain fracture patterns at specific outcrops is still an open question. Hendry’s Creek, Nevada is home to outcrops of alternating metasedimentary McCoy Creek Group rocks of the Northern Snake Range Décollement footwall. Layers of mylonitic quartzite and mica schist are distinguished by distinct styles of brittle deformation; quartzite layers exhibit highly concentrated, sub-vertical joints, whereas mica schist layers exhibit conjugate normal fault systems. These layered strata underwent brittle deformation concurrent with exhumation during the mid-Miocene (17 Ma), a process in which the regional stress state would have remained compressive, yet tensile stresses clearly accumulated within quartzite layers. Here, we test the ability of a layered elastic mechanical stratigraphy model, incorporating material properties, thicknesses of sedimentary layers, and tectonic history of rocks to predict the formation and distribution of the two distinct fracture populations observed at Hendry’s Creek. High-resolution drone imaging and photogrammetric 3D modelling software enabled extraction of data from an entire cliff face of alternating mica schist and quartzite layers including fracture orientation, concentration, and layer thickness. Structural orientation data provide evidence the two fracture populations are kinematically consistent, however, the order of initiation implied by specific field observations appear to contradict the layered elastic geomechanical model, suggesting a purely elastic model of brittle deformation may fail to accurately demonstrate the role of mechanical stratigraphy.
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Keywords
Mechanical Stratigraphy, Brittle Deformation, Hendry's Creek, Snake Range