Fracturing of Sedimentary Rock Around Magmatic Dikes Due to Thermal Pressurization of Pore Fluids
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The Rock Fracture Project was an industrial affiliates project within the Structural Geology and Geomechanics Program in the School of Earth Sciences at Stanford University from 1990 to 2015. The project was co-directed by Professors David D. Pollard and Atilla Aydin. The Rock Fracture Project was one of the largest and most active research groups in the world devoted to conducting state-of-the-art research on problems of rock fracture and related crustal deformation and fluid flow, with special attention to the needs of the petroleum industry. Funding for the project came from more than twenty-five member companies. The 405 scientific reports from 25 annual workshops are archived here.
Examination of the host rock around magmatic dikes at Ship Rock, NM, reveals two sets of joints in the Mancos shale in the immediate vicinity of the dikes. One set is parallel to the dike contact and is believed to have formed just ahead of the dike as it was propagating (Delaney et al. 1986). The other joint set is sub-perpendicular to the dike contact and is the focus of this paper. A high-resolution aerial map of a segment of the northeastern dike at Ship Rock was made using Structure from Motion (SfM), where a camera attached to a helium balloon collects photographs, which are automatically orthorectified and stitched together in Agisoft LLC. Measurements from this map, combined with other field data, shows that the joint set remains perpendicular to the contact along the length of the dike, even when the orientation of the dike changes. Furthermore there is a significant decrease in the fracture spacing towards the center of the dike. We interpret the joints to have formed as a result of heat flow from the dike, and we investigate the role of thermal pore-pressurization in this process. Understanding the formation of these joints is critical to our understanding of brecciation and erosion of host rock around fissure eruptions to produce sustained eruptions through larger cylindrical volcanic vents.
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- Townsend, Meredith and Pollard, David D. (2014). Fracturing of Sedimentary Rock Around Magmatic Dikes Due to Thermal Pressurization of Pore Fluids. Stanford Digital Repository. Available at: http://purl.stanford.edu/gc344vg6165
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