ill. (some col.), maps; Thesis (M.A.)--University of Oregon, 1968; Includes bibliography
An Abstract of the Thesis of Bonnie Lee Stepp Ryden for the degree of Master of Science in the Department of Geology to be taken December 1968 Title: Structural Analysis of the^Llao Rock Dacite, Crater Lake, Oregon Approved: (G. T. Benson, Adviser for the Thesis A preliminary study (Benson and Kittleman, 1968) suggests that the geometry of flow layering in silicic lavas may be diagnostic of the direction of flow movement. The validity of this hypothesis has been examined by means of a detailed structural analysis of the Llao Rock dacite flow located in Crater Lake National Park, Oregon. This flow is exposed in cross section on the wall of Crater Lake caldera, and the direction of movement of the flow is fixed by the bearing and slope of the glacial valley into which it was extruded. The flow consists of microlitic dacite characterized by prominent flow layering. Localized in layers, rod-shaped augite microlites show strong preferred orientation parallel to the layering. Equal-area orientation diagrams of poles to flow layering planes measured in small domains have definite patterns of monoclinic symmetry related to the local lava movement direction. The pattern of layering in the whole flow is interpreted to indicate that the flow advanced on a broad front to the N 50° W, spreading laterally to the east and west where it overflowed the containing valley. Axial structures (folds) are developed perpendicular to the direction of flow, except where flow was definitely channelled and axial structures parallel the flow movement direction. Apparently there are two end-member components to flow movement in a viscous silicic lava—radial spreading and channelled flow. The orientation of flow layering and axial structures as well as phenocrysts and probably microlites in such a flow may suggest the overall pattern of movement of the flow.
An Abstract of the Thesis of Bonnie Lee Stepp Ryden for the degree of Master of Science in the Department of Geology to be taken December 1968 Title: Structural Analysis of the^Llao Rock Dacite, Crater Lake, Oregon Approved: (G. T. Benson, Adviser for the Thesis A preliminary study (Benson and Kittleman, 1968) suggests that the geometry of flow layering in silicic lavas may be diagnostic of the direction of flow movement. The validity of this hypothesis has been examined by means of a detailed structural analysis of the Llao Rock dacite flow located in Crater Lake National Park, Oregon. This flow is exposed in cross section on the wall of Crater Lake caldera, and the direction of movement of the flow is fixed by the bearing and slope of the glacial valley into which it was extruded. The flow consists of microlitic dacite characterized by prominent flow layering. Localized in layers, rod-shaped augite microlites show strong preferred orientation parallel to the layering. Equal-area orientation diagrams of poles to flow layering planes measured in small domains have definite patterns of monoclinic symmetry related to the local lava movement direction. The pattern of layering in the whole flow is interpreted to indicate that the flow advanced on a broad front to the N 50° W, spreading laterally to the east and west where it overflowed the containing valley. Axial structures (folds) are developed perpendicular to the direction of flow, except where flow was definitely channelled and axial structures parallel the flow movement direction. Apparently there are two end-member components to flow movement in a viscous silicic lava—radial spreading and channelled flow. The orientation of flow layering and axial structures as well as phenocrysts and probably microlites in such a flow may suggest the overall pattern of movement of the flow.