Walker, James Allen, 1952-
M.S. (Master of Science)
Department of Geology
Ignimbrite--Chile; Sedimentation and deposition--Chile
The sedimentological characteristics of the San Andres ignimbrite relate information of the preemptive, eruptive and depositional conditions during a large explosive volcanic eruption. Grain size analysis was accomplished by sieving the coarser fractions and pipetting the finer fractions. Separation of the pumice, crystal and lithic components coarser than 1 phi (1/2 mm) were done to examine the grading of the components . Beta quartz and biotite zonation within the ignimbrite supports the existence of a zoned magma chamber. The San Andres ignimbrite was deposited as a pyroclastic flow from a large-volume, high eruption column. The flow was highly fluidized, based on the presence of coarse-tail grading, reverse grading of pumice, normal grading of lithics and lithic-rich breccia lenses. The flow moved by laminar flow based on the preservation of the mineralogic zonations; however, turbulence did occur locally. The formation of some of the lithic breccia concentrations was due to the occurrence of hydraulic jumps.
Fuss, Donna M., "Sedimentological characteristics of the San Andres ignimbrite, central Chile (27⁰S)" (1986). Graduate Research Theses & Dissertations. 4846.
ix, 100 pages
Northern Illinois University
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