| The U.S. Department of Energy began studying Yucca Mountain in 1978 as a potential high-level nuclear waste storage facility. An important part of studying igneous events at the Yucca Mountain repository site is to consider natural analogs.; A 5 million year old shallow basaltic dike system is located in Mohave County, northwestern Arizona. The vent and dike segments considered in this study display several characteristics that make this a good system to study as a natural analog. The dike segments are composed of alkali basalt, which contains large kaersutite xenocrysts, along with olivine, plagioclase, analcime, and other accessory minerals. The surrounding country rock is fanglomerate, a sedimentary rock composed of alluvial fan deposits. The two dike segments exposed along U.S. Highway 93 display interesting distributions of both size and concentration of kaersutite xenocrysts as well as olivine phenocrysts. Also, vesicles within the dikes exhibit a distribution that may suggest the loss of volatiles during magma ascent, a very important factor that can alter eruption types from explosive to effusive. (Abstract shortened by UMI.)... |
