Development and application of argon-40/argon-39 laser-fusion dating and argon-40/argon-39 step-heating dating of quaternary basaltic volcanic rocks: A comparison of conventional potassium-argon dating and argon-40/argon-39 dating methods

Results on the development and application of {dollar}rmsp{lcub}40{rcub}Ar/sp{lcub}39{rcub}Ar{dollar} laser-fusion dating and{dollar}rmsp{lcub}40{rcub}Ar/sp{lcub}39{rcub}Ar{dollar} step-heating methods of Quaternary low potassium basaltic rocks are presented here.; The first chapter contains a brief historical account of radiometric dating, the development of K-Ar and {dollar}rmsp{lcub}40{rcub}Ar/sp{lcub}39{rcub}Ar{dollar} dating, a description of the equipment and methods used in this study, and a tutorial on the {dollar}rmsp{lcub}40{rcub}Ar/sp{lcub}39{rcub}Ar{dollar} dating method. Chapters two, three, and four of this dissertation present the results of a case study comparing the conventional K-Ar method to the more advanced {dollar}rmsp{lcub}40{rcub}Ar/sp{lcub}39{rcub}Ar{dollar} laser-fusion and restance furnace methods and the application of the Paleomagnetic studies on samples from the Lanthrop Wells volcanic center in Southwestern Nevada. The Lathrop Wells volcanic center, the youngest volcano located near Yucca Mountain, Nevada, has significant implications for volcanic hazards to the proposed High-Level Radioactive Waste Repository Site at Yucca Mountain.; {dollar}rmsp{lcub}40{rcub}Ar/sp{lcub}39{rcub}Ar{dollar} step-heating and laser total fusion data age determinations from the Lathorp Wells volcanic center, Nevada indicate an age of 122 {dollar}pm{dollar} 3 ka for the Lathrop Wells volcanic center. This age is consistent with previously determined K-Ar ages. In addition, these results are consistent with the chronology and stratigraphy of the regional Quartenary units and reported surface exposure ages on the Lathrop Wells deposits.; The paleomagnetic data indicate that there are at least two eruptive units at the Lathrop Wells volcanic center, Nevada. The measured directions of remanent magnetization for the two flows are 51.5{dollar}spcirc{dollar} inclination, 2.2{dollar}spcirc{dollar} declination, and 51.5{dollar}spcirc{dollar} inclination, 354.6{dollar}spcirc{dollar} declination. The difference in the paleomagnetic pole directions, 4.7{dollar}spcirc{dollar}, is different at the 99.98 percent confidence level. The discovery of at least two flow units of different age at the Lathrop Wells volcanic center indicates a more complex volcanic history than previously thought. The observed angular difference between the two mean directions suggests a minimum age difference between the eruptive events of at least 100 years. Weighted means radiometric ages on these two units are not significantly different. Based on statistical analyses, the difference in age between the flows is less than or equal to approximately 22.3 ka.; The fifth chapter presents the results of a study of the age of the Cobb Mountain Normal-Polarity Subchron. The main point of the chapter, however, is a comparison of the Geomagnetic Polarity Time Scale with the Astronomical Polarity Time Scale. The new revised age of {dollar}rmsp{lcub}40{rcub}Ar/sp{lcub}39{rcub}Ar{dollar} age of the Cobb Mountain Normal-Polarity Subchron from this study is concordant with the Astronomical Polarity Time Scale, thus validating the use of Milankovitch cycles for estimating the ages of global climatic changes. In addition, a discussion of the need for a Quaternary {dollar}rmsp{lcub}40{rcub}Ar/sp{lcub}39{rcub}Ar{dollar} dating standard is presented and proposes the sanidine from the rhyolite of Alder Creek, California for such a standard. (Abstract shortened by UMI.)...