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This dissertation comprises four studies that apply radiogenic isotopes and 14C as primary tools to investigate problems in igneous petrology and environmental contamination. Two studies utilize uranium (U) isotopes to investigate U contamination related to the former Fernald Feed Materials Production Center (FFMPC) in southwest Ohio. Two other studies utilize Sr, Nd, Pb isotopes, U-series disequilibria and 14C to assess the magmatic evolution and timing of explosive eruptions of Sete Cidades volcano, Sao Miguel, Azores.Two studies examine the utility of tree bark for resolving the areal extent of atmospheric U contamination, using several locations in southwest Ohio that processed U. U concentrations up to ~400 times local background levels, along with progressively more depleted and enriched 235U/238U and higher 236U/238U as the FFMPC is approached, demonstrate the presence of anthropogenic U in the environment, with the minor isotope 236U serving as the most sensitive tracer. Atmospheric dispersal models demonstrate that a 5 um U-rich particle can be transported ~38 km from the FFMPC, providing a mechanism for the non-natural isotopic 236U/238U observed in Hamilton and Oxford, OH. Scanning electron microscopy revealed U-rich particles in tree bark within 1-3 km of the FFMPC.Two studies evaluate the petrogenetic processes and timescales associated with the P1-P17 deposits at Sete Cidades volcano. One study presents the first detailed petrographic, geochemical, and isotopic analyses of the Sete Cidades P1-17 eruptive products, and demonstrates that trachyte pumices from P1-P17 are primarily derived through fractional crystallization of a common parental magma, involving discrete batches of magma following distinct fractionation paths. Isotopic variations among whole rock, sanidine, and glass require the presence of xenocrystic sanidine and assimilation of small degree non-modal, partial melt of syenite wall rock similar to Sete Cidades xenoliths. The second of these studies aimed to better constrain the eruptive timing and the impact of volcanic outgassing on 14C ages. 14C data from paleosols in the P1-P17 eruptive sequence were compared to maximum ages from 226Ra-230Th disequilibria in pumices. We present the first age constraints for the P1 and P8 deposits, and further constrain the age of the P17 deposit. 14C data from modern terrestrial gastropods demonstrates the current contribution of volcanic degassing to 14C ages near volcanic centers. New ages constrain the average eruptive recurrence interval for the P1-P17 deposits at ~220 years. Together these four studies highlight the applicability of isotopic tools to a wide variety of earth systems and scenarios. |
