Source: Dissertation Abstracts International, Volume: 70-01, Section: B, page: 0166.

Adviser: Mark T. Brandon.

As melting products of the mantle, basaltic magmas may be used to interpret magma processes, tectonic changes, mantle compositions, and the fate of recycled lithosphere. Such interpretations are typically made based on scale-dependent spatial and temporal chemical variations. However, it is not yet clear how to interpret short time-scale volcanic geochemical variation that is not due to more shallow processes in the crust. To address this problem, in my dissertation I examine short time- and length-scale phenomena in primitive basalts with two main objectives in mind: (1) to unravel complicated magmatic geochemical histories so that we can fully describe recurring melting and mixing processes that occur in a heterogeneous mantle over < 100 years, and (2) to then use transient events in magmas, such as xenolith entrainment or late stage oxidation to investigate the presence of rare, Mg-endmember olivine in basalts and to develop a new thermochronologic method.

To study recurring intra-eruption variation, I examine the most isolated natural example: the monogenetic vent. The Big Pine Volcanic Field preserves primitive, short-lived (< 100 year) eruptive sequences that show a simple chemical and isotopic evolution, unrelated to shallow-level processes, that repeats at different vents. The chemical evolution for all elements and isotopes is controlled by a single, univariant reaction that is consistent with simple dynamic melting of a heterogeneous source lithology of peridotite and pyroxenite or melt-rock reaction in the mantle. This coupled mixing and melting trend is applicable to the other monogenetic vents in the field, and likely other intraplate primitive single eruption sequences. By comparing these trends to larger scales, I find that long-term trends represent a moving aggregation of the short-term trends, caused by systematic source changes over 10 6 -- 107 yr. Anomalous Fo99.8 olivines in the Papoose Canyon sequence are the most magnesian known natural samples. We show that these rare crystals formed during continuous oxidation of olivine in a late-stage, hot, high fO2 environment, and may be more common that often thought. I also develop a new method of dating young, basaltic eruptions using zircon (U-Th)/He in entrained xenoliths.