Thesis (Ph.D.) - University of Queensland, 2006. / Includes bibliography.

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The last several years have seen renewed interest in the origin of silicic magmas thanks to the developments of new microanalytical techniques allowing the measurement of the isotopic and trace element compositions of erupted magmas on sub-crystal length scales. Concurrently, there has been rapid improvement in the sophistication of computer modeling of igneous systems. This dissertation is an interdisciplinary study of the rhyolites of the Yellowstone hotspot track using both techniques. Chapters II-IV, which have all been published in existing journals, are a detailed study of the O and Hf isotopic compositions of zircon phenocrysts from large rhyolitic eruptions in the central Snake River Plain, and from rhyolites which erupted in Oregon, Idaho, and Nevada coeval with the Columbia River flood basalts. They show that rhyolites are derived from combinations of fractionates of mantle-derived basalts and of different crustal end-members which are identifiable by their distinct isotopic end-member compositions. In the Snake River Plain and Yellowstone, they recognize a common trend where early erupted rhyolites have a strong signature of melting of ancient Precambrian crust, whereas later erupted rhyolites more closely resemble the mantle in their radiogenic isotopes and are more likely to be depleted in oxygen isotopes. Diversity in zircon grain compositions also documents a batch mixing process in which multiple compositionally distinct magma bodies are assembled into a larger common magma body prior to eruption. In Chapters V and VI, the former of which has been published with the latter in preparation, a new series of magmatic-thermomechanical models is presented which assume that melts rising through the crust are arrested by strong rheological contrasts. The strongest such contrast occurs at the brittle-ductile transition at 5-10 km depth, leading to the formation of a 10-15 km thick mafic mid-crustal sill, which separates upper and lower-crustal zones of partial melt, corroborating previous geophysical imaging studies. In Chapter VI, the above isotopic trends are replicated in the modeling scheme, which shows that the source depth of crustal melts tends to shallow with time through a combination of crustal heating and repeated caldera collapses. This dissertation includes both previously published co-authored material.

Ridanäs was an important port of trade on the island of Gotland, Sweden, in use during the 7-11th centuries, AD. Excavations have revealed the presence of two Viking Age (800-1070 AD) graveyards containing over 80 individuals. This study examined the remains of 60 of these individuals buried in the Viking graveyards. Strontium isotope analysis was used to determine whether they were local or non-local to the trading port. It was hypothesized that the Ridanäs population would consist of locals and non-locals who came to Gotland to take advantage of its successful trade economy. 13 archaeological fauna samples were analyzed in order to define the local bioavailable strontium isotope baseline range. Results showed that only 4 of the 60 individuals were non-local to Gotland, indicating that non-locals did not seek long-term residency at this port of trade.

Thesis (M.S.F.S.) / Positive identification of skeletonized human remains is a difficult task when dental records and/or DNA are unavailable. Through archaeological research, strontium (Sr) isotope analysis has successfully been used to trace an individual back to their place of birth using cortical bone and tooth enamel. This method has the potential, in forensic anthropological science, to help narrow down the search for missing persons to a specific geographical location. It has not been tested thoroughly on modern populations though, which is needed before applying in a forensic setting. This study used dental enamel from teeth of 78 individuals in the New England region of the United States (U.S.). The birthplaces represented by these individuals include New England and the greater Northeast of the U.S., Northwest region of the U.S., Central America, Caribbean Islands, West Africa, and Europe. Local faunal and water samples were also collected for local range comparisons. The samples were cleaned, approximately 10 mg of enamel removed from each tooth, acid washed, dried, and dissolved in nitric acid before analyzing the samples using a thermal ionization mass spectrometer (TIMS) for analysis of 87Sr/86Sr ratios. The human 87Sr/86Sr ratios were grouped by geographical region. An analysis of variance was used to test for regional variation and significant differences were found. The samples from the U.S. (excluding those from the Northwest) were significantly different from the samples in Central America, Caribbean Islands, West Africa, and Europe. Central American samples were also significantly different from the other groups. No significant differences were observed between the Caribbean Islands, West Africa and Europe. A significant difference was seen between the strontium ratios in the West Africa group based on bottled water vs. tap water that individuals reported drinking. The faunal samples from Pembroke, MA and water sample from Braintree, MA were not significantly different from the New England human samples, but the Brighton, MA water sample was significantly different. Based on the data, regional differences in 87Sr/86Sr ratios are detectable using strontium isotope analysis, yet a larger sample size for each of the regions is needed to strengthen the statistical results. The results suggest that the differences observed are due to a combination of geological effects and influences from the globalization of food. Further research is warranted by combining the analysis of hydrogen (δ2H) and oxygen (δ18O) isotopes to the strontium analysis. This will complement the strontium data by providing more insight to the local drinking water and potential effects of an increasingly homogenous diet within cultural regions.

Tomatoes (Lycopersicon esculentum L.) require high amounts of nitrogen to maximize fruit production. The type of nitrogen and timing of fertilizer applications are important in tomato production systems to reduce nitrogen losses while optimizing yields. A two-year greenhouse study was conducted to determine the effects of organic and inorganic fertilization treatments on nitrogen and carbon isotopic compositions of tomato plant leaves and fruit at immature and mature stages of plant growth. The carbon and nitrogen isotopic ratios together will also help to better depict trends that develop from conventional versus organically grown tomatoes and their resulting water use efficiency (WUE). ‘Better Bush’ tomatoes were grown in 8 L plastic pots filled with 1:1:1 steamed-sterilized sand:silt loam soil:peat mix. Eight fertility treatments were evaluated: no fertility, synthetic Miracle Grow® (MG), organic bonemeal and bloodmeal (BB), BB with liquid Earthjuice (BBL), BB with 25% vermicompost (VC), BBL with 25% VC, MG with 25% VC, and no fertility with 25% VC. The results indicated that for both growth stages, δ15NAir differed (P ≤ 0.05) between fertility treatments, while no major differences were observed for δ13CVPDB (P > 0.05), although conventionally fertilized tomatoes with MG and MG with 25% VC tended to have lower δ13CVPDB values suggesting a greater transpirational water loss through open stomata. The organic treatments with VC had higher δ15NAir values than the conventional or no added fertility treatments for all five leaflets from three different branches, fruit skins from the first two fruit clusters, fruit juices from the first two clusters and soil samples. Generally, the 15N/14N stable isotope values of tomato foliage and fruit are distinctly different between organic and conventional fertilizers, which could provide a powerful forensic tool in fingerprinting tomatoes grown by organic farming methods. Therefore, nitrogen isotopes can distinguish among different fertility treatments and also help to label the VC applications, which are thought to provide better fertility management due to less soil leaching and volatilization.

Biosignatures have been extensively studied at hot springs sites, such as Yellowstone, because liquid water is fundamental to the existence of life but also owing to the influx of mineral nutrients in these environments. However, some hot springs have upper temperatures exceeding the boundaries capable of sustaining life in all the spring facies, particularly those nearest the vent. Cold springs provide the same nutrient-rich environment with more ambient temperatures potentially capable of sustaining a diverse consortium of microorganisms across the entirety of the system. Ten Mile Graben Cold Springs, located in Southern Utah, is one such site known for its biota and preservation potential. This study aimed to observe the possible effects of the microorganisms on aragonite and calcite precipitation. Scanning electron microscope imagery observed biogenic fabric such as botryoidal aragonite and aragonite microspheres; however, the δ13C enrichment values of +2.80‰ to +7.30‰ imply the springs were dominantly precipitated through CO2 degassing. This discrepancy in the chemical and morphological data has been observed at other astrobiology analog sites such as Yellowstone; therefore, travertine and tufa seemingly do not preserve isotopic chemical biosignatures.

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abstract: Natural variations in 238U/235U of marine carbonates might provide a useful way of constraining redox conditions of ancient environments. In order to evaluate the reliability of this proxy, we conducted aragonite and calcite coprecipitation experiments at pH ~7.5 and ~ 8.5 to study possible U isotope fractionation during incorporation into these minerals. Small but significant U isotope fractionation was observed in aragonite experiments at pH ~ 8.5, with heavier U in the solid phase. 238U/235U of dissolved U in these experiments can be fit by Rayleigh fractionation curves with fractionation factors of 1.00007+0.00002/-0.00003, 1.00005 ± 0.00001, and 1.00003 ± 0.00001. In contrast, no resolvable U isotope fractionation was observed in an aragonite experiment at pH ~7.5 or in calcite experiments at either pH. Equilibrium isotope fractionation among different aqueous U species is the most likely explanation for these findings. Certain charged U species are preferentially incorporated into calcium carbonate relative to the uncharged U species Ca2UO2(CO3)3(aq), which we hypothesize has a lighter equilibrium U isotope composition than most of the charged species. According to this hypothesis, the magnitude of U isotope fractionation should scale with the fraction of dissolved U that is present as Ca2UO2(CO3)3 (aq). This expectation is confirmed by equilibrium speciation modeling of our experiments. Theoretical calculation of the U isotope fractionation factors between different U species could further test this hypothesis and our proposed fractionation mechanism. These findings suggest that U isotope variations in ancient carbonates could be controlled by changes in the aqueous speciation of seawater U, particularly changes in seawater pH, PCO2, [Ca], or [Mg] concentrations. In general, these effects are likely to be small (<0.13 ‰), but are nevertheless potentially significant because of the small natural range of variation of 238U/235U. / Dissertation/Thesis / Masters Thesis Chemistry 2015