Indiana University-Purdue University Indianapolis (IUPUI) / A broad range of samples were collected from the Huron-Erie Lobe, Lake Michigan Lobe, Saginaw Lobe, and Tipton Till Plain of northern Indiana to determine the provenance of Laurentide Ice Sheet till in the Midwest U.S. during the Illinoian and Wisconsinan glaciations. U-Pb age distributions from approximately 300 detrital zircons (DZ) were used as provenance indicators for each till sample. Till from the Lake Michigan Lobe and was found to be largely homogenized. The distinct lobe DZ age distributions are the Lake Michigan Lobe till with a dominant ~1465 Ma peak, the northern Huron-Erie Lobe till with a dominant ~1060 Ma and a secondary peak at ~1450 Ma, the southern Huron-Erie Lobe till with nearly equal peaks at ~1435 Ma, ~1175 Ma, and ~1065 Ma, and the southern Saginaw Lobe till with a dominant peak at ~1095 Ma. Those four DZ age distributions were treated as endmembers in a nonlinear least-squares mixing model to calculate the contribution of each lobe to till in the Tipton Till Plain. Huron-Erie and Saginaw lobe tills were found to be the primary components of the Tipton Till Plain, and Lake Michigan Lobe till was only found in the western Tipton Till Plain. Zircons from the Saginaw Lobe till increased 39 % in the eastern Tipton Till Plain between the Illinoisan and Wisconsinan glaciations. The mixing model was also applied to relate the DZ age distributions of the lobes to bedrock within and near their flow paths. When comparing nearby bedrock to each lobe’s till, mixing model results, yield an approximate maximum transport distance between 500 and 630 kilometers for the matrix vii fraction of till in the Lake Michigan, Huron-Erie, and Saginaw lobes. Samples for the southern Huron-Erie Lobe indicate that the most of the zircon ages within the southern Huron-Erie Lobe till in Indiana were specifically entrained between Niagara County, New York and east-central Indiana. Within the model’s error, 93 – 100 % of the detrital zircons in each of the three lobes are relatable to nearby Paleozoic and Precambrian sedimentary and metamorphic bedrock formations.

京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第17916号 / エネ博第288号 / 新制||エネ||60(附属図書館) / 30736 / 京都大学大学院エネルギー科学研究科エネルギー変換科学専攻 / (主査)教授 小西 哲之, 教授 星出 敏彦, 教授 木村 晃彦 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

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Published detrital zircon geochronological data was compiled to form the Global Detrital Zircon Database (GDZDb). This database provides a reference block for provenance analysis by future detrital zircon geochronological studies. This project entailed three subprojects: 1. crustal growth/crustal recycling patterns, 2. a provenance study of the Triassic Dry Fork Formation of the Danville-Dan River Rift basin of Virginia and North Carolina, and 3. sample size issues in detrital zircon studies. The global detrital zircon age frequency distribution exhibits six prominent, statistically significant peaks: 3.2-3.0, 2.7-2.5, 2.0-1.7, 1.2-1.0, 0.7-0.5, and 0.3-0.1 Ga. These peaks are also observed when the data is sorted for continent of origin, the tectonic setting of the host sediment and for modern river sediments. Hf isotope model ages were also incorporated into the database where grains were dated with both U-Pb and Hf isotopes. The Hf isotope model ages suggest that the majority of detrital zircons U-Pb ages reflect crustal recycling events that generated granitic magmatism, as most grains exhibited Hf isotope ages that are much older than the corresponding U-Pb age. The Triassic Dry Fork Formation was sampled from a site in southern Virginia in the Danville-Dan River Basin. The detrital zircon age frequency distribution for this formation was strongly unimodal with a peak at 400-450 Ma and a paucity of Grenville-age zircons. Comparison of the Dry Fork sample to published east coast data and to the North American record (from the GDZDb) illustrate the unusual nature of the Dry Fork Formation sample. It is probable that older Grenville zircons were blocked from the rift valley by the rift shoulder. Using the GDZDb a study of sample size was conducted in order to estimate the best sample size to use when trying to constrain the maximum age of sedimentation of the host sediment. Rift basins and active margins exhibited smaller offsets from the youngest zircon grain age to host sediment maximum age than observed in samples from passive margins. This study recommends that at least 50 grains need to be age dated on average in order to best constrain the age of the host sediment. / Ph. D.

<p> The Rio Grande Rift is a major tectonomagmatic feature of the North American craton. Physiographically, the present rift is recognized as a series of grabens and half-grabens which extend for over 1000 km from south-central Colorado into Chihuahua, Mexico. Rift structures, however, are recognized as far north as the Colorado-Wyoming border. Basaltic magmatism within the rift began by 30 Ma in southern New Mexico, and by 25 Ma in northern New Mexico and Colorado. Within-rift magmatism is low in volume in comparison to rift-related activity on the rift shoulders and flanks. </p> <p> Petrologic studies of Rio Grande Rift-related volcanics are numerous, yet focus primarily on suites erupted in north-central New Mexico and Colorado. However, recently published abstracts suggest areas of southern New Mexico are receiving much needed attention. Initial attempts at characterizing the petrologic diversity and mantle sources of rift-related volcanics have concentrated on major and trace element data, as well as the application of Sr and Nd isotopes. Only minor attention has been given to Pb isotope variations. </p> <p> This thesis contains the most recent compilation of Pb isotope data for volcanic rocks erupted within the Rio Grande Rift region. The oldest rocks included in this work are· monzonite stocks erupted c. 60 Ma within the Colorado Mineral Belt. Using Pb isotope data in combination with trace element variations and Sr-Nd isotopes, a model is developed which suggests the stocks were initially derived from mantle sources with geochemical properties similar to those which produced rift-related basaltic volcanics in northwest Colorado beginning at 25 Ma. </p> <p> Two chapters of the thesis are devoted to exploring the utility of Pb isotopes as tracers of crustal influence in continental basaltic volcanism. One deals specifically with documenting Pb isotope variations in the northwest Colorado region, whereas the second focuses on variations in the Espanola Basin of north-central New Mexico. Major results of the northwest Colorado study 1) suggest that the asthenosphere contributed to early rift (25 Ma volcanism), 2) better characterize the geochemical signature of lithospheric and asthenospheric sources during periods of active volcanism, and 3) confirm earlier suspicions regarding the effects of crustal contamination in several rock suites. Work on basaltic components of volcanism in the Espanola Basin indicate that crustal contamination was also an important process in producing the observed Pb and Sr isotopic variations in both early and later rift lavas. </p> <p> The remaining chapter of the thesis is a synthesis of all available rift data, from northern Colorado to southern New Mexico. An analysis of changes in the Pb isotopic corn position of the lithosphere with latitude is presented, as well as a cross-rift transect of the central rift region. Further, a model which combines previously published ideas on the tectonomagmatic development of the Rio Grande Rift and the Basin and Range province is proposed. The most important results of the combined model are the proposition that rifting began earlier than previously thought, and that the timing of extension and magmatism in the Rio Grande Rift is very similar to that of the Basin and Range province. Additional data from the rift, particularly the southern region, will help to confirm or deny this model. </p> / Thesis / Doctor of Philosophy (PhD)

The Grenville Province and adjacent Makkovik Province represent two long-lived ancient orogenic belts that contain remnants of Paleoproterozoic crust accreted to the southeastern Laurentian margin during the Great Proterozoic Accretionary Orogen (GPAO). However, the addition of juvenile Paleoproterozoic crust to the Archean craton during this period was followed by a span of intermittent ensialic arc magmatism and high-grade metamorphism that overprinted much of the early- to mid- Proterozoic geologic history of the region. As a result, these ancient orogenic belts contain cryptic terrane boundaries that require extensive geochronologic mapping in order to reconstruct the accretionary and collisional growth of the southeastern Canadian Shield. Accreted Proterozoic terranes in the Grenville and Makkovik Provinces have been previously mapped using Nd isotopes in order to determine their crustal formation ages and the boundaries between them. Since the U-Pb isotope system has completely different chemical behaviour to the Sm-Nd system, whole-rock Pb isotope analysis provides an independent method to test the results of Nd isotope analysis. Likewise, Pb isotope mapping acts as a useful tool for determining the exhumation of highly metamorphosed crust, as uranium is preferentially transported from lower crustal levels into the upper crust during regional metamorphism. Therefore, whole-rock Pb isotope analysis was performed on over 200 Archean and Proterozoic gneisses from the SW Grenville Province and Makkovik Province in order to 1) differentiate areas of accreted Paleoproterozoic crust from the reworked Archean margin, 2) test the location of the Archean-Proterozoic suture previously mapped in both regions by Nd model ages, and 3) investigate the variable degrees of crustal burial-uplift within the Archean foreland of the SW Grenville Province that was exhumed during the Grenville orogeny. In the Makkovik Province, whole-rock Pb isotope data from the Cape Harrison domain are comparable with published Pb data from the central Ketilidian mobile belt of southern Greenland. The similarity in Pb signatures between the two belts points to a crustal component in the Cape Harrison domain that was derived from a Proterozoic mantle-derived source with minimal input from older Archean crust. This is largely different from published Pb signatures for the Aillik domain in southeastern Labrador and border zone in southern Greenland that suggests a crustal component comprised of reworked Archean crust analogous to the pre-Makkovikian Laurentian foreland. Comparison of new and published Pb data from the Makkovik Province and southern Greenland in turn helps to constrain a revised single arc accretionary model for the Makkovik Province. Previous Nd isotope mapping in the SW Grenville Province revels a break in model ages inferred by authors as a cryptic collisional suture between the reworked Archean foreland and an accreted Paleoproterozoic arc. However, some workers have suggested that this terrane actually consists of Archean crust that was magmatically reworked in the Mesoproterozoic. Whole-rock Pb isotope data presented in this study points to a crustal component south of the proposed suture in Ontario that was derived from a Paleoproterozoic mantle source and subsequently reworked by ensialic arc magmatism during the Mesoproterozoic. North of the suture, Pb data reveals an Archean crustal component analogous to reworked Superior basement that was exhumed from different crustal levels during the Grenville orogeny. Here, regions of anomalously radiogenic and unradiogenic Pb signatures differentiate the Archean-Proterozoic suture in Ontario from a tectonic duplex in western Quebec. / Thesis / Master of Science (MSc)

This dissertation focuses on the effects of lead (Pb) on the expression of thyroid hormone distributor proteins and how that affects the developing brain in Xenopus laevis tadpoles. Previous work has shown that Pb has the ability to dysregulate thyroid hormone (TH)-signaling in vertebrates and that Pb can impair brain development. This dissertation reports results for a series of Pb-treatment experiments conducted in Xenopus laevis tadpoles. The first primary hypothesis of this dissertation is that Pb impairs TH-dependent mechanisms of brain development. The second primary hypothesis of this dissertation is that Pb-induced impairments of brain development happen via dysregulation of thyroid hormone distributor proteins (THDPs) transthyretin (TTR) and β-trace. Analyses of the effects of Pb on overall body growth showed dose-dependent decreases in body length with increasing concentrations. Evaluation of the effect of Pb on tectal size and cell death in the developing brain yielded bimodal changes that depended upon Pb concentration in both features. Furthermore, Pb impaired TH-induced changes in brain development, including neurogenesis and brain volume. Pb abolished the T4-mediated increase in proliferating cell nuclear antigen (PCNA) expression, while having only marginal effects on neuronal regeneration related protein (NREP) and Krueppel-like factor 9 (klf9). Analyses of the effects of Pb on TTR and β-trace expression yielded results demonstrating a significant decrease in expression of both proteins in response to Pb-treatment. Contrary to prior studies in the literature, I demonstrate here that TTR is present in the brains of Xenopus. While electroporation of TTR morpholino did result in fewer TTR puncta, electroporation with morpholinos for TTR and β-trace knock down did not mimic the effects of Pb on neurogenesis. However, overexpression of these proteins in the choroid plexus (CP) of these animals was sufficient to produce an increase in neurogenesis. Finally, overexpression of these proteins was sufficient to ameliorate the effects of Pb-treatment on neurogenesis. The results affirm both the primary and secondary hypotheses, illustrating that Pb does, indeed, impair TH-mediated mechanisms of brain development and that these impairments are mitigated by dysregulation of TTR and β-trace. / Doctor of Philosophy / This dissertation focuses on the effects of lead (Pb) poisoning on thyroid hormone (TH)-mediated mechanisms of brain development in Xenopus laevis tadpoles. The work detailed here seeks to shine a light on the effects of Pb on brain development and one mechanism by which those effects may be mediated. This dissertation details experiments done in Xenopus laevis tadpoles, which are a prime animal model for studying environmental toxicants, especially those that disrupt TH physiology. This dissertation focuses on two primary hypotheses within a two journal manuscript format. The first primary hypothesis of this dissertation is that Pb impairs TH-dependent mechanisms of brain development. The second primary hypothesis of this dissertation is that Pb-induced impairments of brain development happen via dysregulation of thyroid hormone distributor proteins (THDPs) TTR and β-trace. The results found in this dissertation are consistent with the conclusions that Pb impairs TH-mediated mechanisms of brain development and that those impairments are mitigated by dysregulation of THDPs in the brain and body.