http://dspace.nmt.edu/dspace The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material. Search the Channel search http://dspace.nmt.edu/dspace/simple-search http://hdl.handle.net/10136/507 Title: Cosmogenic 36-Cl datings of geomorphic surfaces <br/> <br/>Authors: Zreda, Marek G. http://hdl.handle.net/10136/506 Title: Cosimulation of heads and log-transmissitvities using a numeral spectral-perturbation method: A new technique for obtaining stochastic predictions of groundwater flow through heterogenous porous media <br/> <br/>Authors: Zimmerman, D. <br/> <br/>Abstract: A new technique for obtaining stochastic predictions of groundwater flow through heterogeneous aquifer materials is presented. The aquifer properties are viewed as statistically homogeneous stochastic processes which are characterized by covariance functions. The governing stochastic stochastic differential equation for flow is written for mean-removed random variables whose joint distribution is assumed to be Gaussian. This transformed equation is then linearized by applying perturbation theory. Finally, spectral theory is used to obtain a relationship between the head spectrum and the logarithm of Transmissivity (InT) spectrum. Using this relationship, and algorithm is developed for generating discrete random fields of head and InT simultaneously. The probability behavior of the head process can then be estimated by computing its statistics over an ensemble of fields obtained through repeated application of the cogeneration algorithm. This cosimulation procedure is computationally much cheaper and faster than the standard sequential Monte Carlo method which involves solving a system of algebraic equations for each realization of the head field obtained. However, the method is restricted to relatively small input variance. The theory is initially developed for the infinite domain problem in order to avoid complications arising from boundary conditions. It is then extended, using geostatistical methods, to enable the cosimultions to be conditioned on measurement of T and/or head, thus addressing the bounded domain problem. The technique is demonstrated (without conditioning) for steady, confined flow in one and two-dimensional domains with unidirectional, linear mean hydraulic gradient. Practical aspects associated with compute implementation of the procedure are discussed in detail. The cogenerated fields are examined to determine under what conditions they preserve the proper statistical behavior and satisfy the mass conservation principle. http://hdl.handle.net/10136/505 Title: The 40Ar/39Ar geochronology and thermochronology of the Latir volcanic field and associated intrusions: Implications for caldera-related magmatism <br/> <br/>Authors: Zimmerer, Matt <br/> <br/>Abstract: Volcanic and plutonic rocks exposed in the Latir volcanic field, Sangre de Cristo Mountains of northern New Mexico, provide a unique opportunity to study caldera-related magmatism and understand the spatial and temporal relationship between the volcanic and plutonic record. Fifty-one samples were dated using 40Ar/39Ar method. The results indicate a 10 Ma period of Latir volcanic field related magmatism. The volcanic geochronology provides point-in-time information about magmatism whereas the thermochronology of plutonic rocks establishes their emplacement and cooling history. Volcanic rocks provide information about the earliest magmatism associated with Latir volcanic field. Precaldera volcanism began at 28.3 Ma and ended at 25.3 Ma, based on 40Ar/39Ar analysis of hornblende, biotite, and sanidine from exposed volcanic rocks. Combining the published geochemistry with ages of precaldera volcanism from this study indicates that the earliest magmatism was characterized by multiple, small magma chambers, rather than a single, large magma chamber. Peak magmatism occurred during the eruption of the 500 km3 peralkaline Amalia Tuff from the Questa caldera. Sanidine analyses from eleven samples yielded a mean age of 25.23 Ma for the Amalia Tuff. Following the eruption of the Amalia Tuff, four resurgent plutons were emplaced in the shallow crust near the center of the caldera. K-feldspar multiple diffusion domain (MDD) thermal models indicate that the plutons cooled rapidly after emplacement. By 24.7 Ma, within 500 ka of caldera eruption, all the plutons cooled to 150°C. A biotite from the previously undated Canada Pinabete pluton, a resurgent pluton chemically similar to the Amalia Tuff, yields an age 25.28 Ma. Because the Canada Pinabete pluton and Amalia Tuff are geochemically similar and their ages are analytically indistinguishable, the Canada Pinabete pluton is interpreted as non-erupted Amalia Tuff. This supports the idea that ignimbrite magma chambers may not completely drain during eruption and plutons can be directly correlated to large-scale ignimbrite sheets. The remainder of the resurgent plutons are slightly younger than the Amalia Tuff and record a compositional transition to lesser-evolved magmas. Three postcaldera rhyolites yield sanidine ages between 24.9 and 25.0 Ma indicating coeval volcanism with emplacement of the resurgent plutons. After resurgent plutonism, three plutons, probably cupolas of a larger, single intrusion, were emplaced and are now exposed along the southern caldera margin. Biotite ages from the Red River, Sulfur Gulch, and Bear Canyon plutons are 24.8, 24.5, and 24.3 Ma, respectively, suggesting incremental emplacement of the larger intrusion along the southern caldera margin. K-feldspar monotonic MDD thermal histories from the individual plutons display differences of rates and timing of cooling. MDD models suggest the Red River pluton experienced a period of isothermal cooling at 300°C between 24 and 22 Ma, followed by rapid cooling at 21 Ma. One K-feldspar MDD thermal model from the Bear Canyon indicates rapid cooling at 21 Ma, but another Bear Canyon K-feldspar thermal model indicates rapid cooling at 23 Ma, followed by isothermal conditions at 200°C between 22 and 18 Ma. The unconstrained MDD thermal models suggest reheating by younger thermal events possibly related to magma emplacement. The two youngest plutons, Rio Hondo and Lucero Peak, were emplaced 5-15 km south of the caldera. An associated study of U-Pb zircon ages suggest that the Rio Hondo pluton was possibly incrementally emplaced between 23 and 22.5 Ma. Biotite collected from multiple locations in the Rio Hondo pluton yield ages of ~21 Ma, indicating that following incremental emplacement, the different increments comprising the pluton cooled to 350°C at the nearly the same time. K-feldspar MDD monotonic cooling models indicate a period of slow to isothermal cooling between 21 and 16 Ma. Alternatively, the unconstrained modeling results show a thermal perturbation at 16.5 Ma, which corresponds to the age of a Rio Hondo hosted rhyolite dike. A single age of 22.5 Ma from a postcaldera andesite on Brushy Mountain suggests coeval volcanism with the emplacement of the Rio Hondo pluton. Biotite ages are ~19 Ma from both the interior and margin of the Lucero Peak pluton. Similarly, K-feldspar cooling histories from the interior and margin of the pluton both suggest slow cooling between 19 and 16 Ma. The similarity of cooling histories between marginal and interior unites, combined with the lack of robust reheating models, is interpreted to be the result of a complex emplacement history, rather than simple batch emplacement of a pluton. In summary, 40Ar/39Ar results from this study describe magmatism at different times associated with caldera-volcanism, and provide insight into the relationship between the volcanic and plutonic record. http://hdl.handle.net/10136/504 Title: Prediction of wetting front instability in homogeneous soils - Empirical approach and mathematical modeling <br/> <br/>Authors: Yao, Tzung-Mow M.