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Collection Description

The Department of Geological Sciences has a long-standing Senior Thesis research option for the B.S. Degree which involves a written thesis, and a public oral presentation done under the supervision of a faculty member. These independent research projects typically involve field work and laboratory analyses of samples, but can also include laboratory-based experimental projects, numerical modeling of geologic phenomena and literature reviews. Senior theses are kept in the permanent collection of the Malcolm A. Love Library on the SDSU campus.

Authors hold full copyright ownership of their original works. Please contact the repository manager at digital@sdsu.edu for any further questions.

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The petrographic and chemical characteristics of metosomatically altered Oligocene Quechan volcanics
The Picacho area of SE California is underlain by an extensional duplex consisting of four major plates. From oldest to youngest the duplex consists of (1) the Late Cretaceous to Early Tertiary Orocopia Schist, (2) probable Jurassic granodioritic gneiss, (3) probably Jurassic Winterhaven Formation, and (4) Cenozoic volcanic and sedimentary rocks. The oldest unit in structural unit (4) is the Oligocene Quechan Volcanics. The Quechan Volcanics were named by Crowe (1978) who described them as being ~300 meters thick. According to Crowe (1978) the lower part consists of ~30 to ~50 meters of trachybasalt, overlain by a thick section of pyroxene rhyodacite which was in turn overlain by glassy pyroxene dacite. However, Andrea Rowland-Smith has documented that the Quechan Volcanics in the Picacho area consists instead of a lower ~50 m of alkali basalt and an upper ~250 m oftrachybasalt. In order to explore further the composition of the Quechan Volcanics an additional 9 samples were collected from a location approximately 6.5 km along strike from the section sampled and studied by Rowland-Smith. Field observations indicate that the Quechan Volcanics within the studied section are composed of flows varying from ~20 to 30 meters in thickness. Vesiculated and brecciated bases and tops of some flows were noted. Compositionally, the lower ~50 meters is composed of pyroxene porphyry, while the upper ~250 meters is composed of pyroxene-plagioclase porphyry. Thin section study also shows that the cores of plagioclase phenocrysts are completely replaced by calcite, and that both quartz and calcite are common infillings of vesicles. The introduction of calcite and quartz and the extensive fracturing of the sampled section are likely due to its proximity to a young high silica rhyolite plug that introduced hydrothermal circulation cells. New major and trace element chemical data confirm the work of Rowland-Smith even after alteration., San Diego State University
The petrographic and chemical characteristics of the Oligocene Quechan volcanics
The Picacho area of SE California is underlain by an extensional duplex consisting of four major plates bounded by faults. From oldest to youngest the duplex consists of (1) the Late Cretaceous to Early Tertiary Orocopia Schist, (2) probable Jurassic granodioritic gneiss, (3) probably Jurassic Winterhaven Formation, and (4) Cenozoic volcanic and sedimentary rocks. The oldest unit in structural unit (4) is the Oligocene Quechan Volcanics. The Quechan Volcanics were named by Crowe (1978) who described them as being ~300 meters thick. According to Crowe (1978) the lower part consists of ~30 to ~50 meters oftrachybasalt, overlain by a thick section of pyroxene rhyodacite which was in tum overlain by glassy pyroxene dacite. As outlined below, field and laboratory work completed during spring 2003 suggests that this stratigraphic hierarchy is in need of modification. Approximately 14 square miles (23 km2) were mapped at a scale of 1: 12000, and 8 samples were collected for thin section and chemical study. Results of this work indicate that the Quechan is ~300 meters thick, consisting of a lower part, ~50 m thick, of pyroxene basaltic porphyry and an upper part composed of pyroxene-plagioclase porphyry. Phenocrysts in the lower part vary from 0.5 mm to 2.0 mm in size while phenocrysts in the upper part vary from 0.25 mm to 6.5 mm. Intergranular and trachyitic textures are common throughout the Quechan. Chemical analyses confirmed that the lower part of the Quechan is basaltic as SiO2 is ~51 wt. percent while SiO2 values for samples from the upper part vary from ~57 to ~60 wt. percent. On the conventional SiO2 versus alkali diagram, the one specimen analyzed from the lower part plots on the boundary separating trachybasalt from basaltic trachyandesite, while specimens from the upper part plot mostly in the trachyandesite field. On the TiO2/Zr vs Y /Nb classification diagram the one specimen from the lower Quechan plots in the alkali basalt field, while all other specimens cluster tightly within the trachyandesite field. Hence, I conclude that the Quechan Volcanics consist of a two­part stratigraphic hierarchy consisting of alkali basalt in the lower ~50 meters and trachyandesite in the upper ~250 meters., San Diego State University
The petrological and chemical trends associated with the development of corestone and saprolite Santa Margarita ecological reserve Temecula, California
H. Wayne Nesbitt proposed a chemical weathering model for the development of corestone and saprolite that has gained wide recognition in the geological community. However, this model has not been tested in a wide variety of settings and more work is clearly warranted. Hence, the purpose of this thesis is to investigate chemical and petrological trends associated with the development of corestone and saprolite from a single outcrop of tonalite in the Santa Margarita Ecological Reserve, Temecula, California. Nine samples were collected from an ~ I meter traverse across the margin of an outcrop of corestone (relict unaltered tonalite) surrounded by saprolite (in situ weathered tonalite ). Seven samples were thin sectioned, and chemically stained to distinguish potassium feldspar from plagioclase. All collected samples were analyzed by XRF for major and trace element concentrations. From resulting chemical data, the Chemical Index of Alteration (CIA) was calculated as follows: CIA = AI2O3 (molar %) / CaO + Na2o + K2O + AI2O3 (all molar %) In the above formula CaO represents only that proportion in the silicate fraction. Resulting CIA values ranged from 52 to 55, with three saprolite specimens having the highest CIA (54-55). These three relatively highly altered samples were also located the greatest distance from the corestone. The results of point counting 300 points in each specimen revealed that the three saprolite samples with high CIA also were depleted in plagioclase relative to all other analyzed specimens. Given this observation, it is therefore not surprising that on molecular A-CN-K and A-CNK-FM diagrams, the three saprolite samples cluster plotting either more close to the A apex or CNK-FM join than do other samples with lower CIA values. The transport function, 't, was used to evaluate the percent change in elemental mass relative to the mass of a known or suspected immobile element. For the purposes of this study, the immobile element of choice was TiO2. In general, CaO, Na2O, K20, Rb, Sr, and Ba in the saprolite are depleted relative to samples from the corestone, while Fe2O3, MgO, MnO, Sc, V, and Zr appear to have been unaffected by formation of the saprolite and corestone. Hence, data summarized here indicate that corestone-saprolite formation in the Santa Margarita Ecological Reserve follows a predictable trend that is similar to that documented originally by H. Wayne Nesbit., San Diego State University
The petrologically and chemically-based provenance-discrimination models: Do they yield internally consistent results when applied to sandstone turbidites?
Previous investigators utilized a petrologically-based provenance-discrimination model to interpret the source of siliciclastic sandstone turbidites within the post-Cambrian and pre­Upper Devonian Red Hill unit of the Shoo Fly Complex, northern Sierra Nevada, California. The results of this work indicated an average framework composition of Q94,f'4L1. In addition, some quartz framework grains displayed abraded syntaxial overgrowths. On the QFL provenance-discrimination diagram of W. R. Dickinson and colleagues, point-counted samples from the Red Hill unit plot mostly in the continental interior provenance. Thus, I, as well as several previous workers,interpret the source of sandstones within the Red Hill unit to have been old upper continental crust located along or somewhere within the interior of North America. In order to determine whether or not the chemically-based provenance-discrimination model produces an interpretation that is consistent with the petrologically-based discrimination model of W. R. Dickinson and colleagues, five samples of quartz-rich sandstone collected from the Red Hill unit were analyzed for major, trace, and REE. The average AI2 O}/Ti02 ratio based on this work is 16.4 .± 1.4. The average Th/U ratio is 5.6 .± 0.8. Moreover, the five analyzed samples of sandstone display LREE enriched and slightly HREE fractionated chondrite-normalized REE patterns with an average Eu­anomaly of 0.67 .:t 0.06. These results are consistent with the petrological results obtained by previous workers and thus indicate that both the petrologically- and chemically-based provenance­discrimination models yield internally consistent results when applied to siliciclastic sediments derived from the interiors of continents., San Diego State University
The provenance of puddingstones in Peninsular California
Supermature, ultrastable puddingstones collected from conglomerate outcrops in the Cretaceous Valle Group and the Eocene Las Palmas Gravels may not be derived from the unroofing of the Peninsular Ranges batholith (PRB). A detailed petrographic analysis along with framework grain provenance diagrams suggest a tectonic provenance other than the PRB for the Valle Group and possibly the Las Pal mas Gravels as well. Although the Valle Group and Las Palmas Gravels puddingstone cobbles are similar there are significant differences. The QFL plots for the Valle Group display high percentages of quartz, zero feldspar, and/or high percentages oflithics (chert), along with silica cement and no matrix. The QFL plots for the Las Palmas Gravels samples, except for three, contain moderate percentages of quartz, low percentages of feldspar, and high percentages of lithics (i.e. chert and volcanics), along with abundant hematite cement and no matrix. For the Valle Group samples this implies a hot and extremely wet climate in order to remove all but the most stable minerals. Furthermore, Valle Group cobbles contained well rounded quartzite clasts within the cobbles. This implies the weathering and erosion of a metasedimentary sequence that had severe climatic conditions in order to destroy all unstable metasedimentary units within the sequence. The abundant hematite cement in the Las Palmas Gravels samples was probably the result of a hot climate with intermittent periods of moisture allowing for the alteration of iron-bearing detrital grains to form hematite cement. Rounded detrital grains of zircon, tourmaline, and some rutile are present in almost every cobble from both locations indicating a recycling event through an older sandstone originally derived from a plutonic source. However, abundant chert clasts that are angular to rounded are found in almost every sample; this implies an original depositional event. The provenance models used for this investigation do not account for every type of sediment origin and dispersal, therefore intuitive reasoning from previous studies are used along with these models to determine tectonic provenance for both samples., San Diego State University
The rare earth element characteristics of the Rojo Grande and White Wash Units, Picacho State Recreation Area, SE California
The lower Miocene volcanic and epiclastic unit at Picacho State Recreation Area consists of, from stratigraphically lowest to highest, the Quechan volcanics, Rojo Grande unit, Marcus Wash unit, White Wash unit, Walker volcanics, and the ignimbrite of Ferguson Wash. Published laser‐ablation U‐Pb zircon ages for the Quechan volcanics, Walker volcanics and ignimbrite of Ferguson Wash are 23.4 ± 0.4 Ma, 23.5 ± 1 Ma, and 23.2 ± 0.2 Ma respectively. These ages suggest that the entire lower Miocene volcanic and epiclastic unit was likely erupted in a very narrow time interval about 23 Ma and perhaps in as short of a period as about 1 million years. The Quechan and Walker volcanics and the ignimbrite of Ferguson Wash have been studied extensively by previous students, and the major trace element chemistry of the Rojo Grande unit was most recently studied by T. Pelbath. Though all previous studies recognize that the lower Miocene volcanic and epiclastic unit was altered extensively by hydrothermal solutions, none evaluated the effects of such alterations on rare earth elements. On a chrondrite normalized REE diagrams, samples from the Rojo Grande unit display light REE enrichment patterns that are nearly identical to those for the Quechan volcanics. Such patterns are commonly interpreted to be the result of low degrees of partial melting in the garnet stability field, which is commonly cited as lying between 60 and 80 km In depth. In addition, published reconstructions of the Miocene crustal thickness in and around Picacho suggest crustal thickness of around 45 km. Hence, magma that eventually generated the Rojo Grande unit likely originated within the sub-­‐continental crustal lithosphere. In contrast to the Rojo Grande unit, the fine‐grained ignimbrite in the lower part of the White Wash unit, is the most chemically evolved of any unit within the lower Miocene volcanic and epiclastic unit. In addition, chrondrite‐normalized REE distribution patterns reveal a large negative europium anomaly. These data suggest that the magma that erupted as the ignimbrite originated within the plagioclase stability field at depths that were less that about 30 km., San Diego State University
The re-interpretation of gravity data from Borrego Valley, California
This study is an analysis of the U. S. Geological Survey gravity data from Borrego Valley, California. Borrego Valley consists of pre-Tertiary basement underlying the Quaternary age alluvium. The gravity data was obtained by drawing cross-sections perpendicular to the contours on the U.S. Geological Survey residual gravity contour map (Plate 1). These observed data were used in Magix.plus to calculate the depth to bedrock by matching the measured data to the theoretically calculated anomalies. This computed anomaly will give the basement shape and depth. Although the interpretation is non-unique, the ambiguity is decreased by using external constraints on the profile. Each profile contains a point where bedrock depth is zero, a well with a known bedrock depth, and a point where all profiles cross. These constraints help define the shape of the anomaly., San Diego State University
The role of macrocystic pyrifera on iodine speciation in the coastal ocean
Kelps have a major role in marine and atmospheric iodine cycling in the coastal zone of temperate regions. While their efflux of iodide in response to oxidative stress and their role in ground-level ozone destruction in the coastal marine boundary layer have become well established in recent years, little is known about the impact of kelp forests on iodine speciation in the coastal ocean. Based on thermodynamics, iodate should be the only species of iodine found in the water column and yet the concentrations of reduced forms of iodine may range from <0.1-0.3 μM which is significant compared to total iodine’s constant distribution of around 0.45 μM. The concentration of iodide is highest in the euphotic zone and decreases with depth. It is also typically higher in coastal zones as compared with open ocean environments. These anomalies suggest that presence of iodide may be linked to biological productivity. In particular, marine macroalgae such as Macrocystis pyrifera are known to have highly evolved halogen metabolisms and high biological productivity rates which could influence iodine speciation in the coastal regime. We here report a 2015 dataset of iodide and iodate concentrations in seawater from the M. pyrifera forest from the vicinity of Point Loma, CA obtained using cathodic stripping square-wave voltammetry over a full seasonal cycle. Water samples from a kelp free area (Scripps Pier in La Jolla) served as nonbiological control. The results of this year-long study will be presented., San Diego State University
The significance of geochemical signatures in the interpretation of groundwater quality of a landfill
A groundwater seep was historcally observed adjacent to a landill during and shortly after precipitation events. This observation raises the question is groundwater interacting with the landfill waste? Two pairs of piezometers were installed along the northeast perimeter of the landfill to evaluate the relationship between groundwater and the base of the waste, groundwater occurs at approximately thirty feet below the waste of the landfill. The purpose of this thesis is to analyze the groundwater encountered in the piezometers for contaminants that may be indicative of landfill-related impacts. Water quality parameters were measured in the field and groundwater samples were analyzed at a laboratory for general chemistry parameters and metals. Stiff diagrams were used to evaluate the extent of apparent groundwater impacts resulting from landfill leachate. The Stiff diagrams suggest an increasing trend of landfill-related constituents in monitor wells down gradient from the waste. These data indicate that groundwater quality is progressively impacted by landfill-related constituents along the notihern perimeter and down gradient of the landfill., San Diego State University
The structural relationship of the high-angle northeast-trending "Truckhaven" fault with the southern Santa Rosa Mountains detachment fault
interval for the difference in means for quartz, feldspar, and biotite was calculated. If this interval included zero, then I concluded that there was enough statistical evidence to reject H0. The results of the statistical work indicated that there is not enough evidence to reject H0 in favor of Ha for quartz and biotite. However, the data also indicate that Ho should be rejected in favor of Ha for feldspar. Though this result is difficult to interpret, it may simply be due to the difficulty of distinguishing untwined feldspar from quartz in unstained thin sections. Though there is clearly a need for more work on the subject of this thesis, the results of my work point to the potential usefulness of point counting scanned images to determine the modal compositions of rock specimens., San Diego State University
The use of electromagnetic induction logging to track seawater intrusion
Electromagnetic (EM) Induction logging can be an efficient and versatile method for tracking seawater intrusion. Both water chemistry and lithology affect EM logs. EM conductivities of Southern California coastal silts and clays often reach 200 millisiemens per meter (mS/m). Coarse sand and gravel zones intruded by seawater reach EM conductivities greater than 800 mS/m. As part of a United States Geological Survey (USGS) seawater intrusion study, EM log, chloride concentrations and specific conductance data from 9 monitoring wells along the coastal Oxnard Plain in Ventura County, California were used to correlate EM conductivity and water quality and to characterize seawater intrusion. EM logging and water chemistry sampling were done in 1994 and again in 1996. Specific conductance and chloride concentration of water samples analyzed in this study ranged from 100 to 2,000 mS/m and 26 to 6,500 milligrams per liter (mg/1) respectively. Large changes in conductance and chloride concentrations occurred during the 1994 -1996 period. These large changes are directly related to an increase in rainfall after 1994 and the resulting decrease in agricultural pumping within the Oxnard Plain. Linear regression analysis of chloride concentration versus specific conductance, chloride concentration versus EM log conductivity and change in chloride concentration versus change in EM log conductivity show correlation coefficients of 0.89, 0.72, and 0.87, respectively. Contour mapping of EM log conductivity and chloride concentration as well as changes in both parameters show common trends. EM logging can be used to track seawater intrusion along the coastal Oxnard Plain. However, water chemistry sampling techniques must be refined and standardized to get representative samples, which can then be statistically correlated to EM conductivity. Regression analysis indicates a correlation between chloride concentration and EM log conductivity even with the interfering effects of lithology and with improper sampling techniques., San Diego State University
The use of trace element abundances from Loihi Seamount to investigate the chemical heterogeneity of the Hawaiian mantle plume
The hypothesis that oceanic crust enters the mantle at subduction zones and is subsequently recycled as it returns to the surface through plumes plays an important role in the understanding of the chemical composition of Earth’s mantle. This recycled material resurfaces at hotspots such as Iceland, Samoa, and the Hawaiian Islands. Observational data has revealed compositional variations in the lavas of several Hawaiian volcanoes that may be related to this recycling hypothesis. These differences form two geographic trends, the Kea trend and the Loa trend, which each have a distinct isotopic signature. Kea-type lavas (including Kilauea) exhibit characteristics of a long-term depleted source, while Loa-type lavas (including Mauna Loa) have features typically seen in long-term enriched sources. Various models have been proposed to explain these trends, including a large-scale bilateral asymmetry or radial zonation in the composition of the Hawaiian plume. Loihi Seamount is an active volcano located 35 km south of the island of Hawaii. It displays a wide range of rock types from tholeiites to basanitoids and offers much insight into the chemical heterogeneity of the mantle. Geographically, Loihi is situated on the Loa trend and therefore is expected to erupt Loa-type lavas, according to the bilateral asymmetry or radial zonation models. However, previous research shows that, although Loihi lavas exhibit Loa-like Pb isotope values, incompatible trace element ratios from this volcano plot near Kilauea (Kea-type) values. There is very little high-quality trace element abundance data available for Loihi lavas. In order to further investigate these observations, we obtained LA-ICP-MS trace element abundances from 16 fresh glass samples from Loihi. Here we compare these incompatible trace element abundances with literature data from three active Hawaiian volcanoes (Kilauea, Mauna Loa, and Loihi) and one extinct volcano (Koolau). These data provide further evidence that these compositional trends cannot be explained by either bilateral asymmetry or radial zonation. The findings of this study instead offer support for a current model suggesting that the mantle source beneath Hawaiian volcanoes is derived from recycled oceanic crust that has been altered by seawater and variably dehydrated during subduction. The model also proposes that the plume consists of small-scale heterogeneities, oriented NW-SE, that differ in the amount, type, and extent of dehydration of the recycled crust., San Diego State University

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