We've Moved!

Visit SDSU’s new digital collections website at https://digitalcollections.sdsu.edu

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.

Back to top


Melanocratic enclaves in the Oriflamme Canyon pluton: implications for development of 122 ma protomylonites and the cessation of NE-SW shortening strain in the peninsular ranges, SE California
The Peninsular Ranges batholith, southern California, can be subdivided into eastern and western zones based on a number of different discontinuities including the pseudogravity (PSGR) line, 1-S line, and the 8018 line. Located within the batholith is the Oriflamme Canyon shear zone (OCSZ), a small component of the Cuyamaca-Laguna Mountain shear zone, which contains the Lucky 5 and Oriflamme Canyon plutons. These plutons are located within the eastern zone of the batholith and were previously mapped by V. R. Todd who included them in her leucogranitic suite. U-Pb zircon dating yielded an age of 122 ± 1 Ma for the Oriflamme Canyon pluton while unpublished U-Pb work by Professor D. Kimbrough of San Diego State University suggests an approximately 120 million year old age for the Lucky 5 pluton. The Oriflamme Canyon pluton displays a well developed mylonitic foliation while the Lucky 5 lacks any evidence for penetrative strain. In addition, melanocratic enclaves within the Oriflamme Canyon are flattened and stretched out down the dip of the mylonitic foliation. In low pressure regions, material making up the enclaves infill minute cracks and crevices in the coarse grained surrounding granodiorite. In thin section, the melanocratic enclaves are composed predominantly of plagioclase, quartz, biotite, and green amphibole. On the IUUS ternary classification scheme they are mostly tonalite but range to diorite. Chemically, the enclaves are enriched in CaO, FC203, MgO, MnO, P20s, and Ti02 relative to surrounding granodiorite. Samples analyzed from the enclaves and surrounding granodiorite plot as negatively sloping smoothly varying trends on silica variation diagrams I interpret the above described relationships to indicate that the enclaves were emplaced as a melt phase into the cooling and more rigid framework of the granodiorite during mylonitization ~ 122 Ma. Shortly thereafter, the Lucky 5 body was intruded as a post-kinematic pluton. Hence, the Lucky 5 and Oriflamme Canyon plutons were emplaced during the final phase of penetrative Cretaceous age deformation in the Peninsular Ranges., San Diego State University
Metamorphic and structural evolution of the Prospect Meta-granite, SE CA
The Prospect meta-granite represents a fine-grained leucocratic microcline-rich dike–like mass intruded into a ~304 m thick sheet of ~162.5 Ma Jurassic gneiss. The gneiss is truncated along its north margin by the southward dipping Copper Basin reverse fault and along its southern margin by the Sortan detachment fault. Petrologic, geochemical, and field studies of the Prospect meta-granite indicate a complex history involving solid-state recrystallization and fluid-assisted alteration. Peak metamorphic conditions produced a relatively coarse grained weakly to moderately developed foliation and a white mica ± chlorite ± biotite metamorphic assemblage. In addition, sub-grain development along the margins of both plagioclase and microcline suggest that temperatures may have exceeded 400° ± 50°C. Such an interpretation is consistent with the presence of undulose extinction, deformation bands, and sub- and new-grain development within quartz crystals. Throughout much of the Prospect meta-granite, the peak metamorphic assemblage is partially replaced by microcrystalline calcite ± sericite ± chlorite. The latter assemblage in fills a pervasive set of brittle fractures that disrupt the peak metamorphic assemblage and breaks and fragments both quartz and feldspar crystals. The brittle behavior of quartz and feldspar during development of the fractures implies that temperatures fell below 300° ± 50°C. Hence, the calcite ± sericite ± chlorite assemblage is the record of a fluid assisted retrograde event. Thin section work showed that 3 out of 10 samples collected across the Prospect metagranite were significantly less affected by the retrograde event. Using these samples as representative of the Prospect meta-granite prior to fracturing and invasion by fluids, non-central principal component analysis revealed that in molar A-CN-K space, principal component 1 explained 99.6% of the variation of the 7 more altered samples about a well-defined linear compositional trend. Significantly, the resulting trend is directed by the perturbation vector toward the CN apex, and thus is consistent with thin section observations indicating influxes of fluids rich in CO2 and Ca. Though the timing of the retrograde fluid assisted event is not well constrained, it may be related to the exhumation of the Prospect meta-granite and enclosing gneiss complex along the Sortan fault, ~28-24 Ma, and/or the subsequent formation of the Copper Basin reverse fault after ~9.5 Ma., San Diego State University
Metamorphism of prebatholithic rocks from bahia de Los Angeles, Baja California, Mexico
Prebatholithic metamorphic rocks of the southern part of the Peninsular Ranges Batholith near Bahia de Los Angeles, Baja California, comprise a NW striking, steeply dipping package of regionally metamorphosed, strongly foliated schist and gneiss. New mapping at a scale of 1: 12,500 over a 14 km2 area documents four distinct lithologic units: granitic gneiss, metavolcanics, schist, and quartzite plus conglomerate. Thin section analysis of 16 samples reveal that they are all rich in quartz. Quartz, plagioclase, biotite, and muscovite is the most common mineral assemblage in the schist unit, which is strongly quartzofeldspathic. The quartzite plus conglomerate map unit contains an interval of unusually pelitic rich schist which contains the mineral assemblage staurolite + garnet + biotite + quartz which is diagnostic of lower amphibolite facies conditions of metamorphism (520-580°C and 2-3 kbar). The pressure conditions of metamorphism indicate ~6-9 km of uplift and erosion to expose these rocks at the surface. Less diagnostic assemblages from other protoliths are all consistent with this grade of metamorphism. Relict quartz phenocrysts in the metavolcanic tuff document the volcanic origin of this unit. Stained slab and thin sections from the granitic gneiss unit show that the protolith for the gneiss was a monzogranite. The mineralogy of these metasedimentary rocks indicates that the protolith probably consisted of quartz rich sandstones including some very pure quartz arenite sandstone, with lesser amounts of conglomerate and shale, and some interbedded carbonate. The likely depositional setting is a shallow nearshore continental setting., San Diego State University
Mineralogy of the Stewart Mine LCT pegmatite, Pala, California
This study investigated mineral occurrences in the Stewart pegmatite and searched for appropriate minerals in order to determine a U/Pb crystallization age for the pegmatite. Thirtythree minerals were identified by X-ray diffraction (XRD), and an additional three minerals were identified using an energy dispersive X-ray detector (EDAX) on a scanning electron microscope. Six of the minerals identified in this study represent minerals not previously identified from the Stewart pegmatite: polylithionite, foitite, analcime, clinoptilolite, epistilbite, and zircon. Five of these potentially new minerals form structural or solid-solution series with minerals previously identified. An EDAX elemental analysis was able to distinguish between schorl, green elbaite (verdelite), and pink elbaite (rubellite), and also revealed that all the SP tourmalines analyzed were enriched in fluorine. XRD work on tourmalines of varying diaphaneity also reveal replacement of tourmaline by cookeite, muscovite and illite, depending on the original tourmaline composition. Monazite was determined to present the best opportunity for U/Pb dating. The concentration of rare minerals and variations in crystal morphology throughout the Stewart pegmatite agree with previous interpretations that the core of the SP is similar to a giant pocket that lacked sufficient room to allow proper crystal growth. A comprehensive list of minerals and a reliable crystallization age are equally important to understanding the conditions of formation for the SP within the framework of the Peninsular Ranges Batholith (PRB) emplacement. This study aims to expand the known mineralogy of the Stewart Mine, a gem-bearing LCT pegmatite in the Pala Pegmatite District of San Diego County, and to potentially find minerals for U/Pb dating to correlate the geologic history of the Stewart pegmatite with the PRB., San Diego State University
Morphology of the Poway rhyolite clasts, San Diego County, California
Poway rhyolite clasts are the dominant gravel type of the Eocene section in San Diego County. The clasts range from pebbles to boulders in size and are composed of slightly metamorphosed rhyolitic to rhyo-dacitic welded tuffs which have great resistance to mechanical abrasion. The shape evolution of the Eocene Poway rhyolite clasts is primarily due to transportation. Four sites were chosen to measure the clast dimensions for long, intermediate, and short axes from randomly selected cobbles. The different depositional environments studied were an Eocene river channel, alluvial fan apex, submarine canyon fill, and reworked distal fan facies. It was determined that depositional environments have had little effect on clast morphology; this is attributed to a short transport period between sites. The Poway rhyolite clast morphologies plot as disc-spheroidal shape on a variation of the Zingg (1935) model. The Eocene submarine canyon deposit and distal fan facies showed no distinct shape changes as a result of modern beach action., San Diego State University
Moving towards a late Holocene chronology of Lake Cahuilla
The Salton Trough is a tectonically active basin that formed by the northward propagation of the Gulf of California, and is associated with transtensional motion on the southern San Andreas Fault system (SSAFS). The rapid urbanization within the region, along with the ~300 years since the last large surface rupture on the southern San Andreas fault following a period of more than a thousand years when the average recurrence interval was less than 200 years, points to the need to develop long, well-constrained rupture histories for all of the major fault elements of the SSAFS. One past problem with the development of earthquake chronologies in this arid region is the inability to accurately date past ruptures, as charcoal is sparse and commonly has a component of inheritance. Ancient Lake Cahuilla is the name given to a recurring freshwater lake that has periodically inundated the Salton Basin during the Holocene. The Colorado River normally flows south and discharges into the Gulf of California. However, the Salton Trough lies largely below sea level and favors the northward diversion of the Colorado River during large floods, as the gradient into the basin is steeper than to the Gulf. At its peak of ~12 meters above mean sea level, the elevation of the sill formed by the Colorado River delta, Lake Cahuilla extends some 160 kilometers from north of Indio to just south of the International Border near Cerra Prieto, and ranges from 15-80 kilometers in width. During lowstands, native vegetation such as creosote bush and mesquite regrow in areas left exposed after desiccation. Inundation during periodic refilling of the lake causes the native vegetation to die, resulting in in situ stumps that may be left in place or buried by sediments during successive lake highstands. Based on many paleoseismic studies, there have been at least 5-6 highstands of Lake Cahuilla during the past 1200 years. Where the sediment from these past lakes crosses an active fault of the SSAFS, there is the potential to not only date the past earthquakes, but also to cast the regional earthquake history into the same common lacustrine stratigraphic framework and determine the sequence of events. Towards this end, we are developing a high-precision chronology for Lake Cahuilla by dating old stumps in growth position that are embedded within Lake Cahuilla sediments. Radiocarbon dating these stumps dates periods of wood growth that occur during the dry periods when there is no lake. By dating stumps at various elevations throughout the basin, it should be possible to develop a very high resolution chronology of the lakes, which In turn can be used to date the sequence of earthquakes on the SSAFS. An ultimate goal is to use the chronology of the large earthquakes on the San Andreas, San Jacinto, Elsinore, Imperial and Cerro Prieto faults to forward model the evolution of stress, and hopefully better understand long term strain release along a major plate boundary system., San Diego State University
Navigation patterns of advanced geology students in the field
This study presents results of an investigation of the navigation patterns of advanced geology students in the field. We have correlated the GPS tracks (navigation patterns) of students taken during an independent field examination with the quality of their resulting maps. Our hypothesis was that there should be a correlation between an individual's map quality and the efficiency and effectiveness of their navigation patterns in the field. We propose that we can understand mapping expertise and how students acquire these skills using a four part schema model derived from problem solving research in cognitive science. The schema is a vehicle of memory that allows organization of a person's similar experiences by the use of four specific types of knowledge: identification, elaboration, planning, and execution. Using this specific model we predict that students with a fully-formed mental image should navigate through the landscape efficiently and systematically with few mistakes. We collected 15 GPS tracks from students taking a 6 hour independent field examination, monitoring their position every 3 minutes. We scored their resulting maps using criteria such as the location and interpretation of contacts, faults, and folds, using the instructor's map and the published USGS map of the area as a standard. We also examined their notes as a further source of data to monitor their understanding during the field exercise. Results show that students who produced high quality maps also showed evidence of having a good mental model of the structure and the interaction of the structure with the landscape. These students navigated the field area systematically and with little repetition of traverses or reoccupation of locations, moving efficiently through key locations to collect the information they needed to solve the geologic puzzle. These students also used the topography to their advantage and understood where they needed to go next to find useful exposures. As map quality decreased, students showed progressively poorer coverage of the test area and tended to repeat traverses and revisit previous locations frequently and with little evidence of systematic progress. Their notes also expressed confusion, which supports our interpretation of navigation patterns as being a good measure of mental model formation and completeness in the field., San Diego State University
Neogene sedimentary rocks associated with detachment faults, Yaqui Pass, California
An examination of the lithology of the North Pinyon Mountains reveals that they may have been mistakenly mapped and characterized as crystalline rocks of the Peninsular Ranges Batholith. These mountains, as well as Yaqui Ridge and the Vallecito Mountains are the site of extensive mid-Cenozoic detachment faulting associated with the crustal extension of the Salton Trough region. A survey of the rock east of this fault system by field mapping on a 7.5 minute quadrangle, and an examination of air photos reveal a sedimentary character to the rocks. The descriptive lithology of these rocks, and their spatial relationship to the detachment system, suggests that this area was the site of extensive movement during Neogene time. The character of this slidemass is similar to sedimentary deposits north and south of the study area which further suggests a pattern of large scale sedimentation in the down-dip direction of the detachment fault zone., San Diego State University
Nitrate/Nitrite concentrations in San Diego County ground and surface water
An analysis of NO3-1NOr concentrations in ground and surface water samples taken from throughout the Santa Margarita, San Diego, Sweetwater, and Tijuana watersheds. The colorimetric method of analysis was used to measure N03-/ N02- levels in the samples. Groundwater samples were taken from the Tijuana Estuary, the Bonita Well Field, Lawson Valley, and from areas of Camp Pendleton including the Santa Margarita River near Basilone Rd., and a well site near Las Pulgas Rd. Surface water samples were taken from: the Tijuana River at two sites within the estuary, Barrett Lake, and Pine Creek; the Sweetwater River in Bonita, at the crossing of Highway 94, and along Highway 79; the San Diego River at the base of the El Capitan Dam, at the east and west ends of Mission Trails regional park, and a site behind Fashion Valley shopping center; Alvarado creek below San Diego State University; the Santa Margarita River on Camp Pendleton, at three sites within the Santa Margarita Ecological Preserve, a site just downstream, and two sites in Rainbow Creek. Analysis showed elevated relative concentrations in surface waters from the Santa Margarita watershed, particularly in the samples from Rainbow Creek. These levels were below what is required for drinking water standards, and consistent with results of an analysis done in 2000 by the Regional Water Quality Control Board. Higher than normal concentrations were also found in well waters in the Tijuana Estuary, the levels were also below what is considered safe for drinking water concentrations. All other levels ranged from 5 to 350 ppb for N03-, and 2-20 ppb for N02-. Comparisons with previous countywide surveys showed similar values. A comparison with a global surface water average of 810 ppb shows that county levels on the whole are relatively low., San Diego State University
Occurrence and description of a megabreccia deposit and associated rocks near bitter spring, cave mountain 15' quadrangle, Mojave Desert, California
Several unusual breccia deposits occur in southern California, one of which is located immed­iately southeast of Bitter Spring in the Mojave Desert. The deposit is a megabreccia composed of metamorphic material of possible Pre-Cambrian age which rests upon Tertiary lake deposits. Both units are overlain by basalt flows estimated to be uaternary in age. The outcrops of breccia occur as large coherent blocks up to several thousand feet in length as well as less coherent breccias with large clasts. The origin of several of these breccia deposits has been under question. They are either sedimentary deposits, the results of gravity sliding, or tectonic deposits, the results of thrust faulting. This report concludes that the main portion of the Bitter Spring megabreccia is most likely a remnant of a thrust plate, while other portions appear to be gravity slide deposits., San Diego State University
Ocean acidification during the Paleocene-Eocene thermal maximum at Contessa Road, Italy: Insights from weight percent carbonate content
The Paleocene-Eocene Thermal Maximum (PETM; ~55 Ma) is defined as a period of time during which thousands of petagrams of carbon were released into the ocean-atmosphere system, causing significant global warming and ocean acidification. Biotic responses to these environmental changes included large biogeographic shifts, rapid evolution, and changes in trophic ecology, but few groups suffered major extinctions with the exception of benthic foraminifera. Giusberti et al. (2008) conducted detailed analyses of the PETM interval along the classic Contessa Road exposure within the Umbre-Marche Basin, Italy (Western Tethys). The PETM interval at Contessa Road is interpreted to have been deposited at a lower bathyal paleodepth (~1500 m), and consists predominantly of pelagic limestone with two prominent marly beds. The onset of the PETM's negative Carbon Isotope Excursion (CIE) coincides with a drop in carbonate content in the lower marly bed and a second, less prominent, drop also occurs in the upper marly bed. A succession of events and changes in the taxonomic structure of benthic foraminifera has been recognized beginning at the base of the CIE, and is interpreted to be the result of the shoaling of the local carbonate saturation profile (i.e., lysocline, Carbonate Compensation Depth (CCD)) above this site. While Giusberti et al. (2008) established these basic characteristics of the PETM at this section, their sampling resolution was relatively low (~5 cm) through the two marly (low-carbonate) intervals. To refine the structure of the PETM at Contessa Road, we resampled the one-meter interval at one-centimeter resolution, and calculated wt% carbonate variations from dissolved Ca concentrations measured via Inductively Coupled Plasma – Optical Emission Spectrophotometry (ICP-OES). Our results did not reproduce Giusberti et al.'s (2008) first and major drop in wt% carbonate coincident with the CIE onset, but did reproduce the second drop in wt% carbonate within the uppermost part of the CIE. Such decreases in wt% carbonate in the upper marly bed can be interpreted to represent a transient interval of carbonate undersaturation during local shoaling of the carbonate saturation profile in response to carbon release to the ocean-atmosphere system. Resolving such local expressions of the PETM can provide valuable insights into the carbon cycle, climate, and biological responses to environmental alterations. Such local data are critical to provide a more complete global reconstruction of the PETM, an event often invoked as an analog for ongoing anthropogenic climate changes., San Diego State University
Offset of oligocene Marcus Wash trachyte supports one kilometer of displacement along the Taylor Lake fault system, Picacho State Recreation area, Southeastern California
In Picacho State Recreation area, the newly identified Taylor Lake fault transects and disrupts Oligocene volcanic units. Previous investigators mapped and completed geochemical analyses of a pale purple feldspar porphyry. These data suggested a trachyte composition, and, as a result, previous workers named the mapped unit the Marcus Wash trachyte. Though mapping indicated that the Marcus Wash trachyte extended westward, across the Taylor Lake fault previous investigators did not study the chemistry of the westward outcrop belt. In this study samples were collected from the western outcrop belt of the Marcus Wash trachyte and were analyzed for major and trace elemental chemistry. In order to statistically test whether the western and eastern parts of the Marcus Wash trachyte correlate across the Taylor Lake fault the nonparametric bootstrap method and the Aitcheson Measure of Location (AML) were used. If the western and eastern parts of the Marcus Wash trachyte are compositionally similar, then the ratios of c1wrMwlc1ETMW. c2wrMwlc2ErMw, ... ,CnwrMwlcnETMW should equal 1. The subscripts WTMWrefer to samples collected from the western trachyte of Marcus Wash, ETMW refers to samples collected from the eastern trachyte of Marcus Wash, and c1, c2, ... , Cm are AML- based concentrations of chemical components 1 through m. A bootstrap Visual Basic 6 program for determining AML values was used in this study. The results of 10,000 bootstrap replications indicate that at the 95% confidence level, the majority of measured chemical ratios are not statistically different from 1. Ratios that are significantly different are restricted to elements that are indicative of feldspar alteration in the WTMW samples. Hence, the western and eastern parts of the Marcus Wash trachyte are chemically similar, and the Taylor Lake fault displaces this key unit by~ 1 km., San Diego State University