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Theses/Dissertations

Geology

1987

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Full-Text Articles in Physical Sciences and Mathematics

A Trace Element Geochemical Analysis Of The Lake Ellen Kimberlite, Crystal Falls, Michigan, U.S.A., Michelle Ellen Fults Dec 1987

A Trace Element Geochemical Analysis Of The Lake Ellen Kimberlite, Crystal Falls, Michigan, U.S.A., Michelle Ellen Fults

Masters Theses

The Lake Ellen kimberlite located in the Upper Peninsula of Michigan represents a possible bedrock source for the diamonds found in the glacial deposits around the Great Lakes. The purpose of this research was to undertake a geochemical analysis in order to better understand the evolution of the kimberlite body and to elucidate on the garnet xenolith paragenesis.

Both instrumental neutron activation analysis (INAA) and scanning electron microscope analysis (SEM) were utilized in this research. The INAA revealed that with respect to other types of upper mantle rocks, the Lake Ellen kimberlite is enriched in both the light rare earth …


Depth Profiles And Soil Textures Of The Vernal Pools Of The Santa Rosa Plateau Preserve, Riverside County, California, Ralph Charles Workman Jr. Dec 1987

Depth Profiles And Soil Textures Of The Vernal Pools Of The Santa Rosa Plateau Preserve, Riverside County, California, Ralph Charles Workman Jr.

Loma Linda University Electronic Theses, Dissertations & Projects

The purpose of this project was to study the edaphic and topographic characteristics of the 13 vernal pools on the Santa Rosa Plateau Preserve, thus documenting the role soil texture plays in vernal pool formation.

Several field and laboratory procedures were used to demonstrate that there is a higher percentage of clay present within vernal pools than in soils outside the margin of the pools, for 11 out of the 13 pools. Statistical tests showed that the percentage of clay was highly significant within the center soil of the pool as compared to the soil outside the margin of the …


Deposition, Diagenesis, And Porosity Development Of The Middle Devonian, Lucas Formation In The West Branch Oil Field, Ogemaw County, Michigan, Scott Gregory Park Dec 1987

Deposition, Diagenesis, And Porosity Development Of The Middle Devonian, Lucas Formation In The West Branch Oil Field, Ogemaw County, Michigan, Scott Gregory Park

Masters Theses

The Lucas Formation in the West Branch Oil Field contains over 1000 feet of carbonates and evaporites deposited in restricted marine environments. Deposition ranged from a tidal flat environment (Richfield Member) to subaqueous basin central type deposition (Iutzi and Horner Members).

Early diagenesis of the Lucas Formation carbonates included dolomitization and related porosity development in certain depositional facies where physiochemical conditions were favorable. Significant porosity and permeability reduction occurred during burial resulting from anhydrite, celestite, and halite cementation. Calcite pseudopar and microspar (a neomorphic product) also reduced porosity.

Hydrocarbon production from the Lucas Formation in the West Branch Field is …


Discrimination Of Subparallel Beach Ridges Using Detrital Ilmenite Composition And Fourier Shape Analysis, Allen E. Evans Jr. Oct 1987

Discrimination Of Subparallel Beach Ridges Using Detrital Ilmenite Composition And Fourier Shape Analysis, Allen E. Evans Jr.

OES Theses and Dissertations

Elemental composition (Fe, Ti, Mn, Mg, V, Cu, Ni, Zn, and Cr) and Fourier shape analysis of magnetically separated detrital ilmenite from seven Pleistocene and modern beach sand deposits of the Southeastern Virginia Coastal Plain were used to distinguish each deposit. Geomorphic expression, crosscutting relationships and proximity to the present shoreline differentiates the relative age of the seven sampled beach deposits. Analysis of ilmenite elemental composition, independent of geomorphic expression, distinguished beach sands of

different age and was successful in determining that each beach contained ilmenite similar in composition. Of the seven beach ridges tested, subtle yet significant differences in …


Possible Role Of Petroliferous Materials In Sulfide Precipitation At The Frank R. Millikan Mine, Southeast Missouri, Clark Alan Niewendorp Aug 1987

Possible Role Of Petroliferous Materials In Sulfide Precipitation At The Frank R. Millikan Mine, Southeast Missouri, Clark Alan Niewendorp

Masters Theses

The Millikan Mine's ore body contains ubiquitous amounts of petroliferous materials occurring as blebs, coal-like pods and veinlets, and seeps coating mine stope walls. Emplacement of hydrocarbons into the ore occurred before the final episode of mineralization ceased, based on growth of dendritic galena in some coal-like bitumen and other paragenetic relationships. Growth of dendritic galena in a hydrocarbon substance suggests that hydrocarbons provided sulfur for galena mineralization by either abiogenetic reduction of sulfate or thermochemical evolution of organic sulfur. Texturally, it also suggests that the presence of hydrocarbons may have been responsible for some zones of rapid precipitate mineralization. …


A Thermodynamic Study Of The Zeolite Stilbite, David Adams Howell Aug 1987

A Thermodynamic Study Of The Zeolite Stilbite, David Adams Howell

Masters Theses

Stilbite is a calcium-rich zeolite found in low-grade metamorphic and hydrothermally altered environments. In this study, measurements of the enthalpy of formation at 298.15 K, heat capacity from 5 to 350 K, and enthalpy increments horn 350 to 500 K were performed on a specimen of stilbite characterized by electron microprobe analysis. The actual formula of the stilbite is: Ca1.019Na0.136K0.006Al2.180Si6.820O16 . 7.33H2O. Evaluation of the thermodynamic properties for stilbite at T = 298.15 K produced the following values: ΔrHOm(T)= -11034.6+6.6 kJ . mol …


Nitrate Pollution Of Ground Water In Glacial Sediments Underlying A Fertigated Site In Kalamazoo County, Michigan, Michael Wireman Aug 1987

Nitrate Pollution Of Ground Water In Glacial Sediments Underlying A Fertigated Site In Kalamazoo County, Michigan, Michael Wireman

Masters Theses

In the central part of Schoolcraft Township high yield corn crops are successfully grown on soils developed on permeable outwash deposits. The high yields are made possible with the utilization of modern irrigation techniques and regular application of nitrogen fertilizer.

Excess nitrogen which moves past the root zone is easily converted to nitrate and leached to the shallow ground water. Water quality data from 103 ground-water samples in the vicinity of a 160-acre corn field in Section 11 clearly indicate that nitrate concentrations in the ground water beneath the field and beneath the area immediately downgradient from the field are …


Explosion Structures In Grande Ronde Basalt Of The Columbia River Basalt Group, Near Troy, Oregon, Leonard Lee Orzol Jun 1987

Explosion Structures In Grande Ronde Basalt Of The Columbia River Basalt Group, Near Troy, Oregon, Leonard Lee Orzol

Dissertations and Theses

Explosion structures occur in flows of Grande Ronde Basalt in the study area near Troy, Oregon. Data from nineteen stratigraphic sites indicate that the maximum number of flows that contain explosion structures at any one site is six. In the informally named Troy flow, explosion structures are widespread.

Each flow that contains explosion structures can be divided into two cooling units. The first cooling units occupy troughs in the pre-eruption topography and are up to 10 meters thick. The second cooling units contain the explosion structures and are up to 100 meters thick. The thickness of flows that contain explosion …


Lacustrine Deltaic Deposits Of The Sandstone Tongue Of The Wasatch Formation, Fossil Basin, Wyoming, F. Steve Petersen Jun 1987

Lacustrine Deltaic Deposits Of The Sandstone Tongue Of The Wasatch Formation, Fossil Basin, Wyoming, F. Steve Petersen

Loma Linda University Electronic Theses, Dissertations & Projects

Sedimentary structures and facies relations of the sandstone tongue of the Wasatch Formation in Fossil Basin, Wyoming are interpreted as indicative of a rapidly prograding bird's foot delta. Two upward coarsening siliciclastic sequences that contain bottomset, foreset, and topset beds were studied over an area of approximately 400 square kilometers. Vertical and lateral sedimentary changes within this sequence were documented by the measurement and study of over 35 stratigraphic sections. High and low angle cross-bedded sandstone units within the siliciclastic sequences thicken northward significantly before rapidly thinning and grading into the lacustrine Green River Formation. Field observations. lateral correlation of …


Paleoenvironments Of The Eocene Green River Formation (Laney Member) In The Anvil Wash Area, Southwestern Wyoming, M. Elaine Graham-Kennedy Jun 1987

Paleoenvironments Of The Eocene Green River Formation (Laney Member) In The Anvil Wash Area, Southwestern Wyoming, M. Elaine Graham-Kennedy

Loma Linda University Electronic Theses, Dissertations & Projects

The study of abundant conchostracans in the Laney Member of the Green River Formation, Wyoming, has contributed to the resolution of the controversy over the depositional environment of finely laminated sediments. Conchostracans that typically live in ephemeral pools, pulmonate gastropods that require oxygenated water and freshwater ostracods indicate deposition of finely laminated sediments in a well oxygenated, shallow, freshwater lake. Mineralogical evidence indicating that Lake Gosiute was primarily fresh during deposition of the upper portion of the Laney Member includes predominance of calcite over dolomite and the clay composition of diagenetically altered tuffs. The minor amount of dolomite is detrital …


Petrology Of Pliocene (?) Basalts Of Curlew Valley (Box Elder Co.), Utah, Steven Brent Kerr May 1987

Petrology Of Pliocene (?) Basalts Of Curlew Valley (Box Elder Co.), Utah, Steven Brent Kerr

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Basalt outcrops in Curlew Valley consist of several flow remnants and eruptive centers situated along the valley margins. Basalt is also found in association with salic rocks that erupted in the central portion of the valley. The basalts are of probable Pliocene age and were erupted during a period of active extensional tectonics. Since their emplacement, the basalts have been extensively eroded and downfaulted. The present morphology reflects the erosional and depositional processes of prehistoric Lake Bonneville.

Twelve samples were analyzed chemically for major oxides, trace elements, and rare-earth elements. The basalts form a hypersthene normative series ranging from olivine …


Petrology Of The Middle Cambrian Langston And Ute Formations In Southeastern Idaho, Daniel T. Rogers May 1987

Petrology Of The Middle Cambrian Langston And Ute Formations In Southeastern Idaho, Daniel T. Rogers

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The Middle Cambrian Langston and Ute formations were studied in the northern portion of the Bear River Range and the south-central part of the Portneuf Range in southeastern Idaho.

The rocks of the Langston and Ute formations were divided into 17 different rock types. The 17 rock types were formed within four recognizable lithofacies: I) Shoal - or Coastal-Peritidal Carbonate Complex; 2) Agitated Shoal; 3) Inner Marine Shelf; and 4) Outer Marine Shelf. Clastic sediments belonging to the Spence Shale Member of the Langston Formation (outer marine shelf) were deposited over the carbonate complex. A transgressive sequence marks the base …


Surficial Geology Of The Smithfield Quadrangle, Cache County, Utah, Michael V. Lowe May 1987

Surficial Geology Of The Smithfield Quadrangle, Cache County, Utah, Michael V. Lowe

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The Smithfield 7.5' quadrangle is located about 13.8 kilometers (8.6 miles) south of the Utah-Idaho State Line and occupies the central portion of the eastern side of Cache Valley, Utah. The mapped area contains more than 55 square miles. The Bear River Range on the eastern side of the quadrangle contains stratigraphic units ranging from Precambrian to Quaternary age. Cache Valley contains deposits of Tertiary and Quaternary age. Quaternary units in the Smithfield quadrangle are subdivided into thirty-two map units based on age and genesis. Five ages of Quaternary units are identified, and these units are assigned to one of …


Spatial And Temporal Landslide Distribution And Hazard Evaluation Analyzed By Photogeologic Mapping And Relative-Dating Techniques, Salt River Range, Wyoming, John B. Rice Jr. May 1987

Spatial And Temporal Landslide Distribution And Hazard Evaluation Analyzed By Photogeologic Mapping And Relative-Dating Techniques, Salt River Range, Wyoming, John B. Rice Jr.

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The distribution of landslide type and age was analyzed to determine the causes and timing of landsliding, and to assess landslide hazards in the study area. 1173 landslides and zones of landsliding were mapped on 1:15,840 scale air photos and designated by their style of movement and age. Slides were assigned to one of four age classes based on their degree of morphologic modification visible on air photos. Relative dating (RD) methods previously applied to glacial deposits were used to refine and calibrate the age classification.

Eleven RD para meters were measured on 21 rockslide and 19 glacial deposits. Cluster …


Hydrogeology And Hydrochemistry Of Springs In Mantua Valley And Vicinity, North-Central Utah, Karen C. Rice May 1987

Hydrogeology And Hydrochemistry Of Springs In Mantua Valley And Vicinity, North-Central Utah, Karen C. Rice

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Chemical and tritium analyses of groundwater, precipitation and discharge records, fracture orientations, lineaments, and structural, stratigraphic, and topographic relationships have been used to describe the groundwater systems of Mantua Valley, north-central Utah. Groundwater flows through fractured Paleozoic quartzites and carbonate rocks and discharges from eleven perennial springs in Mantua Valley. Permeability in quartzites is the result of intense faulting and jointing. Groundwater in carbonate aquifers flows through fractures and/or fractures modified by solution and discharges as relatively large springs (up to 227 liters per second). Neogene normal faulting, rather than extensive karst processes, has produced valleys which are closed or …


Benthic Foraminiferal Assemblages From Mexican Continental Shelves, Maria De La Luz Mata Apr 1987

Benthic Foraminiferal Assemblages From Mexican Continental Shelves, Maria De La Luz Mata

LSU Historical Dissertations and Theses

The recent benthic foraminifera 1 fauna of the continental margins of Mexico (Gulf of Campeche and Gulf of Tehuantepec) was studied. Surficial sediment samples (lOcc) were collected using a Shipeck dredge and were stained with Sudan Black "B" in order to differentiate the living fauna from the death assemblage. In the 41 samples from the Gulf of Campeche, 279 species were found in the total assemblage in water depths ranging from 9 to 586 m. In the 22 samples in the Gulf of Tehuantepec, 132 species were identified from the total assemblage in water depths of 20 to 180 m. …


Structural Geology And Geothermal Investigation Of The White Sulphur Springs Area, Montana, William G. Gierke Apr 1987

Structural Geology And Geothermal Investigation Of The White Sulphur Springs Area, Montana, William G. Gierke

Masters Theses

Sevier thrusting in the White Sulphur Springs area was associated with left-lateral movement along the Lewis and Clark line . During Middle Miocene time, the Lewis and Clark line exhibited right-lateral movement, forming extensional features that either truncated Sevier structures or followed preexisting Sevier zones of weakness.

The Smith River Valley is a pull-apart basin that is filled with Tertiary volcanic ash and clay-rich sediments that are thermally nonconductive relative to surrounding rocks.

Hydrothermal activity in the area is associated with a structurally controlled circulation system accompanied by a high thermal gradient. Thermal discharge is constrained along the north-trending White …


The Effect Of Well Efficiency On In-Situ Permeability Test Results, Scott T. Dennis Apr 1987

The Effect Of Well Efficiency On In-Situ Permeability Test Results, Scott T. Dennis

Masters Theses

The purpose of this study was to determine what effect well efficiency has upon the results of in-situ permeability tests.

Several in-situ permeability tests were performed on wells during various stages of their development. The well efficiency was determined each time an in-situ test was performed. An accurate value of permeability was determined by performing local aquifer pumping tests. The accuracy of the results of the in-situ tests with respect to the aquifer pump test results were then compared to the efficiency of the well at the time of the test.

Test results showed that a linear relationship exists between …


Provenance Of Sands Within The Lower Chesapeake Bay Based On Ilmenite Composition, Edward Augustus Council Iii Apr 1987

Provenance Of Sands Within The Lower Chesapeake Bay Based On Ilmenite Composition, Edward Augustus Council Iii

OES Theses and Dissertations

Surficial sands deposited in the Chesapeake Bay are a mixture of sands derived from the bay's shorelines, from offshore, and from relict deposits. Direct fluvial input is probably minor except from the James River, which may serve as a local source of sands in the Thimble Shoals area. Sands in the western half of the bay are primarily derived from the erosion of the adjacent shoreline. In contrast, the eastern half of the bay has two major sources of sand. Shoreline erosion is the dominant source north of the town of Eastville, Virginia, while the offshore is the major source …


The Stratigraphy Of Late Quaternary Deposits In The Payan Mining District, Narino, Colombia, South America, Richard Alan Barringer Apr 1987

The Stratigraphy Of Late Quaternary Deposits In The Payan Mining District, Narino, Colombia, South America, Richard Alan Barringer

OES Theses and Dissertations

Late Quaternary terrace deposits along the Rio Magui consist of cobble or pebble gravels with thick volcanic ash caps. These gravel terrace deposits unconformably overlie a cemented volcanic tuff (Ananias Formation), and are subdivided into two formations (Antigua and Panambi formations) based on the cobble lithology and size, depth of weathering, geomorphic relationships, and heavy mineral assemblages. Carbon-14 dates from wood suggest that the Antigua fan deposits are older (greater than 40,000 YBP) than the lower Panambi alluvium (less tahn 25,000 YBP) which is restricted to lower terraces within the modern river valleys.

Two separate ash units identified by differences …


Petrographic Criteria For The Recognition Of 'Magadi-Type' Cherts, Kathryn A. Schubel Jan 1987

Petrographic Criteria For The Recognition Of 'Magadi-Type' Cherts, Kathryn A. Schubel

Honors Papers

The Magadi cherts, inorganic lacustrine deposits from the Lake Magadi area, Kenya, are widely used as a modern analog to explain the origin of ancient inorganic cherts. Formed in a highly alkaline lake, as the result of a transformation from the sodium silicates minerals, magadiite and/or kenyaite, to quartz, the Magadi cherts possess a distinctive set of textural characteristics that allow them to be distinguished from cherts of different origin with only a limited number of samples. Textural characteristics that are diagnostic of the Magadi cherts and that can be used as a test for the occurrence of ancient 'Magadi-type' …


Petrology Of The Kula Volcanic Field, Western Turkey, Julie M. Dyer Jan 1987

Petrology Of The Kula Volcanic Field, Western Turkey, Julie M. Dyer

Geology Theses and Dissertations

The Kula volcanics are a small Pleistocene to Recent volcanic field located on the north shoulder of the Gediz graben, approximately 120 km east of Izmir. The field consists of a mixture of flows, small cones and pyroclastic deposits erupted during three periods of volcanic activity beginning about one million years ago. The volcanics range in composition from basanites to trachybasalts, commonly porphyritic with abundant clinopyroxene, olivine and amphibole phenocrysts. The lavas also host a wide variety of megacrysts, crustal xenoliths and hydrous mantle-derived nodules. These volcanics unconformably overlie Neogene lacustrine sedimentary rocks and the metamorphic basement rocks of the …


Structural Analysis Across The Northeast Boundary Of The Taconic Allochthon, West-Central Vermont, Thomas E. Hoak Jan 1987

Structural Analysis Across The Northeast Boundary Of The Taconic Allochthon, West-Central Vermont, Thomas E. Hoak

Geology Theses and Dissertations

The Taconic Allochthon is an elongate belt of Cambro-Ordovician, argillaceous sediments with lesser occurrences of calcareous and siliceous lithologies. These lithologically distinctive strata lie tectonically juxtaposed over a coeval medial-Ordovician carbonate shelf sequence. This geometry resulted from an arc-continent collision in which a westward-migrating arc (Ammonoosuc Volcanics) collided with an eastern North America passive margin and the accumulated accretionary prism of the forearc region was thrust onto the passive continental margin.
The present thesis examined the structural sequence at the north end of the Allochthon and the continuity of this sequence into the adjacent Parautochthonous Shelf strata. Structurally, the study …


Granitic Pegmatites In The Southeastern Adirondacks: Their Use As Indicators Of Temperature, Pressure, And Fluid Conditions During A Late Stage Of The Grenville Orogeny, John P. Mihalich Jan 1987

Granitic Pegmatites In The Southeastern Adirondacks: Their Use As Indicators Of Temperature, Pressure, And Fluid Conditions During A Late Stage Of The Grenville Orogeny, John P. Mihalich

Geology Theses and Dissertations

Granitic pegmatites associated with the Grenville orogeny intrude a mid-Proterozoic, upper amphibolite to near granulite facies terrane in the southeastern Adirondack Mountains of New York State. The inferred anatectic, fluid-saturated, and minimum melt characteristics of the pegmatites suggest that they can be used as analogs of the "granite" or "haplogranite" system, and as indicators of crustal temperature, pressure, and fluid conditions during a late stage of the Grenville orogeny. Bulk chemical compositions of seven simple, undeformed pegmatites in the southeastern Adirondacks indicate that they are generally depleted in silica and sodium, and enriched in potassium, relative to experimental data on …


Geology, Geochemistry, And Geochronology Of The Lems Ridge Olistostrome, Klamath Mountains, California, Matthias Ohr Jan 1987

Geology, Geochemistry, And Geochronology Of The Lems Ridge Olistostrome, Klamath Mountains, California, Matthias Ohr

Geology Theses and Dissertations

The Lems Ridge olistostrome (LRO), located within the western Jurassic belt of the Klamath Mountains geologic province, is a melange unit showing a distinct block-in-matrix fabric. The conformable relationship to both an igneous basement and the overlying flysch of the Late Jurassic Galice Formation points to a sedimentary origin. The lack of pervasive deformation and the internal stratification also support a predominantly olistostromal origin of the LRO. The matrix of the LRO consists of pebbly mudstone which interfingers with tuffaceous greenstone and tuff-breccias. Subordinate beds of chert, argillite, and sandstone are also present. The matrix contains abundant ophiolitic clasts, fragments …


The Providence Island Formation In The Northern Appalachian Region - A Lower-Lower Middle Ordovician Analogue To Recent Arid-Semiarid Tidal-Flat Carbonates Of The Persian Gulf Trucial Coast, Mauricio Roma Hernandez Jan 1987

The Providence Island Formation In The Northern Appalachian Region - A Lower-Lower Middle Ordovician Analogue To Recent Arid-Semiarid Tidal-Flat Carbonates Of The Persian Gulf Trucial Coast, Mauricio Roma Hernandez

Geology Theses and Dissertations

The Providence Island Formation of Early-early Middle Ordovician age occurs in the Champlain Valley and adjacent areas in eastern New York, western Vermont, and southern Quebec. The unit forms part of a carbonate shelf sequence which occupied the eastern margin of the North American continent from Newfoundland to Alabama, and its lithology is representative of the dolostone lithofacies that characterizes the uppermost Beekmantown Group in this region.
This is the first study documenting depositional environments, diagenesis, and stratigraphic correlations of the Providence Island Formation. This formation consists, in decreasing abundance, of dolostones, limestones, shales, and dedolostones. The dominantly fine grain …


Geology Of The Northern Baie Verte Peninsula, Newfoundland, Canada, Pamela J. Stella Jan 1987

Geology Of The Northern Baie Verte Peninsula, Newfoundland, Canada, Pamela J. Stella

Geology Theses and Dissertations

On the eastern portion of the Burlington Peninsula of northwest central Newfoundland, Canada, there are two different age groups of volcanic and volcaniclastic rocks. There have been arguments in the past as to whether or not these two groups are actually only one group (Cape St. John Group) but with progressive intensity of deformation and metamorphism from south to north. Other workers have divided the rocks into two distinct groups, the Grand Cove Group and the Cape St. John Group based on their differences in deformation style and metamorphic grade. This study ignored previous divisions of the rocks into one …


Structural Investigations On Experimentally And Naturally Produced Slickensides, Thomas Michael Will Jan 1987

Structural Investigations On Experimentally And Naturally Produced Slickensides, Thomas Michael Will

Geology Theses and Dissertations

This work has involved an experimental approach and a study of naturally produced slickensides.
The experiments, carried out on a pyrophyllitic rock, have been performed in order to define some extrinsic parameters that control surface and microstructural features. Normal stress, speed (i.e. strain rate), and amount of slip and total displacement were related to measureable surface features, such as length, and spacing between the developing ridges and grooves. Special attention was paid to a newly recognized type of slickenside lineation (Means, 1986). This lineation produced experimentally cannot be explained in terms of the traditional asperity ploughing or dissolution/precipitation models. It …


Identification Of Endmembers For Magma Mixing In Little Sitkin Volcano, Alaska, Douglas A. Wolf Jan 1987

Identification Of Endmembers For Magma Mixing In Little Sitkin Volcano, Alaska, Douglas A. Wolf

Geology Theses and Dissertations

Little Sitkin island is an Aleutian calc-alkalic volcanic center that has erupted a suite of lavas ranging from andesite through rhyodacite. Whole-rock chemistry of these lavas indicates contrasting evolutionary processes; major-oxide silica variation diagrams exhibit linear trends that are suggestive of magma-mixing while trace-element trends are largely controlled by accessory-phase fractionation.
Plagioclase, the dominant phenocryst phase in all lavas, commonly occurs in two distinct populations with markedly different compositions and textures. Both normal and reverse zonation is noted in the plagioclase and clinopyroxene of several samples. In addition, clinopyroxene is found as rims on orthopyroxene grains and as cores with …


An Analysis Of The Eastern Margin Of The Portland Basin Using Gravity Surveys, Steven Allen Davis Jan 1987

An Analysis Of The Eastern Margin Of The Portland Basin Using Gravity Surveys, Steven Allen Davis

Dissertations and Theses

The recent contributions of several investigators has indicated the Portland basin may be a pull-apart structure associated with wrench tectonism. Because of the large density contrast between sedimentary and volcanic units and because of their reasonably uniform and continuous nature, gravity survey methods can be used to identify covered structures with considerable success. The study utilized gravity modeling techniques to investigate the structure and genesis of the Portland basin's eastern margin.