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Student Research 2003

Student Research   2004   2003   2002   2001   2000   1999   1998

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Nikki Athnos

Faculty Advisor/Collaborator: Karen Havholm

Geologic and Geographic Investigation of Holocene Terraces Along the Lower South Saskatchewan River, Central Saskatchewan, Canada

The purpose of this project is to provide archaeologists with a better understanding of the areal extent, stratigraphy, and geoarchaeological significance of fluvial landforms within the South Saskatchewan River valley, from St. Louis, Saskatchewan downstream to the confluence with the North Saskatchewan River. A collaborater from geography determined the extent of the terraces. Stratigraphy and sedimentology of terrace deposits were investigated by describing, photographing, and sampling (for detailed laboratory analyses) Geoprobe cores and cutbank exposures. Three terraces (T1-T3) and an active floodplain (T0) are observed in the study reach. T1 and T2 are Holocene in age (1000-2000 BP and 5000-9000 BP, respectively) and are composed of a silty vertical accretion (floodplain) facies with numerous thin, weakly expressed buried soil profiles over sand and gravel lateral accretion (channel) facies. Abandonment of these terraces and subsequent incision resulted from adjustments to local base level changes controlled by glacial Lake Agassiz. T3 is cut into till or glaciolacustrine deposits and is graded to levels of glacial lakes Saskatchewan and Agassiz during terminal late-Pleistocene deglaciation. T1 and T2 floodplain sediments have the best potential for preservation of Holocene cultural materials.

Luke Beranek
Faculty Advisor/Collaborator: Phillip Ihinger

Field Geology and Geochemistry of a Layered Intermediate Intrusion (LII), North Doherty Mountain, Southwestern Montana

The North Doherty Mountain Intrusive Complex (NDMIC) is one of several satellite plutons related to the areally extensive Boulder batholith of southwestern Montana. The Boulder batholith comprises multiple plutons and intrusive phases, and the magmatism has long been thought to be subduction-related due to its calc-alkaline granodioritic composition. The NDMIC represents an ideal microcosm of the batholith for petrogenetic and structural studies because it exposes both mafic and felsic units and was emplaced in the limb of a major thrust related fold. We present new geologic mapping and detailed whole-rock major and trace element geochemical analyses to show that the entire mafic-to-felsic suite of rocks in the NDMIC represent a single pulse of dioritic magma that preferentially fractionated generating a layered intermediate intrusion (LII). Three distinct lithologies portray a stratigraphic relationship consistent with progressive crystal fractionation in the form of 1) basal, olivine and pyroxene cumulate; 2) intermediate horizon of diorite to monzodiorite; 3) ceiling capped by thin veneer of felsic granodiorite. The continuous stratigraphy of the LII provides important clues into the evolution of dioritic magmas above subduction zones and lends insight into the origin of continental crust.

Jacob Chmielowiec and Ryan Prechel
Faculty Advisor/Collaborator: Phillip Ihinger

Growth of Hydrothermal Quartz Crystals: Insights from Computer Modeling

We present computer simulations of crystal growth from hydrothermal solution. Our computer models are coded in the object-oriented language, C++, in order that we may better display our results visually using openGL. Our new code uses data gathered from measurements of impurity concentrations within natural quartz crystals. These measurements show that different crystal faces grow at different rates in the natural environment (and hence incorporate different concentrations of impurities). Our code is unique in that we control the growth rate of each individual face during crystal growth. Our results are used to constrain the actual timing involved in the healing of fractures in the geologic environment.

Sarah Gordee and Emily Hauser
Faculty Advisor/Collaborator: J. Brian Mahoney

Magmatic Evolution of the Eastern Coast Plutonic Complex, Bella Coola, British Columbia (93D)

The eastern Bella Coola region straddles the boundary between the Coast Plutonic Complex in the west from Early Jurassic to Early Cretaceous island arc assemblages of the Stikine Terrane in the east. Numerous, compositionally diverse plutons, which become progressively younger and more voluminous from east to west, intrude the layered volcano-sedimentary successions. The plutonic rocks are distinguished and delimited into intrusive suites on the basis of field relationships, lithology, mineralogy, alteration assemblages, geochemical attributes and age. Intrusive suites in the Bella Coola region, include, from oldest to youngest: 1) Firvale suite (ca. 132-149 Ma), characterized by pervasively chloritized mafics, saussuritized plagioclase, and interstitial, dark-pink alkali feldspar which gives a characteristic pink and green mottled appearance. Preliminary geochemical analysis of the Firvale suite suggests an uncontaminated volcanic arc origin. Rapid exhumation of this suite is indicated by an erosional unconformity below the overlying Early Cretaceous volcanic assemblage; 2) Desire suite (ca. 120 Ma), a texturally and compositionally diverse assemblage of hornblende gabbro/diorite to granodiorite which is commonly foliated and contains abundant metavolcanic xenoliths; 3) Fougner suite, a distinct salt and pepper, sphene-bearing tonalite to granodiorite that is syn- to post-kinematic with respect to the Paleocene Coast Shear zone; and 4) Four Mile suite, a homogenous coarse-grained garnet-bearing muscovite-biotite granite that post-dates deformation associated with the Coast Shear zone, and includes a preliminary U-Pb date of 72.9 ± 0.5 Ma. Trace element patterns from the Four Mile suite display a LILE pattern characteristic of continental volcanic arcs. Ongoing petrographic, geochemical, isotopic and geochronological analyses will further refine suite designations and permit a detailed assessment of the magmatic evolution of the Bella Coola region.

Rachel Greve
Faculty Advisor/Collaborator: Kent Syverson

Effect of High-Relief Topography on Deglaciation Ice-Flow Patterns, Phillips 7.5' Quadrangle, West-Central Maine

The Phillips 7.5' Quadrangle, west-central Maine, is located in the foothills of the Appalachians. The Sandy River flows approximately east-west through the QuadStriae on the area's highest points indicate that Late Wisconsinan ice covered the entire landscape. We measured flow indicators in the Phillips Quad to study topographic effects on ice-flow directions during deglaciation. Striae data were sorted into size categories, ranging from large grooves to small, inconspicuous striae, and also separated into two geographical categories (north and south of the Sandy River). In the northern area, rose diagrams show an ESE trend (116° mean) for grooves/striae formed during ice-flow maximum. Younger, smaller striae show a more easterly flow direction (102° mean). In the south, the largest flow indicators have a 133° mean orientation, typical of the west-central Maine's regional ice-flow direction. Smaller striae indicate more easterly flow (108° mean). From this data we infer that during the Late Wisconsinan glacial maximum, some ice flowed SE directly over highlands, while some was funneled down the Sandy River valley by topographic highs to the north and south. As ice thinned and wasted back, flow was deflected more toward the east by the emerging high-relief topography.

Ben Paulson
Faculty Advisor/Collaborator: Phillip Ihinger

Differentiation in the Mafic Alkaline Magmas: The Role of Volatiles at Sub-Solidus Conditions

The Shonkin Sag laccolith in central Montana is a large differentiated intrusive complex that consists of a continuous series of crystals that were progressively removed from a single vat of mafic alkaline magma. Due to crystal fractionation, the Shonkin Sag laccolith is stratified with distinct horizons that represent varying degrees of differentiation. During the summer of 2002, we collected samples within the Shonkin Sag complex that represent different stages of crystallization of this magma. These samples have been sectioned and analyzed petrographically for mineral content and mineral texture. Whole-rock geochemistry of the major and trace elements has been obtained. In addition, detailed mineral chemistry of the principle phases was collected in order to document the crystallization sequence. Our initial results indicate that there has been major remobilization of elements at sub-solidus conditions. These dueteric reactions need to be understood in order to get a sense of the original differentiation trends of this unique rock type. Furthermore, because all magmatic systems experience varying degrees of dueteric alteration, an understanding of the reactions at this locality can be applied in any magmatic system.

Laura Strumness and Taryn Lopez
Faculty Advisor/Collaborator: Robert Hooper and J. Brian Mahoney

Lateral Variability in Heavy Metal Speciation within Lacustrine Environments, Lower Coeur d' Alene River Valley, Idaho

The lower Coeur d' Alene (CDA) river valley of northern Idaho has been heavily impacted by lead and zinc contaminants from the CDA mining district upstream. Variation in hydrologic regime, redox conditions, porosity/permeability, organic content and microbial activity results in complicated metal transport pathways. Documentation of these pathways is a prerequisite to effective remediation. A combination of sequential extraction and scanning electron microscopy provides a comprehensive assessment of particulate speciation of heavy metals within the lacustrine environments. This investigation examines the lateral and vertical variability in heavy metal speciation in four lacustrine environments within the CDA River Valley. Lead and zinc are sequestered as authigenic, biogenic and detrital phases; the mechanism of metal sequestration varies with distance from source. Near the source, lead occurs as coarse authigenic or fine grained detrital material, and downstream as non-stoichiometric, biogenic material. In contrast, in the lower reaches of the valley, Zn occurs as fine grained detrital and coarse grained authigenic material. Curiously, upstream, Zn is apparently sequestered in biogenic phases. The contrasting contaminant behavior may be the result of hydrodynamic sorting, varying residence times, variations in sediment supply, or biotic differences within the lake systems. Ongoing analysis is designed to test these hypotheses.

James Watkins and Jesse Bernhardt
Faculty Advisor/Collaborator: Phillip Ihinger

Alkaline Magmatism from Calc-Alkaline Source Regions: Insights from Square Butte and Sweetgrass Hills, MT

Geochemical analyses of the Square Butte (SQB) and Sweetgrass Hills intrusive suites (SGH) of central and northern MT show strong arc-like affinities similar to the high-potassic magmas that make up the Cretaceous Boulder and Idaho batholiths. This is striking, given the extreme eastern location of these magmas relative to the active arc at the time of their intrusion. We present whole-rock major and trace element analyses, mineral chemistry, and petrographic analyses of a variety of stocks and dikes from SQB and SGH. The intrusive rocks sample low-silica, high-alkalic magmas that were derived from a similar source to that of the older batholiths. Other Eocene alkalic magmas, such as the volatile-rich, ultramafic intrusion at Haystack Butte in central MT, have markedly different trace element signatures and reflect derivation from a separate source. Clearly, at least two distinct sources are involved in the generation of the Eocene magmas. The ultimate cause of the widespread Eocene Cordilleran magmatism is vigorously debated today. Models of shallow slab subduction suggest devolatization as the mechanism for generating these magmas. However, these models cannot account for the concurrent production of two distinct alkalic magma types. We present a new model for formation of alkaline magmas in the western US.

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