A Geochemical Exploration of the Sagehen Volcanic Centre, Truckee-Tahoe Region, California, U.S.A.

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dc.contributor.authorClarke, Christopher Angus Leo
dc.date.accessioned2012-06-13T08:02:55Z
dc.date.available2012-06-13T08:02:55Z
dc.date.created2012
dc.date.issued2012
dc.identifier.urihttp://hdl.handle.net/10393/22899
dc.identifier.urihttp://dx.doi.org/10.20381/ruor-5817
dc.description.abstractThe assemblage of ca. 6–4 Ma volcanic rocks exposed at the Sagehen Research station in the Truckee-Tahoe region of the northern Sierra Nevada, United States, is interpreted to be, within the Ancestral Cascades volcanic arc, a Lassen-type stratovolcano complex. Sagehen is of particular importance because it is one of the few Tertiary arc volcanic centres in California which has not been heavily glaciated during the Pleistocene. The volcanic rocks are variably porphyritic or aphanitic, including abundant plagioclase with clinopyroxene and amphibole. The rocks range from basalt to basaltic-andesite to andesite in composition. Basalts are olivineand clinopyroxene-bearing with minor phenocrysts of plagioclase. The basaltic-andesites are primarily pyroxene bearing while the andesites contain pyroxene-, plagioclase- and hornblende porphyritic phases. Sagehen arc lavas are calc-alkaline and enriched in the large ion lithophile elements and depleted in High Field Strength Elements. The basalts are depleted in Zr and Hf while the andesites are enriched with Zr and Hf relative to the middle rare earth elements. Compared to previously studied Ancestral Cascade arc samples, Sagehen region basalts have lower 143Nd/144Nd isotopic values that do not correspond to proposed mantle-lithosphere mixing lines, while the andesite samples appear to represent the interplay of these two components on a 87Sr/86Sr vs. 143Nd/144Nd. The trace element data and isotopic plots suggest that the melts that produced the basalts are from subduction modified mantle wedge peridotites that ponded near the base of the lithosphere similar to the generation of other subduction related calc-alkaline lavas along convergent continental margins. The andesitic samples appear to be the result of further modification through crustal assimilation as seen in the higher isotopic Sr contents in the andesites and Ce/Smpmn vs. Tb/Ybpmn plots. Finally, the proposed map units from Sylvester & Raines (2007) were found to contain various geochemical facies based on the samples collected indicating that some map units may have to be redefined or sub-divided.
dc.language.isoen
dc.publisherUniversité d'Ottawa / University of Ottawa
dc.subjectSagehen
dc.subjectAndesite
dc.subjectBasalt
dc.subjectLake Tahoe
dc.subjectSr isotopes
dc.subjectNd isotopes
dc.subjectgeochemistry
dc.subjectAncestral Cascades
dc.subjectSierra Nevada
dc.subjectCrustal contamination
dc.subjectCalc-alkaline
dc.titleA Geochemical Exploration of the Sagehen Volcanic Centre, Truckee-Tahoe Region, California, U.S.A.
dc.typeThesis
dc.faculty.departmentSciences de la terre / Earth Sciences
dc.contributor.supervisorFowler, Anthony
dc.contributor.supervisorCousens, Brian
dc.embargo.termsimmediate
dc.degree.nameMSc
dc.degree.levelmasters
dc.degree.disciplineSciences / Science
thesis.degree.nameMSc
thesis.degree.levelMasters
thesis.degree.disciplineSciences / Science
uottawa.departmentSciences de la terre / Earth Sciences
CollectionThèses, 2011 - // Theses, 2011 -

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