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Petrogenetic analysis of the Wenatchee Ridge Orthogneiss in the North Cascade Mountains, Washington State

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dc.contributor.authorZaggle, Richard Haster, author
dc.contributor.authorMagloughlin, Jerry, advisor
dc.contributor.authorRidley, John, committee member
dc.contributor.authorStrauss, Steven, committee member
dc.date.accessioned2007-01-03T06:26:02Z
dc.date.available2007-01-03T06:26:02Z
dc.date.issued2014
dc.description.abstractPetrogenetic analysis of the Wenatchee Ridge Orthogneiss (WRO) in the Nason Terrane of the North Cascade Mountains has been undertaken in order to gain insight into epidote-bearing TTG plutonism associated with mid-Cretaceous orogenesis in the North American Cordillera. Discriminant analysis indicates the WRO is very similar to Archean TTGs based upon characteristic geochemical values (Yb <1, Sr/Y >150, La/Yb >15, Y<6) and thus may provide insight into Archean crustal generation processes. Samples were taken from within the pluton and from within the surrounding banded gneiss. The pluton is chemically heterogeneous and samples all show some degree of foliation which is concordant with the foliation in country rocks. Samples range from leucotrondhjemite to granodiorite and contain oligoclase, quartz, potassium feldspar, muscovite, biotite, and epidote. SiO2 is 56.3-76.8% and REE data show that the samples are highly depleted in HREEs, variably depleted in LREEs, and have an average Eu/Eu* of 1.36±0.5. Though positive Eu anomalies are typically associated with plagioclase accumulation, the WRO appears to lack any correlation between plagioclase and Eu/Eu*. Geochemical results and the tectonic setting of the WRO indicate the initial magma may have formed as a partial melt of overthickened eclogitic crust. The subsequent LREE depletion and high positive Eu anomalies in the most evolved samples may be controlled by amphibole, epidote, and/or titanite fractionation. LA-ICP-MS analyses will indicate whether these phases had significant control on the REE signature of the WRO. Deformation-driven differentiation would have controlled any fractionation of amphibole, epidote, and/or titanite in the WRO magma which has viscosities of ≥106.8 Pa•s at 1000°C. Differentiation likely occurred simultaneously with intrusion into a lower crustal zone of plastic strain, resulting in the WRO's heterogeneity, sheeted nature, and syn-tectonic fabric.
dc.format.mediumborn digital
dc.format.mediummasters theses
dc.identifierZaggle_colostate_0053N_12784.pdf
dc.identifier.urihttp://hdl.handle.net/10217/88617
dc.languageEnglish
dc.language.isoeng
dc.publisherColorado State University. Libraries
dc.relation.ispartof2000-2019
dc.rightsCopyright and other restrictions may apply. User is responsible for compliance with all applicable laws. For information about copyright law, please see https://libguides.colostate.edu/copyright.
dc.subjectcascades
dc.subjectgeochemistry
dc.subjectgneiss
dc.subjectigenous
dc.subjectpetrogenetic
dc.subjectpetrology
dc.titlePetrogenetic analysis of the Wenatchee Ridge Orthogneiss in the North Cascade Mountains, Washington State
dc.typeText
dcterms.rights.dplaThis Item is protected by copyright and/or related rights (https://rightsstatements.org/vocab/InC/1.0/). You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).
thesis.degree.disciplineGeosciences
thesis.degree.grantorColorado State University
thesis.degree.levelMasters
thesis.degree.nameMaster of Science (M.S.)

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