Petrologic Significance of Multiple Magmas in the Quottoon Igneous Complex, NW British Columbia and SE Alaska

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dc.contributor.authorThomas, Jay Bradley Jr.en
dc.contributor.committeechairSinha, A. Krishnaen
dc.contributor.committeememberSinha, A. Krishnaen
dc.contributor.committeememberCrawford, Maria L.en
dc.contributor.committeememberBeard, James S.en
dc.contributor.departmentGeological Sciencesen
dc.date.accessioned2014-03-14T20:51:50Zen
dc.date.adate1998-06-26en
dc.date.available2014-03-14T20:51:50Zen
dc.date.issued1998-05-18en
dc.date.rdate1999-06-26en
dc.date.sdate1998-05-18en
dc.description.abstractThe quartz dioritic Quottoon Igneous Complex (QIC) is a major Paleogene (65-56 Ma) magmatic body in NW British Columbia and SE Alaska that was emplaced along the Coast shear zone (CSZ). The QIC contains two different igneous suites that provide information about source regions, magmatic processes and evolving tectonic regimes that changed from a dominantly convergent to a dominantly strike-slip regime between 65 to 55 Ma. Heterogeneous suite I rocks (e. g. along Steamer Passage) have a pervasive solid-state fabric, abundant mafic enclaves and dikes, metasedimentary screens, and variable color indices (25-50). The homogeneous suite II rocks (e. g. along Quottoon Inlet) have a weak (to absent) fabric developed in the magmatic state (aligned feldspars, melt filled shears), and more uniform color indices (24-34) than in suite I. Suite I rocks have Sr concentrations <750 ppm, avg. LaN/YbN = 10.4, and initial 87Sr/86Sr ratios that range from 0.70513 to 0.70717. The suite II rocks have Sr concentrations >750 ppm, avg. LaN/YbN = 23.1, and initial 87Sr/86Sr ratios that range from 0.70617 to 0.70686. This study proposes that the parental QIC magma (initial 87Sr/86Sr = 0.706) can be derived bypartial melting of an amphibolitic source reservoir at lower crustal conditions. Geochemical data (Rb, Sr, Ba and LaN/YbN) and initial 87Sr/86Sr ratios preclude linkages between the two suites by fractional crystallization or assimilation and fractional crystallization (AFC) processes. The suite I rocks are interpreted to be the result of magma mixing between the QIC parental magma and a mantle derived magma. The samples do not lie along a single mixing line due to continued evolution through fractional crystallization/AFC processes subsequent to magma mixing. The suite II rocks may be generated by AFC. Initial 87Sr/86Sr ratio data suggests that similar processes to those that affected the QIC may also have operated during the generation of other portions of the Great Tonalite Sill of southeast Alaska.en
dc.description.degreeMaster of Scienceen
dc.identifier.otheretd-52598-142754en
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-52598-142754/en
dc.identifier.urihttp://hdl.handle.net/10919/36795en
dc.publisherVirginia Techen
dc.relation.haspartJTHESIS2.pdfen
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectQuottoon plutonen
dc.subjectquartz dioriteen
dc.subjecttonaliteen
dc.subjectmagmaen
dc.subjectBritish Columbiaen
dc.subjectAlaskaen
dc.subjectpetrographyen
dc.subjectmajor elementsen
dc.subjecttrace elementsen
dc.subjectrare earth elementsen
dc.subjectgeochemistryen
dc.subjectSr isotopesen
dc.subjectgeochemical modelingen
dc.subjectGreat Tonalite Sillen
dc.titlePetrologic Significance of Multiple Magmas in the Quottoon Igneous Complex, NW British Columbia and SE Alaskaen
dc.typeThesisen
thesis.degree.disciplineGeological Sciencesen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.levelmastersen
thesis.degree.nameMaster of Scienceen

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