Physical Sciences and Mathematics Commons^™

U-Pb Zircon Geochronology And Structure Of Regional Blueschist Units In The Easton Metamorphic Suite, Northwest Cascades, Wa, Katherine Lang

WWU Graduate School Collection

The Easton metamorphic suite of the Northwest Cascades Thrust System (NWCS) is a well-preserved subduction accretion complex in Washington State. The regional blueschist units of the Easton metamorphic suite include the Mt. Josephine semi-schist, Darrington Phyllite, and Shuksan greenschist/blueschist and all are interpreted to have accreted after the onset of Jurassic subduction beneath North America. This study uses zircon U-Pb geochronology, structure, and field observations to test the regional correlations between units in the Easton metamorphic suite and address models for the timing of subduction accretion along the North American margin in the Late Jurassic – Early Cretaceous. The results …

Timing And Conditions Of Metamorphism In The Cascades Crystalline Core From Garnet Lu-Hf And Sm-Nd Geochronology, Peter Baker

WWU Graduate School Collection

The Chiwaukum Schist and Tonga Formation of Cascades Crystalline Core experienced three distinct metamorphic events: (M1) an early metamorphism that predates regional pluton emplacement, (M2) low-pressure contact metamorphism in the aureoles of the Mount Stuart batholith and Beckler Peak pluton, and (M3) regional Barrovian metamorphism. The timing of these distinct metamorphic events is critical to testing models for the tectonic evolution of the region and mechanisms that lead to burial of rocks within the orogen. I present new garnet Lu-Hf and Sm-Nd isochrons, average pressure and temperature calculations, and pseudosection modeling from the Chiwaukum Schist and Tonga Formation in order …

Paleomagnetism And Detrital Zircon Geochronology Of The Skeena Group, British Columbia, Christopher L. Ward-Guthrie

WWU Graduate School Collection

The mid-Cretaceous Skeena Group of British Columbia is a sedimentary continental margin deposit that overlies the lower Jurassic Hazelton Group of the Stikine Terrane. Nine paleomagnetic sites were collected in 2006 and 2007, demagnetized thermally in 50-15°C steps, and high temperature components fit using principal component analysis. A new Ar⁴⁰/Ar³⁹ age of 93.9 ± 0.6 Ma for a flow of the Rocky Ridge Formation was also collected.

Three volcanic sites of the Rocky Ridge Volcanics possess coherent magnetizations, but did not prove useful. Five of six sedimentary sites from the Rocher de Boule and Bulkley Canyon Formations …

Structure, Metamorphism, And Geochronology Along The Southern Margin Of The Breakenridge Orthogneiss, Coast Range, Southern British Columbia, John A. (John Andrew) Feltman

WWU Graduate School Collection

The Breakenridge orthogneiss is located at the southern end of the Coast Plutonic Complex, in the southwest Canadian Cordillera. It consists of sheeted orthogneiss sills and metamorphosed country rock folded into a tight, upright antiform. The deformational and metamorphic history along the southern margin of this structure is the focus of this study.

The orthogneiss is in original intrusive contact with enveloping metavolcanic rocks of the Jura-Cretaceous Slollicum Schist. A new U-Pb zircon age of 103.8 ± 0.5 Ma, together with a published age of 96 Ma (Parrish and Monger, 1992), establishes an episode of igneous intrusion and crystallization between …