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Date of Award
Winter 2024
Document Type
Masters Thesis
Department or Program Affiliation
Geology
Degree Name
Master of Science (MS)
Department
Geology
First Advisor
Mulcahy, Sean,
Second Advisor
Schermer, Elizabeth, 1959-
Third Advisor
Roland, Emily Carlson,
Abstract
The Easton metamorphic suite (EMS) of the Northwest Cascades is an exhumed Jurassic-Cretaceous subduction complex that can be used to test models for subduction zone deformation. Regionally extensive blueschist/greenschist within the EMS were accreted in a thermally evolving subduction zone (148 – 137 Ma). Two units, the Darrington phyllite and the Shuksan greenschist, were originally interpreted as coherent units that subducted in a zone of distributed deformation. New field mapping, microstructural analysis, and thermometry suggest the Darrington phyllite should be divided into two separate units, the Darrington phyllite and Silver phyllite. The Darrington phyllite, Silver phyllite, and Shuksan greenschist preserve different foliation and deformation histories. In addition, Raman spectroscopy of carbonaceous material (RSCM) thermometry in the Darrington and Silver phyllite and published thermometry from the greenschist suggests the units have different thermal histories. RSCM temperatures for the Darrington phyllite and Silver phyllite are 374 – 400 °C and 430 – 450 °C respectively. In contrast, the Shuksan greenschist formed at conditions of ~360 °C. New deformation and thermometry data combined with existing 40Ar/39Ar ages suggest the Darrington phyllite and Silver phyllite are separate units and that the Silver phyllite and Shuksan greenschist were subducted as tectonic slices rather than as a coherent unit. The style of deformation within the EMS supports models of localized deformation along shear zones that facilitate subduction accretion.
Type
Text
Keywords
subduction zone processes, metamorphic petrology, structural geology, raman spectroscopy, petrography and microstructure
Publisher
Western Washington University
OCLC Number
1424975200
Subject – LCSH
Metamorphism (Geology)--Cascade Range; Geology, Structural--Cascade Range; Schists--Cascade Range; Phyllite--Cascade Range
Geographic Coverage
Cascadia Subduction Zone; Cascade Range
Format
application/pdf
Genre/Form
masters theses
Language
English
Rights
Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author’s written permission.
Creative Commons License
This work is licensed under a Creative Commons Attribution-Share Alike 4.0 License.
Recommended Citation
Gates, Emily, "Strain localization during subduction and accretion of regional blueschist facies units in the Easton metamorphic suite, NW Cascades Washington" (2024). WWU Graduate School Collection. 1263.
https://cedar.wwu.edu/wwuet/1263