Western Washington University Western CEDAR WWU Graduate School Collection WWU Graduate and Undergraduate Scholarship Winter 1986 Structure and Petrology of the Deer Peaks Area Western North Cascades, Washington Gregory Joseph Reller Western Washington University, [email protected] Follow this and additional works at: https://cedar.wwu.edu/wwuet Part of the Geology Commons Recommended Citation Reller, Gregory Joseph, "Structure and Petrology of the Deer Peaks Area Western North Cascades, Washington" (1986). WWU Graduate School Collection. 726. https://cedar.wwu.edu/wwuet/726 This Masters Thesis is brought to you for free and open access by the WWU Graduate and Undergraduate Scholarship at Western CEDAR. It has been accepted for inclusion in WWU Graduate School Collection by an authorized administrator of Western CEDAR. For more information, please contact [email protected]. STRUCTURE AMD PETROLOGY OF THE DEER PEAKS AREA iVESTERN NORTH CASCADES, WASHIMGTa^ by Gregory Joseph Re Her Accepted in Partial Completion of the Requiremerjts for the Degree Master of Science February, 1986 School Advisory Comiiattee STRUCTURE AiO PETROIDGY OF THE DEER PEAKS AREA WESTERN NORTIi CASCADES, VC'oHINGTON A Thesis Presented to The Faculty of Western Washington University In Partial Fulfillment of the requirements for the Degree Master of Science by Gregory Joseph Re Her February, 1986 ABSTRACT Dominant bedrock mits of the Deer Peaks area, nortliv/estern Washington, include the Shiaksan Metamorphic Suite, the Deer Peaks unit, the Chuckanut Fontation, the Oso volcanic rocks and the Granite Lake Stock. Rocks of the Shuksan Metainorphic Suite (SMS) exhibit a stratigraphy of meta-basalt, iron/manganese schist, and carbonaceous phyllite. Tne shear sense of stretching lineations in the SMS indicates that dioring high pressure metamorphism ttie subduction zone dipped to the northeast relative to the present position of the rocks. Exposures of the SMS along Coal Mountain are consistent with interpretation of folding as an isoclinal anticline though discrimination between an F or an F structure is not possible. 1 2 The Deer Peaks unit (DPu) (age unknown) consists of transitional calcalkaline tuffaceous andesite with minor interbedded dacite and less abundant slate and chert, all of v^ich is intruded by diabase dikes. Trace element geochemistry is interpreted to indicate a transitional-to-arc back arc basin origin for the igneous protolith of the DPu. During rnetamorphism, a penetrative foliation (S ) was developed parallel to primary layering. S is 1 1 folded into northeast-souti'iwest trending F folds \jhich are in turn folded 2 about a south-southwest trending F axis. Metamorphic mineral assemblages 3 recognized in the DPu are (in addition to quartz and albite): 1) Chlorite + Punpellyite + Epidote + Actinolite 2) Pumpellyite + Calcium Carbonate + Actinolite 3) Epidote + Calcium Carbonate + Actinolite Calcium carbonate is present as both aragonite and calcite. Metamorphism of o the DPu is of high-P/low-T type, occurring at temperatures between 330 C and o 350 C, and pressures between 7 and 11 Kbar. Rocks of the Deer Pea]<s unit are emplaced above those of the Shuksan Suite along the Deer Peaks tiirust fault. The Eocene Chuckanut Formation nonconformably overlies tlie metamorphic rocks in the study area. The Chuckanut Formation is intruded by quartz-diorite of the Higgins Mountain and Granite Lake stocks, and unconformably overlain by the 43.2 _+ 1.9Ma Oso volcanic rocks. The Chuckanut Formation is folded into north\vest trending open folds. Two northwest trending high angle faults juxtapose the Chuckanut Formation with metamorphic rocks in the area: the Higgins Mountain-Day Lake fault and the Segelson Lake shear zone. The Higgins Mountain-Day Lake fault is a sinistral strike slip fault. ACKNCWLEDGEJyiENTS Ned Brown pointed out the thesis topic, taught me metamorphic petrology, and provided financial support for this thesis. Scott Babcock furnished many useful references as well as good advice throughout my career at Western, and taught me about geochernistry. Dave Engebretson contributed to a broadening in my perspective on botli geology and mathematics. I wish to thank these members of my thesis conmittee for their patience and understanding during my career at Western. Many of the students in the graduate program contributed indirectly to this project through discussions of related topics. I would like to thanJc David Black\>)ell, Brad Carkin, Mike Gallagher, Jeff Jones, Mo Smith, and Chuck Ziegler especially. The Vfeasels, vyyn Hill and David Silverberg, provided intellectual stimulation, moral support, and lots of fun during this study, which \irauld not have been completed without acquaintance with them. Many fruitful discussions of North Cascades geology were held with them. Roger Nichols of the U. S. Forest Service provided access to air photos, and valuable advice during this study. This study also benefited from discussions with Rowland Tabor, of the U. S. G. S. In the field season of 1984 I was ably assisted by Dana Bayuk. During the field season of 1985 Mike Hylland accompanied me without a complaint through rain or shine, over waterfalls and through the jungle. I also enjoyed the company of Arthur Morrill and Shirley Sanchez, two friends from a drier clime, during the 1985 field season, and Bemie Dougan experienced and epic or two with me during the su:nmer of '85 . Special thanks to April Gacsi for emotional support in a time of great need, and to Ken Clark ;\^ose advice and dialogue have assisted me in a multitude of dilemma. Financial support for this thesis was provided by a mapping grant fron the state of Washington, a Forest Service contract through Ned Brown, a National Science Foundation grant to Ned Brcwn, and a teaching assistantship fron the Geology Department. TABLE OF CONTE^^^S Abstract............................................................... i Acknowledgenents....................................................... iii Table of Contents......................................................v List of Figures........................................................ vii List of Tables and Plates............................................. ix Introduction........................................................... 1 Geologic Setting....................................................... 1 Statement of Problem...................................................7 Lithologic Units....................................................... 9 Oso volcanic rocks............................................... 9 Quartz Diorite....................................................10 Chuckanut Formation.............................................. 11 Shuksan Metamoirphic Suite........................................ 12 Shuksan Greenschist......................................... 13 Ferruginous Schist.......................................... 13 Darrington Phyllite......................................... 14 Deer Peak unit....................................................14 Pyroxene Tuff............................................... 14 Dacite and Rhyolite Tuff.................................... 19 Chert and Argillite......................................... 24 Diabase...................................................... 24 Metamorphism.................................................26 Recrystallization History............................. 26 Tenperature of Metamorphisra........................... 27 Pressure of I-fetamorphism...............................28 Comparison witii other Western North Cascade Rocks.......... 30 Geochemistry............................................................34 Introduction...................................................... 34 Classification.................................................... 34 Tectonic Discrimination...........................................44 Vftiole Earth Normalized Elemental Abundance Diagrams............. 44 Cortparison with otlier North Cascades rock units................. 49 Structure............................................................... 50 Structures within the Shuksan Metarnorphic Suite................. 50 Foliation.................................................... 50 Folds........................................................ 51 L Lineations................................................ 54 1 Comparison with regional structural elements.......... 55 Structures observed within tlie Deer Peak unit................... 57 Bedding and Foliation........................................60 Folds........................................................ 60 L Lineations................................................ 62 1 Deer Peaks fault.................................................. 62 High angle faults................................................. 64 Higgins Mountain-Day Lake Fault............................. 64 Segelson Lake shear zone.................................... 66 Folds within the Cliuckanut Formation............................. 66 Conclusion.............................................................. 69 References....... 74 Appendix-1.............................................................. 83 LIST OF FIGURES Figure Page 1 Regional Geologic Map................................................ 2 2 Location of the Study Area........................................... 3 3 Tectonic stratigraphy................................................ 4 4 Photomicrograph of sheared clinopyroxene............................ 16 5 Photomicrograph of sheared