University of Tennessee, Knoxville TRACE: Tennessee Research and Creative Exchange Masters Theses Graduate School 5-2013 EMPLACEMENT MECHANISMS AND MAGMA DRIVING PRESSURE OF THE PROTEROZOIC CURECANTI PLUTON; THE BLACK CANYON OF THE GUNNISON, COLORADO Gordon Leonard Hicks The University of Tennessee, Knoxville, [email protected] Follow this and additional works at: https://trace.tennessee.edu/utk_gradthes Part of the Geology Commons, and the Tectonics and Structure Commons Recommended Citation Hicks, Gordon Leonard, "EMPLACEMENT MECHANISMS AND MAGMA DRIVING PRESSURE OF THE PROTEROZOIC CURECANTI PLUTON; THE BLACK CANYON OF THE GUNNISON, COLORADO. " Master's Thesis, University of Tennessee, 2013. https://trace.tennessee.edu/utk_gradthes/1626 This Thesis is brought to you for free and open access by the Graduate School at TRACE: Tennessee Research and Creative Exchange. It has been accepted for inclusion in Masters Theses by an authorized administrator of TRACE: Tennessee Research and Creative Exchange. For more information, please contact [email protected]. To the Graduate Council: I am submitting herewith a thesis written by Gordon Leonard Hicks entitled "EMPLACEMENT MECHANISMS AND MAGMA DRIVING PRESSURE OF THE PROTEROZOIC CURECANTI PLUTON; THE BLACK CANYON OF THE GUNNISON, COLORADO." I have examined the final electronic copy of this thesis for form and content and recommend that it be accepted in partial fulfillment of the requirements for the degree of Master of Science, with a major in Geology. Micah J. Jessup, Major Professor We have read this thesis and recommend its acceptance: Robert D. Hatcher Jr., Harry Y. McSween Accepted for the Council: Carolyn R. Hodges Vice Provost and Dean of the Graduate School (Original signatures are on file with official studentecor r ds.) EMPLACEMENT MECHANISMS AND MAGMA DRIVING PRESSURE OF THE PROTEROZOIC CURECANTI PLUTON; THE BLACK CANYON OF THE GUNNISON, COLORADO A Thesis Presented for the Master of Science Degree The University of Tennessee, Knoxville Gordon Leonard Hicks May 2013 Copyright © 2013 by Gordon “Donnie” Leonard Hicks All rights reserved. ii DEDICATION To Kali For all the spark; To Annie For finding me in the dark; To Jamey For the massive head start iii ACKNOWLEDGEMENTS The ideas presented in this paper have benefitted significantly from many discussions with James V. Jones III. Field assistance was provided by Remy Leger during summer 2010. Sources of funding for this research included the Geological Society of America, Four Corners Geological Society, Tobacco Root Geologic Society, and The University of Tennessee – Earth and Planetary Sciences Swingle Award, several graduate teaching assistantships, and a graduate research assistantship. I would like to thank my committee members, Dr. Robert D. Hatcher, Jr. and Dr. Harry Y. McSween, for providing critical feedback and revisions. I thank Dr. Micah J. Jessup for his patience, understanding, and insights regarding structural geology and life. Kyle White, Tim Diedesch, and Remy Leger provided edits, clarifications, and ideas regarding the structural models presented in this thesis. Ken Stahlnecker was instrumental in providing access to the Black Canyon of the Gunnison National Park and the Curecanti National Recreation Area for field work. Sue Newman of Sister Kenny provided belief and encouragement in the spaces between, and Liz Lee provided PBR and R&R on the other side of the country. There are obviously far too many individuals and groups to properly acknowledge, but please know that your thoughts, efforts, and love is recognized and appreciated. iv ABSTRACT There is significant obliquity between the margins of the Curecanti pluton, an internal foliation, a coeval swarm of ~400 pegmatite dikes just west of the pluton, and the host rock foliation. This pluton is a 5 km-long, 3 km-wide, and 0.4 km-thick sheet of monzogranite exposed in the Black Canyon of the Gunnison, CO. The pluton is discordant along most of its length, but has a >100-m-thick root at its western margin subparallel to the foliation in the host rock gneisses. A cordierite + anthophyllite + staurolite + garnet schist from the Vernal Mesa pluton aureole was previously dated (1.4 Ga) and indicates emplacement occurred at 600*C [degrees C] ± [plus or minus] 50*C and 300 ± 100 MPa. We present evidence that indicates emplacement of the Curecanti pluton, 25 kilometers-southeast of the Vernal Mesa pluton, may have occurred during similar conditions. The Vernal Mesa pluton was intruded subparallel to, and contemporaneous with movement on the NE-striking, subvertical Black Canyon shear zone. In contrast, Curecanti monzogranite was emplaced as a tongue-shaped sheet that tapers out in the hinge zone of the kilometer-scale F2 Curecanti antiform. The discordance between the pluton margins, an internal foliation, and the host rock foliation is contrary to observations of many other tabular granitoids worldwide that are emplaced parallel to host rock foliation and display a margin-parallel foliation. Three transects through the Curecanti pluton display evidence for solid-state foliation development localized in the pluton floor and in correlative dikes just beneath the pluton. Evidence for submagmatic flow is preserved near the roof of the pluton. Strain accumulated in the pluton at least 75 m above the floor, but did not result in the development of a foliation. The decoupling of wall-rock fabric and Curecanti pluton foliations, along with the presence of high-temperature quartz deformation mechanisms in the pluton, indicate high-temperature subsolidus deformation. In addition, Curecanti pluton geochemistry and magma driving pressure are evaluated to show that a combination of neutral buoyancy, depth to the magma source region, and a rheological impediment are necessary conditions to form this partly discordant peraluminous pluton. v TABLE OF CONTENTS CHAPTER PAGE CHAPTER 1 INTRODUCTION ....................................................................................... 1 1.1 Granitoid emplacement controversy ......................................................................... 1 1.1.1 Granite versus granitoid ..................................................................................... 1 1.1.2 Diking ................................................................................................................ 2 1.1.3 Deformation ....................................................................................................... 2 1.1.4 The search for a unified model .......................................................................... 3 1.2 Mesoproterozoic thermal event & controversy ......................................................... 5 1.2.1 Introduction ........................................................................................................ 5 1.2.2 Mesoproterozoic: Orogeny or no orogeny? ....................................................... 7 CHAPTER 2 GEOLOGIC SETTING .............................................................................. 10 2.1 Regional setting: Laurentia in the Proterozoic........................................................ 10 2.2 Black Canyon geology ............................................................................................ 11 2.2.1 Introduction ...................................................................................................... 11 2.2.2 Deformational history recorded in the Black Canyon of the Gunnison........... 15 2.2.3 Correlating MJBC-43 to the Curecanti pluton ................................................. 17 CHAPTER 3 THE CURECANTI PLUTON .................................................................... 19 3.1 Introduction ............................................................................................................. 19 3.2 Three transects through a mid-crustal pluton .......................................................... 23 3.2.1 Nelson Gulch transect ...................................................................................... 27 3.2.2 Pioneer transect ................................................................................................ 29 3.2.3 Chipeta transect ................................................................................................ 31 Chapter 4 METHODS....................................................................................................... 33 4.1 Field work – mesoscale observations ..................................................................... 33 4.2 Petrography – microscale observations .................................................................. 33 4.3 Magma driving pressure ......................................................................................... 39 4.3.1 Hydrostatic pressure (Ph) ................................................................................. 40 4.3.2 Magma chamber overpressure (Po) .................................................................. 40 4.3.3 Viscous pressure drop (Pvis) ............................................................................. 40 4.3.4 Horizontal stress (Sh) ....................................................................................... 41 4.3.5 Example of a calculated magma driving pressure ........................................... 43 4.4 Stress field during emplacement ............................................................................. 45 4.4.1 Mohr circle construction .................................................................................. 45