University of Vermont ScholarWorks @ UVM Graduate College Dissertations and Theses Dissertations and Theses 2016 The Relationship Between Magmatism and Deformation During the Acadian Orogeny: A Case Study from Eastern-Central Vermont Samuel William Lagor University of Vermont Follow this and additional works at: https://scholarworks.uvm.edu/graddis Part of the Geology Commons, and the Tectonics and Structure Commons Recommended Citation Lagor, Samuel William, "The Relationship Between Magmatism and Deformation During the Acadian Orogeny: A Case Study from Eastern-Central Vermont" (2016). Graduate College Dissertations and Theses. 566. https://scholarworks.uvm.edu/graddis/566 This Thesis is brought to you for free and open access by the Dissertations and Theses at ScholarWorks @ UVM. It has been accepted for inclusion in Graduate College Dissertations and Theses by an authorized administrator of ScholarWorks @ UVM. For more information, please contact [email protected]. THE RELATIONSHIP BETWEEN MAGMATISM AND DEFORMATION DURING THE ACADIAN OROGENY: A CASE STUDY FROM EASTERN-CENTRAL VERMONT A Thesis Presented by Samuel William Lagor to The Faculty of the Graduate College of The University of Vermont In Partial Fulfillment of the Requirements for the Degree of Master of Science Specializing in Geology May, 2016 Defense Date: January 22, 2016 Thesis Examination Committee: Laura E. Webb, Ph.D., Advisor Donald S. Ross, Ph.D., Chairperson Keith A. Klepeis, Ph.D. Jon Kim, Ph.D. Cynthia J. Forehand, Ph.D., Dean of the Graduate College ABSTRACT The Silurian–Devonian metasedimentary rocks of the Connecticut Valley-Gaspé trough (CVGT) were subjected to multiple deformational and metamorphic events during the Acadian orogeny in the Middle–Late Devonian. Plutons intruding the Devonian Waits River and Gile Mountain Formations have been considered post-tectonic, but microstructural studies of the intrusions and their metamorphic aureoles indicate some of these plutons intruded syntectonically. This study investigates the relationship between Acadian deformation and intrusion of the Knox Mountain pluton (KMP) of central Vermont. Structural and geochronological data were collected along a c. 15 km transect from the western limit of the CVGT, where the unconformable Richardson Memorial Contact coincides with the Dog River Fault Zone, into the margin of the KMP in the east. Field and microstructural observations indicate the KMP intruded syntectonically. Evidence for Acadian deformation post-dating intrusion includes folded and boudinaged granitic dikes at the margin of the KMP, and microstructures such as flame perthite, myrmekite, deformation twins, and textures associated with grain-boundary migration recrystallization in the granite. In the metamorphic aureole, biotite porphyroblasts overgrow S3, the earliest Acadian secondary foliation, and were deformed during S4 crenulation cleavage development. The KMP intruded at 377±5.2 Ma based on a U-Th- total Pb monazite crystallization age, which is concordant with the published age of the nearby Barre granite. The timing of S4 foliation development in the CVGT is constrained locally by 40Ar/39Ar geochronology at ~365 Ma, consistent with the microstructurally- inferred relative-age relationships. Plateau/weighted mean 40Ar/39Ar ages from across the transect and minimum ages from argon-loss profiles show a general trend of younging towards the east, suggesting these rocks have been affected by Alleghanian and Mesozoic deformation and exhumation. ACKNOWLEDGEMENTS I regard the completion of this thesis document and master’s program as one of the most significant mental and physical accomplishments of my life. However, seeing this document to completion was certainly not the result of my actions alone, and I remain indebted to countless indivuals (most of whom will not be named here). To my adviser, Dr. Laura Webb, as I have said before, the patience, guidance, and understanding you have shown me throughout this process will take me a lifetime to pay forward. I cannot thank you enough for sharing your wisdom, encouragement, and a laugh with me, and always I needed them most. It has been a pleasure working in the department as a teacher’s assistant under a number of other geology faculty, and I thank you all for the advice, anecdotes, and kindness you have shared with me throughout these three years. I am incredibly grateful for the guidance and passion of Dr. Jeff Chiarenzelli and Dr. Sean Regan since my time working alongside them at St. Lawrence. You gentlemen helped instill my passion for geology, and I look forward to continued collaborations. I need to thank Matt Van Brocklin, who always ensured I had a place to stay, and that the machines were running smooth any time I made it back to Canton. The results of this project would be nowhere-to-be-found were it not for Dan Jones. Thanks for everything from the good beer to the unsolicited advice. Big shout-out to all the assistants I had in the field. Jacob Vincent, Ifan Hywel, Drew Groth, Beth Pidgeon, Hannah Blatchford, and John Gilbert, your second opinions became my preliminary interpretations! Finally, I could not have done this without my friends and family backing me. Hannah, Tess, Elle, Gabe, and Ida, I love you more than words can tell. ii TABLE OF CONTENTS ACKNOWLEDGEMENTS………………………………………………………..……ii LIST OF FIGURES…………………………………………….……………….....…….v LIST OF TABLES……………………………………………………………….….…..vi LIST OF APPENDICES……………………………………………….…...….….…...vii CHAPTER 1: COMPREHENSIVE LITERATURE REVIEW………………………1 1.1. Introduction……………………………………………….……………………...…1 1.2. The Emplacement of Granite During Collisional Orogenies.....................................2 1.2.1. Introduction…………………………………………………..…..……....…2 1.2.2. Generating Melt—Crustal Anatexis, Migmatites, and the Effect of Strain .…...………………………………………………………………………………..4 1.2.3. Melt Focus and Extraction……………………………..………...……........6 1.2.4. Magma Ascent and Emplacement.................................................................8 1.2.5. Emplacement in the Ductile Regime.............................................................9 1.2.6. Emplacement in the Brittle Regime.............................................................10 1.2.7. Construction of Plutons....….......................................................................10 1.2.8. Dikes............................................................................................................11 1.2.9. Geochronology.............................................................................................12 1.2.10. Relevance to this Study………………………………….......……...……14 1.3. Geologic Setting of the Connecticut Valley-Gaspé Trough.......................................15 1.3.1. Regional Geology…………..………………..……..……......……...…….15 1.3.2. Magmatism in the CVGT……………………………….……..….….....…19 1.3.3. Structural Geology………………………………..…...……..…….….…..21 1.4. Geochronology of the Connecticut Valley-Gaspé Trough.........................................23 1.4.1. Formation of Grenvillian Basement.............................................................24 1.4.2. Tectonic Model for the Taconic Orogeny....................................................24 1.4.3. Summary of the Taconic Orogeny in Western Vermont. .......................... 25 1.4.4. Tectonic Model for the Acadian Orogeny...................................................26 1.4.5. Acadian Overprinting on Taconian Rocks...................................................27 1.4.6. Deposition and Deformation of Devonian Rocks of the CVGT..................28 1.4.7. Timing of Magmatism in the CVGT...........................................................30 1.4.8. Summary......................................................................................................31 CHAPTER 2: ARTICLE FOR SUBMISSION.............................................................53 Abstract........................................................................................................................53 1. Introduction.............................................................................................................54 2. Geologic Background.............................................................................................55 2.1. Geologic Setting of the Connecticut Valley-Gaspé Trough……..….……...55 2.1.1. Regional Geology........................................................................................55 2.1.2. Magmatism in the CVGT……………………………………..........……..59 2.1.3. Structural Geology……………………………………………..……...…..61 2.2. Constraints on the Timing of Tectonic Events..............................................63 2.2.1. Formation of Grenvillian Basement.............................................................64 iii 2.2.2. Tectonic Model for the Taconic Orogeny....................................................64 2.2.3. Tectonic Model for the Acadian Orogeny...................................................65 2.2.4. Acadian Overprinting on Taconian Rocks...................................................66 2.2.5. Deposition and Deformation of Devonian Rocks of the CVGT..................68 2.2.6. Timing of Magmatism in the CVGT...........................................................69 3. Methods...............................................................................................................…70 3.1. Microstructural Analysis…………………………………………………...…71 3.2. Ca and K Mapping of Biotite Grains under a Scanning Electron Microscope.....................................................................................................……..72