METAMORPHIC PETROLOGY, PRESSURE-TEMPERATURE PATHS, AND TECTONIC EVOLUTION OF THE MOUNT CUBE QUADRANGLE, NEW HAMPSHIRE AND VERMONT by DANIEL LEWIS ORANGE S.B. Massachusetts Institute of Technology (1985) Submitted to the Department of Earth, Atmospheric and Planetary Sciences in Partial Fulfillment of the Requirements of the Degree of MASTER OF SCIENCE at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY May, 1985 0 Daniel L. Orange 1985 The author hereby grants to M.I.T. permission to reproduce and distribute copies ot this thesis document in whole or in part. Signature of Author Department of Earth,"'Ampheric and Planetary Sciences, May 14, 1985 Certified by Frank Spear Thesis Supervisor Accepted by ___ _._' - - f__ Theodore Madden Chairma ee on Graduate Students Room 14-0551 77 Massachusetts Avenue Cambridge, MA 02139 Ph: 617.253.5668 Fax: 617.253.1690 MITLibraries Email: [email protected] Document Services http://libraries.mit.edu/docs DISCLAIMER OF QUALITY Due to the condition of the original material, there are unavoidable flaws in this reproduction. We have made every effort possible to provide you with the best copy available. If you are dissatisfied with this product and find it unusable, please contact Document Services as soon as possible. Thank you. Some pages in the original document contain text That runs off the edge of the page. (Pages A-100 & A-101) METAMORPHIC PETROLOGY, PRESSURE-TEMPERATURE PATHS, AND TECTONIC EVOLUTION OF THE MOUNT CUBE QUADRANGLE, NEW HAMPSHIRE AND VERMONT by DANIEL LEWIS ORANGE Submitted to the Department of Earth, Atmospheric and Planetary Sciences in Partial Fulfillment of the Requirements for the Degree of Master of Science in Geology May 14, 1985 ABSTRACT The metamorphic history of a traverse across the Mount Cube Quadrangle and Rumney Quadrangle, New Hampshire and Vermont, is investigated using optical petrology, geothermometry, geobarometry, and a garnet zoning technique for calculating pressure-temperature paths. A variety of pelitic assemblages are present across 15 kilometers of strike; these range from garnet-staurolite-kyanite rocks in the Archertown Brook (AB) and Cottonstone Mountain (CM) localities to the west to garnet-chlorite- chloritoid grade rocks along the Northey Hill Line (NHL) to garnet- cordierite-sillimanite grade rocks in-the Baker Pond (BP) locality to the east. Pressure-temperature calculations indicate peak metamorphic conditions in the CM locality of 3.75-5.25 kb and 460-5100 C. The AB locality presents peak conditions of 3-5 kb and 425-5000C. The NHL has lower peak conditions of 2-3 kb and 450-490 0C. Samples from the Jacobs Brook Recumbant Syncline (JBRS) have a peak temperature of 490-575 0C and the pressure is not constrained. The BP locality has peak conditions of 3-5 kb and 490-5500C. The garnets analyzed from the NHL exhibit small zoning gradients. In contrast, garnets from the other localities have steep zoning profiles. Quantitative P-T paths are presented for all but the JBRS and BP localities. Pressure-temperature paths computed from samples west of the NHL suggest up to two nappe-stage compressional events, a near-isothermal dome-stage decompression, and a late-stage isobaric cooling correlative with the development of the Sunday Mountain Cleavage Belt. The NHL samples show an isothermal decompression associated with the Sunday Mountain Cleavage Belt. The isobaric cooling seen west of the NHL is thought to be due either to thrusting of hot rocks over cold rocks or the folding of isosotherms during a late stage back-folding event. Neither of these hypotheses can accomodate the isothermal decompression seen in the NHL samples. A structural break is inferred along the Northey Hill Line, where detailed mapping shows drastic thinning of beds and the highest intensity of the Sunday Mountain Cleavage Belt. To create the P-T path geometry seen in the NHL, this locality must have experienced differential uplift with respect to the samples to the west. In this interpretation, the isobaric cooling in the samples to the west is produced prior to the uplift along the NHL. Thesis Supervisor: Frank Spear Title: Associate Professor of Geology ACKNOWLEDGEMENTS First and foremost, I would like to thank my father for four years of financial and emotional support. I would like to thank my advisor, Frank Spear, for his enthusiasm and support all along, and for the insight he has given me towards metamorphic processes. Don Hickmott deserves special note, for without his constant availability and untiring fielding of my many questions, this thesis would never have been completed. I would also like to thank Dr. Douglas Rumble III for the many days he spent with me in the field explaining the structures of the Mount Cube Quadrangle, and also for providing thin sections for the Cottonstone Mountain and Archertown Brook localities. I would like to thank Larry McKenna for his field assistance. Doug Chor (MIT) and Dave Lange (Harvard) provided many hours of instruction and assistance in the use of the electron microprobe. Matt Kohn typed the majority of this thesis, while Don Hickmott and Dr. Jane Selverstone provided thorough and thought-provoking commentaries on the rough drafts. Dr. Jane Selverstone also provided valuable insight into the role of fluids in metamorphic equilibria. Beatrice Silny assisted in putting the final draft together. I wish to thank my fellow Masters student, Rosamond Kinzler, for the months of constant support and assistance. I wish to thank the Thursday Mandarin lunch/Thirsty Ear crowd for giving me something to look forward to every week, no matter how badly things were going. I wish to thank Baker House for the support in the tough times and three years of the good times. Lastly, I would like to thank John Carl Adams, with whom I'm about to depart on a trip around the world. By consenting to this impending insanity, he has helped get through this year. Let the good times roll! "Hoya Saxa!!" (What Rocks!) iii TABLE OF CONTENTS ABSTRACT........................... ... 11 ACKNOWLEDGEMENTS............. .. 0 . .. .111 TABLE OF CONTENTS................. .. 0 . .. .. LIST OF TABLES AND APPENDICES..... .. 0 . .. .. LIST OF FIGURES................... ...vii I. INTRODUCTION................... ....... II. REGIONAL GEOLOGY.............. III. METHODS OF INVESTIGATION..... ...11 IV. SAMPLE LOCALITIES............. ..................... 0 9 . ...14 V. SYSTEMATIC MINERALOGY.......... .................... ...18 Cottonstone Mountain....... ...19 ..................... 0 0 t B k. ArI c her .UI roo Vown 0 o o*............................. ...21 Northey Hill Line....................... ..... 30 Jacobs Brook Recumbant Syncline......... ...39 Baker Pond.............................. ...41 ..................... a0 0 VI. ELECTRON MICROPROBE ANALYSES............. ...57 Cottonstone Mountain.................... ..................... 0 0 0 0 . ...58 Archertown Brook........................ ...62 ..................... 0 0 Northey Hill Line....................... ...74 Jacobs Brook Recumbant Syncline......... ......82 Baker Pond.............................. ...90 Garnet Zoning: Discussion............... ...95 VII. GEOTHERMOMETRY AND GEOBAROMETRY......... ...97 Cottonstone Mountain.................... ...98 Archertown Brook........................ ...99 Archertown Brook: Comparison............ .......................... 9 0 0 * 0 .107 TABLE OF CONTENTS (cont'd.) VII. GEOTHERMOMETRY AND GEOBAROMETRY (cont'd.) Northey Hill Line..................................................110 Jacobs Brook Recumbant Syncline....................................113 Baker Pond.........................................................117 Regional Cross Section: P-T Space..................................125 VIII. PRESSURE-TEMPERATURE PATHS FROM GARNET ZONING.....................128 Cottonstone Mountain...............................................130 Archertown Brook...................................................141 Northey Hill Line..................................................151 Jacobs Brook Recumbant Syncline....................................157 Baker Pond.........................................................158 IX. DISCUSSION AND CONCLUSIONS..........................................160 REFERENCES..............................................................166 LIST OF TABLES AND APPENDICES TABLE 1: COMPARITIVE SYSTEMATIC MINERALOGY.............................47 APPENDIX 1: MODAL ABUNDANCES-COTTONSTONE MOUNTAIN......................A-1 APPENDIX MODAL ABUNDANCES-ARCHERTOWN BROOK............... ........ 0 0 .. .A-2 APPENDIX MODAL ABUNDANCES-NORTHEY HILL LINE.............. A-4 ...... APPENDIX MODAL ABUNDANCES-JACOBS BROOK RECUMBANT SYNCLINE A-5 ...... APPENDIX MODAL ABUNDANCES-BAKER POND..................... .A- 7 ... APPENDIX MICROPROBE ANALYSES-COTTONSTONE MOUNTAIN........ .. .A-8 ... APPENDIX MICROPROBE ANALYSES-ARCHERTOWN BROOK............ .. A-17 .... APPENDIX MICROPROBE ANALYSES-NORTHEY HILL LINE........... A-53 ...... APPENDIX MICROPROBE ANALYSES-JACOBS BROOK RECUMBANT SYNCLINE... ..... A-64 APPENDIX 10: MICROPROBE ANALYSES-BAKER POND............................A-79 LIST OF FIGURES 1. Location of the Mount Cube and Rumney Quadrangles, New Hampshire and Vermont ........................................................ 3 2. Detailed geologic map of the Mount Cube Quadrangle and the surrounding area ................................................... 5 3. Cross-section across the Mount Cube Quadrangle ..................... 6 4. Stratigraphy of the Mount Cube Quadrangle .........................