The Bedrock Geology and Fracture Characterization of the Maynard Quadrangle of Eastern Massachusetts Author: Tracey A. Arvin Persistent link: http://hdl.handle.net/2345/1731 This work is posted on eScholarship@BC, Boston College University Libraries. Boston College Electronic Thesis or Dissertation, 2010 Copyright is held by the author, with all rights reserved, unless otherwise noted. Boston College The Graduate School of Arts and Sciences Department of Geology and Geophysics THE BEDROCK GEOLOGY AND FRACTURE CHARACTERIZATION OF THE MAYNARD QUADRANGLE OF EASTERN MASSACHUSETTS a thesis by TRACEY ANNE ARVIN submitted in partial fulfillment of the requirements for the degree of Master of Science December 2010 © copywrite by TRACEY ANNE ARVIN 2010 ABSTRACT The bedrock geology of the Maynard quadrangle of east-central Massachusetts was examined through field and petrographic studies and mapped at a scale of 1:24,000. The quadrangle spans much of the Nashoba terrane and a small area of the Avalon terrane. Two stratigraphic units were defined in the Nashoba terrane: the Cambrian to Ordovician Marlboro Formation and the Ordovician Nashoba Formation. In addition, four igneous units were defined in the Nashoba terrane: the Silurian to Ordovician phases of the Andover Granite, the Silurian to Devonian Assabet Quartz Diorite, the Silurian to Devonian White Pond Diorites (new name), and the Mississippian Indian Head Hill Igneous Complex. In the Avalon terrane, one stratigraphic unit was defined as the Proterozoic Z Westboro Formation Mylonites, and one igneous unit was defined as the Proterozoic Z to Devonian Sudbury Valley Igneous Complex. Two major faults were identified: the intra-terrane Assabet River fault zone in the central part of the quadrangle, and the south-east Nashoba terrane bounding Bloody Bluff fault zone. Petrofabric studies on fault rocks in two areas indicated final motion in those areas: the sheared Marlboro Formation amphibolites indicated dextral transpressive NW over SE motion, and the Westboro Formation Mylonites indicated sinistral strike-slip motion. Fracture characterization of entire quadrangle where attributes (orientation, trace length, spacing, and termination) of fractures and joints were used to identify dominant sets of fractures that affect the transmissivity and storage of groundwater. Orientations of SW – NE are dominant throughout the quadrangle and consistent with regional trend. DEDICATION This thesis is dedicated to, and in memory of, my mom Dean Arvin, my father-in-law Ralph Rogers, and my friend Steven Katz. You were all with me every step of the way… i ACKNOWLEDGEMENTS I would like to thank United States Geological Survey for their EDMAP award No. 05QAG0011 that was granted through the National Cooperative Geologic Mapping Program. This award supported my summer mapping project and funded my thin section studies. I thank the Office of the Massachusetts State Geologist. In particular I thank State Geologist Steven Mabee for his instruction on performing the Fracture Characterization portion of this thesis and his willingness spend so much time with me in the field. Also I thank State mapper Joseph Kopera for accompanying me in the field on many informative, fun, and thought provoking occasions and for support in the digital map- making process. This thesis would not have been possible without the support of the entire Department of Geology and Geophysics at Boston College. I thank my professors for excellent courses, the staff for keeping me organized, and the youngsters that were my classmates and who became my friends, Misty, Ross, Mike, and Colin, for laughter, encouragement, and comradery. I would also like to thank my dear friends Joesph and Yvette Perullo; Joe for accompanying me in the field as my fracture mapping assistant on many cold November days while attempting to beat the snow (Joe was also used for scale in an outcrop figure or two) and Yvette for sharing your amazing technical advice and expertize in helping to prepare my maps. Special thanks to my advisors, Chris Hepburn and Noah Snyder. What an honor to be guided by the master of New England geology, Nashoba Terrane in particular, Chris Hepburn. He persevered through an arduous process and even threatened that he would retire before I finished. And Noah Snyder who volunteered to take me on as an advisee, from my oral exams to my thesis. He believed that you could teach an old dog new tricks. A very warm thank you to you both. Finally I wish to thank my life partner and best friend, Mary Beth Rogers, for encouraging and enduring this mid-life odyssey I chose to pursue and for proof-reading my thesis for which she had absolutely no interest. ii TABLE OF CONTENTS DEDICATION ............................................................................................................ i ACKNOWLEDGEMENTS ....................................................................................... ii TABLE OF CONTENTS .......................................................................................... iii LIST OF FIGURES ................................................................................................. vii LIST OF TABLES ................................................................................................... xii Chapter 1 – INTRODUCTION Description of the Study Area.........................................................................1 Regional Geologic Setting ..............................................................................3 Introduction Merrimack terrane Nashoba terrane Avalon terrane Previous Work ................................................................................................9 Regional Maynard quadrangle Methods of Investigation ..............................................................................12 Chapter 2 – STRATIGRAPHY Introduction ...................................................................................................16 The Nashoba terrane .....................................................................................16 Marlboro Formation (COm) .............................................................16 Introduction and Previous Work Exposures Lithological Description Contacts Age Nashoba Formation (On) ..................................................................28 Introduction and Previous Work Exposures Lithological Description Biotite Gneiss Quartzo-feldspathic Gneiss Sulfidic Schist Amphibolite Granulite Contacts Age iii The Avalon terrane .......................................................................................55 Westboro Formation mylonite (Zwm) ..............................................55 Introduction and Previous Work Exposures Lithological Description Contacts Protoliths and Age Chapter 3 - IGNEOUS ROCKS Introduction ...................................................................................................62 The Nashoba Terrane ....................................................................................62 Andover Granite (SOag)……………………………………………62 Introduction and Previous Work Exposures Lithological Description Contacts Age Assabet Quartz Diorite (SDaqd) .......................................................73 Introduction and Previous Work Exposures Lithological Description Contacts Age White Pond Diorite (SDwd)..............................................................79 Introduction and Previous Work Exposures Lithological Description Contacts Age Indian Head Hill Igneous Complex (Miic) .......................................88 Introduction and Previous Work Exposures Phases of the Indian Head Hill Igneous Complex Granite Phase Diorite Phase Granodiorite Phase Contacts Age The Avalon Composite Terrane ..................................................................101 Sudbury Valley Igneous Complex (ZDsv) .....................................101 Introduction Exposures Phases of the Sudbury Valley Igneous Complex Diorite Phase iv Granite Phase Contacts Age and Correlations Chapter 4 - STRUCTURAL GEOLOGY Introduction .................................................................................................115 Bedding and Foliation .................................................................................115 Folds ............................................................................................................116 Major Faults and Shear Zones ....................................................................117 Introduction .....................................................................................117 Assabet River Fault Zone................................................................119 Introduction Location Description Marlboro Formation Ductile Shear Zones (mylonite) ....................123 Introduction Location and Description Sense-of-Shear Bloody Bluff Fault Zone .................................................................124 Introduction Location Description Westboro Formation Ductile Shear Zone (mylonite) .....................127 Introduction Location and Description Sense-of-Shear Other Shear Zones.......................................................................................130 Introduction .....................................................................................130 Nashoba Formation Brittle Shear Zone ..........................................130 Marlboro Formation Brittle Faults and Fractures ...........................132 Chapter 5 - METAMORPHIC GEOLOGY Metamorphism of the Nashoba terrane .......................................................135