ANALYSIS OF POROSITY EVOLUTION DURING LOW TEMPERATURE METAMORPHISM OF BASALTIC LAVAS AND IMPLICATIONS FOR FLUID FLOW By JANE E. GUSTAVSON A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2006 Copyright 2006 by Jane E. Gustavson ACKNOWLEDGMENTS There are many people in my life who have been influential in helping me to obtain my Master of Science. Of those, there are a few that require special mention. My father, James M. Gustavson, did all that he knew to provide the best for his children. If it were not for his selflessness and honest love, I would not be the person I am today. Allyn Spear, though we have a mottled history, was the one who stood beside me and gave me the courage to pursue a higher level of education when I was filled with so much self doubt. Dr. Philip S. Neuhoff was always there with a patient yet guiding hand to see me through my research. He has become more than just my advisor; he is also a good friend. And finally, PJ Moore, who has become the companion I have searched for. His promise to walk beside me gives me the strength to enter the real world with the confidence I need to succeed. iii TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................................................................................. iii LIST OF TABLES............................................................................................................. vi LIST OF FIGURES ......................................................................................................... viii ABSTRACT....................................................................................................................... xi CHAPTER 1 INTRODUCTION ........................................................................................................1 Porosity and Permeability in Vesicular Lavas..............................................................3 Low Grade Alteration of Basaltic Lavas ......................................................................6 Coupling Between Porosity Evolution and Chemical Reactions .................................8 Role of the Present study ..............................................................................................9 2 LOW-GRADE ALTERATION OF THE NORTH SHORE VOLCANIC GROUP, MINNESOTA.............................................................................................................10 Introduction.................................................................................................................10 Geologic Background .................................................................................................12 Methods ......................................................................................................................15 Results.........................................................................................................................17 Primary Basalt Composition and Mineralogy .....................................................17 Regional Alteration Mineralogy..........................................................................22 Laumontite zone lavas..................................................................................26 Stilbite-heulandite zone lavas.......................................................................27 Thomsonite-mesolite zone lavas ..................................................................27 Analcime zone lavas.....................................................................................28 Alteration Mineral Chemistry..............................................................................29 Discussion...................................................................................................................31 Regional Variation of Metamorphic Grade.........................................................31 Conditions of Alteration......................................................................................38 Structural Interpretations.....................................................................................42 iv 3 PETROGRAPHIC AND DIGITAL ANALYSIS OF POROSITY EVOLUTION DURING ALTERATION ..........................................................................................45 Introduction.................................................................................................................45 Methods ......................................................................................................................47 Field Techniques .................................................................................................47 Optical and Digital Techniques...........................................................................48 Observations ...............................................................................................................49 NSVG Field Sites 3, 4 and 6 ...............................................................................49 Reaction Progress ................................................................................................55 Partial infilling at low-grades.......................................................................55 Mafic phyllosilicate to zeolite infilling ........................................................58 Multiple stage zeolite infilling .....................................................................63 Discussion...................................................................................................................63 Nature of Porosity and Permeability in Basalts...................................................63 Controls on Reaction Progress ............................................................................68 4 MODELING OF MINERAL PARAGENESES ........................................................70 Introduction.................................................................................................................70 Methods ......................................................................................................................71 Results.........................................................................................................................75 Mineral Parageneses............................................................................................75 Volume Changes During Alteration....................................................................83 5 DISCUSSION.............................................................................................................86 Reaction Progress in Low-Grade Metabasalts............................................................86 Dependence of Reaction Progress on Pore Size.........................................................88 6 CONCLUSIONS ........................................................................................................96 LIST OF REFERENCES...................................................................................................99 BIOGRAPHICAL SKETCH ...........................................................................................110 v LIST OF TABLES Table page 2.1 Field study locations in the North Shore Volcanic Group. ......................................16 2.2 Whole-rock chemical compositions (wt %) of samples...........................................18 2.3 Representative compositions of plagioclase. ...........................................................20 2.4 Representative compositions of pyroxenes..............................................................21 2.5 Representative compositions of mafic phyllosilicates. ............................................30 2.6 Representative compositions of thomsonites. ..........................................................32 2.7 Representative compositions of mesolite, analcime, and laumontite.......................34 3.1 Statistical analysis of vesicle size (diameter) as a function of reaction progress from outcrop scale measurements at Site 6..............................................................51 3.2 Statistical analysis of vesicle size (area) as a function of reaction progress from measured vesicles of a low-grade metabasalt from East Greenland (thin section 421505).....................................................................................................................57 3.3 Statistical analysis of vesicle size as a function of reaction progress for vesicles filled with chlorite and/or laumontite at the thin section scale (sample NS04-14) from Site 4................................................................................................................59 3.4 Statistical analysis of vesicle areas (mm2) and clay rim thicknesses (mm) for sample 94-80 from eastern Iceland. .........................................................................63 4.1 Bulk rock composition for olivine tholeiite basalt (wt %).......................................72 4.2 Modal abundances and compositions of primary mineral phases in olivine tholeiite.....................................................................................................................72 4.3 Calculated anhydrous bulk composition of basaltic andesite before and after reaction.....................................................................................................................74 4.4 Reactant phase composition, abundance, and relative dissolution rate in basaltic andesite