SEDIMENTARY TECTONICS OF THE MESOPROTEROZOIC LAHOOD FORMATION SOUTHWEST, MONTANA by Nicholas Reid Fox A thesis submitted in partial fulfillment Of the requirements for the degree of Master of Science in Earth Sciences MONTANA STATE UNIVERSITY Bozeman, Montana January 2017 ©COPYRIGHT By Nicholas, Reid, Fox 2017 All Rights Reserved iii ACKNOWLEDGEMENTS I would like to dedicate this work to my wife and family whose love and support have been essential in my pursuit of higher education and research. I would also like to acknowledge my peers who have provided guidance throughout this study. This research would not be possible without funding from the Donald L. Smith Memorial Scholarship, Tobacco Root Geological Society Harrison Scholarship and National Science Foundation. May this thesis be an acknowledgement to the crucial work completed by William J. McMannis (1924-1973) on the Bridger Range geology (1955) and the LaHood Formation (1963), which has been paramount to the interpretations made by this study. iv TABLE OF CONTENTS 1. INTRODUCTION .......................................................................................................... 1 Significance of Research ................................................................................................. 1 Belt Basin Geologic Setting ............................................................................................ 1 Historical Background..................................................................................................... 9 2. FIELD RELATIONS .................................................................................................... 11 Methods ......................................................................................................................... 11 Lithofacies ..................................................................................................................... 14 Lithofacies sG ............................................................................................................ 14 Lithofacies (g)S ......................................................................................................... 22 Lithofacies slM .......................................................................................................... 27 Sedimentary Structures (g)S & slM .......................................................................... 27 Lithofacies Mdc ......................................................................................................... 29 Lithofacies sfM .......................................................................................................... 30 (g)S and Mdc/sfM...................................................................................................... 30 Lithofacies Summary................................................................................................. 38 Fluid Flow Dynamics ................................................................................................ 38 sG. .......................................................................................................................... 38 (g)S & slM. ............................................................................................................ 39 Mdc &sfM. ............................................................................................................. 40 Facies Associations ................................................................................................... 42 Depositional Systems ................................................................................................ 43 Tectonic Environment ............................................................................................... 44 3. STRATIGRAPHIC FRAMEWORK ............................................................................ 47 Introduction ................................................................................................................... 47 Methods ......................................................................................................................... 47 Results ........................................................................................................................... 47 Stratigraphic Sections ................................................................................................ 47 A1 (sG). .................................................................................................................. 47 A2 (sG, (g)S & slM). ............................................................................................. 49 A3 ((g)S and slM). ................................................................................................. 50 B1 (sG) & B2 ((g)S and slM). ................................................................................ 51 B3 ((g)S & Mdc/sfM). ........................................................................................... 51 C1 (sG). .................................................................................................................. 51 C2 ((g)S/slM & Mdc/sfM). .................................................................................... 51 C3 ((g)S & Mdc/sfM). ........................................................................................... 52 D1&D2 ((g)S/slM & Mdc/sfM). ............................................................................ 52 E1 ((g)S/slM & Mdc/sfM). .................................................................................... 52 Stratigraphic Correlations ............................................................................................. 53 v TABLE OF CONTENTS - CONTINUED 4. DIAGENESIS AND METAMORPHISM.................................................................... 60 Introduction ................................................................................................................... 60 Methods ......................................................................................................................... 60 Results ........................................................................................................................... 60 Corbly Canyon Conglomerate Member (sG) ............................................................ 60 Reese Creek Sandstone Member (g)S ....................................................................... 61 Johnson Canyon Carbonate Member ......................................................................... 64 Interpretation ................................................................................................................. 68 5.GEOCHRONOLOGY ................................................................................................... 70 Major and Trace Elements ............................................................................................ 70 Introduction ............................................................................................................... 70 Methods ..................................................................................................................... 71 Major Elements ............................................................................................................. 73 Results ....................................................................................................................... 73 Harker Diagrams. ................................................................................................... 73 CaO-Na2O-K2O. ..................................................................................................... 76 Al2O3/SiO2-MgO+Fe2O3. ....................................................................................... 77 Trace Elements .............................................................................................................. 79 Results ....................................................................................................................... 79 V-Sc. ...................................................................................................................... 79 Ba/La-Eu/Eu*. ........................................................................................................ 81 La/Th. ..................................................................................................................... 82 Cr-Ni. ..................................................................................................................... 84 REE Plots ...................................................................................................................... 85 Results ....................................................................................................................... 85 Interpretation ............................................................................................................. 92 Calculated Chemical Index of Alteration ...................................................................... 93 Introduction ............................................................................................................... 93 Results ....................................................................................................................... 93 Interpretation ............................................................................................................. 94 Sm-Nd Systematics ....................................................................................................... 95 Introduction ..............................................................................................................