University of Montana ScholarWorks at University of Montana Graduate Student Theses, Dissertations, & Professional Papers Graduate School 1999 High temperature fluids and calcite einv formation in the Montana disturbed belt west-central Montana Ruth Lerman The University of Montana Follow this and additional works at: https://scholarworks.umt.edu/etd Let us know how access to this document benefits ou.y Recommended Citation Lerman, Ruth, "High temperature fluids and calcite einv formation in the Montana disturbed belt west- central Montana" (1999). Graduate Student Theses, Dissertations, & Professional Papers. 7132. https://scholarworks.umt.edu/etd/7132 This Thesis is brought to you for free and open access by the Graduate School at ScholarWorks at University of Montana. It has been accepted for inclusion in Graduate Student Theses, Dissertations, & Professional Papers by an authorized administrator of ScholarWorks at University of Montana. For more information, please contact [email protected]. Maureen and Mike MANSFIELD LIBRARY Tlie University of I V I O N T A N A Permission is granted by the author to reproduce this material in its entirety, provided that this material is used for scholarly purposes and is properly cited in published works and reports. ** Please check "Yes" or ’'No'' and provide signature Yes, I grant permission No, I do not grant permission Author's Signature / D ate 12^/ Any copying for commercial purposes or financial gain may be undertaken only with the author's explicit consent. HIGH TEMPERATURE FLUIDS AND CALCITE VEIN FORMATION IN THE MONTANA DISTURBED BELT, WEST-CENTRAL MONTANA B y Ruth Lerman B. A., Union College, 1994 Presented in partial fulfillm ent o f the requirements for the degree of M a s te r o f Science University of Montana 1999 Approved by irman. Board of Examiners Dean, Graduate School D a te UMI Number: EP37933 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. UMI Oissart«Cton Pubiish«ng UMI EP37933 Published by ProQuest LLC (2013). Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code uest ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 ABSTRACT Lerman, Ruth A., Master of Science.-JVIay 1999 Geology Director: Dr. James W . Sears >/ . \ Structural analysis; macroscopically and microscopically, and fluid inclusion analysis, have identified several late Cretaceous and early Tertiary fluid expulsion events from six locations throughout the leading edge of the disturbed belt of west central Montana. The fluid expulsion events led to the widespread formation of calcite veins. The fluid temperature, composition and spatial distribution o f the veins can bracket timing o f magmatic and deformational events within the disturbed belt. Additionally the veins and their fluids provide insight into the thermal history o f possible petroleum resources within the region. Three hypotheses were proposed for the creation o f the calcite veins: 1) Magmatic sills were injected into an undeformed basin and drove o ff basinal brines; 2) Fluids may have been driven out in advance of the thrust plate as it prograded eastward; 3) Rapid accumulation o f the sediments that were shed o ff the rising thrust sheet may have caused compaction and subsequent de watering o f the underlying sediments. Various analytical methods were employed to test the hypotheses. Fieldwork showed a wide variety of spatial distribution and orientation for the veins, while slickenside data is consistent with regional deformation. Lab work determined the minéralogieal composition o f the veins to be predominantly calcite. Microscopic analysis showed a wide range o f microstructures and deformational features, indicating that many o f the veins were a result o f Cretaceous thrust faulting. Fluid inclusion analysis yielded high fluid temperatures with a suite of middle range temperatures that are too hot to be considered a result o f thrust faulting or a geothermal gradient produced by sediment compaction. Many veins were formed by Cretaceous deformation, as indicated by the microstructure analysis and slickenside patterns on stereonets. Yet a significant population o f veins did not conform to the deformation model and seem to be a result o f localized sill injection and regional magmatic activity. Thus, two o f the three original hypotheses were supported by evidence. The thermal and structural evidence obtained from analysis o f the veins also indicates that the hydrocarbons once contained within the disturbed belt may have exceeded their thermal maturation lim m it. The hydrocarbons most likely escaped from their reservoirs along the fractures that facilitated vein fo rm a tio n . 11 TABLE OF CONTENTS Page Abstract ..................................................................................................................................... ü Table of Contents.................................................................................................................... üi List o f Figures and Tables...................................................................................................... iv Acknowledgements ................................................................................................................. v Chapter 1 Background ................................................................................................................... 1 1.1 Introduction ................................................................................................................................. 1 1.2 Study Area.................................................................................................................................. 2 1.3 Structure ....................................................................................................................................... 2 1.4 Stratigraphy............................................................................................................................... 8 1.5 S ills.............................................................................................................................................. 14 1.6 Age by Thermal and Geochronologic Analysis ................................................................... 16 1.7 Petroleum Potential .................................................................................................................... 18 Chapter 2 Methods........................................................................................................................ 20 2.1 Field Methods............................................................................................................................. 20 2.2 Lab Methods............................................................................................................................... 20 2.2.1 X-ray Diffraction Analysis................................................................................................... 20 2.2.2 Thin Section Analysis ........................................................................................................... 21 2.2.3. Fluid Inclusion Analysis ....................................................................................................... 21 Chapter 3 Data............................................................................................................................... 23 3.1 Macroscopic View .................................................................................................................... 23 3.1.1 Hand Samples......................................................................................................................... 23 3.1.2 Spatial Distribution and Vein Orientations....................................................................... 24 3.2 Microscopic View .............................. 25 3.2.1 Microstructures ....................................................................................................................... 25 3.2.2 Fluid Inclusions ....................................................................................................................... 26 Chapter 4 Observations and Interpretations ............................................................................... 28 4.1 Calcite Veins ............................................................................................................................... 35 4.2 Solid Petroleum Veins.............................................................................................................. 44 4.3 Fluid Inclusions ........................................................................................................................ 45 4.4 Fluid Geochemistry ......................................................................... 47 Chapter 5 Discussion ...................................................................................................................... 49 Chapter 6 Conclusions .................................................................................................................... 59 References Cited 60 Appendices 65 Appendix I X-Ray Diffraction Pattems.......................................................................................