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Fluid History of the Western Maryland Piedmont

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Fluid History of the Western Maryland Piedmont FLUID HISTORY OF THE WESTERN MARYLAND PIEDMONT Christopher J. LaFonte A Thesis Submitted to the Graduate College of Bowling Green State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE August 2015 Committee: Charles M. Onasch, Advisor John R. Farver Kurt S. Panter ii ABSTRACT Charles M. Onasch, Advisor Regional fluid migrations associated with orogenic events have a number of significant geologic consequences in the continental interior, such as the emplacement of hydrocarbons, mineralization, and diagenesis. It is currently believed that fluids associated with the Alleghanian orogeny in the central Appalachians where sourced from the eastern portion of the Piedmont, migrated westward, passing below the Blue Ridge, into the Valley and Ridge region, and finally into the craton. Previous studies have provided details about fluids across much of the central Appalachians, but one gap remains: the western portion of the Piedmont. Using fluid inclusion microthermometry on vein samples throughout the western Piedmont, the trapping conditions and fluid composition were found and used to compare the fluid history of this region with that of other regions to determine if the Piedmont was part of the westward fluid migration. The fluids of the western Piedmont were found to be very uniform in terms of trapping conditions and fluid composition regardless of vein type, rock unit and lithology, and sample location. All inclusions were two-phase (L+V) and were found to consist of a low salinity H2O+NaCl brine with a large majority of them having homogenization temperatures between 140 and 200°C. The age of the veins and fluids cannot be well constrained. While most veins are probably associated with early phases of deformation and metamorphism during the late Ordovician Taconic orogeny and/or the early Silurian Cherokee orogeny, the fluid inclusions in them may be younger and related to recrystallization and/or reequilibration during younger events, such as the late Paleozoic Alleghanian orogeny. Considering the regionally uniform iii microthermometric properties of the inclusions, their relatively low trapping temperatures and pressures, low salinity fluid composition, the lack of reequilibration textures, and the lack of evidence for significant Alleghanian deformation in the region, the most likely scenario is that the veins trapped the fluids shortly after this region reached peak metamorphic conditions during the Cherokee orogeny in the early Silurian. This timing, along with the significant differences in fluid history with adjacent regions, indicates that the western Piedmont does not record the effects of a late Paleozoic orogen-wide fluid event. iv ACKNOWLEDGEMENTS First I would like to give a big thank you to my advisor Dr. Charles Onasch for his guidance and devotion towards this project. I want to thank my committee members Dr. John Farver and Dr. Kurt Panter for giving me their insight and providing me with different perspectives. I would also like to thank my parents for the encouragement and support. Without them, this project would not have been completed. Financial support for the field and lab work was made possible thanks to the Furman Economic Geology Research Scholarship, and the Bowling Green State University Department of Geology. v TABLE OF CONTENTS Page INTRODUCTION ......................................................................................................................... 1 GEOLOGIC SETTING ................................................................................................................. 3 Study Area ........................................................................................................................ 3 Stratigraphy ........................................................................................................................ 3 Structure ............................................................................................................................. 6 Vein Types ......................................................................................................................... 8 METHODOLOGY ...................................................................................................................... 12 Field Methods .................................................................................................................. 12 Laboratory Methods ......................................................................................................... 12 Fluid Inclusion Microthermometry .................................................................................. 13 MICROTHERMOMETRY RESULTS ....................................................................................... 15 DISCUSSION .............................................................................................................................. 19 Fluid History .................................................................................................................... 19 Vein type ............................................................................................................. 19 Structural location ............................................................................................... 21 Rock type ............................................................................................................. 25 Trapping Conditions ........................................................................................................ 25 Paleohydrology and the age of fluids of the western Piedmont ....................................... 28 Regional Fluid Migration ................................................................................................. 33 vi CONCLUSIONS.......................................................................................................................... 36 REFERENCES ............................................................................................................................ 37 APPENDIX A: MICROTHERMOMETRY MEASUREMENTS .............................................. 41 APPENDIX B: HOMOGENIZATION TEMPERATURE HISTOGRAMS .............................. 42 APPENDIX C: SAMPLE INFORMATION/NOTES ................................................................. 42 vii LIST OF FIGURES Figure Page 1 Terrane map showing the location of the Westminster terrane where most of the samples were collected............................................................................................................ 6 2 Geologic map of the western Piedmont province modified from USGS 30’ x 60’ quadrangle (Southworth et. al., 2007) with sample locations.................................................. 9 3 Cross section (modified from Southworth et. al., 2006) of line A-A’ in Figure 2................ 10 4 Quartz veins in the Ijamsville Phyllite and their relationships to S1 and each other............. 11 5 Cathodoluminescence and plane polarized light images of typical vein quartz sample........ 14 6 Histogram of final ice melting temperature (Tm) for all primary and secondary inclusions measured.............................................................................................. 16 7 Histogram of homogenization temperature (Th) for all primary and secondary inclusions measured.............................................................................................. 17 8 Th vs. Tm plot for all fluid inclusions measured..................................................................... 18 9 Comparing folded veins to cleavage parallel veins............................................................... 20 10 Th vs. Tm plot separating the Martic thrust and Grove Formation samples from the rest of the inclusions measured............................................................................... 21 11 Homogenization temperatures for the Ijamsville Phyllite, Urbana Formation, and Sugarloaf Mountain Quartzite samples separated by eastern and western limbs of the Sugarloaf Mountain anticlinorium (see text for explanation)................................................................................. 23 viii 12 Final ice melt temperatures of the Ijamsville Phyllite, Urbana Formation, and Sugarloaf Mountain Quartzite samples separated eastern and western limbs of the Sugarloaf Mountain anticlinorium (see text for explanation).............................................................................. 24 13 Th vs. Tm for inclusions in the Ijamsville Phyllite, Urbana Formation, and Sugarloaf Mountain Quartzite samples separated by eastern (lower Th, higher Tm) and western (higher Th, lower Tm) limbs of the Sugarloaf Mountain anticlinorium......................................................................................... 25 14 Estimation for trapping pressure and temperature for the two fluid types (eastern and western limbs of the Sugarloaf Mountain anticlinorium) with lithostatic and hydrostatic pressure conditions and with 30°C/km and 50°C/km geothermal gradients......................................................... 27 15 Estimated homogenization temperatures for a peak metamorphic temperature of 350°C in the western portion of the Westminster terrane............................. 32 ix LIST OF TABLES Table Page 1 Fluid characteristics separated by eastern and western limbs of the Sugarloaf Mountain anticlinorium............................................................................... 22 2 Trapping conditions for eastern and
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