GEOCHEMISTRY, PETROGENESIS AND TECTONIC SETTING OF IGNEOUS ROCKS OF THE HARTVILLE UPLIFT, EASTERN WYOMING A thesis presented to the Faculty of the Graduate School at the University of Missouri-Columbia In partial Fulfillment of the Requirements for the Degree Master of Science by ANTONIO MANJÓN-CABEZA CÓRDOBA Dr. Peter I. Nabelek, Thesis Supervisor MAY 2016 The undersigned, appointed by the dean of the Graduate School, have examined the thesis entitled GEOCHEMISTRY, PETROGENESIS AND TECTONIC SETTING OF IGNEOUS ROCKS OF THE HARTVILLE UPLIFT, EASTERN WYOMING presented by Antonio Manjón-Cabeza Córdoba , a candidate for the degree of master of science, and hereby certify that, in their opinion, it is worthy of acceptance. Professor Peter I. Nabelek Professor Robert L. Bauer Professor Mike D. Glascock To those long video calls… ‘Así como don Quijote entró por aquellas montañas se le alegró el corazón, pareciéndole aquellos lugares acomodados para las aventuras que buscaba.’ ‘As Don Quixote entered between those mountains his heart was filled with happiness, for he thought those places were suited for the adventures he was seeking.’ Don Quijote de la Mancha I, chapter 23. - Miguel de Cervantes Saavedra - ACKNOWLEDGEMENTS I would like to thank the people that made this work possible. First, my advisor, Peter I. Nabelek, without whose assistance, teachings and comments I could not have finished this Master’s thesis, and also for his patience and guidance in the field. The work of Carol Nabelek with the ICP-OES (department of geosciences, University of Missouri) and James Guthrie with the ICP-MS (University of Missouri, Research Reactor) where crucial for the obtainment of the data and their contribution should not go unadvertised. Last, thanks to Eric S. Nowariak, who not only did help with the preparation of the dilutions for the analyses, but also spent valuable time with me in the field, in long discussions and also as a friend. I also would like to thank the Fulbright Comission of Spain, and the ‘fundación REPSOL’ (REPSOL Foundation) of REPSOL S.A. for their finantial support. Without their confidence and help, my studies at the University of Missouri that resulted in this thesis would not have been possible. Last, but not least, thanks to the kind landowners that allowed us to work on their lands and that very kindly informed and assisted us. ii TABLE OF CONTENTS AKNOWLEDGEMENTS ………………………………………………………… ii LIST OF FIGURES ……………………………………………………………….. iv ABSTRACT ………………………………………………………………………. v Section 1. INTRODUCTION ………………………………………………………… 1 2. GEOLOGICAL CONTEXT ………………………………………………. 6 The Wyoming Province ………………………………………………….. 6 The Cheyenne Belt ……………………………………………………….. 7 The Trans-Hudson, Black Hills and Dakotan Orogens ……………….. 8 The Hartville Uplift ……………………………………………………… 9 3. IGNEOUS ROCKS OF THE HARTVILLE UPLIFT ……………………. 12 Mafic Rocks ………………………………………………………………. 12 Granitoids ………………………………………………………………… 17 4. ANALYTICAL METHODS ……………………………………………… 27 5. RESULTS …………………………………………………………………. 29 Mafic Rocks ………………………………………………………………. 29 Granitoids ………………………………………………………………… 33 6. DISCUSSION …………………………………………………………….. 38 Mafic Rocks ………………………………………………………………. 38 Granitoids ………………………………………………………………… 42 7. CONCLUSIONS AND TECTONIC HISTORY …………………………. 46 APPENDIX 1. COMPLETE TABLES OF THE ANALYTICAL RESULTS AND LOCATIONS ……………………………………………………………... 47 REFERENCES ……………………………………………………………………. 55 iii LIST OF FIGURES Figure Page 1. Regional Map showing the study area (Figures 2a and 2b) relative to other Laramide Uplifts that expose Precambrian rocks 3 2. Map of the Hartville Uplift a) Map of the southern part of the Hartville Uplift 4 b) Map of the northern part of the Hartville Uplift 5 3. Photographs of the Muskrat Canyon metabasalt 14 4. Photographs of the Mother Featherlegs metabasalt 16 5. Photographs of the metadiabase dikes. 18 6. Photographs of the Rawhide Buttes granite 21 7. Hand samples of the Twin Hills diorite showing stratification 24 8. Photographs of the Twin Hills diorite 25 9. Major elements vs. Mg# diagrams for the three basaltic suites 31 10. REE patterns for the three basaltic suites 32 11. Chondrite-normalized ‘Spider’ diagrams for the three mafic suites 32 12. Harker Diagrams for the granitoids of the Hartville Uplift 35 13. REE patterns for the granitoids and metapelites of the Hartville Uplift 36 14. Chondrite-normalized ‘Spider’ diagrams for the granitoids and metapelites of the Hartville Uplift 37 15. Total Alkalis vs. Silica (TAS) diagram 38 16. Th/Yb vs. Nb/Yb diagram 40 17. Tectonic discrimination diagrams for the mafic suites 41 iv ABSTRACT The location of the eastern margin of the Wyoming Archaean Province and its Proterozoic evolution are still debated. Previous studies have attributed north-south and east-west directed structures to the Proterozoic Black Hills and Central Plains orogenies, respectively, but the tectonic details of these orogenies are unclear. I have studied igneous rocks in the Laramide-age Hartville Uplift (HU), which exposed Precambrian rocks. At least part of the NNE-trending HU is bisected along its length by the Hartville Fault (HF) that juxtaposes high-grade metamorphic rocks on its eastern side against lower-grade metamorphic rocks on its western side. The objective is to use the geochemical features of the igneous rocks to infer the tectonic settings in which they formed. The oldest dated magmatic rocks are 2.6 Ga Archaean Rawhide Buttes and Flattop Butte granites (SiO2 > 67 wt%; K2O /Na2O wt% > 1; ASI > 1.05). They crop out only in the northern part of the HU and appear to be of crustal origin. The next magmatic episodes involved basaltic volcanism. They are represented by the Mother Featherlegs metabasalt on the eastern side of the HF and the Muskrat Canyon metabasalt on the western side. Compositions of these basalts are attributed to rifting and a mantle plume, respetively. The ages of the metabasalts are unknown, thus it is not certain if they are coeval. However, they may correspond to the ~2 Ga Kennedy dike swarm in the Laramie Range and amphibolites in the Black Hills that show similar extension and plume-related chemical characteristics. In the southern HU, Proterozoic, 1.74 Ga Twin Hills diorite and Haystack Range granite crop out on the eastern side of the HF. The latter appears to be younger as its v dikes cut the diorite. SiO2 of ~55 wt % and K2O /Na2O ratios of < 1 suggest a lithospheric mantle origin for the Twin Hills diorite, whereas SiO2 >69 wt %, K2O/Na2O > 1, and peraluminous composition indicate a crustal origin for the Haystack Range granite, specifically melting of schist that occur in the HU. I suggest that the Archaean granitoids may be related to accretion along the Oregon Trail Structure in southern Wyoming. The region has subsequently undergone rifting, as shown by the basalt suites, possibly related to the breakup of the proto-continent Kenorland. The Twin Hills diorite and the Haystack Range granite appear to be related to westward subduction and collision (respectively) during the Black Hills-Dakotan collisional orogeny. Enigmatic migmatitic, tonalitic pods with an age of 1.715 Ga mark the latest deformation event that is attributed to the terminal collision of Wyoming and Superior cratonic provinces. vi 1. INTRODUCTION The Archean core of the North American continent, Laurentia, was constructed by an amalgamation of small cratons between 2.0 and 1.7 Ga (Hoffman, 1988; Whitmeyer and Karlstrom, 2007). The Wyoming Province has been interpreted as one of these independent Archean cratons (Chamberlain et al., 2003; Mueller and Frost, 2006). On its eastern margin, the Wyoming Province is bordered by the Black Hills-Dakoran Orogens, which resulted from the collision of the Wyoming Province with the Superior Province. In addition, Proterozoic arcs were accreted to the southern margin of the Wyoming Province along the Central-Plains Orogen to form the Yavapai Province (Hoffman, 1988). Despite general agreement on broad aspects of the role of the Wyoming Province in the construction of Laurentia, the scarcity of Archean and Proterozoic outcrops precludes precise field data to unravel the Precambrian geologic history of the southernmost Laurentia. The southern border of the Wyoming Province (Figure 1) is marked by the Cheyenne Belt (Karlstrom and Houston, 1984), a structural lineament attributed to the Medicine Bow Orogeny ca. 1.78 Ga (Chamberlain, 1998). The influence of the orogeny on the development of the Wyoming Province is still debated, as evidenced by the number of models proposed (Karlstrom and Houston, 1984; Chamberlain, 1998; Patel et al., 1999; Resor and Snoke, 2005; Jones et al., 2010). To the east, the limit of the Wyoming province remains unresolved (Chamberlain et al., 2003; Sims et al., 2001; Worthington et al., 2016). Complex deformation associated with the Wyoming-Superior collision, together with multiple distinct ages in the Black Hills, South Dakota, have resulted in the differentiation of two events affecting the eastern Wyoming province: (1) 1 the Black Hills orogen, corresponding to initiation of metamorphism ca. 1.76 Ga (Goldich et al., 1966; Dahl and Frei, 1998) and (2) the Dakotan orogen, corresponding to felsic magmatism ca. 1.72 Ga (Krugh, 1997; Chamberlain et al., 2002). Nabelek et al. (1999, 2001) proposed that the metamorphism and magmatism were the products of a single, protracted collisional event. To unravel the tectonic regimes associated with construction of Laurentia along the eastern margin of the Wyoming Province, this work