STUDENT’S VOICE
Tectonic Significance of the Wood Hills-East Humboldt Range
Metamorphic Core Complex Franklin Wolfe, SA-4334
wolfef16@mail.wlu.edu
Welcome New Student Voice columnist
Senior thesis. Those two words can mean a lot of different things to different people. For some students, it’s a chance to showcase their desire and willingness to take on a lengthy research experience with the intention of learning a new topic in depth, developing their skills as a scientist, and possibly publishing their work. For others, it’s just one last gate- keeper between themselves and gradua- tion or applying to graduate school. For me, “senior thesis” will always resonate as much more. I participated in a senior thesis field experience with the Keck Geology Consortium, a collaboration of 18 liberal arts colleges, now in its 28th year, which provides research and travel opportunities for undergraduates.
Our group (4 professors and 7 under- graduates) spent two weeks camping and conducting fieldwork in northeastern Nevada before traveling to Washington and Lee University in Lexington, Virginia, for a week of data compila- tion and planning for the year to come. Through this experience, I not only honed field skills and learned geologic topics that are sure to make me a bet- ter geologist, but also met some amaz- ing people who truly made this trip special. I will never forget the time we spent circled around the campfire each night, sharing funny stories and mak- ing S’mores… or the trip to the natural hot springs, almost flipping the rental vehicles on the way… or the image of wild horses running through the valley, with the sun setting behind the moun- tains, painting the sky an extraordinary mixture of blues and oranges… or the time we took our sleeping bags outside of the tents and lined them up in the field, eventually all falling asleep under a beautiful starlit sky. The list could go on and on, and it is memories and experi- ences like these that make me extremely
satisfied to have chosen geology as my field of study.
Our research project is titled, “Exhumation and Tectonic Significance of the Wood Hills-East Humboldt Range Metamorphic Core Complex, Nevada.” Our goal is to document the kinemat- ics and thermal evolution of the middle and lower crustal rocks exposed dur- ing exhumation of this core complex. The East Humboldt Range-Wood Hills Metamorphic Core Complex is located far west into the hinterland of the Mesozoic Sevier orogenic belt and expos- es the deepest-seated rocks and the most extensive outcrops of migmatites and peraluminous granites in the northeast- ern Great Basin. Due to these factors, it serves as a great example for studying the fundamentals of metamorphic core complex development and exhumation.
To date, tremendously valuable work has been devoted to map, characterize, and explain many of the structural, petrologic, and topographic relation- ships within this region. One or two phases (ongoing debate) of thrust fault- ing during the Mesozoic time led to duplication of the stratigraphy, intense crustal thickening, and Barrovian-style metamorphism of the footwall rocks. A transition from horizontal contraction to extension occurred circa 84-75 Ma and this trend persists to the present day. During this most recent phase, the Pequop Fault and St. Mary’s River Fault System exhumed these deep rocks (believed to have reached depths of 30 km!) to their present elevations above the surface.
Specific student projects include: (1) comparing quartz mylonites across the study area to characterize crystallo- graphic orientation fabrics (CPO) and strain paths at varying structural depths of the mylonitic shear zone (Lindsay
Plummer of Amherst College), (2) docu- menting the transition of deformation and slip mechanisms in quartz CPOs with depth to relate deformation in the upper crust to the deep ductile flow beneath it (Gabriel Chevalier of Mount Holyoke College), (3) determining the deformational/thermal history of the Wood Hills using quartz CPOs to char- acterize the nature of the transition – abrupt vs. gradual – into the mylonitic shear zone (Sarah Jordan of Carleton College), (4) performing laser ablation to determine age and composition of garnets and amphibolites within a fold nappe of the Angel Lake cirque, as well as creating an outcrop-scale map to document detailed structural relation- ships to characterize folding and the P-T evolution of the nappe (Zoe Dilles of Pamona College), (5) using quartz CPO and thermobarometric data provided from other Keck Nevada projects to numerically model the effects of several variables on the system, including rheol- ogy, geothermal gradient, and boundary conditions, such as extension rate and initial geometry (Josh Latham of the University of Dayton), and (6) utilizing calcite-dolomite and Raman spectro- scopic carbonaceous material thermome- try to determine the geothermal gradient across the study area (Colby Howland of Union College). For my project, I will perform zircon fission-track thermochro- nologic dating to constrain the timing, rate, and pattern of exhumation of the core complex.
During the field experience, we had a unique opportunity to learn from, and interact with, a diverse group of profes- sors from multiple universities, who not only offered us insight into their respec- tive field of expertise, but also facilitated a flexible learning environment with different teaching and mentoring styles. Our professors were Dr. Jeffrey Rahl of
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