EVOLUTION OF THE PRECAMBRIAN ROCKS OF YELLOWSTONE NATIONAL PARK (YNP): OVERVIEW OF AN NSF/REU SITE PROJECT

The northern margin of YNP is underlain by a sequence of Precambrian metasedimentary rocks that have preserved primary sedimentary structures, are of anomalously low metamorphic grade (andalusite-staurolite zone), have undergone polyphase deformation, and have been intruded by at least two granitic plutons and a variety of mafic to intermediate igneous bodies—a remarkable natural laboratory for students to apply the principles and methods learned from the “core” of the geoscience curriculum. The Yellowstone REU project was designed to provide students with a complete research experience consisting of three major components: 1) field mapping and sampling to contribute to a new geologic map of the basement rocks of YNP and formulation of testable hypotheses by smaller working groups of students to address significant questions on the petrogenesis, architecture, tectonic environment and geologic evolution of these Precambrian rocks; 2) direct experience in modern analytical studies including sample preparation, training on modern instrumentation (mineral, whole-rock geochemical, and geo- and thermochronological analysis) including data acquisition, reduction, presentation, and interpretation; and 3) presentation of research results at this GSA meeting and in future journal articles. Some of the key research questions that have been addressed in this project include: 1) What is the relationship of this suite of rocks in the South Snowy Block to the voluminous 2.8 Ga magmatic rocks of the main Beartooth massif to the east and the high-grade, migmatitic and mylonitic gneisses of Yankee Jim Canyon to the west? 2) What are the ages, provenance(s) and depositional environments of the metasedimentary rocks? 3) What is the igneous, metamorphic, and structural history of this area, and what does this tell us about crustal genesis and evolution? 4) Is this suite of rocks allochthonous in their current setting (Mogk, 1984), or do they represent unusual preservation of upper crustal rocks in the midst of mesozonal plutons and higher grade metamorphic sequence exposed across the northern Wyoming Province? The results of this project have produced definitive answers to these research questions, and have produced a cohort of young scientists who are well-prepared to advance to the next stages of their geologic careers.