Collaborative Research: Evaluating tectonic models for the western US Cordillera through the metamorphic history of the Pelona-Orocopia-Rand schists

Apparent inconsistencies between different geologic and geophysical datasets have resulted in decades of active debate about how western North America was formed. One of the longest-held models invokes a shallow subducting oceanic plate beneath the Mojave Desert to Wyoming to large-scale mountain building as far east as the Rocky Mountains. This study tests the viability of the flat slab model against alternative hypotheses, including the collision and translation of a far-traveled terrane, through detailed study of the Pelona-Orocopia-Rand schist. This suite of ancient metamorphic rocks span from California to Arizona, a critical location to distinguish between the tectonic models. The researchers will test predictions about the location, conditions, and timing of tectonic events derived from standard recycling of oceanic crust, flat slab subduction, and terrane collision by determining the age, pressure, and temperature recorded by the metamorphic mineral garnet in the Pelona-Orocopia-Rand schist. The project will promote the development of two early-career women in STEM, foster new collaborations across R1, R2, and PUI campuses, facilitate the training of graduate and undergraduate students from underrepresented groups, and support the development of analytical facilities. The proposed contribution provides a crucial test of conflicting models for the tectonic evolution of the western North American Cordillera by re-evaluating the metamorphic history of the Pelona-Orocopia-Rand schist using modern techniques. The researchers will estimate the conditions of metamorphism using high resolution analytical methods and a variety of modern modeling techniques, including Raman spectroscopy, bulk chemical analysis, and P-T modeling. The timing of events will be evaluated using garnet Sm-Nd and monazite U-(Th)-Pb geochronology. They will provide a unifying regional dataset by sampling across the full extent of documented outcrops rather than using a site-specific approach. The work will support two graduate students from Northern Illinois University and the University of Alabama as well as undergraduate student research at Occidental College. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.