NSF funding started on August 2019
TIMING OF COOLING AND EXHUMATION OF LARAMIDE UPLIFTS INFORMS MODELS OF FLAT-SLAB SUBDUCTION
This project intends to determine the ages of uplift of the major mountain ranges that together constitute the Rocky Mountains of the western interior United States. These ranges are referred to in the geological literature as "Laramide uplifts", after the city and county of Laramie, Wyoming, which is situated in the region where these uplifts are notably developed. The timing of uplift of the Laramide ranges is poorly understood, but critical for assessing the shape and movement direction of tectonic plates in the eastern Pacific basin and western regions of the North American plate. This work is important to the public for several reasons: (a) The Rocky Mountains are the definitive landscape of the mountain west, a landscape that has inspired writers, artists, entrepreneurs, emigrants, and scientists for more than 200 years; yet, no consensus exists among geologists to explain the origins of these mountains. (b) By virtue of its high elevation and north-south orientation, this spectacular landscape impacts the ecology and climate of the entire U.S. (c) The Laramide region is of enormous economic importance to the U.S., containing strategically important groundwater, mineral, and hydrocarbon resources. (d) Although the Laramide uplifts are no longer "active", results of this project will useful for understanding seismic hazards in regions on Earth today where similar tectonic processes are still active (for example, western South America and southern Alaska). Finally, a group of undergraduate and graduate students will be trained in the context of this project.
The primary objective of this project is to determine the timing of exhumation of Laramide uplifts in Montana, Wyoming and Utah. This is essential to inform tectonic and geodynamic models of the Laramide orogeny, which is generally attributed to flat-slab subduction. Such models rely heavily on spatio-temporal patterns of Laramide uplift. Flat-slab subduction of oceanic plateaus and aseismic ridges are important geodynamic phenomena in convergent margins, with respect to regional plateau uplift, termination of arc magmatism, and active seismicity in the overriding plate. This project will apply a multi-component dating approach, including apatite fission track and (U-Th-Sm)/He thermochronology, which, when combined with thermo-kinematic modeling and the record of sedimentation, will constrain the cooling and erosion histories of the Laramide region. Regional patterns in timing and distribution of uplift events will provide constraints for plate tectonic models of the western U.S. Knowledge gained by this research will be exportable to other active and ancient flat-slab tectonic systems such as southern Alaska, Central America and western Argentina.
We are looking for a PhD starting in Fall 2020 to work on this project.
NSF EAR-Tectonics, funding ongoing
ARE REMNANTS OF THE TIBETAN PLATEAU PRESERVED IN THE SOUTHERN HIMALAYAN THRUST BELT?
The Himalaya of Nepal is one of Earth's most rugged and rapidly eroding landscape, with local relief greater than 5,000 meters and a morphology dominated by deep fluvial incision. This regional pattern of relief is broken in western Nepal, where the Bhumichula plateau represents a approximately 250 square kilomter area of low-relief (200-400 meters), but high-elevation (4200-4800 meters) ground isolated amidst surrounding deeply incised topography resembling that of Tibet. This projects investigates how and when the Bhumichula plateau formed. Determining whether the Bhumichula plateau formed as a low-elevation surface that was later uplifted and incised, or whether it was high standing from its earlier stages and part of a larger Tibetan plateau and was later modified by surface processes, is significant for the understanding of the mechanisms forming high topography on Earth. High elevation features such as the Himalaya and Tibet are a product of tectonic processes over geological time, which are responsible today for the location and magnitude of earthquakes. The Himalayas and Tibet also play a significant role on climate by driving the Asian monsoon and thus control the distribution of fresh water on our planet. Important societal outcomes deriving from this project include training of graduate students This project also supports the training of graduate and undergraduate students in an important science, technology, engineering and mathematics discipline (STEM), thereby contributing to the increased economic competitiveness of the United States. The project also contributes to the broadening of underrepresented groups in STEM, thereby promoting diversity in science. and minorities, female research scientists, and promotes diversity in science. It also is supporting the development of an online virtual field trip experiences for general education and upper division classes.
This is a muldisciplinary invesgation that uses geological mapping, low-temperature thermochronology, cosmogenic nuclide dating, geomorphological analysis, stable isotope paleoaltimetry, and 40Ar/39Ar geochronology to determine the age of basement rocks, the timing of deformation, erosion/incision and uplift of the Bhumichula plateau in western Nepal. Although other low-relief, high-elevation surfaces have been identified in the Himalaya, none has been investigated with the complete array of methods to be employed in this work. A principal goal of the project is to establish a workflow for how to analyze and interpret these low-relief surfaces in general, which are common features in the Himalaya to the east of Nepal. This study is the first attempt to apply such a wide array of techniques to unravel the history of landscape development in the India-Asia collisional environment, including the first attempt to determine paleoelevation on the southern slope of the Himalaya. Three main hypotheses will be tested: (1) BP formed as a low-elevation surface that was uplifted to high elevation and incised by antecedent and headward eroding rivers; (2) the BP is a remnant of a once much larger paleo-Tibetan landscape that reached nearly to the front of the Himalaya during the Miocene, and has been etched northward by headward erosion since that time; and (3) the BP formed in response to drainage reorganization and feedbacks between drainage area, erosion, and elevation.
COLLABORATIVE RESEARCH: TECTONIC SIGNIFICANCE OF LONG RUN-OUT COARSE-GRAINED FACIES IN THE CORDILLERAN FORELAND BASIN
Sediments deposited in basins in front of fold-and-thrust belts, also known as foreland basins, record the tectonic growth and development of the belts. One prevalent model for sedimentation in these basins is that fine-grained sediments in record tectonic growth of the thrust belt whereas coarse-grained sediments accumulate during periods of thrust belt inactivity. This project aims to test this model using innovative methods to determine the timing of sedimentation in the Idaho-Wyoming fold-and-thrust belt. A successful challenge of the prevalent model has the potential to change geological understanding of how fold-and-thrust belts belts develop. This is of particular importance because the Idaho-Wyoming thrust belt and associated foreland basins host important hydrocarbon resources. A better understanding of basin development will provide important insights into hydrocarbon exploration. The project would advance other desired societal outcomes through: (1) full participation of women in STEM; (2) improved STEM education and educator development through engagement of a K-12 science teacher or undergrad student in the UTeach program, and participation in the Geoscience Teacher Symposium for K-12 science teachers; (3) increased public scientific literacy and public engagement with STEM through development of displays and videos for the University of Arizona Flandau Center; and (4) development of a globally competitive STEM workforce through training of graduate and undergraduate students.
For over two decades foreland basin stratigraphers and sedimentologists have used the two-phase model of foreland basin subsidence to interpret stratigraphic sequences in foreland settings. This model hypothesizes that episodes of fine-grained distal sedimentation are the syntectonic response to orogenic growth and rapid flexural subsidence, whereas coarse-grained distal facies accumulate during periods of thrust belt inactivity, erosion, and isostatic rebound. This research project will test this model using geo/thermochronologic and magnetic polarity stratigraphic study of mid- to Upper Cretaceous foreland basin deposits in northeast Utah and southwest Wyoming, a classic foreland. Detrital geochronology (U-Pb on detrital zircon and apatite) and thermochronology (apatite fission track) will determine detrital lag-times (the time difference between the exhumation age of a sediment grain from the source terrane and its depositional age in the basin). Second, better age control in the poorly dated proximal part of the basin fill will be established by using magnetic polarity stratigraphy on fine-grained interbeds within thick alluvial fan deposits located adjacent to major thrust faults. This combined approach allows accurate correlation of the proximal and distal facies, and establishment of the time difference between exhumation and depositional ages of the distal, coarse-grained intervals. Long lag-times in the distal coarse-grained facies and irregular long-term trends in lag-time, this would support the two-phase model whereas relatively brief (<5 Myr) lag-times and a steady to decreasing lag time trend would indicate that coarse-grained sediments prograded directly into the distal basin during tectonic events in the thrust belt and therefore would nullify the two-phase model.
National Geographic - pending funding
A RECORD OF MIOCENE EXTREME ENVIRONMENTS FROM THE CENTRAL ANDES
The goal of this project is to study early-middle Miocene (ca. 21-14 Ma) paleo-dune deposits in the Central Andes. The early-middle Miocene was a time in the geological record warmer than today and a potential analogue for modern and future warming. Despite its significance we know very little about the early-middle Miocene continental climate record and this data gap hinders our ability to accurately predict future climate. The Central Andes preserve a unique record of Miocene sand-sea environments across the entire elevation range of the orogenic belt, from low-elevation foreland to high-elevation hinterland, over a latitudinal range of ca. 20o. This is a natural laboratory for documenting the latitudinal distribution of the arid subtropical zone during the Miocene. We plan to date and analyze the sedimentology of Central Andean paleo-dune deposits in order to reconstruct the timing of aridification and the direction and strengths of the winds. Warming and aridification are associated with changes in Hadley circulation which in turn affects the intertropical convergence zone (ITCZ) with impact on water supply for the planet. Results from this study will help constrain the structure of the Hadley cells during the Miocene and provide crucial data for climate models and climate predictions.