RESEARCH

Deformation of Earth's continents profoundly affects our world, forming some of our most striking landscapes, shaping climate, and determining how Earth resources are distributed. However, the controls on where, when, and how this deformation occurs often remain enigmatic. I use sedimentary basin records, topography, and structural geology with the goal of understanding how tectonic factors such as subduction angle, lithospheric foundering, continental collision, and lithospheric heterogeneities affect the evolution of Earth’s continents. I also develop new quantitative and statistical methods for interpreting geologic records. Below, I outline results from several projects that address these research goals.

DEFORMATION OF THE SOUTHERN PUNA PLATEAU, ARGENTINA, AND THE ROLE OF LITHOSPHERIC FOUNDERING

Deformation kinematics within orogens reflect a dynamic interplay between lithospheric gravitational potential energy and tectonic stresses. My work with collaborators Lindsay Schoenbohm (University of Toronto Mississauga), Mitchell McMillan (Georgia Tech), and others, shows a transient period of extensional basin formation during Miocene time in the southern Puna Plateau. This extension is coeval with an episode of lithospheric foundering (detachment and sinking of negatively buoyant mantle lithosphere and lower crust) inferred from volcanic geochemistry and geophysical data from the region, and upper crustal extension is consistent with some numerical models of foundering. Thus, the changes in kinematics recorded in the Southern Puna Plateau may have resulted from lithospheric foundering.

We will test this hypothesis using new work with collaborators Joyce Sim (Georgia Tech), Marissa Tremblay (Purdue), and Patricio Payrola (Universidad Nacional de Salta) recently funded by NSF. I am planning fieldwork with Utah Tech students now!

The figures below show a map of the Southern Puna Plateau (left) with faults, locations of volcanic rocks that have been interpreted to result from foundering (e.g., Kay et al., 1994), earthquake locations (Mulcahy et al., 2014), and location of a lower crustal zone of low seismic velocity interpreted to reflect post-foundering heating (Beck et al., 2015). Our inferred tectonic evolution of the Salar de Antofalla area (right) is also shown.

UNDERSTANDING EARLY CONTINENTAL COLLISION IN THE CAUCASUS

My PhD dissertation examined the Greater Caucasus mountain range as a natural laboratory for early continental collision. The orogen accommodates convergence between the Lesser Caucasus tectonic block and the Eurasian interior (see figure below). The eastern Greater Caucasus accommodates rapid convergence (16 mm/yr; Reilinger et al., 2006) and deep earthquakes indicate the presence of a subducted slab beneath the range (Mellors et al., 2012; Mumladze et al., 2015), whereas the western Greater Caucasus accommodates slower convergence (4 mm/yr; Reilinger et al., 2006) and shows no evidence of a subducting slab (Mumladze et al., 2015). These observations have led to the hypothesis that the orogen is undergoing a diachronous transition from subduction to collision that began within the past few million years.

I used detrital zircon U-Pb geochronology, together with colleagues, to refine the record of collision in the orogen and its effect on foreland basin sediment dispersal (Tye et al., 2021, Basin Research, link here). Our data reveal a timeline for initial entrance of the lower plate continental margin into the subduction zone, migration of strain away from the subduction megathrust, foreland basin drainage reorganization, and exhumation of deeper crustal levels in the upper plate. With colleagues, I also conducted a structural and thermochronometric study of the eastern Greater Caucasus that revealed a distributed style of shortening accommodated by pervasive folding and cleavage development in turbiditic strata that constitute the bulk of the orogen, compatible with observations from seismically imaged accretionary prisms (Tye et al., 2022, Tectonics). Together, these studies expand our understanding of how the initiation of collision is affecting deformation within the orogen.

The figure below shows the location of the Caucasus region within the Arabia-Eurasia collision zone, as well as an oblique perspective figure of the present tectonic configuration of the range. The yellow arrow in panel (a) indicates the perspective of panel (b).

STATISTICAL MODELING METHODS FOR DETRITAL GEOCHRONOLOGY

Statistical distributions of detrital geochronological data are complex and typical sample sizes do not resolve some of their details. Together with colleagues Aaron Wolf and Nathan Niemi, I have approached this problem using a Bayesian statistical framework to infer an ensemble of age distributions from which a given detrital geochronology age sample may have been drawn. This approach allows for the assessment of uncertainties in detrital geochronology age distributions inferred from samples. By showing which features of a sample age distribution are statistically robust, this approach can help a user determine which features reflect Earth processes and which are likely a result of limited sampling. This work is published in Chemical Geology (link here), and the approach I develop is implemented in open source MATLAB scripts and standalone applications (available here).

The plots below show the ensembles of age distributions inferred for three random subsamples of size n=60, 100, and 300 of a large detrital zircon U-Pb age dataset (Pullen et al., 2014). As sample size increases, the ensembles of age distributions become more tightly constrained, reflecting the benefits of increased sample sizes. Dot plots below each panel show the zircon U-Pb age measurements for which the ensembles are inferred.

PALEOSEISMIC SLIP HISTORIES FROM STRENGTH AND ROUGHNESS OF BEDROCK NORMAL FAULT SCARPS

With colleague Tim Stahl (University of Canterbury), I investigated paleoseismic slip histories recorded by the distribution of rock strength on bedrock normal fault scarps. We used a Schmidt hammer to measure rock strength in vertical transects up bedrock fault scarps. Schmidt hammer results suggest lateral, meter-scale bands of uniform weathering intensity that we interpret as rupture patches exposed during successive major earthquakes. This method, combined with cosmogenic nuclide sampling targeted according to rupture patch geometry, may present a fast and relatively cheap way to recover paleoseismic slip histories. We published promising results from the Hebgen Lake Fault Scarp (link here) and the Pleasant Valley Fault Scarp (link here).

The figure below shows a cartoon representation of Schmidt hammer results for a bedrock fault scarp exposed over a sequence of three earthquakes.

References (excluding those that appear on the CV page)

Beck, S. L., Zandt, G., Ward, K. M., & Scire, A. (2015). Multiple styles and scales of lithospheric foundering beneath the Puna Plateau, central Andes. In Geodynamics of a cordilleran orogenic system: The central Andes of Argentina and northern Chile (pp. 43-60). Geological Society of America.

Kay, S. M., Coira, B., & Viramonte, J. (1994). Young mafic back arc volcanic rocks as indicators of continental lithospheric delamination beneath the Argentine Puna plateau, central Andes. Journal of Geophysical Research: Solid Earth, 99(B12), 24323-24339.

Mellors, R. J., et al. (2012). Deep earthquakes beneath the Northern Caucasus: evidence of active or recent subduction in western Asia. Bulletin of the Seismological Society of America, 102(2), 862-866.

Mulcahy, P., Chen, C., Kay, S. M., Brown, L. D., Isacks, B. L., Sandvol, E., Heit, B., Yuan, X., & Coira, B. L. (2014). Central Andean mantle and crustal seismicity beneath the southern Puna plateau and the northern margin of the Chilean‐Pampean flat slab. Tectonics, 33(8), 1636-1658.

Mumladze, T., Forte, A. M., Cowgill, E. S., Trexler, C. C., Niemi, N. A., Yıkılmaz, M. B., & Kellogg, L. H. (2015). Subducted, detached, and torn slabs beneath the Greater Caucasus. GeoResJ, 5, 36-46.

Pullen, A., et al. (2014). What happens when n=1000? Creating large-n geochronological datasets with LA-ICP-MS for geologic investigations. Journal of Analytical Atomic Spectrometry, 29(6), 971-980.

Reilinger, R., et al. (2006). GPS constraints on continental deformation in the Africa‐Arabia‐Eurasia continental collision zone and implications for the dynamics of plate interactions. Journal of Geophysical Research: Solid Earth, 111(B5).