The Not-So-Boring Billion: 1.4 Ga Picuris Metamorphism and Deformation

The interior of the North American continent experienced intense deformation and magmatism 1.4 billion years ago, at a time that used to be considered tectonically "boring". Beautifully deformed conglomerates from the Picuris Mountains offer a new widow into the metamorphism and deformation of the middle crust at this time. Combined petrologic, microstructural, and isotope geochemistry analysis of will provide details of thermal and structural evolution of this cryptic, intraplate mountain-building event.

Electron backscatter diffraction (EBSD) maps of an intensely deformed garnet from the Marqueñas metaconglomerate of the Picuris Mountains, New Mexico (USA). Top image: distribution of shattered and sheared garnet. Bottom image: crystallographic orientations (different colors) of the shattered garnet fragments.

Oxygen-isotope zoning & fluids in metamorphic core complexes 

Titanite porphyroclast with SIMS oxygen isotope analysis pits

The oxygen-isotope composition of a mineral reflects the temperature and fluids present when the mineral grew, underwent recrystallization, or experienced heating. Combining spatially resolved oxygen-isotope analysis with microstructural analysis of deformed minerals has the potential to place unique constraints on the timing of heating and/or fluid infiltration relative to the timing of deformation in shear zones. Metamorphic core complexes offer opportunities to examine multistage exhumation-related thermal histories and investigate the role of fluids in detachment dynamics.

National Science Foundation Award 1650355. “Intragrain Oxygen-isotope Zoning and the Fast Grain Boundary Model: A New Approach to Thermal Histories and Fluid-rock Interactions”. 2017-2020.

Understanding the Role of Altered Crystalline Basement Horizons in Fluid Flow

Many basinal sequences lie nonconformably on crystalline rocks that have been chemically altered. This altered nonconformity horizon represents a hydrogeomechanically distinct unit relative to the overlying sediments and the underlying unaltered crystalline rocks, yet its role in basin-scale fluid flow is as yet poorly known. Analysis of the physical and chemical variations in the altered nonconformity will improve understanding of its geochemical development and inform predictions regarding its role in fluid transmission and storage.

ACS-PRF Doctoral New Investigator Program grant. “Origin of altered horizons beneath nonconformities: Implications for induced seismicity and basin-scale fluid flow”. 2016-2019.


Former M.S. student Ke Li collects data and samples along the Great Unconformity in Grand Canyon National Park

Phenomenology of the nuclear fireball

Glassy fallout debris from nuclear explosions shows unique compositional characteristics that reflect processes occuring within the nuclear fireball. Geochemical-style microanalysis of compositionally heterogeneous fallout debris can provide information about the specific processes that lead to chemical and isotopic fractionation, which is of interest to nuclear forensic investigators.

Phase map of glassy fallout bead from the Trinity nuclear test, the world's first atomic explosion


Melt-flow networks in migmatite terranes

Pockets of melt formed during high-temperature metamorphism within large orogens can coalesce and migrate to form large intrusive bodies higher in the crust. Field studies of migmatites in Proterozoic rocks of central Arizona suggest that development of these melt-flow networks occurs in systems that attain a state of (self-organized) criticality.

Collapse of the Grenville orogen

P-T-t paths determined from traditional, multi-mineral thermochronology for Grenville rocks in the Adirondack region  suggest a long, slow cooling history following climactic mountain-building and high-temperature metamorphism. Quantitative modeling of oxygen-isotope zoning in titanite instead suggests an episodic cooling history that included a period of very rapid cooling at 1050 Ma. The timing of this rapid-cooling episode is consistent with gravitational collapse of the Grenville mountains immediately following or even slightly overlapping climactic, high-temperature metamorphism.

Finite strain analysis & deep crustal flow

Localization of strain to form distinct shear zones in the deep orogenic crust is rare, yet the development of large structures, such as the Mt. Hay sheath fold of central Australia, suggests that strain is not homogeneous in these hot, deep rocks. Field mapping and finite strain analysis across the 10-km-scale Mt. Hay sheath fold shows that while strain magnitude is similar throughout this structure, the strain shape varies systematically as a function of structural position.  Thus, different deformation fabrics can develop even when strain is not localized.