Current Projects

One of my primary research interests is accessory mineral geochemistry. Accessory minerals contain rare or unusual elements that cannot fit into the structures of other rock-forming minerals, thus can potentially provide more information about their environment.  Accessory minerals are not essential to the proper classification of a rock, so I am interested in a wide variety of rock types.

I developed a technique to date the accessory mineral allanite using an ion microprobe. Allanite has the relatively simple mineral formula of A₂M₃Si₃O₁₂(OH), but the A-sites can contain large cations, such as Ca, Sr, or any rare earth elements, whereas the M-sites admit Al, Fe, Mn, or Mg.  Almost every element in the periodic table has been reported to be present in allanite, including Th, U, Zr, P, Ba, Cr, and others. Because of this complicated chemistry, allanite is a common mineral.

One application of the allanite-dating project was to determine the initiation age of a large-scale thrust fault in the Himalayas. The Himalayan mountain range, created by the collision of India with Asia, which began 50 million years ago, is an ideal laboratory for understanding the response of continental lithosphere to plate tectonic forces.  Although the ages of allanite we dated in the Himalayas were pre-collisional, we found remarkably young monazite ages from rocks collected adjacent to the Main Central Thrust, the crustal-scale thrust largely responsible for the creation of the range. 

Monazite is a radiogenic and rare earth element-bearing phosphate mineral that commonly appears as inclusions in garnets. Garnet-bearing rocks allow peak pressure and temperature conditions to be determined, and when combined with monazite age data, are a powerful combination for ascertaining the evolution of metamorphic terranes.  As part of a National Science Foundation Grant, I have been working with Oklahoma State University (OSU) and University of Delhi geologists of explore the extent of the young ages in association with the Main Central Thrust by conducting fieldwork in northwest India.

I apply monazite-dating techniques to the Menderes Massif in western Turkey, a ~40,000 km² exposure of polymetamorphic rocks. Unlike the Himalayas, the massif is a complex product of compression followed by extension, and a graben system continues to deform the range today. Numerous studies report ages that support a polyphase deformation history of the massif, but their link to the nature of specific events remains difficult and controversial.  

Monazite age data from a single rock is sometimes inconsistent with a single population, thus I published a paper outlining scenarios that geochronologists can use to examine sources of uncertainty and explain complicated age distributions.

One of my projects was recently published in Science, in which I dated subduction zone phengitic muscovite grains that contain large amounts of Ba. The goal was to understand the processes by which volatile components release during metamorphism in subduction zones. Because phengitic muscovite is stable to >750°C and >7 GPa, it can transport alkali and alkaline-earth elements to great depths. Dehydration of the mineral may facilitate material transfer from the subducted slab to the overlying mantle wedge at higher pressures than those at which the slab melts.  Large (500mm- to 4mm-sized) Ba-rich grains are present in eclogites and associated metasomatites from both the Samana Peninsula (Dominican Republic) and the Franciscan Complex (northern California). Their patchy variations in Ba likely related to different compositions of fluids interacting with the mineral during crystallization or alteration. The ages of the grains, which record almost 50 million years of fluid-rock interaction in Franciscan and 25 million years in the Samana eclogites, may prove to be important constraints that links fluid-rock interactions to broader tectonic events.

As a former center faculty of the Arkansas-Oklahoma Center for Space and Planetary Sciences, I am interested in the mineralogy of planets, meteorites, and of the Early Earth. As director of the OSU Electron Microprobe Laboratory, I am interested in developing and maintaining partnerships with scientists that use the instrumentation.

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