I am the Curator of the Oscar E. Monnig Meteorite Collection. This is one of the world’s largest university-based meteorite collections, which also includes a world-class museum, the Monnig Meteorite Gallery. Its presence at TCU offers both my undergraduate and graduate students unique opportunities in research, curation, and public outreach. I have been a Research Associate at the Smithsonian Institution’s National Museum of Natural History (NMNH) for much of time here at TCU. In 2010, I was a member of the Antarctic Search for Meteorites field team, spending 2 months in Antarctica collecting meteorites whilst trying to stay warm.
My research explores the processes that occurred during the early history of our Solar System, with a primary focus on understanding the formation of differentiated bodies (those with a core, mantle, crust structure). My students and I primarily study the mineralogy, geochemistry, and spectra of asteroidal meteorites to gather information about planetary formation and Solar System evolution
Areas of Expertise (3)
University of Tennessee, Knoxville: PhD, Geology
Edinburgh University: BSc, Geology
Media Appearances (1)
2nd Largest Meteorite Belongs To TCU
CBS News online
'“This is the building blocks,” Mayne said. “This is before all that happened. This is what the earth would have looked like before it melted...”'
Hiding in the howardites: Unequilibrated eucrite clasts as a guide to the formation of Vesta's crustMeteoritics & planetary science
2016 National Meteorite Collection at the Smithsonian were examined for the presence of fine-grained eucrite clasts, with the goal of better understanding the formation of the uppermost crust of asteroid 4Vesta. Eight clasts were identified and characterized in terms of their textures and mineral chemistry, and their degree of thermal metamorphism was assessed. The paucity of fine-grained eucrites, both within the unbrecciated eucrites and as clasts within the howardites, suggests that they originate from small-scale units on the surface of Vesta, most likely derived from partial melting. Six of the eight clasts described were found to be unequilibrated, meaning that they preserve their original crystallization trends. The vast majority of eucrites are at least partially equilibrated, making these samples quite rare and important for deciphering the petrogenesis of the vestan crust. Biomodal grain populations suggest that eucrite melts often began crystallizing pyroxene and plagioclase during their ascent to the surface, where they were subject to more rapid cooling, crystallization, and later metasomatism. Pyroxene compositions from this study and prior work indicate that the products of both primitive and evolved melts were present at the vestan surface after its formation. Two howardite thin sections contained multiple eucrite composition clasts with different crystallization and thermal histories; this mm-scale diversity reflects the complexity of the current day vestan surface that has been observed by Dawn.
Experimental insights into Stannern‐trend eucrite petrogenesisMeteoritics & planetary science
2017 The incompatible trace element‐enriched Stannern‐trend eucrites have long been recognized as requiring a distinct petrogenesis from the Main Group‐Nuevo Laredo (MGNL) eucrites. Barrat et al. (2007) proposed that Stannern‐trend eucrites formed via assimilation of crustal partial melts by a MGNL‐trend magma. Previous experimental studies of low‐degree partial melting of eucrites did not produce sufficiently large melt pools for both major and trace element analyses. Low‐degree partial melts produced near the solidus are potentially the best analog to the assimilated crustal melts. We partially melted the unbrecciated, unequilibrated MGNL‐trend eucrite NWA 8562 in a 1 atm gas‐mixing furnace, at IW‐0.5, and at temperatures between 1050 and 1200 °C. We found that low‐degree partial melts formed at 1050 °C are incompatible trace element enriched, although the experimental melts did not reach equilibrium at all temperatures. Using our experimental melt compositions and binary mixing modeling, the FeO/MgO trend of the resultant magmas coincides with the range of known Stannern‐trend eucrites when a primary magma is contaminated by crustal partial melts. When experimental major element compositions for eucritic crustal partial melts are combined with trace element concentrations determined by previous modeling (Barrat et al. 2007), the Stannern‐trend can be replicated with respect to both major, minor, and trace element concentrations.
The origin of Vesta’s crust: Insights from spectroscopy of the VestoidsIcarus
2011 High quality VNIR spectra of 15 Vestoids, small asteroids that are believed to originate from Vesta, were collected and compared to laboratory spectra and compositional data for selected HED meteorites. A combination of spectral parameters such as band centers, and factors derived from Modified Gaussian Model fits (band centers, band strengths, calculation of the low to high-Ca pyroxene ratio) were used to establish if each Vestoid appeared most like eucrite or diogenite material, or a mixture of the two (howardite). This resulted in the identification of the first asteroid with a ferroan diogenite composition, 2511 Patterson. This asteroid can be used to constrain the size of diogenite magma chambers within the crust of Vesta. The Vestoids indicate that both large-scale homogeneous units (>5km) and smaller-scale heterogeneity.
Petrologic insights from the spectra of the unbrecciated eucrites: Implications for Vesta and basaltic asteroidsMeteoritics & Planetary Science
2010 We investigate the relationship between the petrology and visible–near infrared spectra of the unbrecciated eucrites and synthetic pyroxene–plagioclase mixtures to determine how spectra obtained by the Dawn mission could distinguish between several models that have been suggested for the petrogenesis of Vesta’s crust (e.g., partial melting and magma ocean). Here, we study the spectra of petrologically characterized unbrecciated eucrites to establish spectral observables, which can be used to yield mineral abundances and compositions consistent with petrologic observations. No information about plagioclase could be extracted from the eucrite spectra. In contrast, pyroxene dominates the spectra of the eucrites and absorption band modeling provides a good estimate of the relative proportions of low- and high-Ca pyroxene present. Cr is a compatible element in eucrite pyroxene and is enriched in samples from primitive melts. An absorption at 0.6 μm resulting from Cr3+ in the pyroxene structure can be used to distinguish these primitive eucrites. The spectral differences present among the eucrites may allow Dawn to distinguish between the two main competing models proposed for the petrogenesis of Vesta (magma ocean and partial melting). These models predict different crustal structures and scales of heterogeneity, which can be observed spectrally. The formation of eucrite Allan Hills (ALH) A81001, which is primitive (Cr-rich) and relatively unmetamorphosed, is hard to explain in the magma ocean model. It could only have been formed as a quench crust. If the magma ocean model is correct, then ALHA81001-like material should be abundant on the surface of Vesta and the Vestoids.