skip to main content
Explore Scholarly Publications and Datasets in the NSF-PAR

  • NSF Public Access
  • Search Results
  • Accepted Manuscript: Using Multigrain Crystallography to Explore the Microstructural Evolution of the α-Olivine to γ-Ringwoodite Transformation and ε-Mg2SiO4 at High Pressure and Temperature
Title: Using Multigrain Crystallography to Explore the Microstructural Evolution of the α-Olivine to γ-Ringwoodite Transformation and ε-Mg2SiO4 at High Pressure and Temperature
The introduction of multigrain crystallography (MGC) applied in a laser-heated diamond anvil cell (LH-DAC) using synchrotron X-rays has provided a new path to investigate the microstructural evolution of materials at extreme conditions, allowing for simultaneous investigations of phase identification, strain state determination, and orientation relations across phase transitions in a single experiment. Here, we applied this method to a sample of San Carlos olivine beginning at ambient conditions and through the α-olivine → γ-ringwoodite phase transition. At ambient temperatures, by measuring the evolution of individual Bragg reflections, olivine shows profuse angular streaking consistent with the onset of yielding at a measured stress of ~1.5 GPa, considerably lower than previously reported, which may have implications for mantle evolution. Furthermore, γ-ringwoodite phase was found to nucleate as micron to sub-micron grains imbedded with small amounts of a secondary phase at 15 GPa and 1000 °C. Using MGC, we were able to extract and refine individual crystallites of the secondary unknown phase where it was found to have a structure consistent with the ε-phase previously described in chondritic meteorites.
Authors:
; ; ;
Award ID(s):
1464014 2054951
Publication Date:
NSF-PAR ID:
10329117
Journal Name:
Minerals
Volume:
11
Issue:
4
Page Range or eLocation-ID:
424
ISSN:
2075-163X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ( , Progress in Earth and Planetary Science)
    Abstract

    The goal of classifying shock metamorphic features in meteorites is to estimate the corresponding shock pressure conditions. However, the temperature variability of shock metamorphism is equally important and can result in a diverse and heterogeneous set of shock features in samples with a common overall shock pressure. In particular, high-pressure (HP) minerals, which were previously used as a solid indicator of high shock pressure in meteorites, require complex pressure–temperature–time (P–T–t) histories to form and survive. First, parts of the sample must be heated to melting temperatures, at high pressure, to enable rapid formation of HP minerals before pressure release. Second, the HP minerals must be rapidly cooled to below a critical temperature, before the pressure returns to ambient conditions, to avoid retrograde transformation to their low-pressure polymorphs. These two constraints require the sample to contain large temperature heterogeneities, e.g. melt veins in a cooler groundmass, during shock. In this study, we calculated shock temperatures and possibleP–Tpaths of chondritic and differentiated mafic–ultramafic rocks for various shock pressures. TheseP–Tconditions and paths, combined with observations from shocked meteorites, are used to constrain shock conditions andP–T–thistories of HP-mineral bearing samples. The need for rapid thermal quench of HP phases requires a relatively lowmore »bulk-shock temperature and therefore moderate shock pressures below ~ 30 GPa, which matches the stabilities of these HP minerals. The low-temperature moderate-pressure host rock generally shows moderate shock-deformation features consistent with S4 and, less commonly, S5 shock stages. Shock pressures in excess of 50 GPa in meteorites result in melt breccias with high overall post-shock temperatures that anneal out HP-mineral signatures. The presence of ringwoodite, which is commonly considered an indicator of the S6 shock stage, is inconsistent with pressures in excess of 30 GPa and does not represent shock conditions different from S4 shock conditions. Indeed, ringwoodite and coexisting HP minerals should be considered as robust evidence for moderate shock pressures (S4) rather than extreme shock (S6) near whole-rock melting.

    « less
  2. ; ; ; ; ( , Atmospheric Chemistry and Physics)
    Abstract. Volatility and viscosity are important properties of organic aerosols (OA),affecting aerosol processes such as formation, evolution, and partitioning ofOA. Volatility distributions of ambient OA particles have often beenmeasured, while viscosity measurements are scarce. We have previouslydeveloped a method to estimate the glass transition temperature (Tg) ofan organic compound containing carbon, hydrogen, and oxygen. Based onanalysis of over 2400 organic compounds including oxygenated organiccompounds, as well as nitrogen- and sulfur-containing organic compounds, weextend this method to include nitrogen- and sulfur-containing compoundsbased on elemental composition. In addition, parameterizations are developedto predict Tg as a function of volatility and the atomicoxygen-to-carbon ratio based on a negative correlation between Tg andvolatility. This prediction method of Tg is applied to ambientobservations of volatility distributions at 11 field sites. Thepredicted Tg values of OA under dry conditions vary mainly from 290 to 339 Kand the predicted viscosities are consistent with the results of ambientparticle-phase-state measurements in the southeastern US and the Amazonianrain forest. Reducing the uncertainties in measured volatility distributionswould improve predictions of viscosity, especially at low relative humidity.We also predict the Tg of OA components identified via positive matrixfactorization of aerosol mass spectrometer (AMS) data. The predicted viscosity ofoxidized OA is consistent with previously reportedmore »viscosity of secondary organic aerosols (SOA) derivedfrom α-pinene, toluene, isoprene epoxydiol (IEPOX), and diesel fuel.Comparison of the predicted viscosity based on the observed volatilitydistributions with the viscosity simulated by a chemical transport modelimplies that missing low volatility compounds in a global model can lead tounderestimation of OA viscosity at some sites. The relation betweenvolatility and viscosity can be applied in the molecular corridor orvolatility basis set approaches to improve OA simulations in chemicaltransport models by consideration of effects of particle viscosity in OAformation and evolution.« less
  3. ; ( , American Mineralogist)
    We quantify the metamorphic pressure-temperature (P-T) conditions for a newly discovered silica-undersaturated high-pressure granulite (HPG) from the Central Maine Terrane (CMT) in northeastern Connecticut, U.S.A. The rocks lie within the Acadian-Neoacadian orogenic belt (Devonian) and form part of the Brimfield Schist. The Brimfield and the adjacent Bigelow Brook Formation contain silica-saturated rocks that have previously been shown to have undergone ~1000 °C metamorphism. The pressure was less well constrained at ≥ ~1 GPa. Silica-undersaturated rocks hold underutilized potential for pinpointing peak metamorphic conditions, particularly pressure, because of their resilience to melting and the variety of refractory minerals they contain. The typical silica-undersaturated mineral assemblage is garnet + spinel + corundum + plagioclase + K-feldspar + biotite + ilmenite. Leucosomes are syenites consisting of two feldspars ± biotite. Plagioclase is commonly antiperthitic, particularly in feldspathic domains surrounding peritectic garnet; such garnet crystals reach ~10 cm in diameter. Alkali feldspars are perthitic. The rocks contain remarkable ellipsoidal spinels as much as 5.5 cm long comprising discrete crystallographic domains hosting crystallographically oriented lamellae of a Fe-Ti phase, most likely ilmenite. Corundum is usually colorless, but can also be found as sapphire in shades of pink, purple, and blue, particularly in antiperthite-rich domains surroundingmore »large garnets. Some sapphires are concentrically color zoned. We carried out a P-T estimation using ternary feldspar reintegration thermometry of metamorphic antiperthites together with pseudosection modeling. Samples texturally and chemically record near-eclogite facies equilibration at minimum conditions of ~1040 °C and ~1.8 GPa, establishing the CMT in northeastern CT as the first known HPG locality in the U.S. These results are consistent with high P2O5 levels found in garnet (0.18 wt%), Ti-in-biotite thermometry, regional sillimanite pseudomorphs after kyanite, and preliminary experimental work on melt inclusions in garnet (Ferrero et al. 2017). The leucosomes provide strong evidence that partial melting of silica-undersaturated rocks at HPG conditions can produce syenitic magmata. Strongly melt-depleted silica-undersaturated rocks may also be protoliths for garnet + spinel + corundum xenoliths reported from kimberlites. The presence of HPG gneisses demonstrates that the large-scale thrusts of the CMT sample the deepest roots of the orogenic belt (60–70 km), and perhaps even deeper subduction zone lithologies as well.« less
  4. ; ; ( , American Mineralogist)
    Abstract We have examined the suitability of a quartz-inclusions-in-epidote (qtz-in-ep) mineral barometer to better constrain P-T histories of epidote-bearing lithologies. Theoretical calculations applying an isotropic elastic model suggest that the qtz-in-ep barometer exhibits minimal temperature dependence, and thus, offers the potential to constrain growth conditions of epidote in various geologic environments, including skarn deposits, epidote-bearing granitoids, and metamorphic rocks. To test if the applied equations of state and isotropic elastic model reasonably simulate the elastic evolution of two anisotropic minerals, we measured Raman shifts of the 464 cm–1 band of quartz inclusions relative to that of an unencapsulated quartz standard. We calculated a quartz inclusion pressure (Pincl464) at various temperatures and compared these values with temperature-dependent Pincl predicted by elastic modeling (Pinclmod) at elevated temperatures. Three epidote-bearing samples with reasonably well-constrained P-T histories were also examined: (1) sample HF14C from the Upper Schieferhuelle in the Western Tauern Window, Italy (Pincl464=0.01 GPa); (2) sample LdC-31C from Lago di Cignana, Italy (Pincl464≈0.16 GPa); and (3) sample FT1E from the Frosnitz Tal in the Western Tauern region, Austria (Pincl464=0.57 GPa). Entrapment pressures (Pent464) calculated from Pincl464 determined at various temperatures show nominal differences from Pent calculated from Pinclmod, suggesting that for qtz-in-ep pairs, the calculated Pentmore »does not significantly vary with the temperature of measurement. Furthermore, our calculated Pent464 for a sample from the Upper Schieferhuelle is in agreement with petrographic context and previously established P conditions, and the Pent464 determined for the Frosnitz Tal sample closely approximate previously reported pressures. The Lago di Cignana sample is derived from an epidote vein that is encased in a high-P foliation, and the calculated Pent464 is consistent with early, low-P epidote vein formation that pre-dates high-P metamorphism, or alternatively, late vein formation during exhumation, and confirms that the epidote did not form at or near peak conditions (~2.0 GPa). The results of this study indicate that the qtz-in-ep barometer potentially provides another tool that geoscientists can employ to better constrain P-T conditions in some epidote-bearing environments, where conventional thermobarometric techniques cannot be applied.« less
  5. ; ; ; ; ( , Science Advances)
    Understanding dynamics across phase transformations and the spatial distribution of minerals in the lower mantle is crucial for a comprehensive model of the evolution of the Earth’s interior. Using the multigrain crystallography technique (MGC) with synchrotron x-rays at pressures of 30 GPa in a laser-heated diamond anvil cell to study the formation of bridgmanite [(Mg,Fe)SiO 3 ] and ferropericlase [(Mg,Fe)O], we report an interconnected network of a smaller grained ferropericlase, a configuration that has been implicated in slab stagnation and plume deflection in the upper part of the lower mantle. Furthermore, we isolated individual crystal orientations with grain-scale resolution, provide estimates on stress evolutions on the grain scale, and report {110} twinning in an iron-depleted bridgmanite, a mechanism that appears to aid stress relaxation during grain growth and likely contributes to the lack of any appreciable seismic anisotropy in the upper portion of the lower mantle.
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email