Kyle Ashley

I am a PhD candidate and ICTAS Doctoral Scholar at Virginia Tech with an anticipated graduation date in May 2014. My principle research interests include the integration of nano-scale observations/measurements to reconstruct orogeny-scale tectonic enviornments and evolution. This includes (i) constraining PTtD histories for metamorphic tectonites (pseudosection modeling, petrographic observations, EMPA monazite age dating, paleostress and strain rate analysis, quartz fabric analysis, etc.), (ii) understanding Ti incorporation mechanisms in quartz, (iii) Ti-in-quartz redistribution and effects on dynamic recrystallization, (iv) paleomicrostructure preservation, (v) refinements on inclusion thermobarometry (using Raman spectroscopy) for improved pressure estimation in high-pressure terranes, (vi) kinematic estimation on mylonites in ductile shear zones, (vii) coupling inclusion measurements for independent P-T determination, (viii) low-density polymorph transformations in tensile stress regimes, and (ix) X-ray diffraction of oceanic muds for sediment sourcing. Below is some information on a selection of these topics and the approach I have taken in this work:


  Application of Ti-in-quartz to metatectonites

  Mineral inclusion geobarometry

  PTD evolution in ductile shear zones

Kyle:    CV   email

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Publications

Ashley, K.T., Thigpen, J.R., and Law, R.D., in press. Prograde evolution of the Scottish Caledonides and tectonic implications, Lithos.

Ashley, K.T., Darling, R.S., and Bodnar, R.J., in review. Significance of "stretched" mineral inclusions for reconstructing P-T exhumation history, submitted to Geology.

Ashley, K.T., and Law, R.D., 2015, Modeling prograde TiO2 activity and its significance for Ti-In-quartz thermobarometry of pelitic metamorphic rocks, Contributions in Mineralogy and Petrology, 169, 1-7.

Ashley, K.T., Carlson, W.D., Law, R.D., and Tracy, R.J., 2014, Ti resetting in quartz during dynamic recrystallization: Mechanisms and significance, American Mineralogist, DOI: http://dx.doi.org/10.2138/am-2014-4943.

Rygel, M.C., Sheldon, E.P., Stimson, M.R., Calder, J.H., Ashley, K.T., and Salg, J., 2014, The Pennsylvanian Springhill Mines Formation: Sedimentological framework of a portion of the Joggins Fossil Cliffs UNESCO World Heritage Site. Atlantic Geology, 50, 249-289.

Ashley, K.T., Caddick, M.J., Steele-MacInnis, M., Bodnar, R.J., and Dragovic, B., 2014, Geothermobarometric history of subduction recorded by quartz inclusions in garnet.. Geochemistry, Geophysics, Geosystems, 15, 350-360.

Ashley, K.T., Steele-MacInnis, M., and Caddick, M.J., 2014. QuIB Calc: A MATLAB® script for geobarometry based on Raman spectroscopy and elastic modeling of quartz inclusions in garnet, Computers and Geosciences, 66, 155-157.

Ashley, K.T., Webb, L.E., Spear, F.S., and Thomas, J.B., 2013, P-T-D histories from quartz: A case study of the application of the TitaniQ thermobarometer to progressive fabric development in metapelites. Geochemistry, Geophysics, Geosystems, 14 (9), 3821-3843.

Law, R.D., Stahr, D.W., Francsis, M.K., Ashley, K.T., Grasemann, B., and Ahmad, T., 2013, Deformation temperatures and flow vorticities near the base of the Greater Himalayan Series, Sutlej Valley and Shimla Klippe, NW India, Journal of Structural Geology, 54, 21-53.

Spear, F.S., Ashley, K.T., Webb, L.E., and Thomas, J.B., 2012, Ti diffusion in quartz inclusions: Implications for metamorphic time scales, Contributions in Mineralogy and Petrology, 164, 977-986.

Badger, R.L., Ashley, K.T., and Cousens, Brian, 2010, Stratigraphy and geochemistry of the Catoctin Volcanics: Implications for mantle evolution during the breakup of Rodinia, in Tollo, R.P., Bartholomew, M.J., Hibbard, J.P., Karabinas, P.M., eds, From Rodinia to Pangea: The Lithotectonic Record of the Appalachian Region: Geological Society of America Memoir 206, Boulder, Colorado, p. 397-416.

Conference Abstracts

Waters-Tormey, C., Ashley, K.T., and Tracy, R.J., 2014, Two-stage deformation, and two styles of localization, In a deep crustal normal sense shear zone: Mount Hay Block, Central Australia, GSA Abstract.

Ashley, K.T., Law, R.D., and Thigpen, J.R., 2014, Caledonian evolution of the Moine Supergroup: Prograde garnet growth and context for quartz fabric-based deformation thermometry, EGU Poster.

Ashley, K.T., Thigpen, J.R., Law, R.D., and Caddick, M.J., 2014, Decompressional garnet growth during prograde metamorphism: Implications for Caledonian tectonic reconstruction in NW Scotland, Penrose Talk.

Ashley, K.T., Caddick, Mark J., Steele-MacInnis, M., and Bodnar, R.J., 2014, Inclusion thermobarometry: Beyond quartz, NE GSA Talk.

Webb, L.E., Dyess, P.G., Ashley, K.T., Spear, F.S., and Thomas, J.B., 2013, TitaniQ records of P-T-D paths from metapelites during burial metamorphism and orogenesis: Evidence for the role of pressure solution creep, AGU abstract.

Ashley, K.T., Thigpen, J.R., Law, R.D., and Caddick, M.J., 2013, Decompressional garnet growth during prograde metamorphism in Caledonian thrust sheets, NW Scotland, GSA Talk.

Ashley, K.T., Law, R.D., Stahr, D.W., Thomas, J.B., Caddick, M.J., Spear, F.S., and Webb, L.E., 2013, Improved crustal PTtD evolution constraints using TitaniQ thermobarometry, Goldschmidt Talk.

Webb, L.E., Dyess, P.G., Ashley, K.T., Spear, F.S., and Thomas, J.B., 2013, Probing quartz for P-T-D paths, Goldschmidt Poster.

Ashley, K.T., Law, R.D., Tracy, R.J., Thomas, J.B., Caddick, M.J., Bodnar, R.J., and Stahr, D.W., 2013, Exploiting quartz for metamorphic evolution: Applications in Greece, Scotland and the Himalayas, ICTAS Poster.

Ashley, K.T., Law, R.D., Thomas, J.B., Caddick, M.J., and Stahr, D.W. III, 2013, Exploiting quartz to constrain pressure-temperature-time-deformation histories in metamorphic rocks through recent innovations in thermobarometry and geospeedometry, EGU Talk.

Law, R.D., Waters, D., Morgan, S., Stahr, D.W. III, Francsis, M., Ashley, K.T., Kronenberg, A.K., Thomas, J.B., Mazza, S., and Heaverlo, N., 2013, Quartz fabric-based deformation thermometry: Examples of its application, relationships to petrology-based PT paths, and potential problems, EGU Poster.

Law, R.D., Waters, D., Morgan, S., Stahr, D.W. III, Francsis, M., Ashley, K.T., Kronenberg, A.K., Thomas, J.B., Mazza, S., and Heaverlo, N., 2013, Quartz fabric-based deformation thermometry: Examples of its application, relationships to petrology-based PT paths, and potential problems, UK Tectonics Studies Group Talk.

Ashley, K.T., Caddick, M.J., and Bodnar, R.J., 2012, Improving pressure estimation in high pressure terranes with Raman spectroscopy: New calibration and implementation on blueschists from Sifnos, Greece, GSA Talk.

Ashley, K.T., Webb, L.E., Spear, F.S., and Thomas, J.B., 2012, P-T-D histories and reequilibration of Ti in quartz: Using the TitaniQ thermobarometer in poly-deformed tectonic terranes, Goldschmidt Poster.

Spear, F.S., Ashley, K.T., Webb, L.E., and Thomas, J.B., 2012, Tectonic implications of short metamorphic episodes, Goldschmidt Talk.

Ashley, K.T., 2012, Titanium-in-quartz thermobarometry: Implications from nanometer- to orogeny-scale with assessment of water weakening on quartz fabric opening angle thermometry, and associated monazite EMPA geochronology investigations, ICTAS Poster.

Ashley, K.T., Webb, L.E., Spear, F.S., and Thomas, J.B., 2010, Constraining P-T-D histories with the TitaniQ thermobarometer: Preliminary findings from the Strafford Dome, Vermont, AGU Poster V31C-2334.

Ashley, K.T., 2009, Petrology of a multiple meta-igneous intrusive outcrop, Tupper Lake, New York, The Green Mountain Geologist, 36, no. 3, 3.

Ashley, K.T. and Badger, R.L., 2009, Petrology of a multiple meta-igneous intrusive outcrop, Tupper Lake, New York, GSA Abstracts with programs, 41, no. 3, 108.

Ashley, K.T., Stephan, Emily L., Salg, J., and Rygel, M.C., 2009, Depositional environments and alluvial architecture of the Springhill Mines Formation (Pennsylvanian), Cumberland Basin, Nova Scotia, GSA Abstracts with programs, 41, no. 3, 27.

Sheldon, E.P., Ashley, K.T., and Rygel, M.C., 2009, The Springhill Mines Formation, Cumberland Basin, Nova Scotia: Evolution of channel body architecture within a Pennsylvanian fluvial system, GSA Abstracts with programs, 41, no. 3, 27.

Stephan, E.L., Ashley, K.T., and Rygel, M.C., 2009, Sedimentology of the Pennsylvanian Ragged Reef Formation, Cumberland Basin, Nova Scotia, GSA Abstracts with programs, 41, no. 3, 27.

Application of Ti-in-quartz to Metatectonites

Since its initial calibration, the Ti-in-quartz thermobarometer has been applied to a variety of igneous and metamorphic environments. Recent work shows the benefit of this application to mid-crustal metapelites in monitoring Si-flux (Si-producing metamorphic reactions, dissolution and precipitation, Si-charged fluid influx, etc.; Ashley et al., 2013). This technique requires knowledge of the titania activity of the system that equilibration occurs under. In metapelitic rocks, where Ti-phases are abundant, it is generally assumed that the activity must be ~1. However, Ashley and Law (in review) calculate the component activity through P-T space, noting significant decreases in titania activity under certain conditions. Using thermodynamic models to determine system TiO2 chemical potentials, Ashley and Law provide a method to constrain dynamic activities that can be correlated with quartz-producing, metamorphic events. Recent work is focused on characterizing Ti distribution in quartz inclusions in garnet. Growth-composition models are being implemented to determine the source of very early prograde quartz production. Fluid inclusions will be analyzed for fluid composition and quartz c-axis fabric analysis will be used for deformation temperature constraints, integrated together with Ti concentrations to unravel the early prograde history of ancient mountain belts.

Mineral Inclusion Geobarometry

Using inclusions in porphyroblasts to infer metamorphic pressure is not a new idea – the pioneering work of Rosenfeld (1969) used birefringence halos in garnet to estimate formation conditions. However, recent innovations using Raman spectroscopy on in-situ quartz inclusions in garnet porphyroblasts have allowed for precise inclusion pressure estimation. These results can be elastically modeled to determine formation pressures (if formation temperature can be reasonably constrained). We have been working to develop this technique, applying it initially to quartz recording subduction zone conditions (e.g. Ashley et al., 2012 GSA talk).

Click to see figures:

Figure 1 Figure 2 Figure 3

In extensively dynamically recovered terranes the redistribution mechanisms may be different. Recent single crystal X-ray diffraction measurements suggest Ti-doped quartz have larger volumes and lattice strain. This strain is most likely the result of the “uncomfortably close” fit of the Ti cation in the tetrahedral site resulting in minor lattice deformation. Defect energy simulations of Ti substitution in a pristine quartz lattice through increasing supercell dimensions suggests large concentrations of substitution are required to provide significant energetic perturbation to drive diffusion out of the lattice. Therefore, during dynamic recrystallization (a lattice-strain minimization mechanisms), reequilibration must occur on a localized scale; regulated by intergranular fluid that is most likely titania undersaturated (Ashley et al., 2014). In exceedingly dry quartz (H+<100 ppm), Ti would not be able to diffuse (no fluid medium to aid in the diffusion) and paleomicrostructures may be preserved in the trace element distribution.

Click to see figures:

Figure 4 Figure 5

PTD Mineral Inclusion Thermobarometry

Using inclusions in porphyroblasts to infer metamorphic pressure is not a new idea – the pioneering work of Rosenfeld (1969) used birefringence halos in garnet to estimate formation conditions. However, recent innovations using Raman spectroscopy on in-situ quartz, apatite and zircon inclusions in garnet have allowed for precise temperature and pressure estimation of encapsulation, when elastic modeling is applied. We have made several advances on the technique, with applications to constrain subduction zone conditions (Ashley et al., 2014) and Adirondack garnet growth (with quartz preserving tensile stresses; Ashley et al., in review). Cristobalite inclusions in garnets from Gore Mountain, Adirondacks (New York), are well removed from the low-density silica polymorph’s stability field (~1400 °C at atmospheric pressure). The inclusion pressure evolution through exhumation would result in large tensile stresses that overstep the extrapolated polymorph stability, suggesting elastic effects alone may account for the presence of this unexpected phase (Ashley, Darling and Bodnar, in review). This work is analogous to a well interconnected metamorphic rock, where lobate grain boundaries provide a rigid network in the matrix. An elastic consequence of matrix interconnectivity could be significant pressure heterogeneities being preserved on a thin section scale. Many conventional thermobarometric techniques are founded on a basis of chemical equilibration in metamorphic minerals being established at certain pressure and temperature conditions. If large pressure differentials persist, it could be detrimental to the obtainable accuracy in metamorphic petrology when using chemical systems.

Click to see figures:

Figure 6 Figure 7

PTD Evolution in Ductile Shear Zones

The Moine Supergroup (NW Scotland) and Sutlej Valley (Himalaya) have been highly studied areas in structural and metamorphic geology. Recent work integrating petrographic observations, pseudosection modeling, and microstructural/kinematic measurements have resulting in PTD path refinements. In particular, prograde decompression garnet growth in Scotland has significant implications on tectonic model refinements (Ashley et al., in prep). Current ongoing work is providing insight into the metamorphic evolution in these field sites. In addition, strain rate analysis refinements are being conducted using mix-fluid fugacity calculations, rather than assuming a pure H2O phase, allowing for better confidence in the historical stress-kinematic reconstructions.