Metamorphic Studies

Faculty

Harold H. Stowell (Ph.D., Princeton 1987), Professor: Metamorphic Petrology, Geochronology, & Tectonics

Affiliated Scientists

Karen Parker (M.S., University of Alabama 2010), Geochronology, Thermobarometry, & Pressure-Temperature-time Paths

Students

Matthew Gatewood [Ph.D.]: Using Garnet Major element and Isotopic Zoning
as a tool to Evaluate the Scales of Equilibrium in Metamorphic Rocks and
the Rates of Rectonic Processes

Robert Holler [M.S.]: Metamorphism of the Wenatchee Ridge Orthogneiss,
Washington: Application of Sm-Nd and U-Pb Chronology and Phase Equilibrium
Modeling

Crystal Hout [M.S.]: Eclogite metamorphism, Fiordland, New Zealand

Jeffrey Madden [M.S.]:

Recent Graduates

Gerrit Bulman (B.S. Brown, 2000), M.S. 2005, Tectonic Evolution of the Labyrinth Mountain Area, Cascades Crystalline Core, Washington: Unraveling Intertwined Deformation, Intrusion and Metamorphism, currently CH2M Hill, FL

Ellen Stein, M.S. 2007, Origin and Significance of Plagioclase on Garnet Coronas, Nason Terrane, North Cascades, Washington, USA: Pseudosection Modeling and X-ray Computed Tomography

Matthew McKay M.S. 2011, Petrology and Samarium-Neodymium Geochronology of the Eastern Salmon River Belt, West Central Idaho: Timing of Island Arc Accretion and Tectonic Implications

Karen Parker M.S. 2010, Geochronology and P-T Conditions of Mid-to Lower Crustal Processes in a Cretaceous Magmatic Arc, Fiordland, New Zealand

Doug Tinkham (M.S. Illinois, 1997), Ph.D. 2002, MnNCKFMASH Phase equilibria, garnet activity modeling, and garnet samarium-neodymiumchronology: applications to the Waterville Formation, Maine, and south-central Nason terrane, Washington, currently Department of Earth Sciences Laurentian University Canada

Carlos Zuluaga (B.S. La Universidad Nacional De Colombia, 1993), Ph.D. 2004, Thermodynamic modeling applied to metamorphic processes in migmatites: an example form the Nason Ridge Migmatitic Gneiss (Cascades Core, WA), currently Department of Geociencias Ciudad Universitaria Edificio manuel Ancizar Colombia

Research:

Phase Equilibria: Pseudosections

Current research utilizes phase diagrams for specific bulk-rock compositions (pseudosections) to develop metamorphic P-T-t paths and better understand the dependence of phase equilibria on bulk rock composition. Pseudosections are constructed using the program THERMOCALC (Powell & Holland, 1988) and/or DOMINO (de Capitani & Brown, 1987), and the Holland and Powell (1998 & recent updates) internally-consistent thermodynamic database.

References

deCapitani, C., and Brown, T.H., 1987, The computation of chemical equilibrium in complex systems containing non-ideal solutions. Geochimica Cosmochimica Acta, v. 51, p. 2639-2652. Holland, T.J.B., and Powell, R., 1998, An internally consistent thermodynamic data set for phases of petrological interest: Journal of Metamorphic Geology, v. 16, p. 309-343.

Holland, T.J.B., and Powell, R., 1998, An internally consistent thermodynamic data set for phases of petrological interest: Journal of Metamorphic Geology, v. 16, p. 309-343.

Powell, R., and Holland, T.J.B., 1988, An internally consistent dataset with uncertainties and correlations: 3. Applications to geobarometry, worked examples and a computer program: Journal of Metamorphic Geology, v. 6, p. 173-204.

Pressure-Temperature-time Paths

Research emphasis is on determining the utility of pseudosections for estimating pressures and temperatures (P-T), and pressure-temperature-time (P-T-t) paths for metamorphic rocks. P-T estimates can be based on mineral assemblage stability fields estimated for P-T pseudosections and or the compositions of solid solutions plotted on the diagrams. Pressure and temperature estimation from pseudosections has several advantages over other thermobarometric methods:

1. the P-T conditions of mineral nucleation can be estimated from the core mineral composition of zoned minerals (e.g., garnet), and

2. mineral assemblage stability fields can precisely reflect conditions for a specific rock composition – especially when combined with thermobarometric estimates.

P-T-t paths are constructed from the core compositions of zoned minerals (e.g., garnet), pseudosection phase equilibria, and rim composition thermobarometry. Integration of geochronology with the P-T paths provides a means of constructing a quantitative path. Examples of this technique have been published in the Journal of Metamorphic Geology, Geological Society Special Publication 220, and American Mineralogist (see Stowell et al., JMG, 2001), and additional work is in progress. Recent work has investigated bulk rock fractionation during growth of zoned porphyroblasts. This research has included calculating the effects of garnet growth on phase equilibria in pelites (Zuluaga et al., AM 2005).

Quantitative P-T-t Paths from Integrated Thermodynamic Modeling and Metamorphic Textures: A Short Course Manual

P-T-t paths and pseudosections for pelitic rocks and quartzofeldspathic gneiss from the North Cascades, Washington

P-T-t paths and pseudosections for pelitic rocks from the Coast Mountains, southeastern Alaska

P-T-t paths and pseudosections for granulite orthogneiss from Fiordland, New Zealand

References

Stowell, H.H., Taylor, D.L., Tinkham, D.K., Goldberg, S.A., and Ouderkirk, K.A., 2001. Contact metamorphic P-T-t Paths from Sm-Nd Garnet Ages, Phase Equilibria Modelling, and Thermobarometry: Garnet Ledge, Southeastern Alaska, Journal of Metamorphic Geology, 19, p. 645-660.

Stowell, H.H. and Tinkham, D.K., 2003, Integration of Phase Equilibria Modelling and Garnet Sm-Nd Chronology for Construction of P-T-t Paths: Examples from the Cordilleran Coast Plutonic Complex, USA. Geological Society Special Publication 220, p. 119-145.

Stowell, H.H., Tinkham, D. K., and Zuluaga, C. A., 2005. Quantitative P-T-t Paths from Integrated Thermodynamic Modeling and Metamorphic Textures: A Short Course Manual. Cordilleran Section of the Geological Society of America. April 2005, 87 pp.

Zuluaga, C.A., Stowell, H.H., and Tinkham, D.K., 2005. The effect of zoned garnet on metapelite pseudosection topology and calculated metamorphic P-T paths. American Mineralogist, 90, p. 1619-1628.

Stowell, H.H., Bulman, G.R., Zuluaga, C.A., Tinkham, D.K, Miller, R.B., 2007. Mid-Crustal Late Cretaceous Metamorphism in the Nason Terrane, Cascades Crystalline Core, Washington, USA: Implications for Tectonic Models, in Hatcher, R.D., Jr., Carlson, M.P., McBride, J.H., & Martínez Catalán, J.R., eds., 4–D Framework of Continental Crust, Geological Society of America Memoir 200, p. 211-231.

Zuluaga, C.A., Stowell, H.H., 2008. Multidisciplinary approach to study migmatites: origin and tectonic history of the Nason Ridge Migmatitic Gneiss, Wenatchee Block, Cascades Crystalline Core, WA, USA, Earth Sciences Research Journal, 12, p. 235-265.

Stowell, H.H., Tulloch, A., Zuluaga, C.A., and Koenig, A., 2010, Timing and duration of garnet granulite metamorphism in magmatic arc crust, Fiordland, New Zealand: Chemical Geology, 273, p. 91-110.

Stowell, H.H., Bulman, G.R., Tinkham, D.K, Zuluaga, C.A., 2011. Garnet growth during crustal thickening in the Cascades Crystalline Core, Washington, U.S.A. Journal of Metamorphic Geology, 29, p. 627-647.

Stowell, H.H., Zuluaga, Boyle, A., C.A., Bulman, G.R., 2011. Garnet sector and oscillatory zoning linked with changes in crystal morphology during rapid growth, North Cascades, Washington. American Mineralogist, 96, p. 1354-1362.

Bulk Rock Compositional Variation in Pelites and Phase Equilibria

Research focuses on investigating the variation in phase equilibria for ‘typical’ pelite compositions with variation in bulk rock chemistry. In particular, variations in Al and Fe/Mg. Results for the Waterville Formation (Maine) and select pelite compositions from the literature were published in the online journal Geological Materials Research: Additional work includes: analysis of a suite of >300 Chiwaukum Schist samples (many bearing aluminum silicates) from the North Cascades of Washington and research on ‘triple point’ rocks from northern New Mexico.

References

Tinkham, D.K., Zuluaga, C.A., and Stowell, H.H., 2001. Metapelite phase equilibria modeling in MnNCKFMASH: The effect of variable Al2O3 and MgO/(MgO+FeO) on mineral stability. Geological Materials Research, 3, 1, p. 1-42.

Geochronology: Garnet Sm-Nd

The precise timing of thermal events is important for understanding the causes of metamorphism. For example, it is important to know if regional metamorphism is pre-, syn-, or post-plutonic in order to determine the relationship between intrusion of batholiths and temperatures that result in metamorphism.

Many geochronological techniques provide precise ages for either intrusion, or cooling through a temperature below which elemental diffusion is negligible. In addition, many minerals can preserve isotopic ratios [and ages] that predate metamorphic events. However, few commonly utilized methods are likely to directly date the growth of metamorphic minerals. Garnet Sm-Nd geochronology is one of the techniques that can provide ages that directly reflect the timing of garnet growth or garnet zone metamorphism.

Current research focuses on utilization of garnet Sm-Nd ages to determine: 1) the duration of garnet zone metamorphism, rates of garnet growth, and rates of heating, 2) the timing of metamorphic events in polyphase metamorphic rocks, 3) the age of regional metamorphic events and constrain the relationships between pluton emplacement, metamorphism, and crustal thickening.

References

Stowell, H.H., and Goldberg, S.A., 1997. Sm-Nd garnet dating of polyphase metamorphism: northern Coast Mountains, south-eastern Alaska. Journal of Metamorphic Geology, 15, 439-450.

Stowell, H.H. and Tinkham, D.K., 2003. Integration of Phase Equilibria Modeling and Garnet Sm-Nd Chronology for Construction of P-T-t Paths: Examples from the Cordilleran Coast Plutonic Complex, USA. in Vance, D. Muller, W., & Villa, I., eds. Geochronology: linking the isotopic record with petrology and textures. Geological Society Special Publication 220, p. 119-145.

Duration and Rates of Tectonic Processes

Precise ages for segments of individual crystals can provide important information about the rates of heating/cooling, loading/unloading, and growth of crystals. Such studies are currently underway for garnet crystals in the western metamorphic belt of the Coast Mountains (Alaska), Fiordland (New Zealand), and the Cascades Crystalline Core (Washington).

American Geophysical Union Poster 2005

Field-based Petrologic, Geochronologic, and Tectonic Research

Field-based research is currently underway in the western metamorphic belt of the Coast Mountains (Alaska), Fiordland (New Zealand), and the Cascades Crystalline Core (Washington):

Coast Mountains, Alaska
Fiordland, New Zealand
Cascades Crystalline Core, Washington
Salmon River Suture Zone, Western Idaho

The University of Alabama

Metamorphic Studies