Integrating Geophysics and Geochemistry to Understand Tectonics

Gros Morne National Park, Newfoundland, Canada

William Shinevar

NSF EAR Postdoctoral Fellow

University of Colorado, Boulder

About Me

My research focuses on understanding the chemical and physical evolution of continental and oceanic lithosphere over different periods of Earth history. In particular, I am interested in interpreting geophysical data sets, especially seismic wave speed and heat flow, in terms of geochemical and geological processes using interdisciplinary methods like thermodynamic modelling.

Download my CV.

Interests

Geophysics
Petrology
Crustal Formation and Evolution
Rheology
Tectonics

Education

PhD in Geophysics, 2021

MIT/WHOI Joint Program
BS in Geophysics, 2015

Brown University
BA in German Studies, 2015

Brown University

Featured Article

WJ Shinevar, O Jagoutz, MD Behn

August, 2022 Published in Geochemistry, Geophysics, Geosystems

WISTFUL: Whole-Rock Interpretative Seismic Toolbox for Ultramafic Lithologies

To quantitatively convert upper mantle seismic wave speeds measured into temperature, density, composition, and corresponding and uncertainty, we introduce the Whole-rock Interpretative Seismic Toolbox For Ultramafic Lithologies (WISTFUL). WISTFUL is underpinned by a database of 4,485 ultramafic whole-rock compositions, their calculated mineral modes, elastic moduli, and seismic wave speeds over a range of pressure (P) and temperature (T) (P = 0.5–6 GPa, T = 200–1,600°C) using the Gibbs free energy minimization routine Perple_X. These data are interpreted with a toolbox of MATLAB® functions, scripts, and three general user interfaces: WISTFUL_relations, which plots relationships between calculated parameters and/or composition; WISTFUL_geotherms, which calculates seismic wave speeds along geotherms; and WISTFUL_inversion, which inverts seismic wave speeds for best-fit temperature, composition, and density. To evaluate our methodology and quantify the forward calculation error, we estimate two dominant sources of uncertainty: (a) the predicted mineral modes and compositions, and (b) the elastic properties and mixing equations. To constrain the first source of uncertainty, we compiled 122 well-studied ultramafic xenoliths with known whole-rock compositions, mineral modes, and estimated P-T conditions. We compared the observed mineral modes with modes predicted using five different thermodynamic solid solution models. The Holland et al. (2018, https://doi.org/10.1093/petrology/egy048) solution models best reproduce phase assemblages (∼12 vol. % phase root-mean-square error [RMSE]) and estimated wave speeds. To assess the second source of uncertainty, we compared wave speed measurements of 40 ultramafic rocks with calculated wave speeds, finding excellent agreement (Vp RMSE = 0.11 km/s). WISTFUL easily analyzes seismic datasets, integrates into modeling, and acts as an educational tool.

WJ Shinevar, O Jagoutz, JA VanTongeren

April, 2021 Published in Journal of Petrology

Gore Mountain Garnet Amphibolite Records UHT Conditions: Implications for the Rheology of the Lower Continental Crust during Orogenesis

Our results on peak metamorphic P–T conditions based on thermobarometry, diffusion models, and thermodynamic modelling indicate that the Gore Mountain Megacrystic Amphibolite (GMGA) formed at ultrahigh-temperature (>900 °C) conditions (P = 9–10 kbar, T = 950 ± 40 °C), significantly hotter than previously estimated. Diffusion models pinned by nearby cooling ages require the GMGA to initially cool quickly (9·1 °C Ma–1), followed by slower cooling (2·6 °C Ma–1).

Posts

Outreach at Blue Mountain Elementary School

Scientific outreach is an essential part of being a geoscientist, which is why I have been working with CU Science Discovery to educate K-12 students on geology! A few weeks ago in early March 2022, I spent a day teaching 1st and 2nd graders at Blue Mountain Elementary School in Longmont, CO.

Last updated on Mar 22, 2022 1 min read

Outreach at Blue Mountain Elementary School

Research and Code

Southern California Thermal Model

This link will take you to the SCEC website which hosts the 1D/diffused 2D steady-state geotherm model code used in Shinevar et al. (2018).

WISTFUL (Whole Rock Interpretative Seismic Toolbox For Ultramafic Lithologies)

This MATLAB toolbox allows for the interpretation of mantle seismic wave speed in terms of composition and temperature. See Shinevar et al. (2022) for more details!

Lower Crustal Rheology

Lower crustal rheology is important to understand crustal deformation and post-seismic stress transfer for earthuqakes, vital to better understand earthquake risk in tectonically active regions! Lower crustal rheology is dependent on many parameters: temperature, pressure, strain rate/stress, mineral assemblage/whole-rock composition, water content, and grain size!

Spherical Garnet Diffusion Model

The linked github repository includes a finite-difference multi-component garnet diffusion model for a radially symmetric sphere using the garnet diffusivities from Chu and Ague (2015) used in Shinevar et al. (2021).

Publications

WJ Shinevar & V Schulte-Pelkum (2023). Cold Tibetan Lower Crust from the Eclogite-Granulite Seismic Thermometer. submitted to Geology.

Cui, Shinevar, Guo, Xu, Zhang, & Jin (2023). Geophysical-Geochemical Modeling of Deep Crustal Compositions: Examples of Continental Crust in Typical Tectonic Settings and North China Craton. Journal of Geophysical Research: Solid Earth.

DOI

Shinevar, Golos, Jagoutz, Behn, & Van der Hilst (2023). Mantle Thermochemical Variations beneath the Continental United States Through Petrologic Interpretation of Seismic Tomography. Published in Earth and Planetary Science Letters.

Cite DOI

WJ Shinevar, O Jagoutz, MD Behn (2022). WISTFUL: Whole-Rock Interpretative Seismic Toolbox for Ultramafic Lithologies. Published in Geochemistry, Geophysics, Geosystems.

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WJ Shinevar, O Jagoutz, JA VanTongeren (2021). Gore Mountain Garnet Amphibolite Records UHT Conditions: Implications for the Rheology of the Lower Continental Crust during Orogenesis. Published in Journal of Petrology.

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L Guo, O Jagoutz, WJ Shinevar, HF Zhang (2020). Formation and composition of the Late Cretaceous Gangdese arc lower crust in southern Tibet. Published in Contributions to Mineralogy and Petrology.

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WJ Shinevar, HF Mark, F Clerc, EA Codillo, JGong, JA Olive, SM Brown, PT Smalls, Y Liao, VLe Roux, MD Behn (2019). Causes of oceanic crustal thickness oscillations along a 74‐M mid‐atlantic ridge flow line. Published in Geochemistry, Geophysics, Geosystems.

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WJ Shinevar, MD Behn, G Hirth, O Jagoutz (2018). Inferring crustal viscosity from seismic velocity: Application to the lower crust of Southern California. Published in Earth and Planetary Science Letters.

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WJ Shinevar, MD Behn, G Hirth (2015). Compositional dependence of lower crustal viscosity. Published in Geophysical Research Letters.

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Contact

wshinevar@gmail.com
Benson Earth Sciences, 2200 Colorado Ave, Office 465, Boulder, CO 80301
Office Hours for Summer 2022 course GEOL1010 TBD