Rock and Mineral Physics Lab
University of Minnesota
Dept of Geology & Geophysics


Jake Tielke

Ph.D. Candidate
Rock & Mineral Physics Lab
Department of Earth Sciences
University of Minnesota

310 Pillsbury Drive SE
Minneapolis, MN 55455

Email: tielk003 at umn.edu



Research Interests

Deformation of Olivine Single Crystals at Lithospheric Temperatures

Collaborators: David Kohlstedt (advisor), Mark Zimmerman, Amanda Dillman

Olivine is the most abundant and (arguably) the weakest mineral in Earth's upper mantle and therefore largely controls the rheological behavior of this region of Earth's interior. Many experiments have been carried out to study the rheological properties of olivine at asthenospheric temperatures. However, relatively few investigations have focused on characterizing the mechanical properties of olivine at lithospheric temperatures. Furthermore, recent experiments carried out in our lab suggest that extrapolation of flow laws from olivine deformed at asthenospheric temperatures to lithospheric temperatures results in an overestimation of olivine viscosity. Our goal is to use mechanical data and Fourier transform infared spectroscopy (FTIR) analyses to derive flow laws that describe the strain-rate of olivine crystals in different orientations as a function of stress, hydrogen concentration, silica activity, and temperature.

We start with single crystals of San Carlos olivine (left), which are then oriented (center) using electron backscatter diffraction (EBSD), and cut into rectangular prisms  (right).

The oriented crystals are surrounded by buffering material and placed in a nickel capsule. The capsule is then positioned between ceramic pistons inside an iron sleeve (left). Deformation is carried out in a series of constant stress steps at high temperature in a gas-medium deformation apparatus. After deformation (right), FTIR analyses are used to measure hydrogen concentration and dislocation structures are observed using optical and electron microscopy.


High Strain Deformation of Gabbroic Rocks

Collaborators: David Kohlstedt (advisor), Mark Zimmerman, Lars Hansen

Rocks that are rich in plagioclase and pyroxene dominate much of the crust of terrestrial planets such as Venus. In order to more fully characterize the strength of the crust of terrestrial planets, we are carrying out high-strain deformation experiments on Columbia diabase. Our goal is to derive flow laws that describe the rheological properties of these rocks under steady-state conditions. By deforming the rocks to high strain, we can investigate the influence of grain size and fabric development on the mechanical properties of crustal rocks.

Diabase_Dogbone

We drilled cores of dehydrated Columbia diabase with reduced diameter sections (left). This "dogbone" geometry allows us to concentrate strain in a small section while keeping friction high on the edge on the sample so that it can be deformed in torsion (middle). Microstructural analyses of deformed samples (right) confirms that all of the strain occurred in the reduced diameter section and was associated with significant grain size reduction and fabric development.


Use of Electron Backscatter Diffraction to Determine Paleostress from Calcite Deformation Twins

Collaborators: Mike Terry (advisor), Edward Duke, Haoran Xia, John Craddock, Richard Groshong

Calcite, which is one of the most abundant and widely distributed minerals in Earth's upper crust, primarily deforms by generation of twin lamellae at low temperatures and pressures. This deformation mechanism provides an unique opportunity for understanding the state of stress in the geologic past. By analyzing the orientation and crystallographic relationships between host calcite crystals and their twin lamellae, it is possible to determine the orientation and magnitude of stress in Earth's past. These data can be used to gain insight into tectonic processes such as mountain building events. Previous studies of calcite deformation twins relied on using optical microscopes to make crystallographic measurements of deformed calcite. Working at South Dakota School of Mines and Technology, we used a scanning electron microscope with EBSD to significantly improve the accuracy of crystallographic measurements used in calcite deformation twin analyses.

In optical micrographs (left), calcite twins appear as thin linear features within larger calcite grains. We use EBSD to collect orientation data (middle) from calcite grains which are used to construct orientation maps (right) of calcite-rich rocks.

Once orientation data are collected from a large number of grains in a sample, we process the data in a program we developed (left), which can be used to determine the orientation of paleostress in the sample (right).


Alkalic Volcanism in Central Mongolia

Collaborators: Brennan Jordan (advisor), Karl Wegmann, Bruce Idleman, Brian Kastl, Javkhlan Otgonhuu

Alkalic volcanism has occurred intermittently in central Asia, including regions of Russia, China, and Mongolia, throughout the Cenozoic Era. Volcanic deposits in central Mongolia are similar in nature and timing to other deposits found throughout central Asia. In order to evaluate the magmatic origin and magmatic evolution of Cenozoic volcanism in central Mongolia, and its relation to the larger central Asian volcanic province, we conducted a detailed study in the context of a Keck Geology Consortium undergraduate research project. Fieldwork was carried out in the central Hangay Mountains.

Fieldwork involved mapping volcanic structures (left) and collecting samples for laboratory analyses, which sometimes required unique transportation methods (right) (Photo Credit: Brennan Jordan).


Laboratory analyses included petrographic analyses (above), x-ray fluorescence spectrometry, inductively-coupled plasma mass-spectrometry, and Ar/Ar dating. These data were used in melt generation and mass balance models to investigate the composition, depth, and degree of partial melting in the magma source region and the processes involved in magmatic evolution.


Education

Ph.D. Candidate, Geophysics, University of Minnesota (Advisor: David Kohlstedt)

M.S. Geology and Geological Engineering, 2010, South Dakota School of Mines and Technology (Advisor: Michael Terry)

B.S. (honors) Earth Science, 2008, University of South Dakota (Advisor: Brennan Jordan)



Teaching Assistantships

Fluid Earth Dynamics Lab (UMN), Fall 2014

Structural Geology Lab (SDSM&T), Spring 2010

Petrology Lab (SDSM&T), Fall 2009

Structural Geology Lab (SDSM&T), Spring 2009

Petrology Lab (SDSM&T), Fall 2008


Presentations, Theses, and Publications

Tielke, J.A., Hansen, L.N., and Kohlstedt D.L., 2015, Observations of grain-size sensitive power-law creep of olivine aggregates over a large range of lattice-preferred orientation strength, submitted to Journal of Geophysical Research: Solid Earth. 

Tielke, J.A., Hansen, L.N., and Kohlstedt D.L., 2013, The role of grain boundary sliding in deformation of olivine as determined from calculations of plasticity for experimentally deformed aggregates, Deformation, Rheology, and Tectonics Conference. 

Tielke, J.A., Zimmerman, M.E., Dillman, A.M., and Kohlstedt D.L., 2012, Direct shear of olivine single crystals under anhydrous conditions: implications for lattice preferred orientation and seismic anisotropy in the lithospheric mantle, American Geophysical Union, Fall Meeting. 

Tielke, J.A., Zimmerman, M.E., and Kohlstedt D.L., 2012, The influence of hydrogen content on the viscosity of olivine single crystals under lithospheric conditions, Lunar and Planetary Science Conference, Spring Meeting.

Tielke, J.A., Zimmerman, M.E., and Kohlstedt D.L., 2011, The effects of silica activity, water content, and temperature on the viscosity of olivine single crystals: insight into the rheological behavior of the lithospheric mantle, American Geophysical Union, Fall Meeting.

Tielke, J.A., 2010, Development and application of a method for determining paleostress from calcite deformation twins using electron  backscatter diffraction [M.S. thesis]: Rapid City, South Dakota School of Mines and Technology, 133 p.

Tielke, J.A., Terry, M.P., and Lisenbee, A.L., 2010, Examining the paleostresses responsible for the Black Hills Uplift through analysis of calcite deformation twins using electron backscatter diffraction: Geological Society of America Abstracts with Programs, Vol. 42, No. 3, p. 50.

Tielke, J.A., 2008, Stratigraphy of Miocene lavas of the Hangay Mountains, Mongolia: Implications for magmatic origin, magmatic evolution, and orogeny [honors thesis]: Vermillion, University of South Dakota, 76 p.

Tielke, J.A., Terry, M.P., Duke E.F., Craddock J.P., Xia, H., Lui, J., and Groshong R.H., in prep, Determining strain from calcite twin lamellae using electron backscatter diffraction, for submission to Journal of Structural Geology.

Tielke, J.A., Kastl, B.C., and Jordan, B.T., 2007, Origin and evolution of Tertiary Lavas of the Hangay Mountains, central Mongolia:  Geological Society of America Abstracts with Programs, v. 39, n. 6, p. 387.

Tielke, J.A., Kastl, B.C., Otgonhuu, J., and Jordan, B.T., 2007, Genesis and evolution of Tertiary Lavas of the central Hangay Mountains, Mongolia: Keck Symposium, v. 20, p. 14-24.

Tielke, J.A., Jordan, B.T., Kastl, B.C., and Otgonhuu, J., 2007, Petrogenesis of Tertiary plateau lavas of the Hangay Mountains, central Mongolia: National Conference on Undergraduate Research, Abstract, v. 21, p. 96.