garnet

New paper alert!

Another chapter of Zhen’s PhD thesis has just been accepted for publication in Contributions to Mineralogy and Petrology - congratulations!

In this work, Zhen investigated texturally and chemically sector-zoned garnet crystals in rocks from the Danba dome (eastern Tibetan Plateau, SW China), integrating petrographic analyses with XR-µCT, EPMA, LA-ICP-MS, EBSD, and phase equilibrium modelling. The results of this research suggest that abundant graphite likely played a pivotal role in changing fluid conditions and reducing the solubility of SiO2 to grow sector-zoned garnet, as well as impeding matrix coarsening. Development of sector-zoned core and dodecahedral faces of garnet may be related to rapid growth with changes in crystal morphology. Irregular sectors may have developed through fluid infiltration and local chemical adjustments.

Li ZMG, Gaidies F, Chen Y-C, Zhao Y-L, Wu C-M (2024) Petrogenesis of sector-zoned garnet in graphitic metapelite from the Danba dome, eastern Tibetan Plateau (SW China). Contributions to Mineralogy and Petrology. CTMP-D-24-00029

New paper alert: Mechanisms and durations of metamorphic garnet crystallization in the lower nappes of the Caledonian Kalak Nappe Complex, Arctic Norway

Congratulations to Thereza who just published the first chapter of her PhD thesis!

This paper outlines the results of detailed microstructural and compositional investigations of garnet populations, and how this information can be used to estimate the durations of metamorphic events:

Yogi* MTAG, Gaidies F, Heldwein* OKA, Rice AHN. Mechanisms and durations of metamorphic garnet crystallization in the lower nappes of the Caledonian Kalak Nappe Complex, Arctic Norway. Journal of Metamorphic Geology doi:10.1111/jmg.12766.

Microstructural analysis of a garnet population. See Yogi et al. (2024) for details.

Compositional analysis of a garnet population. Details in Yogi et al. (2024).

Polymetamorphism during the Grenvillian Orogeny in SE Ontario: Results from trace element mapping, in-situ geochronology, and diffusion geospeedometry

Our latest research unlocks the fascinating history of metamorphic rocks from the Grenville Province of SE Ontario. Using a variety of techniques, including high-resolution XR-µCT, LA-ICP-MS, and in-situ Lu-Hf geochronology, we are able to provide evidence for repeated metamorphic events during the Grenvillian Orogeny. Garnet crystals, which formed during these events, developed spectacular compositional and microstructural properties, and, once again, acted as the geological time capsules needed to gain insight into our planet’s past.

Read the preprint here, and the published version here:

Gaidies F, McCarron T, Simpson A, Easton RM, Glorie S, Putlitz B, Trebus K (2023) Polymetamorphism during the Grenvillian Orogeny in SE Ontario: Results from trace element mapping, in-situ geochronology, and diffusion geospeedometry. Journal of Metamorphic Geology, DOI: 10.1111/jmg.12745

Sneak preview of some recent research on elongated garnets with hexagonal symmetry!

Garnet is isometric, forming dodecahedral or trapezohedral crystals? Well, the ones shown in color below have hexagonal symmetry, with their long, three-fold rotation axes aligned at large angles to the rock matrix foliation.

Stay tuned for some recent results, integrating CT scanning, LA-ICP-MS mapping and in-situ Lu-Hf geochronology!

New THERIA_G version!

The influence of pressure on the energy barrier of multi-component diffusion in garnet when using the Chakraborty and Ganguly (1992) dataset has been slightly underestimated in previous versions of THERIA_G. The updated version (available for MacOS here; PC version will be added soon) rectifies this. Thanks to Hugo Dominguez (PhD student @unibern with @PierreLanari) for pointing this out!

#opensource #Theria_G

Modelling diffusion in garnet

Interested to model diffusion in garnet using a simple MATLAB script? The full multi-component case in 3D is available here. Please don’t judge: it’s the very first code I had written many years ago. But maybe it’s still useful for you?

diffuseo9.m is a MATLAB script designed to simulate multi-component diffusion (Mn, Fe, Mg, Ca) in garnet at a constant pressure, temperature, and fO2 assuming that the rim composition of garnet is fixed during the diffusion (open system). The kinetic data are those of Chakraborty and Ganguly (1992) with the option to modify fO2; by default, equilibration with graphite is assumed. Input is a compositional profile (core to rim), with the distance data (in cm) contained in vector Xnodecm, and the corresponding compositional data in the vectors Xmn, Xfe, and Xmg. Output from Theria_G (e.g., garnet_gen001.txt) can be used as input (and is included as example). However, other input can also be used if the script is adjusted.

Run the script and enter the required information into the Command Window (temperature, pressure, fO2, duration of diffusion). Also, when requested by the script, specify in the Command Window the spacing between isochrones to be plotted, as well as the size of the time step for the simulation. Ideally, the size of the time step should not exceed the number given. However, it is advisable to start the modelling with larger time steps to obtain first estimates quickly, and to decrease these time steps to the size given for final results.

This MATLAB script creates the files spss_profiles.mat, alm_profiles.mat, grs_profiles.mat, and py_profiles.mat which can be edited with text editors and spreadsheet software. These files contain the calculated compositional profiles after diffusion, with the first column containing the duration of diffusion (in years) and the first row containing the radius (in cm). The files will be replaced during each run of this script.

This model is part of Theria_G (Gaidies et al., 2008), so please refer to it if this script turns out to be useful for you. Happy modelling!

Update (June 2022):

Some people have expressed an interest to use this multi-component diffusion script in their teaching, so I updated it a little (diffuse_oMC.m). I also added a script to model the 1-component case (diffuse_o1C.m). Both scripts can be found here: diffuse_o.zip. The 1C model allows to quickly account for the influence of pre-exponential constant and activation energy, which may be useful when testing proposed Y,REE diffusion data. As always: feedback and questions are welcome.

Conditions, timing and rates of metamorphism of the Snowcap assemblage, west‐central Yukon

Happy to announce our new JMG paper on the conditions, timing and rates of metamorphism of the Snowcap assemblage. With former student Yannick Morneau, and an awesome team from the @GSC_CGC, including @dpettsy, Simon Jackson, Alex Zagorevski, and Jim Ryan!

LA_ICP_MS copy.png

JMG Early Career Research Paper Prize to former team member Dr. Freya George

GeorgeGaidies2020-copy.png

According to the Journal of Metamorphic Geology, “The research presents a comprehensive set of observations, acquired through a state‐of‐the‐art multidisciplinary approach, on the 3D microstructural features, chemistry and compositional zoning of garnets in metapelites from an inverted Barrovian sequence in the Sikkim Himalaya. The excellent petrological characterization and careful observations, complemented by nice and self‐explaining figures, are set in the context of other minerals, bulk rock composition and texture. The results are used to model the process of garnet growth at an extreme level of detail, allowing the discussion of the potential tectonic significance of post‐kinematic porphyroblasts in strongly segregated matrices.”

Dr. George is currently a research fellow at Johns Hopkins University (Baltimore, USA).

Running Theria_G in batch mode

Running multiple Theria_G simulations in batch mode is a great way to save time when you want to systematically test how variations in input data (e.g., thermodynamic models of phases, chemical composition of system, P-T-t path, diffusion parameters, CSD of garnet, etc.) influence the simulation results. Your computer can run such a batch job for you!

An example of how to set this up using the Theria_G compilation provided here, is given below. Let me know if you have any questions!

  1. Create a new folder for each case scenario you want to model. In the example given here, I wanted to test three different scenarios, and so I created the subfolders Scenario1, Scenario2, and Scenario3 (of course, you can use different names for these folders if you wish).

    If you use a Windows PC, the paths for the subfolders would be:

    C:\TheriakDominoWIN\GeochemSoc2020\Working\Scenario1
    C:\TheriakDominoWIN\GeochemSoc2020\Working\Scenario2
    C:\TheriakDominoWIN\GeochemSoc2020\Working\Scenario3

    The respective paths for MacOS would be:

    /Users/fredsmacbookpro/TheriakDominoMAC/GeochemSoc2020/Working/Scenario1
    /Users/fredsmacbookpro/TheriakDominoMAC/GeochemSoc2020/Working/Scenario2
    /Users/fredsmacbookpro/TheriakDominoMAC/GeochemSoc2020/Working/Scenario3

    where “fredsmacbookpro” is your Home Directory.

  2. Now make sure to put into each of these subfolders the Theria_G input files for each scenario: THERIN.txt, theriag_CSD.txt, theriag_DIF.txt, theriag_PTt.txt. Don’t forget to include the database file. In this example, I used ds5_5.txt in Scenario1 and JUN92bs.txt in Scenario2, but the other input files are identical. Scenario3 differs from Scenario1 and Scenario2 by the heating rate defined in theriag_PTt.txt, and it uses the database ds5_5.txt.

  3. Using a simple text editor (e.g., Notepad, TextEdit), create the file input.txt and add a copy of it into each scenario subfolder. This file contains the name of the database you want to use in each modelling scenario. It is important that input.txt contains two lines, and that the second line is empty.

    So, in this example, the content of input.txt in the Scenario1 folder is

    ds5_5.txt

    and input.txt in the Scenario2 folder looks like

    JUN92bs.txt

    input.txt in the Scenario3 folder is identical to input.txt in the Scenario1 folder.

  4. Now create the batch file.

    On a Windows PC, use Notepad and create a file with the following content:

    cd C:\TheriakDominoWIN\GeochemSoc2020\Working\Scenario1
    theriag<input.txt
    cd C:\TheriakDominoWIN\GeochemSoc2020\Working\Scenario2
    theriag<input.txt
    cd C:\TheriakDominoWIN\GeochemSoc2020\Working\Scenario3
    theriag<input.txt

    Make sure that the last line in this file is empty. Save this file as theriag_job.bat and put it into the folder

    C:\TheriakDominoWIN\GeochemSoc2020\Working

    With MacOS, use TextEdit and create a file that contains the following lines:

    cd /Users/fredsmacbookpro/TheriakDominoMAC/GeochemSoc2020/Working/Scenario1
    theriag<input.txt
    cd /Users/fredsmacbookpro/TheriakDominoMAC/GeochemSoc2020/Working/Scenario2
    theriag<input.txt
    cd /Users/fredsmacbookpro/TheriakDominoMAC/GeochemSoc2020/Working/Scenario3
    theriag<input.txt

    Again, make sure to replace “fredsmacbookpro” with your Working Directory. Also note that the last line needs to be empty. Save the file as theriag_job and put it into the folder

    /Users/fredsmacbookpro/TheriakDominoMAC/GeochemSoc2020/Working

    where ”fredsmacbookpro” is your username.

    Now, open Terminal, enter “dom” into the console window, and hit the return key. Then type

    chmod a+x theriag_job

  5. You are now ready to run the Theria_G simulations in batch mode.

    On a Windows PC, use File Explorer to go into the folder

    C:\TheriakDominoWIN\GeochemSoc2020\Working

    and double-click the ”start.bat” file. This will open a console window. Enter theriag_job and hit the return key.

    Using MacOS, open Terminal, type ”dom” into the console window, and hit the return key. Now enter theriag_job and hit return again.

  6. The Theria_G simulations will now run one after the other, with the output files generated in each scenario subfolder.

Online workshop of the Geochemical Society on the PTt trajectories of metamorphic processes

Interested in the PTt trajectories of metamorphic processes? Want to know how to quantify them? Check out this @geochemsoc Online Workshop organized by Shah Wali Faryad (Prague), Sumit Chakraborty (Bochum) and myself! https://geochemsoc.org/events/online-workshops/ptt-trajectory-metamorphic-processes

#Perple_X #Theriak-Domino #Theria_G