Igneous and Metamorphic Petrology
Igneous and Metamorphic Petrology happened to be a reprise of Geochemistry for the first couple weeks, with a solid review of Bowen's reaction series, the layers of the Earth and of the three major plate tectonic margins. I did however begin to better appreciate that tectonic motion is strongly tied to mantle convection and my first introduction to thermodynamics as they apply to earth systems was a refreshing change from the more elementary chemistry and physics explanations I had received in college. Our textbook for the class Principles of Igneous and Metamorphic Petrology 2nd Edition by John D. Winter is really a great reference and was the first geology text I wanted to make sure I kept.
My main take away from the course however was how igneous and metamorphic textures of minerals within a rock aid in determining the petrogenetic history of that rock. Phase and Ternary diagrams were also used to their full effect in this class, and these really helped me to understand the basics of the processes occurring within magma chambers during crystallization, melting, and recharge events. Overall though, it was nice to actually deal with rocks in hand sample (even if we did get a bit sick of basalts) and to use thin sections and to find which skills we acquired in optical mineralogy were most useful was also a thrill.
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| Mafic enclave within rhyolitic or dacitic rock in Cleophus Canyon, near Ft. Selden, NM. Access is limited since there are petroglyphs within the area as well. |
Sed/Strat was a significant curve ball for me and I did not start out strongly in the class. We began the course by learning about carbonate rocks of every basic sort and I had an exceptionally difficult time estimating the percentage of matrix each rock had. Once I had a decent handle on grain and matrix estimation I did fairly well in the class. I enjoyed thinking about sediment transportation in various environments and the sedimentary structures / bedforms that characterize each environment.
I took my first measured section in this class outside of La Luz, NM and learned about the complexities of deciding how best to depict and correlate that section. I struggled (and probably still aren't comfortable) with the intricacies of sequence stratigraphy and learned that seismic interpretation is also not my forte. I did enjoy the well log assignments we did in the class, and isopach maps were also fun to interpret and use.
One of the most memorable part of the class however was reading the short book The Nature of the Stratigraphical Record by Derek V. Ager which was a great complimentary text to our first introductions to sedimentology and stratigraphy. Among other concepts, Ager establishes and defends his theory that the bulk of the geological record appears to be preserved remains of catastrophic events which occur irregularly but within uniformitarian conditions. I highly recommend reading the book if you can borrow or easily purchase it, since it so eloquent and yet humorous in its treatment of the geologic record.
Structural Geology
I found in structure what I consider to be a geologists butter to a petrology and sedimentology bread. We learned about the finer points of stress, strain, and shear as well as the bookkeeping methods used to interpret what a rock has experienced since deposition. I found Mohr's circles to be neat and for a time geometry had returned to being useful. We learned more on metamorphic fabrics than we did in Petrology, and in this class I finally began to appreciate the complexities of folds and more importantly of faults. This class was the first exposure I had to the physical aspects of thrust processes, the typical geometries thrusted rocks take, and the complimentary basins that form from the thrusting.
Possibly even more important though, this class introduced the first legitimate geologic map work we had to do. I took my first strike and dip for this class, made my first scaled cross section, and learned to appreciate the "Rule of V's" in the field and on maps. However, an assignment where we were required to hand record more than one hundred strikes and dips and plot them by hand onto a stereonet led me to have a slight distaste for any work with stereonets.
Isotope Geochemistry
Isotopes began, like Geochemistry and Petrology, with an introduction to the nucleosynthesis, the different layers of the earth, and a brief review of the tectonic margins. Then we learned about the mass and temperature dependence of fractionation of isotopes, expressed as vibrational speed differences which determine bonding and other physical effects which can separate isotopes of the same element from one another. I'll remember that so well because we had to dance at different speeds relative to our neighbors to understand how we would fractionate from one another. We then went over the general behavior of Rb, Sr, Sm, Nd, U, Th, and Pb in earth systems (restite versus melt partitioning of igneous systems, mobility in oxidized systems, etc.). We also briefly went over K-Ar isotopes and the very basics of U-series disequilibrium. This class also had a required lab project and paper to write by the end of the semester, and it was very hectic to get enough data and paper written by the deadline but it was nice to do more work on Valles Caldera. Our coverage of the stable isotopes were a little heavy on oxygen, but I feel I learned enough to adapt to any other stable isotope systems thrown my way with a little effort and thought.
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| Leucocratic banding in a Proterozoic amphibolite or gneiss from the Caballo Mountains. The contact aureole was well expressed in our trip area. |
Cartography & GIS
This was a class I had high expectations for. The enrollment was extremely high for a non-general elective and I had heard from some peers that it was a difficult course. However, difficult and time consuming are not the same to me and I did not have any trouble academically in the course. We learned largely about how to construct a serviceable map and how to operate the major functions in ArcGIS. I was hoping to get more into the geodesy side of cartography and at least learn a bit about projection systems as they relate to geodetic ideas, but we only briefly addressed these topics. I was also hoping to see more scientific data in our maps, but beyond a very interesting map with well water data we did mostly social and political maps. I learned a fair amount and it was an informative class but it did not mesh well with my expectations and so it left me wanting. I did however get reminded of this part of a West Wing episode which was probably worth the cost of admission.-----------------------------------------------------------------------------------------
Overall, it was a great semester and I learned more in this semester than I have in any other since my acceptance to NMSU. I am certain I will look back on the Fall of 2010 as the semester when I could say: "By then I was sure I wanted to be a geologist".
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