Since I am an addicted reader of novels, the suggestions for active reading that I summarized in my last post sounded tedious and cumbersome to me when our teacher suggested them. Therefore I decided to work through one paper using those techniques here on this blog, because if I do it publicly, I will feel obligated to continue the process all the way through to the end, rather than giving up and returning to lazy reading techniques. If, at the end of this process it feels like the extra effort has been worth it, I shall let you know.
Today’s paper is Gordon et al. (2010)*. This paper was chosen for today’s reading because my PhD advisor suggested it and another article from the same issue of the journal as having structures similar to what I should be aiming at when I write the paper summarizing what I did for my PhD research. Therefore the questions I will keep in mind when reading this paper are:
1) What structure did they choose, and how effective do I feel it is in presenting their work? 2) How many different techniques did they use for this project, and how did they organize their presentation of these various techniques? 3) How effective is that organizational method? 4) Would another order be more appropriate? 5) Do they indicate how much more work they undertook in addition to the specific results they share? 6) Is there any indication as to how they selected these specific results? 7) How do their results and the presentation thereof lead to the conclusions they draw? 8) Do their results and the subsequent discussion convince me that their conclusions are appropriate? 9) Why or why not?
Step one in the active reading is simply to look over the entire thing. This is a 20 page document, the first 17 of which contain text, tables, and figures. The headings used in this article reduce to the following outline:
GEOLOGICAL OVERVIEW OF THE SKAGIT GNEISS AND ROSS LAKE FAULT
. Eastern margin of the Skagit Gniess
. Ross Lake Fault Zone
. Ruby Mountain and Elijah Ridge
PETROGRAPHY AND MINERAL CHEMISTRY
. Garnet amphibolite
. Metapelitic rocks
. . Ruby Mountain Metapelites
. . Elijah Ridge Metapelites
THERMOMETRY AND BAROMETRY
. Previous interpretations of Ruby Mt-Elijah Ridge tectonic history
. Re-evaluation of Ruby Mt Elijah Ridge tectonometamorphic history
The article contains 13 figures.
Figure 1 contains both a simplified geologic map of the region of study area and an annotated Google Earth image (the latter is in colour in the pdf version). The notes include details of sample locations, locations of geological units, and pressure temperature estimates.
Figure 2 is a closer-scale geologic map of just the fault zone region
Figure 3 shows a series of cross-sections across the region.
Figure 4 contains colour photomicrograph of thin sections of two samples
Figure 5 contains colour photomicrograph of thin sections of three samples
Figure 6 contains colour photomicrograph of thin sections of three samples
Figure 7 contains both a colour photomicrograph of one thin section and major element x-ray maps for the garnet in that thin section for Mn, Fe, and Mg (this garnet is obviously much richer in Fe than Mg or Mn)
Figure 8 contains both a colour photomicrograph of another thin section and major element x-ray maps for the garnet in that thin section for Ca, Mn and Fe, (this garnet has a core which is Ca-poor and a rim (nearly as thick as the core) which is Ca-rich—the core is richer in Mn than the rim. Both the core and rim contain a similar amount of Fe overall, but there is an Fe-poor region at the core-rim boundary, which could be related to the greater quantity of inclusions in that region (my observation, not what the caption said))
Figure 9 is a P-T diagram showing the estimates obtained for various samples plotting in a clump just above the ky-sil boundary in the range 600-800 C and 7-11 kbars. It also includes arrows to show the near-isothermal decompression they infer for these samples based upon mineral assemblages and textures.
Figure 10 contains two (colour) photomicrographs of the orthogneiss, showing two different grain sizes.
Figure 11 contains field photos illustrating intense constrictional fabrics to two different rock types from the region.
Figure 12 contains Muscovite 40Ar/39Ar age spectra for two different samples.
Figure 13 contains a map-view cartoon sketch of the transpressional step-over and duplex structures of the region.
Of the questions I asked myself at the beginning, I feel that just looking at the headings and figures permits me to answer the following:
1) They present an introduction and regional geology, followed by six different sections presenting each of their different types of results, followed by a discussion section where they first list previous interpretations of the area and then share how they feel their new data modifies those interpretations (Isn’t it funny how I can state that with confidence, even though I have yet to actually read the paper and so have no idea what their interpretation is, nor what the older interpretations might have been?)
2) The six techniques they used are geological mapping, petrography/mineral chemistry analysis, thermobarometric calculations, P-T paths, microstructural analysis, and geochronology, listed in that order. The order may well have been chosen because one must first do the field work and obtain the samples before anything else happens. The microstructural section could just as easily have come before the petrography/mineral chemistry section, but that work is essential for the geothermobarometric calculations, which, in turn, is essential to determine a P-T path. The age dating could have been presented at any point after the field work, unless 40Ar/39Ar technique requires information obtained in the petrography/mineral chemistry section.
3), 4) How effective is that organizational method? The organizational method looks logical thus far, I’d have to actually read the paper to see if it is truly effective and if another would have been more appropriate.
The remaining questions can’t be answered till I read the text itself. This post is now quite long enough, so I will take a break from “reading” this paper and share with you my progress to this point. Stay tuned for my paragraph by paragraph summaries of this paper, once I’ve done them.
*Gordon, S.M., Whitney, D.L., Miller, R.B., McLean, N., and Seaton, N.C.A., 2010, Metamorphism and deformation at different structural levels in a strike-slip fault zone, Ross Lake fault, North Cascades, USA: Journal of Metamorphic Geology, 28, 117-136.
2 days ago