Rock saws, epoxy, and stereonets: Creating a baseline to work with

The learning curves for this project haven proven to be steep this first week, but not nearly as steep as the grungy desert outcrop surface I had to scramble up to collect my samples in the first place.  The past 5 days in research have brought me face to face with a number of techniques and methods I’ve encountered in the literature over the past semester in preparation for this project, but am just now putting to use. A great deal of time this past week has been spent prepping my samples, while also familiarizing myself with the processes and practicing my methods.

Prep work consisted of glue and the rock saw. My samples are deformed glacial diamictite, a metamorphosed glaciogenic conglomerate that is prone to break apart when frequently handled because of the silty/clayey matrix. To combat this, I ignored my epoxy allergy and coated my samples in ~2mm of the glue with the intent to prevent fracturing when I passed them through the saw. These diamictites contain clasts of varying lithology, so cutting them open perpendicular to the foliation allows me access to both the types of clasts within the sample (with which I can later identify competency by), and the axes of maximum elongation Xand maximum shortening Z(necessary for quantifying deformation via strain analysis). So far, the epoxy has been fairly successful in preventing additional fracture to the rocks, but I could improve on the method by placing the coated, uncured samples in either a bell jar or another type of vacuum chamber to encourage the glue to hold in the pore spaces of the rocks.

Traditional strain analysis involves tools such as hyperbolic stereo nets, protractors/rulers, and an advanced calculus competency. While it’s certainly valuable to understand the process of obtaining results manually, computers can greatly expedite the process, and I don’t intend to take calculus anytime soon. I’ve learned to both manually and computationally render strain ellipses from the cut faces of my samples. I’ve used and modified the Mother of Rf/phi Analysis Spreadsheet (Chew, 2003) to process my raw data, and am confident in my understanding of what the majority of it means. I created Stereonets for each of my 6 outcrops, and was able to find the fold axis of a fold from my field note measurements. Adobe Illustrator has allowed me to efficiently take measurements

While my process is far from perfect, the practice is becoming more familiar and my large mistakes are spaced farther apart now than in the beginning of the week. I am far from an answer, but have values that make sense and that are shaping up nicely for a firm foundation.

 

Note: This is the post for the week of May 27-31, 2019

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