Remote Mapping and Analytical data integration: Coal Creek quartzite and Ralston shear zone, Colorado

Kevin H. Mahan (kevin.mahan@colorado.edu) and Michael G. Frothingham (michael.frothingham@colorado.edu), University of Colorado at Boulder

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Summary

This is a combination of an online mapping project (igneous and metamorphic terrain) and a subsequent module for group collaboration with associated analytical datasets (e.g., geochronology and microstructure). Rock types are Paleoproterozoic granitoids, quartzite, and schist, and the field area is located in the Front Range of Colorado. The mapping exercise could be done alone without the associated analytical datasets. Keyword search terms include Mapping, cross-section, 3D visualization, Mineralogy, Petrology, Structural Geology, Collaborative project, Geologic Interpretation, Data Management, Google Earth, and StraboSpot.

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Context

Audience

These activities are intended for use in an upper-level undergraduate field course for geology majors. At CU, the course for which I use this activity is one of several 2-credit advanced field courses from which our majors must choose at least two (but none are required individually).

Skills and concepts that students must have mastered

Students should have already been introduced to basic field methods. Ideally, students will have had an introduction to structural geology, mineralogy/petrology, and geochemistry, but it is conceivable to manage the activity in such a way that only one of the above courses would be a required pre-requisite. The basic structure is a km-scale synform of Coal Creek quartzite and schist structurally overlying Boulder Creek granodiorite, with one limb of the fold overprinted by the Ralston ductile shear zone. Outcrop-scale structures include relict bedding and local stretched-pebble conglomerate, multiple generations of foliation/schistosity, folds, axial planar foliation, mylonite, mineral and stretching lineations, and shear sense indicators.

How the activity is situated in the course

The mapping exercise (Part I), integration of analytical datasets (Part II), and report writing/presentations make up the bulk of a whole 2-credit course.

Activity Length

We estimate Part I mapping to take 4-5 days including introduction/instructions if conducted as part of an immersive, all day field course, and mapping as either individuals or in pairs with periodic virtual accompaniment by instructor(s). Part II, where small groups of students choose one from among several available datasets to integrate into the project, and present their integrated results should take another week. Part I (mapping) could be done without the rest.

Goals

Content/concepts goals for this activity

This module was designed to address the following learning outcomes, which are part of the list developed by the NAGT- and IAGD-sponsored Designing Remote Field Experiences project:

1- Design a field strategy to collect or select data in order to answer a geologic question.

2- Collect accurate and sufficient data on field relationships and record these using disciplinary conventions (field notes, map symbols, etc.).

3- Synthesize geologic data and integrate with core concepts and skills into a cohesive spatial and temporal scientific interpretation.

4- Interpret earth systems and past/current/future processes using multiple lines of spatially distributed evidence.

5- Develop an argument that is consistent with available evidence and uncertainty.

6- Communicate clearly using written, verbal, and/or visual media (e.g., maps, cross-sections, reports) with discipline-specific terminology appropriate to your audience.

7- Work effectively independently and collaboratively (e.g., commitment, reliability, leadership, open for advice, channels of communication, supportive, inclusive).

The basic goals of Part I are to provide students with an experience involving geologic mapping where they must design a mapping strategy and collective enough information to plot on a map and guide map construction, as well as recognizing numbers of deformation events, cross-cutting relationships, and relative timing relationships. Visualizing the basic three dimensional structure of the study area.

Higher order thinking skills goals for this activity

Part I provides a mapping exercise, but Parts II/III offer the opportunity for students to see how real science in a field area is commonly conducted. That is, it doesn't end with the map and cross-section, but rather samples and analytical data are commonly collected and integrated with the field observations as well.

For Part I, some station descriptions include quite a lot of information, so students must learn to recognize what is the most basic information needed to conduct the mapping portion of the exercise. For Part II, some students with appropriate structural geology background could choose to analyze the more complex field structural data, generating stereonets, and more cross-sections. Alternatively, they could choose one of several geochronology datasets, or a petrology dataset, or a microstructure dataset (including EBSD quartz data). The goal for this part of the course is to give students an opportunity to explore what is possible with additional laboratory analytical tools. This part is also envisioned as being conducted in small groups. Part III involves synthesizing the results from the analytical datasets with the basic field observations for a more wholistic understanding of the geological history of the field area. And providing a written report and oral presentation.

Other skills goals for this activity

For Part I, students will need to practice planning, time management and, if working in pairs, teamwork. For Parts II and III, data and time management, teamwork, and leadership, and oral and written communication will all be important.

Description and Teaching Materials

Part I - Mapping (Google Earth + StraboSpot). 1-Students select limited # stations per day from Google Earth tour , 2-request data from each station, 3-build map in StraboSpot (or on paper maps, not provided)

Part II - Small groups select 1 of several additional datasets to research and integrate with their field observations. Options include:
Field structure (fold geometry, SZ structure, X-sections).
Geochronology (U-Pb Zircon in granodiorite, detrital zircon in quartzite, or metamorphic monazite in the Ralston shear zone).
Microstructure (Optical images and a small EBSD dataset from quartzite mylonite).
Min/Pet (Optical images, Raman spectroscopy (Al2SiO5 polymorphs)).

Part III - Communicate, synthesize, written/oral presentations, covering concepts of overall structure, # deformation events, relative vs. absolute timing, P-T history, (± uncertainties). Several published papers are available for reading/discussion.


Materials provided for Part I (mapping)
1. Google Earth Web project called "Golden Gate mapping project." Link is here:
https://earth.google.com/web/@39.85688127,-105.37240525,2582.47057327a,2912.6031447d,30y,0h,0t,0r/data=MicKJQojCiExbWNCYXBSMnVvcXJFVS1zNVNyOVZDVkRFR25pdkh1cXA
Use this for an introduction to the field area, where one can take advantage of the 3-D feature provided by Google Earth and the higher quality satellite imagery. Students call also use this to supplement their strategic planning for mapping. There are 110 field stations and 9 View points. The viewpoints contain general photo perspectives of the field area. Click on them in the listing on the left, and the view will zoom to the 3-D perspective from which the photo was taken. Alternatively, one can save a KML file of this same project from within GEW, which can be viewed in Google Earth Pro, although the photos at the view points are not available.

2. A zipped Shapefile that contains all 110 station locations that can be uploaded to StraboSpot. Use this to pre-populate the 110 station locations as Spots (the file contains locations only). Students can then add data to the spots, and turn off the display of the ones that they do not use.

3. A Word document listing step-by-step instructions for getting started with StraboSpot, including how to load the above Shapefile, and some tips for setting up the mapping project in Strabo.

4. A zipped folder containing station descriptions and data (e.g., lithology, outcrop and structural descriptions, photos, sketches, and strike/dip and/or trend/plunge measurements). Some stations do not contain all of these components. Each station folder contains a Word document (.docx) and a pdf. Higher resolutions versions of any of the photos are available upon request from Mahan.

5. An excel (.xlsx) file with the same text for each station that is found in the individual station descriptions, and the structural measurements – for ease of use should digital stereonet construction be desired.

6. A pdf document with screenshots of draft geologic maps (several versions showing different Spot datasets) made from all stations, and summary stereonets of the basic structural components. In my version of the course, students will probably only work with about half of all of the stations for their map. Other versions of the geology in this locality are published and referenced below.

7. A blank pre-course assessment form as a Word document.

8. A blank station description request form as a Word document - students (or pair of students as mapping partners) fill out this form in order to justify their strategy for the next day's mapping.

9. An introductory document that provides some background motivation for why one might want to map the geology of Colorado's basement rocks, and some "working questions" to help guide the student's thinking while mapping. The full reference for the Tweto and Sims (1963) paper is given below.

Available and mostly published analytical datasets for Part II of the course activity include (full references in Resources section):

Metamorphic monazite geochronology and geochemistry from quartzite, schist, and granodiorite (X-ray maps, dates ±errors, geochemistry table) from McCoy (2001, MS thesis) and McCoy et al. (2005).

Detrital zircon U-Pb geochronology from quartzite and schist (dates ±errors, histogram plots, Excel spreadsheet) from Jones and Thrane (2012).

Igneous zircon U-Pb SHRIMP geochronology (dates ±errors in datatable, Concordia plots) from Premo and Fanning (2000).

Quartzite mylonite microstructure (Optical photos, EBSD dataset) from Ward et al. (2012).

Mineralogy/Petrology (Optical photos, some unpublished Raman spectra) from McCoy (2001) and McCoy et al. (2005) and Eric Ellison (CU Boulder, Raman spectroscopy).
GG_stations zipped shapefile (Zip Archive 7kB Jun3 20) 
Instructions for getting started with StraboSpot (Microsoft Word 2007 (.docx) 21kB Jun3 20) 

 
 

Pre-assessment.docx (Microsoft Word 2007 (.docx) 18kB Feb9 21)

Mapping_Station_Request_and_Justification_Form_GG_2021.docx (Microsoft Word 2007 (.docx) 14kB Feb9 21)

Intro and motivation for mapping Colorado's basement rocks.docx (Microsoft Word 2007 (.docx) 15kB Feb9 21)

Technology Needs

This activity used Google Earth and StraboSpot. Google Earth Web requires real-time internet access. StraboSpot can be used with either the Web version (requires real-time access) or the app for smartphones and pads. The detailed instructions are optimized for the Web version of StraboSpot.

Teaching Notes and Tips

We have taught this module twice now at CU. Once with 6 students and again with 10 students.

We start the students with a task to read and discuss a short paper that introduces some of the main aspects of Colorado's Proterozoic tectonic history but that don't immediately give away some of the ideas that are encountered in the specific mapping area. A good example paper is Tyson et al. (2002). The full reference is given below.

We recommend planning for the equivalent of 4 full (all day) mapping days. The first running of the course was in the summer so the remote mapping took 4 actual days. The second running occurred during a regular academic semester when students were taking other courses; in this case, we scheduled each "full map day" to occur over a period of 4 actual days (16 days in all). The students were grouped into pairs (mapping partners) and conducted the mapping and data requests as a team, although we required them to have their own StraboSpot account and build and turn in their own maps and cross-sections. In addition to a set of regularly scheduled class times where everyone attends, we also recommend scheduling separate and regular ~30 min "drop-in" meetings with each mapping team when you can "visit" individual outcrops (stations) together and help them process the information, build their Strabo database, and develop their maps. This mimics the instructor or TA moving about the field area during the day and periodically joining different mapping teams.

Assessment

Assessment for the module is addressed by several mechanisms. First, students are asked to fill out pre- and post-course forms that provide self-reported data on their degree of confidence with each of the 7 learning objectives identified in the course goals. The pre-course assessment also has a question that addresses some of the specific geological concepts that will be encountered in this activity, and it contains a list of targeted questions related to the analytical datasets, which are aimed at assessing the depth of understanding that students initially have with the utility of such datasets. These questions prompt for answers with prose and by numerical rating. A copy of this pre-course assessment is provided below. Second, during the mapping portion of the module (Part I), students are required to submit a form as part of their request for new station data for each new "day" of mapping. The form prompts for a brief description of the strategy and reasoning behind their next day of mapping, with considerations for physical access and time management, field safety, and geological reasoning. Specific requirements include a list of multiple working hypotheses based on their current map and ways that they plan to test them. The results of these forms (4 in all for the equivalent of 4 full days of mapping) can be used to track how well the students develop their understanding of the map relations over time and how comfortable they become with hypothesis testing. A copy of this form is also provided below. The third and final type of mechanism for assessment is the suite of assignments that are turned in for grading, which includes an exported "field notebook" from StraboSpot, draft and final geological maps, cross-sections, as well as the written and oral reports that integrate the analytical datasets.

References and Resources

McCoy, A. M., 2001, The Proterozoic ancestry of the Colorado mineral belt: Ca. 1.4 Ga shear zone system in central Colorado [M.S. thesis]: University of New Mexico, Albuquerque, New Mexico, 158 p.

McCoy, A. M., Karlstrom, K. E., Shaw, C. A., and Williams, M. L., 2005, The Proterozoic ancestry of the Colorado Mineral Belt: 1.4 Ga shear zone system in central Colorado, in Keller, G. R., and Karlstrom, K. E., eds., The Rocky Mountain region—an evolving lithosphere: Tectonics, geochemistry, and geophysics: Washington, D.C., American Geophysical Union Geophysical Monograph 154, p. 71–90.

Jones, J.V., III and Thrane, K., 2012, Correlating Proterozoic synorogenic metasedimentary successions in southwestern Laurentia: New insights from detrital zircon U-Pb geochronology of Paleoproterozoic quartzite and metaconglomerate in central and northern Colorado, U.S.A., Rocky Mountain Geology, v. 47, p. 1-35.

Premo, W. R. and Fanning, C. M., 2000, SHRIMP U-Pb zircon ages for Big Creek gneiss, Wyoming and Boulder Creek batholith, Colorado: Implications for timing of Paleoproterozoic accretion of the northern Colorado Province, Rocky Mountain Geology, v. 35, p. 31-50.

Tweto, O. and Sims, P.K., 1963, Precambrian ancestry of the Colorado Mineral Belt, Geological Society of America Bulletin, v. 74, p. 991-1014.

Tyson, A.R., Morozova, E.A., Karlstrom, K.E., Chamberlain, K.R., Smithson, S.B., Dueker, K.G., and Foster, C.T., 2002, Proterozoic Farwell Mountain-Lester Mountain suture zone, northern Colorado: Subduction flip and progressive assembly of arcs, Geology, v. 30, p. 943-946.

Ward, D., Mahan, K., and Schulte-Pelkum, V., 2012, Roles of quartz and mica in seismic anisotropy of mylonites, Geophysical Journal International, doi: 10.1111/j.1365-246X.2012.05528.x.



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