U/Pb Dating from zircon grains near Morgan Valley, UT
Summary
Students use real U/Pb data from zircon grains to determine the best age for field samples. Students learn about Concordia Diagrams to determine if ages from zircon grains are true. Students look at the spread of ages within a sample to determine if the sample is detrital or volcanic. Students then determine the rate of sedimentation and the source of the volcanic grains. This activity gives students a background in real scientific techniques used to collect dating data, and allows students to work with real data.
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Context
Audience
Undergraduate (typically sophomores) required course in geology
Skills and concepts that students must have mastered
- Understand the basics of basin and range
- Understand the basics of fluvial transport
- Have covered major North American orogenies
How the activity is situated in the course
This activity is done in-class over two 50-minute class periods.
Goals
Content/concepts goals for this activity
- Introduce students to scientific tools and techniques used to collect age data
- U/Pb dating systems
Higher order thinking skills goals for this activity
- Data analysis
- Hypotheses of sedimentation origin
Skills goals for this activity
- Working with data sets
- Simple map reading
- Working in groups
- Working with local data
Description and Teaching Materials
1. PowerPoint for day 1 Walks through the location of the Wasatch fault and discusses U/Pb dating and how we get to those ages
2. Data for the samples (this data is reduced to only give students' ages, Concordia, and only 30 grains rather than 300 grains per sample)
3. Sample ages and locations worksheet
4. Sedimentation Worksheet
5. Volcanic source worksheet
PowerPoint Day 1 (PowerPoint 2007 (.pptx) 10MB Jun19 25)
All Data (Excel 2007 (.xlsx) 39kB Jun19 25)
Student Handout for Sample Ages (Microsoft Word 2007 (.docx) 2.2MB Jun19 25)
Sedimentation Rate Worksheet (Microsoft Word 2007 (.docx) 25kB Jun19 25)
Day 2 Yellowstone Hotspot Worksheet (Microsoft Word 2007 (.docx) 1.2MB Jun19 25)
Teaching Notes and Tips
I used printouts of the data and had students highlight the youngest grains/ discordant grains. I found it made them talk to each other more than if they used Excel. Also, I had them do group discussions after completing each worksheet to see if there were questions and make sure the whole class had an agreement about ages and sedimentation rates.
Before Day 2 depending on where the students were in the activity, sometimes I did a review PowerPoint of the activity (what was U/Pb dating, where were the samples, etc. just to help them jump back in). Also, before giving students the Day 2 Yellowstone Hotspot Worksheet, I did a whole class discussion about where volcanic grains could be coming from. Getting students to think about what areas were producing volcanic grains in that time period. This is a great discussion and the students generally arrive at Yellowstone on their own.
Assessment
I used participation as an assessment. This activity was meant to be a way to introduce students to tools used in geoscience.
References and Resources
https://sites.google.com/laserchron.org/arizonalaserchroncenter/home (Where the data was collected, if you have questions about the process)