20572 – Calibration of the (U-Th)/He geochronometer by analysis of the Mt. Mazama ash flow

Investigator’s Annual Reports (IAR’s) for Crater Lake National Park

Calibration of the (U-Th)/He geochronometer by analysis of the Mt. Mazama ash flow tuff and granodiorite xenoliths


Report Number: 20572

Permit Number: CRLA-2001-SCI-0001

Principal Investigator: Jeremy Boyce, Cambridge, MA

Date Received: Jan 17, 2002

Reporting Year: 2001

Additional investigator(s): Jorge Vazquez, Kip Hodges, Michael Clynne

Park-assigned Study Id. # CRLA-01023

Permit Expiration Date: Jul 05, 2001

Permit Start Date: Jun 05, 2001

Study Starting Date: Jul 15, 2000

Study Ending Date: Jan 01, 2003

Study Status: Continuing

Activity Type: Research

Subject/Discipline: Geochemistry (inc. Minerals / Petrology)

Objectives: An evaluation of the (U-Th)/He (uranium-thorium-helium) method of dating rocks (or “geochronometer”), by attempting to apply it to an eruption with a well-constrained age. One known problem with (U-Th)/He is that for young rocks, the age calculated may be incorrect unless significant time has elapsed between crystallization and eruption. If this time is short, the subsequent helium accumulation will be increased/decreased and therefore the age obtained will be wrong. The crystallization age of these crystals is known to be >10,000 yrs before eruption, making them ideal for this study.

Findings and Status: Sample preparation has commenced, but no ages have yet been calculated. We anticipate that the analytical stage of this project will begin in the spring of 2002.

For this study, were one or more specimens collected and removed from the park but not destroyed during analyses? No

Funding provided this reporting year by NPS: 0

Funding provided this reporting year by other sources: 1600

Full name of college or university: n/a

Annual funding provided by NPS to university or college this reporting year: 0


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