The development and application of microanalytical (U-Th)/He thermochronology

The (U-Th)/He thermochronmeter is the foremost tool available to geoscientists for the purposes of constraining the thermal evolution of the crust below 250°C. However, the potential of the technique is far from fully explored. The existing de facto (U-Th)/He age standard, the fluorapatite of Cerro de Mercado (Durango, Mexico), does not yield reproducible dates, an observation confirmed at several laboratories. A series of experiments combining analytical and numerical techniques suggests that variations in U and Th measured in a single sectioned crystal could result in several percent apparent age variation due to unequal alpha recoil exchange across internal zone boundaries. Heterogeneities may also play a role in the variability observed in the diffusive behavior of He in strongly zoned minerals, such as monazite. He diffusion experiments on monazite indicate that the closure temperature for (U-Th)/He thermochronometry is between 206°C and 286°C, but varies from grain to grain, even within suites of crystals obtained from one rock. This may be due to compositional variations in the host monazite. Typically heterogeneous monazite crystals may have different closure temperatures, and single crystals may preserve large portions of the cooling history of a rock.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Earth, Atmospheric, and Planetary Sciences.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2006

Author dc:creator

• Boyce, Jeremy Welles

Advisor dc:contributor.advisor

• Kip V. Hodges.

• Earth, Atmospheric, and Planetary Sciences.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/34662
• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Identifier URI

http://dspace.mit.edu/handle/1721.1/34662

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/34662