Persistent Link:
http://hdl.handle.net/10150/282369
Title:
Applications of noble gas cosmogenic nuclides to geomorphology
Author:
Phillips, William Morton
Issue Date:
1997
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
The buildup of the cosmogenic nuclides ³He and ²¹Ne in surficial rocks permit exposure ages and erosion rates to be estimated. This dissertation extends the cosmogenic exposure technique to garnets, plagioclase with significant nonspallation ²¹Ne components, and alluvial fill terraces. Garnets from Nanga Parbat, Pakistan have low nucleogenic ³He and moderate radiogenic ⁴He concentrations. ³He exposure ages from garnets in glacial erratics indicate glacial advances at Nanga Parbat at about 16 ka and 55 ka. 3He in alluvial garnets suggests that denudation in small unglaciated basins proceeds 5 to 7 times slower than glacial erosion, and 10 to nearly 100 times slower than regional rock exhumation and surface uplift. Rocks older than several million years possess nucleogenic and mugenic ²¹Ne and ³He components that must be resolved for accurate exposure ages. These nonspallation components in plagioclase and clinopyroxene from the Miocene Columbia River Basalt Group are best isolated with shielded samples. Analyses of ⁴He, U, Th, and Li systematically underpredict the amount of nonspallation ²¹Ne and ³He present in shielded samples, probably because of mugenic production. Step heating experiments suggest that ²¹Ne diffusive loss from plagioclase is possible, but most samples do not exhibit such ²¹Ne loss. The ratio of ²¹Ne in plagioclase and ³He in clinopyroxene is generally constant after correction for the nonspallation component, indicating that little or no ²¹Ne loss has occurred. The last highly erosive floods at Grand Coulee occurred at about 21 ka, early in the cycle of Missoula flooding. Nuclide inheritance must be resolved for accurate exposure ages of stream fill terraces. Depth profiles of cosmogenic ²¹Ne in quartz from terraces on the Pajarito Plateau, northern New Mexico resolve nuclide inheritance. Three patterns of depth profiles are recognized: (1) downward decreasing; (2) downward increasing; and (3) uniform; types 2 and 3 are associated with cumulate deposits and bioturbation, respectively. Inheritance corrected exposure ages for the terraces agree with independent radiocarbon and soil development ages. Denudation rates estimated from the profiles are higher for fill terraces than for straths.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Physical Geography.; Geology.; Geochemistry.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Geosciences
Degree Grantor:
University of Arizona
Advisor:
Quade, Jay

Full metadata record

DC FieldValue Language
dc.language.isoen_USen_US
dc.titleApplications of noble gas cosmogenic nuclides to geomorphologyen_US
dc.creatorPhillips, William Mortonen_US
dc.contributor.authorPhillips, William Mortonen_US
dc.date.issued1997en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractThe buildup of the cosmogenic nuclides ³He and ²¹Ne in surficial rocks permit exposure ages and erosion rates to be estimated. This dissertation extends the cosmogenic exposure technique to garnets, plagioclase with significant nonspallation ²¹Ne components, and alluvial fill terraces. Garnets from Nanga Parbat, Pakistan have low nucleogenic ³He and moderate radiogenic ⁴He concentrations. ³He exposure ages from garnets in glacial erratics indicate glacial advances at Nanga Parbat at about 16 ka and 55 ka. 3He in alluvial garnets suggests that denudation in small unglaciated basins proceeds 5 to 7 times slower than glacial erosion, and 10 to nearly 100 times slower than regional rock exhumation and surface uplift. Rocks older than several million years possess nucleogenic and mugenic ²¹Ne and ³He components that must be resolved for accurate exposure ages. These nonspallation components in plagioclase and clinopyroxene from the Miocene Columbia River Basalt Group are best isolated with shielded samples. Analyses of ⁴He, U, Th, and Li systematically underpredict the amount of nonspallation ²¹Ne and ³He present in shielded samples, probably because of mugenic production. Step heating experiments suggest that ²¹Ne diffusive loss from plagioclase is possible, but most samples do not exhibit such ²¹Ne loss. The ratio of ²¹Ne in plagioclase and ³He in clinopyroxene is generally constant after correction for the nonspallation component, indicating that little or no ²¹Ne loss has occurred. The last highly erosive floods at Grand Coulee occurred at about 21 ka, early in the cycle of Missoula flooding. Nuclide inheritance must be resolved for accurate exposure ages of stream fill terraces. Depth profiles of cosmogenic ²¹Ne in quartz from terraces on the Pajarito Plateau, northern New Mexico resolve nuclide inheritance. Three patterns of depth profiles are recognized: (1) downward decreasing; (2) downward increasing; and (3) uniform; types 2 and 3 are associated with cumulate deposits and bioturbation, respectively. Inheritance corrected exposure ages for the terraces agree with independent radiocarbon and soil development ages. Denudation rates estimated from the profiles are higher for fill terraces than for straths.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectPhysical Geography.en_US
dc.subjectGeology.en_US
dc.subjectGeochemistry.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineGeosciencesen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorQuade, Jayen_US
dc.identifier.proquest9738945en_US
dc.identifier.bibrecord.b37460237en_US
All Items in UA Campus Repository are protected by copyright, with all rights reserved, unless otherwise indicated.