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Unblocking temperatures of viscous remanent magnetism in displaced granitic boulders, Icicle Creek glacial moraines (Washington, USA)
Author(s) -
Crider Juliet G.,
Globokar Danika M.,
Burmester Russell F.,
Housen Bernard A.
Publication year - 2015
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2015gl066381
Subject(s) - moraine , geology , remanence , demagnetizing field , rock magnetism , glacial period , natural remanent magnetization , geomorphology , geochemistry , magnetization , magnetic field , physics , quantum mechanics
Viscous remanent magnetization (VRM) may partially overprint original magnetization in rocks displaced by geomorphic events. An established theoretical relationship between the time and temperature of acquisition of VRM and the time and temperature of demagnetization suggests that laboratory demagnetization (unblocking) of VRM can be used to estimate the displacement age of rocks. We test this hypothesis at four nested glacial moraines in the Icicle Creek drainage of central Washington, the ages of which were previously determined by cosmogenic surface exposure dating. The moraines are composed primarily of granodiorite boulders, and magnetic remanence is carried dominantly by magnetite. Both the maximum and average pVRM demagnetization temperatures ( T D ) increase with relative age of the moraines. For the three younger moraines, the average T D yields an age comparable to the cosmogenic age, within uncertainty of pVRM acquisition temperature. Uncertainty in the acquisition and demagnetization temperatures can limit the utility of pVRM for absolute dating.