Viscous remanent magnetization, VRM
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 (TD) increase with relative age of the moraines. For the three younger moraines, the average TD 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.
Geophysical Research Letters
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©2015. American Geophysical Union. All Rights Reserved DOI: 10.1002/2015GL066381
Crider,J.G.,D.M.Globokar,R.F.Burmester,and B. A. Housen (2015), Unblockingtemperatures of viscous remanentmagnetism in displaced graniticboulders, Icicle Creek glacial moraines(Washington, USA), Geophys. Res. Lett., 42,10,647–10,654, doi:10.1002/2015GL066381.