Title

Rapid, high-temperature formation of large-scale rheomorphic structures in the 2.06 Ma Huckleberry Ridge Tuff, Idaho, USA.

Publication Title

Geology

Publication Date

3-2010

Document Type

Article

DOI

10.1130/G30492.1

Keywords

paleomagnetism, magnetization, anisotropy

Disciplines

Geology

Abstract

n the Teton River Canyon, eastern Idaho, the ca. 2.06 Ma, 130-m-thick Huckleberry Ridge Tuff exhibits large-scale rheomorphic fold geometries defined by eutaxitic fabrics parallel to both the primary internal zonation and the basal contact with older strata. Paleomagnetic data from a large-amplitude (>150 m), northwest-trending, overturned fold near the failed Teton Dam indicate folding above maximum magnetization unblockingtemperatures (>580 °C). The in situ characteristic remanent magnetization (ChRM) direction is indistinguishable from previous studies of undeformed Huckleberry Ridge Tuff, and a fold test is negative (k minimized at 100% unfolding). Anisotropy of magnetic susceptibility data reveal magnetic foliation planes that dip northeast, roughly parallel to the axial surface of the fold. Because deformed and undeformed Huckleberry Ridge Tuff exposures preserve the same anomalous ChRM direction, large-scale rheomorphicstructures in the tuff must have formed rapidly at high temperatures shortly after development of compaction fabrics. Post-welding, high-temperaturedeformation is consistent with field evidence indicating rapid, plastic secondary deformation of much of the tuff prior to devitrification.

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