Paleomagnetism of welded tuffs of the Yellowstone group

Journal of Geophysical Research



Two of the three ash flow tuffs of the Yellowstone Group are stably magnetized throughout their extent: the Lava Creek tuff (0.60 m.y.) in a normal direction and the Mesa Falls tuff (1.22 m.y.) in a reversed direction. In contrast, much of the Huckleberry Ridge tuff, which was erupted during a polarity transition or field excursion 1.92 m.y. ago and initially magnetized in an intermediate direction (D = 214.5°, I = −2.2°, and α95 = 4.1°), has been partially remagnetized in a normal field. Much of the overprint of the Huckleberry Ridge tuff is carried in low‐temperature oxidation products with low coercivities and low blocking temperatures, so that it is commonly removed in peak alternating fields less than 200 Oe or at temperatures less than 400°C. Hematite, having higher coercivities and blocking temperatures, is partly responsible for remagnetization in some specimens, but neither alternating field nor thermal demagnetization enables recovery of the original thermal remanent magnetization in these samples. The chemical overprinting is most pronounced in the devitrified tuff of the flow interior. Stable magnetization is observed in the Huckleberry Ridge tuff in the less porous densely welded portions at the base and boundaries of partial cooling units and in the tuff of the distal margins, where groundwater influences were minimal. Paleomagnetic directions of chilled margins within compound cooling units of the Lava Creek and Huckleberry Ridge tuffs support geological evidence that eruption of each ash flow sheet was rapid and that the source calderas were formed during a short period of time.

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Publication type Article
Publication Subtype Journal Article
Title Paleomagnetism of welded tuffs of the Yellowstone group
Series title Journal of Geophysical Research
DOI 10.1029/JB082i026p03677
Volume 82
Issue 26
Year Published 1977
Language English
Publisher American Geophysical Union
Contributing office(s) Geosciences and Environmental Change Science Center
Description 17 p.
First page 3677
Last page 3693
Country United States
State Idaho, Montana, Wyoming
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