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Preliminary paleomagnetic data from the Jurassic Humboldt Lopolith, west‐central Nevada: Evidence for thrust belt rotation in the Fencemaker Allochthon
Author(s) -
Hudson Mark R.,
Geissman John Wm.
Publication year - 1984
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 - 10.1029/gl011i009p00828
Subject(s) - allochthon , paleomagnetism , geology , clockwise , paleontology , cenozoic , seismology , thrust fault , mesozoic , rotation (mathematics) , declination , nappe , tectonics , geometry , mathematics , structural basin , physics , astronomy
Layered and massive gabbros of the Humboldt Lopolith and extrusive equivalents in west‐central Nevada yield well‐grouped paleomagnetic data on a site basis. With corrections for attitudes of compositional layering in gabbros and flow contacts in lavas (k corr /k in situ = 5.5), the mean of 15 site means is: D = 307°, I = 21°, α 95 = 9°, k = 17. While K‐Ar data imply a Late Jurassic age, we prefer an older, probably Early Jurassic, age for the lopolith and its magnetization based upon magnetization data and relations of these rocks with host strata. Compared with Early Jurassic expected directions, the data reveal a discordancy in declination of −37° (+/− 14‐22°) which implies a significant counterclockwise rotation of the lopolith. Local rotation of Fence‐maker allochthon units most likely occurred when southeasterly‐directed thrust sheets obliquely contacted a generally north‐south trending shelf margin. Mesozoic deformation will be more accurately estimated with better age control and measurement of possible Cenozoic crustal rotation.