Directional change during a Miocene R-N geomagnetic polarity reversal recorded by mafic lava flows, Sheep Creek Range, north central Nevada, USA

TitleDirectional change during a Miocene R-N geomagnetic polarity reversal recorded by mafic lava flows, Sheep Creek Range, north central Nevada, USA
Publication TypeJournal Article
Year of Publication2017
AuthorsBogue S.W, Glen J.MG, Jarboe N.A
JournalGeochemistry Geophysics Geosystems
Volume18
Pagination3470-3488
Date Published2017/09
Type of ArticleArticle
ISBN Number1525-2027
Accession NumberWOS:000413042600012
Keywordscore; excursions; geomagnetic; mantle control; Miocene; Nevada; non-dipole field; paleomagnetism; reversal; rift; secular variation; steens mountain; transition
Abstract

Recurring transitional field directions during three Miocene geomagnetic reversals provide evidence that lateral inhomogeneity of the lower mantle affects flow in the outer core. We compare new paleomagnetic results from a composite sequence of 15.2 Ma lava flows in north central Nevada (Sheep Creek Range; 40.7 degrees N, 243.2 degrees E), erupted during a polarity reversal, to published data from Steens Mountain (250 km to the northwest in Oregon) and the Newberry Mountains (650 km to the south in California) that document reversals occurring millions of years and many polarity switches earlier. Alternating field demagnetization, followed by thermal demagnetization in half the samples, clearly isolated the primary thermoremanent magnetization of Sheep Creek Range flows. We correlated results from our three sampled sections to produce a composite record that begins with a single virtual geomagnetic pole (VGP) at low latitude in the Atlantic, followed by two VGPs situated near latitude 30 degrees N in NE Africa. After jumping to 83 degrees N (one VGP), the pole moves to equatorial South America (one VGP), back to NE Africa (three VGPs), to high southern latitudes (two VGPs), back to equatorial South America (three VGPs), and finally to high northern latitudes (nine VGPs). The repeated visits of the transitional VGP to positions in South America and near NE Africa, as well as the similar behavior recorded at Steens Mountain and the Newberry Mountains, suggest that lower mantle or core-mantle boundary features localize core flow structures, thereby imparting a discernible regional structure on the transitional geomagnetic field that persists for millions of years.

DOI10.1002/2017gc007049
Short TitleGeochem. Geophys. Geosyst.
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