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| Titel |
Late Devonian paleomagnetism of the North Tien Shan, Kyrgyzia: Does secular variation vary at a short time scale ? |
| VerfasserIn |
Mikhail Bazhenov, Rob Van der Voo, Natalia Levashova, Ada Dominguez |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250046645
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| Zusammenfassung |
| We studied sixty lava flows from an about 600-meter thick pile of Upper Devonian (Frasnian) basalts and andesites of the Aral Formation in the North Tien Shan (Kyrgyzia, Central Asia). With the aid of stepwise thermal demagnetization, a high-temperature dual-polarity component was reliably isolated from most flows. These new data were combined with those from the lower part of this formation [Levashova et al., 2007]. The primary origin of the high-temperature component is demonstrated by positive reversal, conglomerate and fold tests. The most prominent and intriguing feature of this Late Devonian dataset is a clear distinction in angular dispersion between the lower and upper parts of the studied section: a rather low concentration parameter (k ~13) and several excursions are found in the former, while about four times better grouping is observed for dual-polarity vectors from the upper part of the formation. We favor a geomagnetic origin for this difference and advocate a hypothesis that the magnitude of secular variation could randomly vary several-fold over time intervals of 100 ky -1 My. This is in sharp contrast with other models of secular variation, where this magnitude is assumed to be time-independent (for a certain latitude). Our hypothesis accounts for the observed irregularities in paleomagnetic data but makes it more difficult to successfully establish a correlation between secular variation and other parameters like geographic latitude, reversal frequency, or age. |
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