Very rapid geomagnetic field change recorded by the partial remagnetization of a lava flow
Abstract
A new paleomagnetic result from a lava flow with a distinctive, two-part remanence reinforces the controversial hypothesis that geomagnetic change during a polarity reversal can be much faster than normal. The 3.9-m-thick lava (“Flow 20”) is exposed in the Sheep Creek Range (north central Nevada) and was erupted during a reverse-to-normal (R-N) geomagnetic polarity switch at 15.6 Ma. Flow 20 began to acquire a primary thermoremanence while the field was pointing east and down but was soon buried, reheated, and partially-remagnetized in a north-down direction by the 8.2-m-thick flow that succeeded it. A simple conductive cooling calculation shows that the observed remagnetization could not have occurred unless Flow 20 was still warm (about 150°C near its base) when buried and that the 53° change from east-down to north-down field occurred at an average rate of approximately 1°/week, several orders of magnitude faster than typical of secular variation.
- Publication:
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Geophysical Research Letters
- Pub Date:
- November 2010
- DOI:
- Bibcode:
- 2010GeoRL..3721308B
- Keywords:
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- Geomagnetism and Paleomagnetism: Reversals: process;
- timescale;
- magnetostratigraphy;
- Geomagnetism and Paleomagnetism: Time variations: secular and longer;
- Geomagnetism and Paleomagnetism: Rapid time variations;
- Geomagnetism and Paleomagnetism: Remagnetization