Characterizing the dispersal and distribution shapes of the geomagnetic field directions of the Late Miocene Columbia River Basalts
Abstract
This study comprises 118 discrete volcanic flows from the Late Miocene in the eastern Columbia River Basalt (CRB) Group with the aim of testing the distributions of the geomagnetic field directions, as predicted by various geomagnetic models. This is important because little is known empirically about the behavior of the geomagnetic field before the last 5 million years. The results of this study will allow us not only to extend the temporal coverage of geomagnetic field models, but also allow for potential improvements in these models. The rock magnetic analysis of the samples for this collection shows that the primary magnetic directions are uniformly carried by titanomagnetite throughout all the sites; some minor amounts of hematite are present, most likely formed during weathering. Thus, the magnetic behavior of the samples is caused by changes in the magnetic field and not due to changes in magnetic mineralogy. The paleomagnetic directions of the flows show southerly and up (N: 45, Dec: 180.1, Inc: -64.5, k: 25.7, alpha-95: 4.3) and northerly and down site means (N: 57, Dec: 6.3, Inc: 62, k: 29, alpha-95: 3.6). For reference, the local inclination of the geocentric co-axial dipole field is about 64 degrees. Furthermore, deviating directions are also present, possibly due to excursions as part of secular variation, or as intermediate transitions between reversed and normal polarity intervals. No new rock ages were necessary for this study since the CRB has undergone extensive geochronological study with high-quality, reproducible results. Additionally, integrating the ages of the flows and their corresponding paleomagnetic directions will allow us to observe the evolution of the paleosecular variation (PSV) for the Late Miocene, which can be compared with the published characteristics of the geomagnetic field in the last 5 million years.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMGP51B1160D
- Keywords:
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- 1522 GEOMAGNETISM AND PALEOMAGNETISM / Paleomagnetic secular variation