GEOMAGNETIC PALEOINTENSITIES DERIVED FROM VOLCANIC-ROCKS OF THE QUATERNARY EAST EIFEL VOLCANIC FIELD, GERMANY

Authors
Citation
E. Schnepp, GEOMAGNETIC PALEOINTENSITIES DERIVED FROM VOLCANIC-ROCKS OF THE QUATERNARY EAST EIFEL VOLCANIC FIELD, GERMANY, Physics of the earth and planetary interiors, 94(1-2), 1996, pp. 23-41
Citations number
31
Categorie Soggetti
Geochemitry & Geophysics
ISSN journal
00319201
Volume
94
Issue
1-2
Year of publication
1996
Pages
23 - 41
Database
ISI
SICI code
0031-9201(1996)94:1-2<23:GPDFVO>2.0.ZU;2-X
Abstract
Geomagnetic paleointensities have been determined for 18 rock units of basanitic, thephritic or nephelinitic composition from the Quaternary East Eifel volcanic field (Germany). In general the rocks are well su ited for paleointensity determination and gave consistent results of p aleointensity. For each rock unit at least five individual values have been measured with the Thellier method. Compared with the present day field of 48 mu T the unweighted mean paleointensity values range from 29 to 62 mu T With relative standard errors mostly below 10%. Paleoin tensity values are concentrated at 30 and 50 mu T with a gap at 40 mu T. The distribution is bimodal rather than Gaussian, although all pale opoles lie close to the geographic pole. This cannot be explained by t he very discontinuous distribution of volcanic activity in time which took place mainly around 200 and 400 ka. In each age group both low an d high paleointensity values are found. However, a further temporal se paration within each age group cannot be excluded. Furthermore, the pa leointensity values of the West Eifel volcanic field show a similar bi modal distribution which indicates that this case seems to be connecte d with a geomagnetic excursion recorded in those rocks. Therefore it m ight be considered that the East Eifel rocks recorded a characteristic feature of the earth's magnetic field namely a quasi-cyclic variation of paleointensity. On the other hand, the now available global data s et of 128 virtual dipole moment values from the Brunhes chron and olde r than 30 ka shows an almost Gaussian distribution with a mean value o f 7.4 +/- 3.4 . 10(22) Am-2, if 14 values with transitional pole posit ions are excluded. A quasi-cyclic variation of the dipole moment there fore does not seem to be a persistent global characteristic of the ear th's magnetic field.