Statistical properties of paleomagnetic directions in Kerguelen lava flows: Implications for the late Oligocene paleomagnetic field

摘要

We present the results of a paleomagnetic study of seven new volcanic sections (146 flows) from Kerguelen Archipelago. For two of these sections, preliminary (40Ar/39Ar) ages are reported to aid in the calibration of the paleomagnetic results. The primary contribution of this report, however, is a compilation of these new data with those already published in order to describe statistically the characteristics of the paleomagnetic field as recorded by the Kerguelen flood basalts. In total, 258 paleomagnetic directions sampled at 13 stratigraphic sections through the lava pile are available and span an approximately 5 Ma window: from 25 to 30 Ma. The composite section represents at least 11 polarity zones that are correlated to the reference geomagnetic polarity timescale. Our approach is to investigate the average normal and reversed polarity field directions over this 5 Ma window. We calculated a paleomagnetic pole found to be located at λ = 85.5°N, = 189.3°E (A95 = 2.3°, K = 16.5, N = 233). This pole is in close agreement with the coeval paleomagnetic poles obtained from different worldwide places when analyzed in the Indo-Atlantic hot spot reference frame. In the statistical analysis we tackle the specific question: Is the secular variation isotropic? This question is directly related to the occurrence of a longitudinal confinement of the virtual geomagnetic poles, which is still a matter of debate among paleomagnetists. By means of statistical tests we show that the paleomagnetic data from Kerguelen agree with an isotropic model for paleosecular variation. Finally, we present adjustments to Camps and Prévot's (1996) statistical model, developed for some Northern Hemisphere latitudes, to the Southern Hemisphere paleomagnetic data from Kerguelen.