Pangea, the geoid, and the paths of virtual geomagnetic poles during polarity reversals

VIZÁN HAROLDO; MENA MABEL; VILAS JUAN

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 1993 vol. 6 p. 253 - 266

0895-9811

t---The elongated distribution of virtual geomagnetic poles (VGPs) of South American Jurassic units has been interpretedas reflecting: 1) the behavior of the Earth´s magnetic field (EMF), and 2) apparent polar shift of the South American plate beforethe breakup of Gondwana. New paleomagnetic data do not support the latter. We analyze these Jurassic VGPs together with thoseof other Pangean continents, considering a model based on the foUowing assumptions: 1) Pangea was assembled over the presentAfrican-Atlantic $e, oid high; 2) the hotspot fi´amework has not been significantly deformed over the last 200 Ma; 3) the presentgeoid matches the present topography of the core mantle boundary (CMB); 4) the overall topography of the CMB remainsunchanged for long periods of time. We plotted Jurassic VGPs of units of Pangean continents, previously returned to a fixedhotapotframework, on a map of the present topography of the CMB. The VGPs seem to follow the trend of regions of increasedCMB seismic velocities. When a polarity reversal was registered by a Jurassic unit, the path of the VGPs was channeUed on zonesthat have been observed in transitional paths for the last 10 Ma.