Jurassic-Early Cretaceous intermediate virtual geomagnetic poles and Pangaean subduction zones

Abstract

The objective of this paper is to show that the distribution of Jurassic-Early Cretaceous intermediate virtual geomagnetic poles (VGPs) seems to be conditioned by Pangaean subducted slabs. Palaeomagnetic data from between ∼ 200Ma and 125Ma were compiled from reliable studies and their VGPs repositioned in their Jurassic-Early Cretaceous geographic location considering a "zero-longitude" motion of Africa over the last 200m.y. and the corresponding palaeomagnetic poles from each sequence. Those repositioned VGPs lying between latitudes of ± 60° were considered to be intermediate. To avoid bias as a function of simple sampling numbers for those sequences with more data, each VGP was weighted by Love's methodology. A colour-scale map (shadow-scale map in printed issue) of density of the weighted intermediate VGPs was obtained and compared with the Pangaean subduction zones. There is a good visual correlation between the distribution of these VGPs and the location of the subduction zones during the Jurassic, suggesting that there is a relationship between the Jurassic-Early Cretaceous geomagnetic reversals and the plate tectonic setting at that time. Minima of intermediate VGPs correlate well with the absence of VGPs predicted with a tomographic model and the intermediate VGP distribution is also well correlated with zones of faster seismic wave propagation in the lower mantle (just above of the core-mantle boundary), which suggests that the Jurassic geomagnetic polarity transitions could have been controlled by a structure of the core-mantle boundary similar to that at the Present time. We suspect that the subducted lithospheric slabs refrigerated the deepest mantle causing more heat than average flowing out from the core and controlling the geometry of the Jurassic-Early Cretaceous polarity transitions. The Earth's lithospheric plate motion history could have played a controlling role in the geometry of the geomagnetic reversals.