Analysis of long-term variations in the geomagnetic poloidal field intensity and evaluation of their relationship with global geodynamics

A generic geodynamic model is proposed to explain the relationship between observed long-term changes in GPFI and global geodynamic processes. The model predicts that changes in GPFI result from a chain of geodynamic processes extending from crust to core, beginning with plate reorganizations at the surface and culminating in increases in the vigour of outer core convection. Supercontinents are transient surface expressions of such geodynamic processes and provide the potential to test the generic model. Four time stages are proposed to describe the major long-term changes in GPFI since the Early Devonian: 400–350, 350–250, 250–175 and 175–10 Ma. The GPFI features within these stages are convincingly explained within the context of major events in the evolutionary cycle of Pangaea. Two major avalanching and mantle reorganization events, facilitating whole-mantle convection, are proposed; one linked with the amalgamation of Pangaea, the other (possibly less catastrophic) with the dispersal phase of the supercontinent. These events were separated by a period of mantle insulation during the time when the supercontinent was assembled and a layered mantle convection regime existed. The explanations are consistent with independent evidence from seismology, mantle modelling and mantle dynamics, though some ambiguities and intriguing relationships remain, which can only be addressed by the addition of high-quality palaeointensity data in key time windows targeted by the statistical analysis. The potential of using GPFI variation from the Archaean to the Mid-Palaeozoic to enhance our understanding of Earthʹs early geodynamic evolution is highlighted. Such data are currently lacking and their acquisition represents a significant challenge for future palaeointensity work.