Paleomagnetic Evidence for Inverse Correspondence between the Relative Contribution of the Axial Dipole Field and CMB Heat Flux for the Past 270 Myr

Daniel Ribeiro Franco,Wellington Paulo De Oliveira,Ian Muzy Camarão Peixoto,Cosme Ferreira Da Ponte Neto,Felipe Barbosa Venâncio De Freitas,Diego Takahashi

doi:10.1038/s41598-018-36494-x

Daniel Ribeiro Franco, Wellington Paulo De Oliveira + Show 4 more

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https://doi.org/10.1038/s41598-018-36494-x

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Abstract

We provide an evaluation of the paleolatitudinal dependence of the paleosecular variation throughout the Paleozoic-Mesozoic transition – linked to the high geomagnetic reversal frequency interval Illawarra Hyperzone of Mixed Polarity (IHMP; ~266.7–228.7 Myr). Our findings were compared with those for intervals of distinctive geomagnetic reversal frequencies within the Phanerozoic. Our results for the IHMP were conducted through estimates of angular dispersion (SB) of virtual geomagnetic pole (VGP) data groups, taken from a high quality paleomagnetic database. Model G was fitted to these data, providing its shape parameters a and b (respectively related to the antisymmetric and symmetric harmonic terms for the time-average geomagnetic field). Results for the IHMP exhibited compatible patterns with two well-known intervals of higher reversal frequency – Jurassic and the last 5 Myr. A comparison of b/a ratio results – considered as an efficient indicator for the relative contribution of the axial dipole field – for the last 270 Myr, indicated an inverse correspondence with the relative core-mantle boundary (CMB) heat flux, according to recent discussions, clarifying the physical meaning of the Model G shape parameters a and b.

Highlights

Daniel Ribeiro Franco 1, Wellington Paulo de Oliveira 1, Felipe BarbosaVenâncio de Freitas[1], Diego Takahashi[1], Cosme Ferreira da Ponte Neto1 & Ian Muzy Camarão Peixoto[2]
We provide an evaluation of the paleolatitudinal dependence of the paleosecular variation throughout the Paleozoic-Mesozoic transition – linked to the high geomagnetic reversal frequency interval Illawarra Hyperzone of Mixed Polarity (IHMP; ~266.7–228.7 Myr)
Some of the long-standing questions refer to the Earth’s magnetic field (EMF) reversibility and its large-scale variations in average reversal rate are still a demand. It is well-known that the geomagnetic polarity timescale (GPTS) for the last 160 Myr indicates wide changings for the rate of geomagnetic reversals, reflecting the variable stability of geodynamo – from around 4-5 Myr−1, with an average duration for the polarity chrons of ~200 kyr for the past 15 Myr, reaching down to ~0.05 Myr−1 during the so-called 84–125 Myr Cretaceous Normal Superchron (CNS)[11,12,13,14]

Summary

Introduction

Daniel Ribeiro Franco 1, Wellington Paulo de Oliveira 1, Felipe BarbosaVenâncio de Freitas[1], Diego Takahashi[1], Cosme Ferreira da Ponte Neto1 & Ian Muzy Camarão Peixoto[2]. Some authors (e.g., refs 20–23) suggest that such changes in reversal rate would be a result of spatial variability of the heat flux at the core-mantle boundary (CMB) throughout the Phanerozoic, the connections between the geomagnetic reversal frequency and long-term mantle dynamics are still far from being completely clarified[16] It has been discussed by some authors (e.g., refs 9,24) that the geodynamo exhibited more stability conditions (i.e. lower geomagnetic reversal rates) in periods when the main contribution to the geomagnetic field is given by the axial dipole field – which can be given by the antisymmetric spherical harmonic terms, as www.nature.com/scientificreports/

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