Geomagnetic field generation due to surface destruction of the solid core

Starchenko Sergey, sstarchenko@mail.ru, IZMIRAN, Troitsk, Moscow region, Russian Fed
Pushkarev Yuriy, ydcanon@rambler.ru, IPGG, St.-Petersburg, Russia

Abstract
Already during half of century it is generally accepted that geodynamo is mainly driven by compositional convection. Such convection began due to liquid core crystallization between 0.5 and 2.0 Ga. Therefore geomagnetic paleointensity should have a low value before 2.0 Ga, because it was determined only by an inefficient thermal convection. This is in contradiction with the paleomagnetic records detecting the geomagnetic field up to ~3.5 Ga. We named such discrepancy as geomagnetic paradox. The paradox can be resolved if we suggest that the main part of the modern Earth’s solid core has never been formed due to the liquid core crystallization, but represents a small relic of the protocore on which heterogenic accretion has begun. The protocore consists of heavy iron-nickel component and some quantity of light chondrite silicate material. During first 100 My after the end of accretion the liquid core geosphere was formed from external parts of the planet which in the case of heterogenic accretion were enriched with sulfur. This geosphere moves down slowly destroying the protocore. Such distruction is the result of iron-nickel component sulfurization which decreases its melting temperature. The silicate chondrite material is liberated by this way, floats-up through metallic melt and generates composition convection, which mainly supports the geodynamo. The model calculations demonstrate that gravitational energy of such floating is sufficient not only for magnetc field generation but also for overheating of the lower mantle basement and even for the plume formation. We predict geomagnetic and isotope effects for verification of our protocore conception. This conception regenerates the model of heterogenic accretion solving its main problem – formation of the liquid core.