Improved Simulation of Lava Flow Cooling Supports Hypothesis of Rapid Transitional Geomagnetic Field Change

Abstract

Results from an improved one-dimensional conductive cooling model confirm the findings of Bogue and Glen (2010) that a partially thermally remagnetized lava flow in the Sheep Creek Transition Zone records a rapid transitional field change (RTFC). The update of the model includes a simulated release of latent heat as the flow crystallizes from the top and base into the interior of the flow. As each layer crystallizes, it remains isothermal until all the latent heat is conducted away. The cooling models treat the lower and upper flows from the Sheep Creeks as stacks of infinite, 10cm thick slabs with temperature and porosity dependent thermal diffusivity. To match the paleomagnetic data, I determined that the upper flow would have to be emplaced at approximately 1300?C to reheat the lower flow sufficiently. 1300?C is an unrealistically high temperature for an andesitic basalt. Using a realistic estimate for the upper flow emplacement temperature (1050?C), the lower flow must have still been warm (125 ?25?C) when the upper flow was emplaced. I also found that when the percentage of glass varies between 0% and 40% glass, it only changes the temperature curve by approximately 20?C, showing that any believable glass content falls within the uncertainty of the lower flow temperature. The initial capped temperature of the lower flow at the time of the upper flow emplacement shows the geomagnetic field must have changed by 53? in approximately 420 days. The simulation shows that the RTFC theory is viable in the Sheep Creek Transition Zone.