Cooling of Igneous Rocks from the Serra Geral Event

We investigate the effects of the solidification and cooling of intrusive and extrusive bodies on the temperature history and surface heat flow of the Parana Basin. The Serra Gerallgneous evant (130-135 Ma) covered most of this basin with flood basalts. Associated with this event numerous sills and dikes Intruded the sediments and basement and possibly, extensive underplating occurred in the lower crust underneath the basin. We develop an analytical model of the conductive cooling of a sill-like intrusive body and use it to calculate temperatures within the sediments as a function of time since the intrusion/extrusion. Depending on the thickness of these igneous bodies and the timing of sequential emplacement, the thermal history of a given locus in the basin can range from a simple extended period of higher temperatures, to multiple events of peak temperatures. The cooling of surface flood basalts, sills and dikes Is capable of maintaining temperatures above normal geothermal gradient temperatures for a few hundreds of thousands of years. while large scale underplating may influence temperatures for up to 10 Million years. We conclude, therefore, that any residual heat from the cooling of the Serra Geral Igneous rocks has long since decayed to Illslgnlflcant values and that present-day temperatures and heat flow are not affected. However, the burial of the sediments beneath the thick basalt cap could have caused a temperature Increase of up to 40°C in the sediments since the beginning of the Cretaceous period.