Thermal Buffering by Basement Rocks in Numerical Simulations of Basin-Scale Heat Flow
Jeffrey A. Nunn, Guichang Lin, and David Deming
The Earth's crust is an enormous thermal reservoir that releases or absorbs heat energy in response to rapid changes in near surface temperatures. Numerical simulations of basin-scale heat transport which set the lower thermal boundary condition at the sediment-basement interface assume that temperature changes in the near surface have no effect on basement rocks and vice versa. We compare two numerical models of transient fluid flow and heat transport by topographically driven recharge in a foreland basin. In the non-extended model, a constant heat flow boundary condition is set at the sediment-basement contact. In the extended model, the same thermal constraint is set at a depth of 15 km. For rapid changes in temperatures caused by fluid flow (~1 m.y.), thermal bufferin by basement rocks reduces cooling of deep basin sediments near the fold-thrust belt by fresh water recharge and warming of the basin margin by upward discharge of pore fluids from depth. The non-extended model predicts an exaggerated thermal transient or pulse, a temporary warming of basin sediments by hot fluids in excess of steady-state temperatures, in the discharge region of the basin. Exaggerated or spurious temperature predictions also can occur in numerical simulations of heat advection by other geodynamic processes or thermal problems where heat refraction is important. For thermal systems that change slowly (~100 m.y.) and where heat refraction is minor, the choice of lower thermal boundary condition makes little difference.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California