THE EFFECT OF DEFORMATIONAL FABRICS AND STRUCTURES ON THERMAL CONDUCTIVITY AND RHEOLOGY

The nonelastic rheological behavior of rocks is strongly dependent on temperature and therefore the evolution of heat flux through time. Many rock-forming minerals such as quartz and mica are strongly anisotropic in their thermal conductivity, and therefore rocks formed by these minerals can also be strongly anisotropic. Despite the potential importance of this anisotropy in specific geological circumstances such as thermal dissipation in shear zones and around igneous intrusions, the thermal properties of rocks are generally treated as isotropic. Here we use the TESA (ThermoElastic and Seismic

Analysis) Toolbox to numerically explore how the development of rock fabrics (e.g., foliations) and structures (e.g., folds) can modify the anisotropy of thermal conductivity and therefore the spatial variation in heat flux. In rocks containing abundant mica and quartz, foliation development leads to

strongly enhanced anisotropy. In contrast, folding of this same foliated rock can mute the anisotropy with resulting thermal properties dependent on the fold geometry and orientation. As part of our analysis, we evaluate the thermal structure of the subvertical Sandhill Corner shear zone, which is one of

the largest seismogenic strands of the Norumbega fault system in Maine. The core of the shear zone separates quartz- and feldspar-rich rocks to the NW from a strongly vertically foliated biotite schist to the SE. Our analyses explore the potential impact of this geological configuration and it's resulting highly anisotropic heat flux on the rheological evolution of the shear zone.