Thermal development of low-pressure metamorphic belts: results from two-dimensional numerical models

We have used two-dimensional numerical models and analytical solutions to heat flow equations to investigate the mechanisms and the spatial and temporal development of regionally extensive low-pressure facies-series metamorphism (LPM). Two-dimensional models are necessary for describing the evolution of isotherms in the crust where lateral heat flow and local time-dependent heat sources are important. The models demonstrate that felsic intrusions can produce regionally extensive LPM where their abundance through time in the upper crust exceeds approximately 50%. Evenly spaced intrusions elevate vertical metamorphic gradients in regions between intrusions by ~5° to 10°C km^-1 over background values at ~40% abundance and by ~15° to >30°C km^-1 at ~70% abundance. Other mechanisms, such as intrusion of mafic magmas in the lower crust, crustal extension, or aqueous fluid advection, cannot independently produce maximum temperatures in such regions. If coeval with intrusion, these other processes will contribute to maximum temperatures; however, the distribution of isotherms and the timing of metamorphism in the upper crust are governed by the shallow intrusions. -from Authors