The influence of igneous intrusions on the peak temperatures of host rocks: Finite-time emplacement, evaporation, dehydration, and decarbonation

摘要

Using a 13-m-thick basic sill and its limestone host rocks of the Permian Irati Formation from the Parana Basin, South America, as an example, this paper presents a numerical investigation based on heat conduction models on the effect of the emplacement mechanism of igneous intrusions, pore-water evaporation, and dehydration and decarbonation of host rocks on the peak temperature (T_(peak)) of host rocks. Our results demonstrate that: (1) the finite-time intrusion mechanism of magma can lower the predicted T_(peak) of host rocks by up to 100℃ relative to the instantaneous intrusion mechanism, and although pore-water evaporation together with dehydration and decarbonation reactions can also depress the thermal effect of the sill on its host rocks, the maximum effect of these mechanisms on T_(peak) only reaches approximately 50 ℃. (2) The effect of pore-water evaporation on T_(peak) is obviously greater than that of the dehydration and decarbonation reactions: the former can cause a maximum deviation of 40 ℃ in the predicted T_(peak). whereas the deviation due to the latter is less than 20 ℃. Further, the effect of the dehydration and decarbonation reactions on T_(peak) is less than 10 ℃ if pore-water evaporation is allowed simultaneously in the models and can hence be ignored in thermal modeling. (3) The finite-time intrusion mechanism of magma probably represents the natural condition of the sill. Pore-water evaporation and dehydration and decarbonation of host rocks are also likely to play important roles in lowering the thermal effect of the sill.