A thermomechanical model of heat and mass transfer in the vicinity of a subduction zone

Izvestiya - Russian Academy of Sciences. Physics of the Solid Earth(December 1999), 35(12):967-976

Index Terms/Descriptors: Andes; asthenosphere; Bouguer anomalies; crust; gravity anomalies; heat flow; lithosphere; lower crust; mantle; mass transfer; Nazca Plate; numerical models; plate tectonics; seismicity; South America; subduction; thermomechanical properties

Latitude & LongitudeS55°00'00'' - N13°00'00'' and W82°00'00'' - W35°00'00''

Abstract:

A numerical thermomechanical model of the mantle above a subducting lithospheric slab is developed. For a subduction rate of 10 cm/yr and a subduction angle of 30 degrees , the temperature reaches its maximum of 1800 K at a depth of 100 km, in the zone of maximal dissipative heat production of a forced asthenospheric flow. The model values of the anomalous thermal flux (125 mW/m ² ) and relief (4 km) are in good agreement with observations in the Andes, where the Nazca plate subduction is well described by the model. The modeled Bouguer anomaly minimum above the maximum heating zone in the mantle is -30 mGal. Due to the forced flow in the mantle wedge, the continental lithosphere base is thermally eroded at a rate of about 3 km/Myr. The numerical model was analytically approximated. Analysis of the model stability with respect to 3-D disturbances of thermomechanical parameters shows that the disturbances most drastically increase at a certain distance from the deep-sea trench. Assuming that the largest volcanic structures and their groups from above the fastest ascending convective currents, the model provides an explanation of the spatial periodicity of volcanoes and the distance between the Andes volcanic chain and trench. The efficiency of the heat supply to the lithosphere base in a volcanic zone increases by an order of magnitude due to the convective heat transfer.