Investigation and Comparison of the mantle convection cells for different assumptions of the heating sources of inner Earth

Earth is the third planet of solar system with approximate radius of 6300 km and an 87 mWm-2 thermal rate is transferred from the surface to surrounding atmosphere. The heat is brought about by different sources inside the ground. Among these sources، estimate that about 80% of the present surface heat flow can be attributed to the decay of radioactive isotopes presently in the mantle and the crust while about 20% comes from the cooling of the Earth. The high heat inside the mantle is displaced by convection that is most important heat transfer to lower levels of the crust. Form of convectional cells، flow speed and total temperature of the mantle depend on thermal sources inside the ground. In present study، properties of convectional cells (assuming that the viscosity and the special thermal capacity are held constant) have been dealt with in three models: A) Heating from the lowest layer of the mantle which is connected to the core (according to some researchers، it is rarely possible) -B) distribution of thermal sources throughout the mantle -C) distribution of heating sources on the zone 150 km farther than lower mantle. Results obtained from simulation show that the more extensive the distribution of thermal sources in the mantle، the more the width of convectional cells so that the highest number of convectional cells are brought about by core heating and the lowest number are brought about by distribution of thermal sources throughout the mantle. Concerning floor heating and thermal distribution in 150 km from lower mantle، the ascending velocity of convectional cells is nearly equal to their subduction velocity while in thermal distribution throughout the mantle; the width in which the mantle moves upward is broader than that of subduction. Therefore، mantle ascending speed is lower than that of subduction due to mass conservation and stable fluid movement. If all thermal sources are concentrated in 150 km from lower mantle، the temperature is higher than the other two models in this zone. But when thermal sources are dispersal throughout the mantle، the highest temperature seen inside the mantle is relates to middle part of the mantle since the velocity is very slow in middle of convectional cells. Therefore، temperature is increased in this zone compared to other zones because the mantle has low conduction coefficient and high heat capacity. Therefore، the heat is transferred by displacement and the heat produced in middle of convectional cells by decay of radioactive elements is not transferred (due to low mantle speed in these zones) and the temperature is increased in these zones. Cold fluid close to the crust is deepened due to subduction and the temperature is reduced in depth. More over، simulation indicates that the second models convectional speed is higher than the other two models. The dimension and the number of convection cells of these models and their comparison to the earth observation measures (plates side) shows that the two internal heating models have better correspondence with the earth observations. As a result، the feature of convection cells and the temperature of mantle have strong dependence on the distribution of thermal resources inside the earth. Therefore، identifying properties of convectional cells may contribute surface activities and some of them have been addressed in present research.