Modeling the Thermal and Chemical Evolution of Magmatic Systems in Extensional Environments

Extensional and hybrid tectonic environments can occur in a variety of magmatic settings, and can encourage successive magma intrusions and lithospheric thinning, which modify the thermal, mechanical, and chemical structures of the crust. Therefore the amount, temperature, composition, and timescales of melt residing in the crust, which are controlled by the rate of tectonic extension and magma intrusions, are important in analyzing crustal magma dynamics. In this work, we monitor the crustal evolution in diverse extensional settings through a two-dimensional thermal conduction model. The model simulates repetitive basaltic intrusions from the mantle-crust boundary and covers a wide range of tectonic extension and magma intrusion rates that are limited by geophysical observations in different volcanic areas. The model tracks the interaction of mantle-derived and crustal materials, the efficiency of crustal melting, and volume, composition, and fraction of magma in the volcanic system. We find that extensional tectonic and basalt flux rates have a coupled control on the magmatic system. Total amount of melt residing in the crustal column increases with increasing tectonic extension rates and basalt flux rates, and for most conditions is dominated by the residual mantle-derived melt. Efficiency of crustal melting at these conditions reaches its maximum value of 5%. We report on the optimal crustal melting conditions as well, occurring in regions of extreme extension. The results allow us to evaluate the role tectonics plays in augmenting melt production and crustal evolution in active magmatic systems.