FORMATION OF THE POSTCOLLISIONAL GRANITES OF THE KARA OROGEN ( <i>North Taimyr, Central Arctic</i> ) PRIOR TO SIBERIAN PLUME ACTIVITY: FROM 2D TO 3D MODELING

Using 3D numerical modeling, we consider the formation of the postcollisional granitoids of the Kara orogen in Northern Taimyr 280–250 Ma under conditions of elevated heat flow due to the orogen’s breakup, prior to the magmatic activity of the Siberian mantle plume. The initial geometry of the model area, the boundary conditions and physical properties of the crust and mantle were set to be close to the structure of the Earth crust in the junction zone of the Kara, Central Taimyr and Siberian blocks. The model shows widespread melting in the granite–gneiss–andesite–basalt layer of middle crust, and a 1–2 km thick melting zone forming at the base of the crust in the granulite layer with the possible participation a mantle component. The magma ascent rate and the formation of groups of adjacent granitoid plutons depend on the value of the elevated mantle heat flow and on the rheology of the melting protolith rocks. The model shows the conditions for intrusion of magma and formation of plutons 10–20 km in diameter at depths 5–8 km in unmetamorphosed rocks. 3D modeling shows the mechanism of periodic magma intrusion pulses at the postcollisional stage during 30–40 Myr. The proposed formation mechanism for the plutons allows to reproduce such shapes and emplacement periodicity that are comparable to their actual geological position and age of the postcollisional granitoids of the Kara orogen. We compare the results of modeling in 2D and 3D configuration with identical model parameters and physical properties of the rocks. We conclude that 3D modeling is a more realistic and accurate means of description of the respective magmatic processes compared to the 2D one.