Thermochronology of the Cordilleran-Type Metamorphic Core Complex: The Example of the Song Chay Massif, Northern Vietnam

Resumo

Based on reconstruction of the thermal evolution of the Song-Chai gneiss–granite massif (Northern Vietnam), the long-term occurrence of granitoid magma at deep levels of the Earth’s crust (H = 15–20 km, Δt ~ 20–50 Ma) is established. The geodynamic analysis and mathematical modeling of the history of consolidation and cooling of the granitoid batholith shows that the magmatic chamber was a thermal trap at the lower level of the Earth’s crust, preserving the residual granite melt for a long time. The removal of this thermal trap from the quasi-stationary state occurs in the zones of transform sliding of lithospheric plates and is accompanied by tectonic exposure of large segments of the Earth’s crust. Ultimately, this leads to transformation of the batholiths into a metamorphic core complex of the Cordilleran-type, to emplacement of residual melts, and, consequently, to the formation of commercial rare-metal deposits.