Cyclic tectono-magmatic evolution of TTG source regions in plum-lid tectonics

Geological-geochemical evidence points towards higher mantle potential temperature and a different type of tectonics, known as plume-lid tectonics, in the early Earth. In order to investigate tectono-magmatic processes associated with plume-lid tectonics and the formation of felsic TTG-like crust, we conduct a series of 3D high-resolution magmatic-thermomechanical models at elevated mantle temperature corresponding to Archean conditions. The numerical experiments show two distinct phases in coupled cyclic tectono-magmatic crust-mantle evolution: a long quiet growth phase followed by a short catastrophic overturn phase. Results of the detailed model analysis presented here suggest that

1) low- and medium-pressure TTGs are formed at the bottom of the crust during both phases; growth and overturn phase. The formation of low- and medium-pressure TTGs is linked with Moho depth and the ratio changes during crustal growth or thinning.

2) To form high-pressure TTGs an entirely different mechanism is required as hydrated basaltic rocks need to be buried below the crust. Cold eclogitic drips can be excluded as a valid mechanism due to their low temperatures and rapid sinking into the deep mantle, instead we suggest delamination or subduction as the main process for high-pressure TTG production.