[S-IT17] Mass and energy transport in the crust and mantle: from properties to processes

[SIT17-11] Fluid assisted heat dissipation during exhumation-cratonization of ultra-hot deep crust: 2-D simulation model and its application

*Kaushik Das^1,2、Tomoeki Nakakuki^1,2 (1.Hiroshima University、2.Hiroshima Institute of Plate Convergence Region Research)

キーワード：Heat dissipation, 2-D advection-conduction simulation models, Dry and fluid-infiltrated fault planes, Exhumation of ultra-hot deep crust, Field evidence and application

Craton-margin orogenic belts are the places of continental growth by accretionary and collisional tectonics, where the deep crustal rocks quite often get thrusted up at the craton margin forming a fold-thrust belt. Now, the thrusting up of ultra-hot deep orogenic crust on the cold shallow preexisting cratonic crust occurred at different points of the Earth's history at different continents and has its obvious consequence on heat dissipation across the boundary shear zones. Such large-scale structural boundaries provide also the pathways of crustal fluid flows. The resultant shallow crustal processes including sedimentary basin formation, and ore fluid infiltration are also among other consequences. However, studies from the exposed rocks across such thrust boundaries often produce qualitative and speculative ideas on the effect of heat for such thrusting due to the “limited” mineralogical growths and lack of data on fluid activities along such structural boundaries. Supported by field evidence of fluid-induced growth of minerals close to the western thrust boundary of the Proterozoic Eastern Ghats Belt (EGB), India, we have simulated this hot thrusting on cold Archean cratonic crust using 2-dimensional advection-conduction models across single- to multiple fault slice systems. Geologically appropriate boundary conditions, and a fault angle of about 20°, with movement only on the EGB side at a velocity of 2.0 cm/yr were used in this modeling. Precise spatial temperature distribution patterns during the final cratonization are estimated using both the absence and presence of hot fluid/melt at the fault plane for a limited period. Time sequential thermal profilings are done at 15 km depth (i.e. the present-day surface level after exhumation-erosion) across the thrust, both for dry faulting and for faulting associated with hot fluid/melt. The experimental run data show a large temperature increase for the latter case, i.e. up to 700 °C at 5 km, 600 °C between 15 to 30 km from the fault to the Eastern Ghats Belt side, and close to 500 °C at 5 km from the boundary on the cratonic side. The simulation data corroborate closely with the limited available mineralogical data.