5:15 PM - 6:30 PM
[SCG46-P08] Fracture behavior of silicate network phase-separating from aqueous fluid
Keywords:Fracture, Silicate netowrk, Aqueous fluid, Phase separation or phase demixing
Assuming the crustal structure with “actively-shrinking” lower crust of silicate network phase-separating from aqueous fluid below “passively-deformed” upper crust of usual rocks, I tried to explain the crustal activities including the intra-crustal seismicity in the short time scale and the crustal stabilization from its compaction in the long time scale (Koyama, JpGU 2019, JpGU-AGU2020, JPS2020, AGU2020). One of the important problems in the deformation of the “active” lower beneath the “passive” upper is the strength of the lower-crustal network solid filled with the fluid, because the fluid pressurized into cracks in rocks can weaken the rocks through inducing the fracture, which is a known fact (Hubbert and Rubey, 1959; Michaelske, 1982).
This fluid effect promotes mechanically and chemically fracture of crustal rocks: In the case of aqueous fluids, H2O can slide the cracks through opening the impermeable crack walls with the pressure (Hubbert and Rubey, 1959) and can propagate the crack tips through disconnecting the bonds of the rock materials around there with the chemical reactions (Michaelske, 1982). These must result from the contact between the two materials originating from their different thermodynamic states, which create their impermeable interface for their counter pressures and their chemical potential gradient for their mutual dissolution around the interface.
Then, how do the fluid effect arises in the fluid-solid coexistence in the same single thermodynamic state? Phase separation between shrinking amorphous network solid and diffusing fluid realizes this situation (Tanaka, 2000, 2017; Koyama, 2009, 2018); In phase separation between shrinking silicate network and diffusing aqueous fluid, the question is whether the fluid effect on the network fracture are the same with the case of the contact between fluid and rock from different origin or not. I expect to be not, because thermodynamic relation between H2O and SiO2 in the phase separation is the opposite from that in the above fluid-rock contact: In the two coexisting phases from the same origin the pressure is common between them and the fluid can diffuse through the network, and chemical potential gradient demixing them in the phase separation, on the other hand, must prevent the reactions for network dissociation. Thus, the counter pressure and the crack tip propagation by the fluid must be difficult to arise on the coexisting network: The fluid must be difficult to weaken the network.
If these are true, the network coexisting with the fluid in the lower crust can keep its strength under the fluid-filled situation. On the other hand, the fluid diffusing from the shrinking lower-crustal network can weaken the usual upper-crustal rocks as a result of its permeation from the crustal lower to the upper. Thus, we can consider the possibility that the lower-crustal network is stronger than the upper-crustal rocks, and that the “actively-shrinking” former deform the latter one-sidedly.
This fluid effect promotes mechanically and chemically fracture of crustal rocks: In the case of aqueous fluids, H2O can slide the cracks through opening the impermeable crack walls with the pressure (Hubbert and Rubey, 1959) and can propagate the crack tips through disconnecting the bonds of the rock materials around there with the chemical reactions (Michaelske, 1982). These must result from the contact between the two materials originating from their different thermodynamic states, which create their impermeable interface for their counter pressures and their chemical potential gradient for their mutual dissolution around the interface.
Then, how do the fluid effect arises in the fluid-solid coexistence in the same single thermodynamic state? Phase separation between shrinking amorphous network solid and diffusing fluid realizes this situation (Tanaka, 2000, 2017; Koyama, 2009, 2018); In phase separation between shrinking silicate network and diffusing aqueous fluid, the question is whether the fluid effect on the network fracture are the same with the case of the contact between fluid and rock from different origin or not. I expect to be not, because thermodynamic relation between H2O and SiO2 in the phase separation is the opposite from that in the above fluid-rock contact: In the two coexisting phases from the same origin the pressure is common between them and the fluid can diffuse through the network, and chemical potential gradient demixing them in the phase separation, on the other hand, must prevent the reactions for network dissociation. Thus, the counter pressure and the crack tip propagation by the fluid must be difficult to arise on the coexisting network: The fluid must be difficult to weaken the network.
If these are true, the network coexisting with the fluid in the lower crust can keep its strength under the fluid-filled situation. On the other hand, the fluid diffusing from the shrinking lower-crustal network can weaken the usual upper-crustal rocks as a result of its permeation from the crustal lower to the upper. Thus, we can consider the possibility that the lower-crustal network is stronger than the upper-crustal rocks, and that the “actively-shrinking” former deform the latter one-sidedly.