Investigation of Microscale fracture opening in host inclusion systems

Due to high confining pressure and weak rheology, the mechanism for Earthquakes below brittle-ductile transition zones which starts from 10-15 km remains an open question. The main mechanisms proposed in many literature studies need either a hydrous mineral or a pre-existing ductile shear zone. But in some recent studies, it has been found that pseudotachylyte from the dry lower crust contains neither fluids nor mylonites which are the main ingredients for the viability of the proposed mechanisms. These observations imply that the currently available mechanisms are inadequate to explain the cause and a new mechanism is required. In crustal rocks, host inclusion systems, where a mineral fully encloses another one are extremely common. The mechanical stability of host inclusion pairs is clearly different from that of the two single minerals taken separately. At shallow depth pressure and temperature, a large deviatoric strain is subjected to the host due to the exhumation of the host-inclusion system, which further deteriorated by the induction of large strain due to the transformation of α-quartz into β- quartz by a martensitic phase transition. Preliminary results demonstrate that such behaviour of the host-inclusion system might create a sizeable non-hydrostatic stress field, thus including significant shears that could be responsible for crack initiation and propagation in the host. Moreover, cracks from two or more inclusions can interact and coalesce to form a macro crack resulting in a fault. This thesis aims to propose an alternative theory to explain this open question and to check its feasibility using numerical methods by simulating the actual host-inclusion system. In addition to that, the effect from ‘shape of inclusion’ and ‘Exhumation of the host-inclusion system’ for the crack initiation and propagation have been investigated thoroughly.