tailieunhanh - Tạp chí: ĐỊA CHẤT

Những thông tin và kiến thức về địa chất cho các bạn học chuyên ngành tham khảo | Shear zone is a general term used to describe narrow zones of planar or tabular structures in the Earth’s crust with subparallel boundary, along which the shear strain is localized. The relative undeformed wall rocks on opposite sides of the zone were displaced relatively to one another in a direction parallel to the plane of the shear zone. Shear zones were formed under various deformation conditions and can be subdivided into three main types. Brittle shear zones (faults and fault zones) occur in the upper-most part of the crust, where the rocks experience brittle deformation with little or no metamorphism. Brittle-ductile shear zones occur below the brittle zone, where the ductilely deformed rocks within the shear zone were fractured and dismembered in a moderate pressure and temperature environment. Ductile shear zones are situated in the deeper part of the crust, where both temperature and pressure are high with no discontinuity across the ductile shear zone. Shear strain magnitude varies smoothly across the zone and the fabric of the rocks within the zone was modified by plastic deformation processes. Each type of shear zones is characterized by shear products, fabric and kinematic indicators that can be observed at various scales. The depth of the transition between brittle, brittle-ductile and ductile deformation varies greatly depending on many physio-chemical factors of the deformation environment, the physical property of the rocks, as well as the presence of pre-existing structures.