TRANSFORMATION FROM DUCTILE SHEAR ZONES TO SHEAR FRACTURE AND RELATED LITHO METALLOGENESIS

It has been known from rock deformation experiments that,under moderate load,creep may finally develop into fractures in rocks.In laboratory experiment of rocks with 3 different axial stresses shear fractures have been found within the very tiny ductile shear zones.It is realized that myloinites are not necessarily favourable to the accommodation of later faults.However,it is very common for both fracture and ductile behaviour to oceur together.Because of the significant difference in strain rates of drag folding and faulting,the most possible mechanism is that to dragging may precede faulting.Therefore,ductile shear zones can lead to shear fracture at the same structural level where ductile deformation develops.The high temperature and abrupt pressure drop ensuing in the process may result in partial melting,material migration and unloading of hydrothermal fluids to trigger litho-metallogenesis.The authors consider that this mechanism can afford to explain such problems as the dynamical process for rock and mineral formation and the formation of duplex structure.