韧性剪切带向剪破裂的转化与成岩成矿作用

岩石应力-应变实验表明,在中等载荷(等于或大于岩石蠕变极限)作用下,岩石蠕变最终可导致破裂;三轴差应力实验后的试件中,多见极小的韧性剪切带中存在剪破裂;研究发现,糜棱岩并不一定有利于后来断层的叠加,然而二者共存一处的现象却十分普遍;牵引褶皱和剪切断层的应变速率差别极大,只能先牵后断。由此可见,韧性剪切带在同一构造层次情况下,可在变形较强的部位产生剪破裂;此时温度较高和压力骤降,导致部分熔融和流体卸载,这一转化过程产生的温度、压力和流体浓度等梯度变化,促使流体(物质)运移与富集导致成岩成矿。这一认识对解释动力成岩成矿、断层双层结构模式等诸多问题有重要意义。 

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.