关键词: 辉长岩, 辉绿岩, 脆塑性转化, 水

Abstract: Previous studies showed that the deformation of dry mafic lower crust is semi-brittle,which may locate in transition of semi-brittle slip to semi-brittle flow. Therefore,we perform tests on brittle-plastic transition of four kinds of dry and wet mafic rocks in order to comprehend the mechanical behavior of continental lower crust. The experimental confining pressure ranges between 450～500MPa,and strain rate is 1×10^-4s^-1. The results of experiments show that the samples of dry Jinan gabbro (sample C),dry Yanqin diabase (sample D) and wet Yanqin diabase (sample D) have experienced deformation regimes of faulting,cataclastic flow,semi-brittle flow and plastic flow under 300～900℃; and dry Panzhihua fine grained gabbro (sample A) and fine-to medium grained gabbro (sample B) have experienced deformation regimes of semi-brittle flow and plastic flow under 700～900℃. The temperature of brittle-ductile transition of dry gabbro is 100℃,higher than that of dry diabase. The temperature of brittle-plastic transition of all dry mafic samples is 700℃,but the microstructures of semi-brittle flow are variable. For example,grain-size reduction and preferred orientation of plagioclase and clinopyroxene occurred in deformed diabase,displaying the typical structures of protomylonite. However,this kind of microstructure did not appear in the deformed samples of gabbro. In contrast to the semi-brittle flow regime,the strength and microstructure of all dry mafic samples are basically the same in the plastic flow regime under higher temperature,when dislocation glide becomes the predominant deformation mechanism. The main effect of water on brittle-plastic transition of mafic rocks is embodied by both the change of strength and temperature of brittle-ductile transition and brittle-plastic transition. The strength of wet diabase is much lower than that of dry gabbro and diabase at the experimental condition. The temperature of both brittle-ductile transition and brittle-plastic transition of wet diabase is 100℃ lower than that of dry diabase,and 200℃ lower than that of dry gabbro. The temperature of transition from semi-brittle flow to plastic flow of wet samples is much lower than that of dry samples.

Key words: gabbro, diabase, brittle-plastic transition, water