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

摘要： 研究表明,干的基性下地壳处于半脆性摩擦与半脆性流变的过渡状态,因此,文中采用多种基性岩样品进行了干的和含水基性岩的脆塑性转化实验,以深入理解大陆下地壳的力学性质。实验围压450～500MPa,应变速率1×10^-4s^-1。实验结果表明,济南辉长岩(样品C)、延庆辉绿岩(样品D)和含水辉绿岩从300℃到900℃经历了脆性破裂、碎裂流动、半脆性流动和塑性流动几个变形域,而细粒攀枝花辉长岩(样品A)和中细粒攀枝花辉长岩(样品B)从700℃到900℃经历了半脆性流动和塑性流动2个变形域。干的辉长岩样品比干的辉绿岩样品发生脆延性转化的温度高100℃;所有干的基性岩样品的脆塑性转化都发生在700℃,但半脆性流动域变形微观结构有差别,辉绿岩中斜长石和辉石发生了细粒化,并存在强烈的定向,形成初糜棱岩结构,辉长岩样品的细粒化和定向特征不明显。干的基性岩在以位错滑移为主的高温塑性流变域的强度和微观结构基本相同。水对基性岩脆塑性转化的影响体现在岩石的强度和脆延性与脆塑性的转化温度两方面。在实验温度范围内,含水辉绿岩样品的强度远小于干的辉绿岩和辉长岩样品的强度,含水辉绿岩发生脆延性转化和脆塑性转化的温度比干的辉绿岩低了100℃,比干的辉长岩低了200℃,而进入塑性变形域的温度则更低。

关键词: 辉长岩, 辉绿岩, 脆塑性转化, 水