基性岩流变的复杂性与成分对岩石流变影响的实验研究

Rheological complexity of mafic rocks and the effect of mineral component on creep of rocks

在采用天然基性岩样品进行的流变实验中,存在因实验温度低而样品处于半脆性变形域与因实验温度高而样品颗粒边界出现熔体的矛盾。文献中给出的流变参数中,应力指数n的可靠性高,具有良好的重复性,激活能Q在一定范围内具有重复性,而系数A重复性差。采用6种样品进行流变实验。结果表明,矿物成分对岩石流变的影响比根据端员组分确定的双组分和多组分岩石流变物理模型要复杂得多。由斜长石、单斜辉石和角闪石组成的样品中,当斜长石和单斜辉石含量接近,而角闪石含量低于10%,斜长石和单斜辉石控制了岩石的流变;如果样品中有超过10%的角闪石参与流变,角闪石在变形中所起作用非常显著。由斜长石、石英和角闪石组成的样品,当石英含量小于10%而斜长石和角闪石含量接近时,斜长石和角闪石控制了岩石的流变;当斜长石含量达到70%时,样品变形更接近长石特性;如果石英含量超过20%时,石英在变形中起到主要作用。选择与基性麻粒岩中主要矿物成分接近的天然辉长岩(辉绿岩),或者从天然基性麻粒岩中挑选出主要矿物,通过热压合成人工样品,进行高温流变实验是研究基性麻粒岩流变的最有效途径。

In the rheological experiments for natural mafic rock samples there will be semi-brittle deformation under lower temperature ranges, in contrast, there will appear melts at grain boundaries in the sample under higher temperatures, and this could greatly effect the rheologieal behaviors of samples. In the literature, the stress exponent n is mostly reliable and with high recurrence rate, the activation energy Q is, in some extent, reiterative, however, the coefficient A is poorly reiterative. We performed creep tests using 6 kinds of samples with different mineral components. The mechanical data show that it is more complicated for the effect of mineral component on rheology of rocks than physical models based on flow laws of two phase and polyphase aggregates determined by end-member components. For the sample consisted of plagioclase, clinopyroxene and hornblende, rheologieal behaviors are controlled by plagioelase and clinopyroxene when the content of hornblende is less than 10%, however, the role of hornblende could become significant for deformation of samples when the content of hornblende is higher than 10%. For the sample with major mineral of plagioclase, quartz and hornblende, rheologieal behaviors are dependent on plagioclase and hornblende when content of quartz is less than 10%, but when plagioclase content is near 70% it will decide the deformation behaviors of the sampies. In contrast to that, quartz could completely control the creep of samples when its content is higher than 20%. The most effective method to study rheology of mafic granulite is to perform creep tests using natural gabbro （or diabase） as well as using hot pressed synthetic samples prepared from the major mineral components extracted from mafic granulite.