摘要
为了研究橄榄岩位错蠕变过程中粒间滑动所起的作用,对经脱水干燥的橄榄石集合体试件进行了一系列的变形试验。三轴压缩蠕变试验在T=1473K、P=200和400MPa条件下使用一台高分辨率气体介质变形装置进行,每个试件在介于100～250MPa之间的不同应力水平下变形,得到的应变率介于10^(-4)～10^(-6)S^(-1)之间。随着差应力的增加,得到扩散蠕变到位错蠕变的过渡,在位错蠕变域,易滑动体系在～50MPa和颗粒尺寸为15μm时伴随粒间滑动。这一粒径敏感蠕变域由应力指数3.2±0.1和粒径指数1.8±0.2来刻划。将这一流动律与其他扩散和位错蠕变结果进行对比,表明本文得出的流动律可应用于粒度小于100μm和差应力大于20MPa时的岩石流动。因此,与粒间滑动相伴的位错蠕变可能是上地幔岩石圈剪切带变形局部化的主要变形机制。
To investigate the role of grain boundary sliding during dislocation creep of dunite, a series of deformation experiments were carried out under anhydrous conditions on fine-grained samples synthesized from powdered San Carlos olivine. Triaxial compressive creep tests were conducted under a temperature of 1473 K and confining pressures of 200 and 400 MPa using a high-resolution gas-medium deformation apparatus. Each sample was deformed at several levels of differential stress between 100 and 250 MPa to yield strain rated of 10(4) to 10(6) s(-1). With increasing differential stress, a transition from diffusion creep to dislocation creep regime in which motion on the easy slip system is accomodated by grain boundary sliding (GBS) occurs at similar to 50 MPa for samples with a grain size of 15 mu m. This grain size sensitive creep regime is characterized by a stress exponent of 3.2 +/- 0.1, and a grain size exponent of 1.8 +/- 0.2. Comparison of our flow law for dislocation creep accommodated by grain boundary sliding with those for diffusion slip system reveals that the present flow law is important for flow of rocks with grain sizes of <100 mu m at differential stresses >20 MPa. Hence, GBS-accommodated dislocation creep is likely to be the dominant deformation mechanism in deep-rooted, highly localized shear zones in the lithospheric upper mantle.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2009年第3期708-712,共5页
Acta Petrologica Sinica
基金
国家自然科学基金项目(40821062,40874043,40872133)
美国NSF (EAR - 0079827,INT -0123224)资助,
关键词
橄榄石
高温高压
粒间滑动
位错蠕变
实验研究
Olivine
High temperature high pressure
Grain boundary sliding
Dislocation creep
Experimental study
