橄榄石集合体扭转大变形实验研究  

High strain torsion experiment on olivine aggregates.

作　　者：赵永红[1,2] 綦超[1] 李杨[1] M. Zimmerman D. L. Kohlstedt 

机构地区：[1]北京大学地球物理学系,北京100871 [2]美国明尼苏达大学地质与地球物理系MN55455

出　　处：《岩石学报》2008年第6期1411-1416,共6页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(40521002,40474035)资助

摘　　要：对(Mg_(0.5),Fe_(0.5))_2SiO_4和(Mg_(0.7)、Fe_(0.3))_2SiO_4橄榄石集合体进行了高温高压扭转大变形实验研究。试验在高精度和高分辨率 Paterson 气体介质变形试验机上进行,试验温度为1473K,围压为300MPa,应变率为10^(-4)～10^(-5)S^(-1),剪切应力为82～124MPa,剪切应变为～400%,将变形后试件沿轴向切开进行了显微结构分析,确定了不同纵截面上橄榄石的颗粒尺寸。由蠕变数据拟合出的流动律中,应力指数为与三轴压缩实验给出的应力指数吻合。利用 EBSD 方法分别对变形前后试件中橄榄石的晶格最优取向(LPO)进行了测定。在富铁橄榄石样品中观测到的最优晶格取向表明滑动属于(okl)[100]滑动系统。这个结果与 Bystricky 等人在 Fo_(90)种观测到的最优晶格取向特征是一致的。Torsion experiments were conducted in a high-pressure and high-temperature gas medium torsion apparatus under anhydrous conditions to shear strains of - 4 at a constant angular velocity, a temperature of 1473K and a confining pressure of 300MPa. The compositions of the aggregates were Fo50 and Fo70synthesized from Fa100 and Fo90 mixture. The geometry of the samples was a cylinder with 9.4mm in diameter and 5.0mm in length encapsuled by the Ni sleeve to buffer oxygen fugacity at olivine stability field. The small element in the sample undergoes deformation at constant strain rate by simple shear. The applied shear strain rate ranged from 10^-4 to 10^-5 s^-1, yielding shear stresses of 82 - 124 MPa supported by the sample. Microstructures were analyzed with optical and electron mieroseopies. A series of parallel sections were examined starting near the outside edge of the cylindrical sample and proceeding to the central section （ Fig. 1 ）. The EBSD was performed on a profile to determine the LPO changes with different strains. The LPO indicates that slip on the （010） [ 100] slip system dominated. This observation is consistent with the LPO reported by Bystricky et al. for samples of Fo90.

关 键 词：橄榄石集合体 高温高压 扭转大变形 晶格最优取向(LPO) 实验研究 

分 类 号：P578.942[天文地球—矿物学] P589.1[天文地球—地质学]