摘要
野外地质观察发现,在大陆地壳变质岩中可以广泛观察到围绕一个大的单晶或者硬质点的两端区域填充低粘度相物质形成的压力影。为了定量研究岩石材料中压力影的形成条件,本文利用高精度Paterson气体介质变形装置,对含有刚性球的圣卡罗橄榄石和洋中脊玄武岩(MORB)的混合物圆柱型样品进行了高温高压扭转变形试验。变形实验前样品的初始熔融均匀分布,比例为φ≈0.05,变形试件尺寸为D8.9mm×L5.5mm,内含8粒直径约1mm的刚性球。扭转变形试验温度为1473K,围压为300MPa,应变率为γ≈1×10^(-4)s^(-1),最大剪切变形为γ≈4。实验结果表明,岩石受到扭转力的作用产生变形之后,当局部剪切应变达到γ≈1时,可以在刚性球周围形成熔融富集带和熔融贫乏带,即压力影构造,围绕刚性球对称分布。由于熔融分布的不均一性,富集带熔融比例上升,最高可以达到φ_(high)=0.1~0.3,熔融贫乏带熔融比例下降,含量为φ_(low)=0.01~0.02。由于刚性球对其周围的压力分布的扰动区域大约为刚性球的尺度范围,因此,在离开刚性球一定距离后,熔融趋于均匀分布。
Field geological observation showed that, pressure shadows with two regions filled with a low-viscosity phase located around a large single crystal or hard inclusion are widely observed in metamorphic rock. To quantitatively study the forming conditions of pressure shadow, samples which composed of fine-grained San Carlos olivine plus mid-ocean ridge basalt （MORB） containing dispersed sub-millimeter-sized single crystal beads of olivine or zirconia were deformed in torsion at high-pressure and high- temperature. The melt initially homogeneously distributed with a melt fraction of 0. 05 before deformation. Specimen is size of D8.9mm × 15.5mm containing 8 particles size of Dlmm. The torsion experiment was done at a temperature of 1473K, confining pressure of 300MPa, shear strain rate of γ≈ 1 × 10-4s- 1 and the maximum shear strain is 4. Indicted by the experimental results, melt-enriched and melt-depleted regions around the beads became observable and symmetrically distributed round the rigid olivine bead （ i. e. pressure shadow structure ） when the local shear strain reaches 1 and rocks were deformed by torsional force. Inhomogeneous distribution of melt formed due to the pressure gradient, melt-enrich region fraction varies from 0. 1 to 0. 3 and the melt-depleted regions fraction varies from 0. 01 to 0.02. Due to the disturbance area of the pressure distribution around the rigid ball is about the scale of the rigid ball scope, therefore, melt distribution tends to be homogeneous at a certain distance away from the rigid ball.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2016年第1期264-270,共7页
Acta Petrologica Sinica
基金
国家自然科学基金项目(40874043
41274094)资助
关键词
橄榄石
扭转实验
高温高压
部分熔融
压力影
Olivine
Torsion experiment
High temperature and high pressure
Partial melt
Pressure shadow
