叶蛇纹岩脆性-半脆性破裂研究  

Brittle and semi-brittle fractures of antigorite serpentinite in triaxial compression

作　　者：邵同宾[1] 宋茂双[1] 李建峰[1] 张桂男[1,2] 夏莹[1,2] 

机构地区：[1]中国科学院广州地球化学研究所同位素地球化学国家重点实验室,广州510640 [2]中国科学院大学,北京100049

出　　处：《岩石学报》2016年第6期1675-1687,共13页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41174072;41090373;40772029);中国科学院知识创新工程重要方向项目(KZCX2-YW-Q08-03-4);中国科学院战略性先导科技专项(B类)(XDB18010402)联合资助

摘　　要：利用Paterson气体介质高温高压流变仪对纯叶蛇纹岩在100-400MPa围压、25~700℃温度和10-5-1.5×10-6s-1应变速率下进行了三轴压缩变形实验。实验结果表明叶蛇纹石在低压条件下表现为脆性破裂,高压或脱水条件下表现为半脆性破裂。随着温度的增加,叶蛇纹石的强度显示逐渐降低的趋势;尤其在脱水条件下,温度的增加可导致叶蛇纹石强度大幅度地降低,而且此时预热时间对强度的影响比未发生脱水时更加显著。结合前人的研究并对比发现,围压在室温下的增加导致叶蛇纹岩强度增加;但在高温下围压的增加导致试样强度整体上降低,这很可能是试样内聚力的局部损失与韧性增强引起的。围压和温度的升高,以及断层面上流体的增加很可能会增加破裂面的韧性,从而减小摩擦系数。此外,叶蛇纹石并非以往人们所认为的那样具有极低的强度,其强度要比低温蛇纹石（如利蛇纹石和纤蛇纹石）的大得多,即便在高温（大约600℃）下差应力大于约600MPa和中-低温（≤400℃）下差应力大于约1000MPa时仍没有表现出明显屈服的迹象。在脱水条件下,蛇纹岩并没有发生脱水致脆,相反脱水使得试样的断裂行为变得更加温和些。因此,俯冲带蛇纹岩脱水更可能诱发其周围更加脆性的岩石发生地震而不是脱水的蛇纹岩本身发生地震。Deformation experiments on antigorite serpentinites at confining pressures of 100 - 400 MPa,temperatures of 25 -700℃,and strain rates of 10（-5）- 1. 5 × 10（-6）s（-1）indicate that semi-brittle and brittle fractures take place,respectively,at high pressures（ or /and dehydration conditions） and low pressures. Gradual and dramatic decreases in strength of samples are observed in the absence and presence of dehydration,respectively,with the increase of temperature. The preheating time has a more important effect on the strength under high temperatures（ e. g.,600℃） where antigorite may dehydrate during the experiment than under low temperatures（ e. g.,550℃） which are too low to enable dehydration in our laboratory experiments. Combined and compared with previous studies,we found that increasing confining pressure leads to increase in the strength at room temperature but to the overall trend of decreasing strength in the presence of dehydration,probably due to the partial loss of cohesive strength and the increase of ductility. The ductility of fault surface can increase with temperature,confining pressure,and fluid content on fault surface increasing,resulting in friction coefficient decreasing. Antigorite,which is not yielded even after differential stress exceeded ca. 600 MPa at high temperatures（ ca.600℃） and ca. 1000 MPa at low-moderate temperatures（ ≤ 400℃）,has a strength much stronger than that of low temperature serpentines（ e. g.,lizardite and chrysotile）. Surprisingly,dehydration embrittlement,a classic hypothesis proposed for generating intermediate-depth earthquakes,is not observed for dehydrating antigorite in our laboratory. Dehydration of antigorite in subduction zones may therefore induce seismogenic failure in the brittle wall rocks rather than in the dehydrating serpentinite itself.

关 键 词：叶蛇纹石 三轴压缩 脆性-半脆性 脱水致脆 中源地震 俯冲带 

分 类 号：P589.1[天文地球—岩石学]