断层带中假玄武玻璃成因机制及非稳态流变意义
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本文为国家自然科学基金资助项目(编号: 41972220、41722207)和国家重点研发计划项目(编号: SQ2017YFSF040030) 的成果


Formation mechanisms of pseudotachylyte in fault zone and significance of unsteady rheology
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    摘要:

    假玄武玻璃呈玻璃质或隐晶质特性,常常与断层带相伴出现,其形成能有效地降低断层摩擦强度,被认为是古地震快速滑动的化石纪录。因此,对假玄武玻璃的研究对深入了解深部就位的断层变形和地震成因机制等具有重要意义。尽管国内外学者对假玄武玻璃开展了长期的研究,也积累了丰富的资料,然而,由于天然假玄武玻璃非常少见或零星地被报道,再加上其形成环境和过程的复杂性,对假玄武玻璃的构造特征、形成环境和成因机制仍然存在诸多争议及亟待解决的关键科学问题。研究表明,假玄武玻璃可以发育在大陆岩石圈不同深度范围内,即中下地壳乃至上地幔以糜棱岩为主的韧性变形领域(>60 km),或中上地壳层次以碎裂岩为主的脆性变形域(<12 km)。越来越多证据也显示出在断层带的脆—韧性转换域中形成的假玄武玻璃跟浅源地震活动直接关联,也意味着中上地壳脆性变形和中下地壳塑性变形之间存在着更为复杂的耦合关联,同时对不同深部岩石强度和力学行为提出了挑战。对假玄武玻璃形成机制存在由断层面上的摩擦热导致的摩擦熔融体或仅仅是断层面岩石超碎裂粉碎作用认识的争议。而有研究认为干的环境有利于假玄武玻璃形成,因为流体的存在会降低断层面的有效正应力,不利于热量的积累以及摩擦熔融的进行;然而,另外一种观点认为流体的存在可以降低矿物熔融温度有利于断层摩擦熔融及形成假玄武玻璃。本文从假玄武玻璃的形成机制、形成深度、流体影响、形成后对断层强度的影响、以及保存与破坏机制几方面进行了最新总结,并对假玄武玻璃中非晶态物质的成因、脆—韧性转换带之下岩石的变形机制以及对陆壳强度的影响和非稳态流变意义进行探讨。

    Abstract:

    Tectonic pseudotachylyte is rare glassy or aphanitic rock, which often occurs in fault zones. It is considered as a fossil record of rapid sliding of paleo-earthquakes. Formation of pseudotachylyte can effectively reduce the friction strength of rock or fault. Therefore, the study of pseudotachylyte is of great significance to understand the fault deformation and seismic genetic mechanism in deep crust. Although many studies have carried on pseudotachylyte, due to the rare occurring of natural pseudotachylyte and its complexity formation process, there are still many disputes and key scientific problems to be solved such as the structural characteristics, formation environment, and genetic mechanism of pseudotachylyte. The pseudotachylyte can be developed in different depth ranges of continental lithosphere, that is, a ductile deformation domain dominated by mylonite in the middle to lower crust and even the upper mantle (> 60 km), or a brittle deformation domain dominated by cataclastic rock in the middle to upper crust (< 12 km). More evidence shows that the pseudotachylyte form in the brittle—ductile transition domain of the fault zone, which is directly related to shallow seismic activity. It also means that there is a more complex coupling relationship between the brittle deformation of the middle—upper crust and the plastic deformation of the middle—lower crust. There is a long debate on the formation mechanisms of pseudotachylyte, which is caused by friction heating on the fault plane or only the rock comminution on the fault plane. It is believed that the dry environment is conducive to the formation of pseudotachylyte. Because the existence of fluid will reduce the effective normal stress of fault plane, which is not conducive to the accumulation of heat and the progress of friction melting. However, another view is suggested that the presence of fluid can reduce the melting temperature of minerals, which is conducive to fault friction melting and the formation of pseudotachylyte. This paper summarizes the formation mechanism, formation depth, fluid influence, influence on fault strength after formation, and preservation and failure mechanism of pseudotachylyte. Then it further to discuss the origin of amorphous materials in pseudotachylyte, the deformation mechanism of rocks under brittle—ductile transition zone, and the influence on continental crust strength and significance of unsteady rheology.

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李文元,曹淑云.2022.断层带中假玄武玻璃成因机制及非稳态流变意义[J].地质论评,68(3):1006-1032,[DOI].
LI Wenyuan, CAO Shuyun.2022. Formation mechanisms of pseudotachylyte in fault zone and significance of unsteady rheology[J]. Geological Review,68(3):1006-1032.

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  • 收稿日期:2021-09-06
  • 最后修改日期:2022-01-04
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  • 在线发布日期: 2022-05-19
  • 出版日期: 2022-05-15