阿尔金断裂双层花状构造的厘定

FLOWER-STRUCTURES FORMED IN TWO LEVELS ALONG THE ALTUN FAULT

阿尔金断裂带主要经历了两阶段的构造演化 ,形成不同层次且具有不同特点的典型花状构造型式。宏观断层构造组合、断层擦痕产状的变化以及节理组合充分反映出晚期阶段浅部层次花状构造的存在 ,早期阶段中部层次花状构造由反映区域应变型式的糜棱状岩石中其它应变标志性组合的存在表现出来。结合Ar Ar记年与矿物对测温结果 ,表明前者形成于距今 46Ma ,是一次规模最强烈的变形叠加事件 ;后者由距今 91～ 89Ma的韧性走滑运动形成 ,并伴有断层带内的低级变质作用 (温度 2 70～ 5 0 0℃ ,压力 0 .0 5～ 0 .45GPa)。两阶段双层花状构造并存充分说明区域性走滑作用过程及其调节作用的多阶段性与继承性 ,其出现部分地调节了由印度板块和欧亚板块陆—陆碰撞过程中区域性地壳物质的向东蠕散和隆升过程。

Two stages of structural evolution were recognized in the Altun fault zone, which created flower structures in varied crustal levels with different features. The existence of fault breccias, fault zones and fault groups suggested a faulting in the upper crustal level. Meanwhile, it was indicated, by occurrence of the mylonites, related structures and metamorphic rock associations in the fault zone, that the faulting experienced a stage of evolution in the middle crustal level. A later stage flower structure was evidenced by fault groups, striae on fault planes and related joints, while the earlier stage flower structure was characterized by strain indicators in the mylonites, such as occurrence variation of the mylonitic foliations, types, fabric patterns and strain patterns of tectonites. The 40Ar- 39Ar dating and geothermometer-geobarometer estimation revealed that the former was a superimposition event about 46 Ma ago, and the latter a ductile faulting about 91～89 Ma ago, accompanied with low-grade metamorphism (temperature 270～500 ℃ and pressure 0.05～0.45 GPa). The co-occurrence of two stages of flower structures might suggest the multistage development and inheritance of development of regional strike-slip faulting due to the continent-continent collision between the Eurasia and Indian plates. The strike-slip faulting along the main fault recorded the eastward regional creeping, and the development of two stages of flower structures and related thrusting on both sides provided chances for regional uplifting and for upwelling of deep crustal materials.