摘要
在甘肃北山一个东西向展布、椭圆状的晚古生代花岗岩体内主要发育着3期岩墙群,其中中期基性岩墙群最密集,呈现出弧形展布的特征,在该侵入体北部呈北北东向趋势,向南逐渐偏转为北北西向。关于中期岩墙群弧形展布的原因有两种可能的解释,即:纵弯褶皱和应力场扰动。野外观察不支持第一种解释,因为在岩墙或围岩内都没有观察到与褶皱有关的变形构造。本文利用Poly3D软件模拟了近东西向隐伏断层活动对上覆应力场的扰动。计算结果表明,当北北西—南南东向的区域性拉张叠加上沿着隐伏断层发生不协调的右行走滑时,水平大主压应力迹线在隐伏断层上方出现类似的弧形展布。这意味着稍早的花岗岩侵入体冷凝冷却并没有完全焊接地壳内一些大尺度断层,地壳断块的相对独立活动可以造成沿着这些断层发生与区域变形场不协调的右行走向滑动,进而形成岩墙群弧形展布所需要的地应力场。
Within an elliptical, W-E trending Hereynian granitoid in the Northern Mountain, northwestern Gansu Province three main sets of dike swarms were recognized. The second set has a majority of dikes throughout the granitoid. It is mafic in composition,and distributed in a curved pattern. The dike swarm in the set changes the strike gradually from the north-northeast in the north to the north-northwest in the south. This curved pattern may be ascribed to two possible mechanisms, multi-layer buckling and local stress-field perturbation. The former mechanism seems inappropriate,depending upon the fact that no or almost a few deformational structures related to buckling were observed either in the dikes or their contacts at outcrops. For the latter mechanism, Poly3D numerical software was used in this paper to study the influence in the local stress-field perturbation of a presumably hidden,reactivated fault beneath the granitoid. Numerical results show that, under the NNW to SSE extension in the region, a large amount of discordant dextral strike slip along the hidden fault is required to produce a similar map of the curved trajectory of the larger horizontal stress above. This suggests the incomplete welding of the sides of the fault by the granitic intrusion along it, which afterwards permitted the reactivation of the fault, probably due to the relatively independent movement of the faulted blocks,as a dextral transcurrent fault.
出处
《地质科学》
CAS
CSCD
北大核心
2010年第1期80-91,共12页
Chinese Journal of Geology(Scientia Geologica Sinica)
基金
国家科技部重要基础研究发展规划项目(编号:2007CB411307)
中国科学院"百人计划"项目(编号:KZCX0543081001)资助
