Scale-dependent influence of pre-existing basement shear zones on rift faulting: a case study from NE Brazil
Scale-dependent influence of pre-existing basement shear zones on rift faulting: a case study from NE Brazil
复制标题
预先存在的基底剪切带对裂谷断层的尺度依赖性影响：巴西东北部的案例研究
DOI：
10.1144/jgs2012-043
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发表时间：
2013
影响因子：
2.7
通讯作者：
Kirkpatrick J
中科院分区：
文献类型：
--
作者：
Kirkpatrick J
大陆地壳的断裂引发了断层，这些断层通常受到先前存在的构造的影响。我们记录了新发现的断层切割前寒武纪单位在内部的东北巴西边缘，以评估结构继承裂谷几何形状和断层结构的影响。地层和构造资料表明，断裂在冈瓦纳裂谷主期活动。先存构造对中生代裂谷断裂活动的影响与规模有关。在区域上，断层走向平行于近垂直，地壳规模的Brasiliano（c。750-540 Ma）剪切带。剪切波分裂所显示的糜棱岩面理和下地壳广泛分布的低应变控制了裂谷断层的总体方向和运动学。然而，断层的露头观测表明，在高达数百米的尺度上，糜棱岩面理对断层结构的影响很小。断层横切剪切带，通常不利用叶理面作为剪切断裂。相反，滑动带和断裂具有与局部面理方向形成锐角的一系列方向。这一观察解释了与大陆内部地区的古代剪切带相一致的地震活动相关的震源机制的范围。
Rifting of continental crust initiates faults that are commonly influenced by pre-existing structures. We document newly identified faults cutting Precambrian units in the interior of the NE Brazilian margin to assess the effects of structural inheritance on both rift geometry and fault architecture. Stratigraphic and structural data indicate that the faults were active in the main phase of rifting of Gondwana. The influence of pre-existing structures on the Mesozoic rift faulting is scale dependent. Regionally, the faults trend parallel to subvertical, crustal-scale Brasiliano (c. 750–540 Ma) shear zones. Mylonitic foliations and broadly distributed low strain in the lower crust indicated by shear-wave splitting controlled the overall orientation and kinematics of the rift faults. However, outcrop observations of the faults show that at scales up to hundreds of metres, mylonitic foliations have little influence on fault architectures. Faults cross-cut shear zones and do not commonly utilize foliation planes as shear fractures. Instead, slip zones and fractures have a range of orientations that form acute angles to the local foliation orientation. This observation explains the range of focal mechanisms associated with seismicity that coincides with ancient shear zones in intra-continental areas.