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首页> 外文期刊>Anais da Academia Brasileira de Ciencias >Kinematics and geometry of structures in the southern limb of the Paraíba do Sul divergent structural fan, SE Brazil: a true transtensional shear
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Kinematics and geometry of structures in the southern limb of the Paraíba do Sul divergent structural fan, SE Brazil: a true transtensional shear

机译：巴西东南部Paraíbado Sul发散结构扇南肢结构的运动学和几何学：真正的拉伸剪切

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摘要

Shear zones geometry in the Paraíba do Sul belt, southeastern Brazil, delineates a NE-trending fan-like structure. Shear zones dip towards SE in the northern limb, and towards NW in the southern one. This geometry has been interpreted either due to transpression or to late folding of flat-lying thrust surfaces. Stretching lineation plunges to ENE-ESE in the northern limb and towards NNE-NE in the southern one. Structural data in the southern limb of the divergent fan suggest a two stage kinematic evolution in high-temperature conditions: an earlier stage with top-to-SSW/SW sinistral thrusting and orogenic-parallel tangential motion, and a later stage with top-down to NNE/NE transtensional deformation. We propose a heterogeneous deformation model to explain the observed shear reversal, and suggest that the imposed transpressional displacement gradient may change during progressive deformation due to transient rheological inhomogeneities in bulk pure shear strain. In the earlier stage, the partially molten material could easily accommodate the imposed strain rates, giving rise firstly to the SW-directed shearing. As the thermal disturbance tended to vanish and the convergence increased, the NNE-directed transtensional shearing developed. We propose that the transtensional deformation characterized in this paper could be related to extrusion processes during regional transpressional strain.
机译：巴西东南部的Paraíbado Sul带中的剪切带几何形状描绘了一种NE趋势的扇形结构。剪切带在北肢向东南倾斜，在南部向西北倾斜。这种几何形状是由于压平或平躺推力面的后期折叠而解释的。伸展线突然向北延伸至ENE-ESE，向南延伸至NNE-NE。发散扇南肢的结构数据表明，在高温条件下运动发生了两个阶段的演变：早期发生了顶-SSW / SW左倾和造山-平行切向运动，后期发生了自顶向下的运动。 NNE / NE拉伸变形。我们提出了一种非均质变形模型来解释观察到的剪切逆转，并提出由于大体积纯剪切应变中的瞬时流变不均匀性，施加的压迫位移梯度可能在渐进变形过程中发生变化。在早期阶段，部分熔融的材料可以轻松适应施加的应变率，首先导致了西南定向剪切。随着热扰动趋于消失并且收敛增加，NNE定向的超张剪力发展了。我们认为本文所描述的拉伸变形可能与局部压应变过程中的挤压过程有关。

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