ABSTRACT

The factors controlling the inception of continental-scale transcurrent shear zones are still under debate. In order to a better understanding of the origin and evolution of the 400 km long West Pernambuco shear zone (WPSZ), we undertook a structural, geochronological and geochemical study in an area around its eastern termination. The WPSZ is one of the most expressive strike-slip shear zones in the Borborema Province of NE Brazil, which resulted from orogenic processes associated with the assembly of western Gondwana in the Late Neoproterozoic. Previous studies have shown that 1000–940 Ma-old granitic orthogneisses are located immediately to the south of the western and central portions of the WPSZ. Based on LA-ICP-MS U-Pb zircon dating, we show that rocks with similar ages (995–956 Ma) also occur to the East. The geochemical characteristics of this magmatism and the alignment of the bodies along a narrow, less than 40 km-wide belt point to emplacement in a continental rift-related setting. The WPSZ thus follows the trend of a pre-existing rheological discontinuity, which induced strain localization during the post-collisional stage of the Brasiliano-Pan-African orogeny.

摘要

控制大陆尺度跨流剪切带开始的因素仍在争论中。为了更好地了解400 km长的西伯南布哥剪切带（WPSZ）的起源和演变，我们在其东端附近进行了结构，地质年代和地球化学研究。WPSZ是巴西东北部Borborema省最富有表现力的走滑剪切带之一，其源于与新元古代晚期西部冈瓦纳的组装有关的造山过程。以前的研究表明，在WPSZ西部和中部的南部紧邻有1000-940 Ma的花岗岩古生片麻岩。基于LA-ICP-MS U-Pb锆石测年，我们显示出东部也出现了类似年龄（995–956 Ma）的岩石。这种岩浆作用的地球化学特征以及沿一条狭窄的，小于40 km宽的带体的排列指向了与大陆裂谷有关的环境中的位置。因此，WPSZ遵循预先存在的流变不连续性的趋势，该趋势在巴西利亚－潘－非洲造山运动的碰撞后阶段引起了应变的局部化。