ABSTRACT

The Borborema Province in NE Brazil is part of a large Neoproterozoic orogenic system related to the assembly of West Gondwana. Its evolution is contentious, due to the superposition of events that overprinted former records. We present a compilation of geological, isotopic (U-Pb detrital zircon and whole-rock Sm-Nd), and geophysical data that support a terrane accretion model for the Transversal subprovince (central Borborema Province). Bounded by thrust- and strike-slip shear zones of regional extent, the terranes vary in nature and age, and magmatic-arc related rocks, retro-eclogites, and dismembered ophiolites provide evidence of accretion. In addition, detrital zircon compilation suggests variable sources, including Palaeoproterozoic detritus related to the Rio Capibaribe and Alto Moxotó terranes and Neoproterozoic sources attributed to the Alto Pajeú and Piancó-Alto Brígida blocks. Accordingly, Archaean and Palaeoproterozoic Nd T_DM model ages are concentrated within the Alto Moxotó and Rio Capibaribe terranes, whereas early- to late Mesoproterozoic isotopic sources dominate in the Alto Pajeú and Piancó-Alto Brígida. A compilation of robust geophysical data shows contrasts in magnetic, gamma-spectrometric, and gravity signatures between the terranes, whereas modelled depths and density values are variable, coinciding with the proposed terrane boundaries. Our analysis suggests that now eroded oceanic lithospheric branches existed within the Transversal subprovince, later converted into dry suture zones. Terrane accretion is a plausible mechanism to rearrange the crustal pieces of West Gondwana, including those of the Borborema Province, and should be considered in other orogenic belts of South America.

摘要

巴西东北部的 Borborema 省是与西冈瓦纳组装有关的大型新元古代造山系统的一部分。由于叠印了先前记录的事件叠加，它的演变是有争议的。我们提供了地质、同位素（U-Pb 碎屑锆石和全岩 Sm-Nd）和地球物理数据的汇编，这些数据支持横向副省（Borborema 省中部）的地体吸积模型。以区域范围的逆冲和走滑剪切带为界，地体的性质和年龄各不相同，与岩浆弧相关的岩石、后榴辉岩和肢解的蛇绿岩提供了增生的证据。此外，碎屑锆石编译表明来源可变，包括与 Rio Capibaribe 和 Alto Moxotó 地块相关的古元古代碎屑，以及归因于 Alto Pajeú 和 Piancó-Alto Brígida 地块的新元古代资源。因此，太古代和古元古代 Nd T_DM模型年龄集中在 Alto Moxotó 和 Rio Capibaribe 地体中，而早至晚中元古代同位素来源在 Alto Pajeú 和 Piancó-Alto Brígida 中占主导地位。强大的地球物理数据汇编显示了地体之间的磁性、伽马光谱和重力特征的对比，而建模的深度和密度值是可变的，与建议的地体边界一致。我们的分析表明，现在被侵蚀的海洋岩石圈分支存在于横向副省内，后来转变为干缝合带。地体吸积是重新排列西冈瓦纳地壳（包括 Borborema 省的地壳）的一种合理机制，应在南美洲的其他造山带考虑。