Abstract

The Egyptian Nubian Shield (ENS), the northwestern continuation of the East African Orogen (EAO), comprises a variety of three lithologically and structurally different tectonic provinces—southern compressional-, central transpressional/wrench-, and northern extensional- provinces. The extensional tectonic province (ETP) extends from Qena‒Safaga shear belt up to the northern tip of the ENS. Several lines of evidence indicate extensional regime in the ETP, such as mantle delamination-induced post-orogenic magmatism and bimodal Dokhan Volcanics, together with the pervasive E‒W dyke swarms and the E‒W (to ENE‒WSW) oriented extensional fractures. The present work is devoted to carry out the fault striae analysis and paleostress reconstruction of the northern tectonic province (ENS) in attempt to add more contribution to the brittle deformation history of the northern EAO. Field measurements collected from six areas (I‒VI) have been processed using Win-Tensor Software. Analysis of fault-slip data revealed four paleostress tensor stages (groups or regimes) that prevailed in the ENS. The stress states and related tectonic regimes are characterized by the stress regime index R' and the horizontal stress axes as follows: 1st stage: transpression (R' = 1.91), E‒W compression (SH_max = N090°‒270° E); 2nd stage: transtension (R' = 1.16), N‒S compression (SH_max = 174°‒354° E); 3rd stage: transpression (R' = 1.81), NE‒SW compression (SH_max = N053°‒233° E); 4th stage: extension (R' = 0.31), E‒W extension (Sh_min = N074°‒254° E). The 1st stage can be related to the oblique convergence between E and W Gondwanalands. The 2nd stage was probably concurrent with the N- to NNW-ward migration of the Central Eastern Desert syn-collisional delamination (triggering orogen-parallel extensional collapse) to the North Eastern Desert post-collisional delamination. The 3rd stage was controlled by the generally N‒S shortening which affected the northern and central ENS, post-dating the formation of volcanosedimentary Hammamat Basins. The 4th stage is akin to retreat of the Cadomian arc and the Red Sea rifting.

中文翻译：

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北部构造省（埃及努比亚地盾）断层条纹分析与古应力重建：洞察东非造山带北部脆性变形历史

摘要

埃及努比亚地盾 (ENS) 是东非造山带 (EAO) 的西北延续，由三个岩性和结构不同的构造区组成：南部挤压区、中部压扭区和北部伸展区。伸展构造省（ETP）从 Qena-Safaga 剪切带延伸至 ENS 北端。一些证据表明 ETP 存在伸展机制，例如地幔分层引起的造山后岩浆作用和双峰式 Dokhan 火山，以及普遍存在的东西向岩墙群和东西向（至 ENE-WSW）取向的伸展裂缝。本工作致力于开展北部构造省（ENS）的断层条纹分析和古应力重建，试图为EAO北部的脆性变形历史做出更多的贡献。使用 Win-Tensor 软件处理从六个区域 (I-VI) 收集的现场测量结果。对断层滑动数据的分析揭示了 ENS 中盛行的四个古应力张量阶段（组或体系）。应力状态和相关构造形态由应力状态指数 R' 和水平应力轴表征如下： 第一阶段：压扭（R' = 1.91）、东西向压缩（SH _max = N090°∼270° E） ;第二阶段：变形（R'=1.16），N-S压缩（SH _max = 174°-354°E）；第三阶段：压压（R'=1.81），NE-SW压缩（SH _max =N053°-233°E）；第四阶段：延伸（R' = 0.31），东西延伸（Sh _min = N074°∼254° E）。第一阶段可能与东冈瓦纳大陆和西冈瓦纳大陆之间的倾斜汇聚有关。第二阶段可能与中东沙漠同碰撞脱层（引发造山带平行伸展塌陷）向北向北西向迁移到东北沙漠后碰撞脱层同时发生。第三阶段受总体北南缩短的控制，影响了ENS北部和中部，晚于火山沉积哈马马特盆地的形成。第四阶段类似于卡多米亚弧的后退和红海裂谷。