| Transpressive Structures in the Ghadir Shear Belt, Eastern Desert, Egypt: Evidence for Partitioning of Oblique Convergence in the Arabian-Nubian Shield during
Gondwana Agglutination |
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| 作者姓名： | Mohamed ABD EL-WAHED Samir KAMH Mahmoud ASHMAWY Aly SHEBL |
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| 摘 要： | Transpressional deformation has played an important role in the late Neoproterozoic evolution of the ArabianNubian Shield including the Central Eastern Desert of Egypt. The Ghadir Shear Belt is a 35 km-long, NW-oriented brittleductile shear zone that underwent overall sinistral transpression during the Late Neoproterozoic. Within this shear belt, strain is highly partitioned into shortening, oblique, extensional and strike-slip structures at multiple scales. Moreover, strain partitioning is heterogeneous along-strike giving rise to three distinct structural domains. In the East Ghadir and Ambaut shear belts, the strain is pure-shear dominated whereas the narrow sectors parallel to the shear walls in the West Ghadir Shear Zone are simple-shear dominated. These domains are comparable to splay-dominated and thrust-dominated strike-slip shear zones. The kinematic transition along the Ghadir shear belt is consistent with separate strike-slip and thrustsense shear zones. The earlier fabric(S1), is locally recognized in low strain areas and SW-ward thrusts. S2 is associated with a shallowly plunging stretching lineation(L2), and defines ～NW-SE major upright macroscopic folds in the East Ghadir shear belt. F2 folds are superimposed by ～NNW–SSE tight-minor and major F3 folds that are kinematically compatible with sinistral transpressional deformation along the West Ghadir Shear Zone and may represent strain partitioning during deformation. F2 and F3 folds are superimposed by ENE–WSW gentle F4 folds in the Ambaut shear belt. The sub-parallelism of F3 and F4 fold axes with the shear zones may have resulted from strain partitioning associated with simple shear deformation along narrow mylonite zones and pure shear-dominant deformation in fold zones. Dextral ENEstriking shear zones were subsequently active at ca. 595 Ma, coeval with sinistral shearing along NW-to NNW-striking shear zones. The occurrence of upright folds and folds with vertical axes suggests that transpression plays a significant role in the tectonic evolution of the Ghadir shear belt. Oblique convergence may have been provoked by the buckling of the Hafafit gneiss-cored domes and relative rotations between its segments. Upright folds, fold with vertical axes and sinistral strike-slip shear zones developed in response to strain partitioning. The West Ghadir Shear Zone contains thrusts and strikeslip shear zones that resulted from lateral escape tectonics associated with lateral imbrication and transpression in response to oblique squeezing of the Arabian-Nubian Shield during agglutination of East and West Gondwana.
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| 收稿时间： | 2018/11/9 0:00:00 |
| 修稿时间： | 2019/1/29 0:00:00 |
Transpressive Structures in the Ghadir Shear Belt,Eastern Desert,Egypt: Evidence for Partitioning of Oblique Convergence in the Arabian‐Nubian Shield during Gondwana Agglutination |
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| Authors: | Mohamed ABD EL-WAHED Samir KAMH Mahmoud ASHMAWY and Aly SHEBL |
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| Institution: | Geology Department, Faculty of Science, Tanta University, Tanta 31527, Egypt;Geology Department, Faculty of Science, Tanta University, Tanta 31527, Egypt;Geology Department, Faculty of Science, Tanta University, Tanta 31527, Egypt;Geology Department, Faculty of Science, Tanta University, Tanta 31527, Egypt |
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| Abstract: | Transpressional deformation has played an important role in the late Neoproterozoic evolution of the Arabian‐Nubian Shield including the Central Eastern Desert of Egypt. The Ghadir Shear Belt is a 35 km‐long, NW‐oriented brittle‐ductile shear zone that underwent overall sinistral transpression during the Late Neoproterozoic. Within this shear belt, strain is highly partitioned into shortening, oblique, extensional and strike‐slip structures at multiple scales. Moreover, strain partitioning is heterogeneous along‐strike giving rise to three distinct structural domains. In the East Ghadir and Ambaut shear belts, the strain is pure‐shear dominated whereas the narrow sectors parallel to the shear walls in the West Ghadir Shear Zone are simple‐shear dominated. These domains are comparable to splay‐dominated and thrust‐dominated strike‐slip shear zones. The kinematic transition along the Ghadir shear belt is consistent with separate strike‐slip and thrust‐sense shear zones. The earlier fabric (S1), is locally recognized in low strain areas and SW‐ward thrusts. S2 is associated with a shallowly plunging stretching lineation (L2), and defines ～NW‐SE major upright macroscopic folds in the East Ghadir shear belt. F2 folds are superimposed by ～NNW–SSE tight‐minor and major F3 folds that are kinematically compatible with sinistral transpressional deformation along the West Ghadir Shear Zone and may represent strain partitioning during deformation. F2 and F3 folds are superimposed by ENE–WSW gentle F4 folds in the Ambaut shear belt. The sub‐parallelism of F3 and F4 fold axes with the shear zones may have resulted from strain partitioning associated with simple shear deformation along narrow mylonite zones and pure shear‐dominant deformation in fold zones. Dextral ENE‐striking shear zones were subsequently active at ca. 595 Ma, coeval with sinistral shearing along NW‐ to NNW‐striking shear zones. The occurrence of upright folds and folds with vertical axes suggests that transpression plays a significant role in the tectonic evolution of the Ghadir shear belt. Oblique convergence may have been provoked by the buckling of the Hafafit gneiss‐cored domes and relative rotations between its segments. Upright folds, fold with vertical axes and sinistral strike‐slip shear zones developed in response to strain partitioning. The West Ghadir Shear Zone contains thrusts and strike‐slip shear zones that resulted from lateral escape tectonics associated with lateral imbrication and transpression in response to oblique squeezing of the Arabian‐Nubian Shield during agglutination of East and West Gondwana. |
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| Keywords: | Arabian-Nubian Shield Ghadir shear belt transpression splay-dominated and thrust-dominated strike-slip shear zones Egypt |
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