Formation of Neoproterozoic metamorphic core complexes during oblique convergence (Eastern Desert, Egypt)
Formation of Neoproterozoic metamorphic core complexes during oblique convergence (Eastern Desert, Egypt)
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DOI：
10.1016/s0899-5362(97)00004-3
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发表时间：
1996-10-01
影响因子：
2.3
通讯作者：
Dallmeyer, DR
中科院分区：
文献类型：
--
作者：
Fritz, H;Wallbrecher, E;Dallmeyer, DR
埃及东部沙漠中的泛非造山带的大部分是新元古代岛弧吸积作用形成的。这些地区的特点是没有主要的地壳增厚。变质核杂岩与东部沙漠造山带走向平行。这些穹隆表现出多期变质和变形，与构造上覆的推覆构造形成对比，后者包括蛇绿混杂岩和岛状火山岩。这些推覆构造在造山带内部表现为北西向、造山带平行的逆冲推覆，在造山带外部表现为自西向西南方向的叠置作用。与变质核杂岩折返有关的构造划分为不同的位移路径，位于纳吉德断裂系统的地壳规模的扭动走廊内。北西向造山带平行的左旋走滑断层定义了穹顶的西缘和东缘。南北倾角正断层沿穹隆的南北缘发育，并在它们之间形成伸展桥梁。剪切带内同构造白云母的40Ar/39Ar年龄给出新元古代年龄为595.9±0.5 Ma和588.2±0.3 Ma。走滑与正断层的同步活动反映了一次区域性的东西向缩短，变质核杂岩下的深部基底滑脱和同时代的西北-东南、造山带平行的伸展作用协调了这一过程。这种伸展伴随着山内磨拉石的沉积和钙碱性深成岩体的侵位。由于核杂岩中片麻岩的快速折返不能用地壳增厚来解释，作者赞成一个模型，该模型呼吁沿Najd断裂系统增强热流，这将使同伸展深成作用的形成成为可能，并触发变质核杂岩的折返。侧向浮力集中在Najd扳手走廊内，使造山带能够平行伸展。版权所有(C)1997爱思唯尔科学有限公司埃及东部沙漠中的泛非造山带的大部分是在新元古代由岛弧沉积形成的。这些地区的特点是没有主要的地壳增厚。变质核杂岩与东部沙漠造山带走向平行。这些穹隆表现出多期变质和变形，与构造上覆的推覆构造形成对比，后者包括蛇绿混杂岩和岛状火山岩。这些推覆构造在造山带内部表现为北西向、造山带平行的逆冲推覆，在造山带外部表现为自西向西南方向的叠置作用。与变质核杂岩折返有关的构造划分为不同的位移路径，位于纳吉德断裂系统的地壳规模的扭动走廊内。北西向造山带平行的左旋走滑断层定义了穹顶的西缘和东缘。南北倾角正断层沿穹隆的南北缘发育，并在它们之间形成伸展桥梁。剪切带内同构造白云母的40Ar/39Ar年龄给出新元古代年龄为595.9±0.5 Ma和588.2±0.3 Ma。走滑与正断层的同步活动反映了一次区域性的东西向缩短，变质核杂岩下的深部基底滑脱和同时代的西北-东南、造山带平行的伸展作用协调了这一过程。这种伸展伴随着山内磨拉石的沉积和钙碱性深成岩体的侵位。由于核杂岩中片麻岩的快速折返不能用地壳增厚来解释，作者赞成一个模型，该模型呼吁沿Najd断裂系统增强热流，这将使同伸展深成作用的形成成为可能，并触发变质核杂岩的折返。侧向浮力集中在Najd扳手走廊内，使造山带能够平行伸展。版权所有(C)1997爱思唯尔科学有限公司。
Major portions of the Pan-African Orogen in the Eastern Desert of Egypt were formed by island-are accretion in the Neoproterozoic. These areas are characterized by their lack of major crustal thickening. Metamorphic core complexes occur parallel to the strike of the Eastern Desert Orogen. These domes exhibit polyphase metamorphism and deformation in contrast to the structurally overlying nappes which include ophiolitic melanges and island-are volcanic rocks. These nappes show northwest directed, orogen-parallel thrusting in the internal parts and west to southwest directed imbrication in the external parts of the orogen. Structures related to exhumation of the metamorphic core complexes partition into different displacement paths localized within a crustal-scale wrench corridor of the Najd fault system. Northwest trending orogen-parallel, sinistral strike-slip faults define the western and eastern margins of the domes. North and south dipping low-angle normal faults developed along the northern and southern margins of the domes and form extensional bridges between them. 40Ar/39Ar ages obtained from syntectonic muscovites within the shear zones gave Neoproterozoic ages of 595.9 +/- 0.5 and 588.2 +/- 0.3 Ma. The synchronous activity of strike-slip and normal faults suggests a regional east-west shortening which was accomodated by deep-level basal decollement beneath the metamorphic core complexes and a coeval northwest-southeast, orogen-parallel extension. This extension was accompanied by intramontane molasse sedimentation and emplacement of calc-alkaline plutons. Since the rapid exhumation of gneisses in the core complexes cannot be explained by thickening of the crust, the authors favour a model which calls for enhanced heat flow along the Najd fault system which would have enabled the formation of syn-extensional plutonism and triggered the exhumation of the metamorphic core complexes. Lateral buoyancy forces were concentrated within the Najd wrench corridor and enabled orogen-parallel extension. Copyright (C) 1997 Elsevier Science Ltd.Major portions of the Pan-African Orogen in the Eastern Desert of Egypt were formed by island-are accretion in the Neoproterozoic. These areas are characterized by their lack of major crustal thickening. Metamorphic core complexes occur parallel to the strike of the Eastern Desert Orogen. These domes exhibit polyphase metamorphism and deformation in contrast to the structurally overlying nappes which include ophiolitic melanges and island-are volcanic rocks. These nappes show northwest directed, orogen-parallel thrusting in the internal parts and west to southwest directed imbrication in the external parts of the orogen. Structures related to exhumation of the metamorphic core complexes partition into different displacement paths localized within a crustal-scale wrench corridor of the Najd fault system. Northwest trending orogen-parallel, sinistral strike-slip faults define the western and eastern margins of the domes. North and south dipping low-angle normal faults developed along the northern and southern margins of the domes and form extensional bridges between them. 40Ar/39Ar ages obtained from syntectonic muscovites within the shear zones gave Neoproterozoic ages of 595.9 +/- 0.5 and 588.2 +/- 0.3 Ma. The synchronous activity of strike-slip and normal faults suggests a regional east-west shortening which was accomodated by deep-level basal decollement beneath the metamorphic core complexes and a coeval northwest-southeast, orogen-parallel extension. This extension was accompanied by intramontane molasse sedimentation and emplacement of calc-alkaline plutons. Since the rapid exhumation of gneisses in the core complexes cannot be explained by thickening of the crust, the authors favour a model which calls for enhanced heat flow along the Najd fault system which would have enabled the formation of syn-extensional plutonism and triggered the exhumation of the metamorphic core complexes. Lateral buoyancy forces were concentrated within the Najd wrench corridor and enabled orogen-parallel extension. Copyright (C) 1997 Elsevier Science Ltd.