T A Ducharme, D A Schneider, B Grasemann, V Scoging, C Bakowsky, K P Larson, A Camacho
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Structural investigation of the different lithotypes in the flysch reveals tectonic fabrics related to general flattening strain are developed most strongly in the pelitic matrix, whereas the compositionally diverse blocks exhibit differential preservation of older structures. Quartz c-axis distributions from quartz veins in the schists reflect an early, moderate temperature plane strain deformation. Colder deformation is evident in some pelitic schists, capturing Z-centered girdles consistent with the oblate finite strain ellipsoid inferred from macroscopic structures. New in situ <sup>40</sup>Ar/<sup>39</sup>Ar and <sup>87</sup>Rb/<sup>87</sup>Sr geochronology delineate the timing of the two deformation events. Geochronological data reaffirm the first-order observations of strain partitioning behavior at the scale of the shear zone, and confirm that the structure records two resolvable tectonometamorphic events: an early Oligocene HP-LT event, and a late Oligocene-early Miocene greenschist facies overprint coinciding with ductile thinning. The diffuse and discontinuous style of deformation recorded within the shear zone is unusual for major structures facilitating exhumation in the Aegean Sea, and may represent an analogue to mélange-hosted shear zones that accommodate progressive strain during subduction.</p>","PeriodicalId":22351,"journal":{"name":"Tectonics","volume":"43 11","pages":"e2024TC008412"},"PeriodicalIF":3.3000,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11582021/pdf/","citationCount":"0","resultStr":"{\"title\":\"Strain Partitioning in a Flattening Shear Zone: Re-Evaluation of a Cycladic Style Detachment.\",\"authors\":\"T A Ducharme, D A Schneider, B Grasemann, V Scoging, C Bakowsky, K P Larson, A Camacho\",\"doi\":\"10.1029/2024TC008412\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<p><p>The Almyropotamos tectonic window on southern Evia island in the NW Aegean Sea divides two high pressure-low temperature metamorphic units, representing distinct Hellenic thrust sheets. 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引用次数: 0
摘要
爱琴海西北部埃维亚岛南部的阿尔米罗波塔莫斯构造窗口划分出两个高压低温变质岩单元,分别代表不同的希腊推力片。沿着主要的低角度埃维亚剪切带的延展性减薄使下部(基底单元)大理岩-萤石层序在结构上紧密地并置在斯蒂拉大理岩(基克拉泽斯蓝岩单元)之下。部分衰减的萤石岩包括以辉绿岩片岩为主的基质,以及分散的厘米至百米级的大理岩、碳酸盐片岩、石英岩和偏闪长岩块。对萤石岩中不同岩型的构造调查显示,与总体扁平应变有关的构造结构在辉绿岩基质中发育得最为强烈,而成分多样的岩块则表现出对古老构造的不同保留。片岩中石英脉的石英 c 轴分布反映了早期的中温平面应变变形。在一些辉绿岩片岩中,低温变形非常明显,捕捉到了与宏观结构推断的扁圆形有限应变椭球体一致的Z中心腰带。新的原位 40Ar/39Ar 和 87Rb/87Sr 地质年代划分了两次变形事件的时间。地质年代数据再次证实了剪切带尺度上应变分区行为的一阶观测结果,并确认该构造记录了两次可解析的构造变质事件:一次是早渐新世的HP-LT事件,另一次是晚渐新世-中新世早期的绿泥石面叠加事件,与韧性变薄同时发生。在该剪切带内记录到的弥漫和不连续的变形风格,在爱琴海促进掘起的主要构造中并不常见,可能代表了在俯冲过程中容纳渐进应变的蜕变带。
Strain Partitioning in a Flattening Shear Zone: Re-Evaluation of a Cycladic Style Detachment.
The Almyropotamos tectonic window on southern Evia island in the NW Aegean Sea divides two high pressure-low temperature metamorphic units, representing distinct Hellenic thrust sheets. Ductile thinning along the major low-angle Evia Shear Zone has closely juxtaposed the lower (Basal Unit) marble-flysch sequence structurally below Styra marbles (Cycladic Blueschist Unit). The partially attenuated flysch comprises a matrix dominated by pelitic schist, with dispersed cm- to hm-scale blocks of marble, carbonate schist, quartzite, and metabasite. Structural investigation of the different lithotypes in the flysch reveals tectonic fabrics related to general flattening strain are developed most strongly in the pelitic matrix, whereas the compositionally diverse blocks exhibit differential preservation of older structures. Quartz c-axis distributions from quartz veins in the schists reflect an early, moderate temperature plane strain deformation. Colder deformation is evident in some pelitic schists, capturing Z-centered girdles consistent with the oblate finite strain ellipsoid inferred from macroscopic structures. New in situ 40Ar/39Ar and 87Rb/87Sr geochronology delineate the timing of the two deformation events. Geochronological data reaffirm the first-order observations of strain partitioning behavior at the scale of the shear zone, and confirm that the structure records two resolvable tectonometamorphic events: an early Oligocene HP-LT event, and a late Oligocene-early Miocene greenschist facies overprint coinciding with ductile thinning. The diffuse and discontinuous style of deformation recorded within the shear zone is unusual for major structures facilitating exhumation in the Aegean Sea, and may represent an analogue to mélange-hosted shear zones that accommodate progressive strain during subduction.
期刊介绍:
Tectonics (TECT) presents original scientific contributions that describe and explain the evolution, structure, and deformation of Earth¹s lithosphere. Contributions are welcome from any relevant area of research, including field, laboratory, petrological, geochemical, geochronological, geophysical, remote-sensing, and modeling studies. Multidisciplinary studies are particularly encouraged. Tectonics welcomes studies across the range of geologic time.