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首页> 外文期刊>Journal of geodynamics >Cretaceous-Eocene compression in the central Southern Alps (N Italy) inferred from 40Ar/39Ar dating of pseudotachylytes along regional thrust faults
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Cretaceous-Eocene compression in the central Southern Alps (N Italy) inferred from 40Ar/39Ar dating of pseudotachylytes along regional thrust faults

机译：根据沿区域逆冲断层的假速溶质40Ar / 39Ar测年推断南阿尔卑斯山中部（意大利北部）的白垩纪-始新世压缩

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摘要

The integration of structural analyses with 40Ar/39Ar dating of fault-related pseudotachylytes provides time constraints for the reconstruction of the Alpine evolution of the central portion of the South Alpine orogenic wedge. In the northern sector of the belt a Variscan basement is stacked southward on the Permian to Mesozoic cover along regional faults (Orobic and Porcile thrusts). Fault zones, slightly post-dating a first folding event of Alpine age, experienced a complex evolution through the ductile and brittle deformation regime, showing greenschist facies mylonites overprinted by a penetrative cataclastic deformation. Generation of fault-related pseudotachylyte veins marks the onset of brittle conditions, lasting up to the youngest episodes of fault activity. 40Ar/39Ar dating of the pseudotachylyte matrix of 9 samples give two separated age clusters: Late Cretaceous (80-68 Ma) and latest Palaeocene to Middle Eocene (55-43 Ma). These new data provide evidence that the pre-Adamello evolution of the central Southern Alps was characterised by the superposition of different tectonic events accompanying the exhumation of the deepest part of the belt through the brittle-ductile transition. The oldest pseudotachylyte ages demonstrate that south-verging regional thrusting in the central Southern Alps was already active during the Late Cretaceous, concurrently with the development of a synorogenic foredeep basin where the Upper Cretaceous Lombardian Flysch was deposited. Our reconstruction provides direct evidence for an important Cretaceous "EoAlpine" orogenic event which was nearly coeval to the HP metamorphism affecting the Austroalpine units of the eastern Alps. In our view, the Upper Cretaceous Southern Alps can be interpreted as the south-verging retrobelt, which formed during subduction phenomena active to the north in the Austroalpine realm.
机译：与断层相关的假速溶质的40Ar / 39Ar测年的结构分析的集成为重建南高山造山楔的中央部分的高山演化提供了时间限制。在该带的北部，一个Variscan地下室沿区域断层（奥贝纪和孔洞逆冲）在二叠纪至中生代覆盖层上向南堆积。断层带稍早于阿尔卑斯时代的第一次褶皱事件，在韧性和脆性变形机制下经历了复杂的演化过程，显示出绿化相岩棉质岩被渗透性碎裂变形所覆盖。断层相关的假速溶脉的生成标志着脆性条件的发作，持续到断层活动的最年轻时期。对9个样品的假速溶质基质进行40Ar / 39Ar测年，给出了两个分离的年龄簇：白垩纪晚期（80-68Ma）和新世至中新世（55-43Ma）。这些新数据提供了证据，表明南阿尔卑斯山中部的阿达米洛前演化的特征是伴随着脆性-韧性过渡带掘出的最深部分，伴随着不同的构造事件的叠加。最古老的假速溶时代表明，白垩纪晚期，南阿尔卑斯山中部向南的区域性逆冲作用已经活跃，与此同时，上白垩纪伦巴第大复盖岩也沉积了一个前生盆地。我们的重建工作为重要的白垩纪“ EoAlpine”造山事件提供了直接证据，该事件几乎与影响东部阿尔卑斯山的奥图高山单元的HP变质作用相当。在我们看来，上白垩统南阿尔卑斯山可以解释为南向逆转带，它是在俯冲现象期间形成的，该俯冲现象活跃于奥索高山领域的北部。

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  • 来源
    《Journal of geodynamics》 |2011年第4期|p.245-263|共19页
  • 作者

    StefanoZanchetta; Paolo DAdda; AndreaZanchi; ValentinaBarberini; Igor M. Villa;

  • 作者单位

    Dipartimento di Scienze Geologiche e Ceotecnologie, Universitd degli Studi di Milano Bkocca, P.za delta Scienza 4, Milano 20126 Italy;

    rnDipartimento di Scienze Geologiche e Ceotecnologie, Universitd degli Studi di Milano Bkocca, P.za delta Scienza 4, Milano 20126 Italy;

    rnDipartimento di Scienze Geologiche e Ceotecnologie, Universitd degli Studi di Milano Bkocca, P.za delta Scienza 4, Milano 20126 Italy;

    rnDipartimento di Scienze Geologiche e Ceotecnologie, Universitd degli Studi di Milano Bkocca, P.za delta Scienza 4, Milano 20126 Italy;

    rnDipartimento di Scienze Geologiche e Ceotecnologie, Universitd degli Studi di Milano Bkocca, P.za delta Scienza 4, Milano 20126 Italy Institutfilr Geologie. Unlversitat Bern, 3012 Bern, Switzerland;

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  • 正文语种 eng
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  • 关键词

    pseudotachylyte; 40 ar/39ar dating; orobic thrust; porcile thrust; compressive deformation;

    机译：假速溶质;40 ar / 39ar年代;射流冲力;多孔冲力;压缩变形;

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