Petrological and geochronological investigations on the individual nappes of the Meran-Mauls nappe stack (Austroalpine unit/South Tyrol, Italy)

IF 1.7 4区 地球科学 Q2 Earth and Planetary Sciences
H. Pomella, D. Costantini, Paul Aichholzer, M. Reiser, R. Schuster, P. Tropper
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引用次数: 1

Abstract

Abstract The Meran-Mauls nappe stack is part of the Austroalpine unit in South Tyrol (Italy). There it holds a special position directly in front of the Southalpine Dolomites indenter and west of the Tauern Window. It is situated in the hanging wall of the Southalpine unit, above a NW dipping segment of the Periadriatic fault system, namely the Meran-Mauls fault. Also all other sides are defined by Oligocene-Miocene strike-slip and normal faults. Based on recent mapping the Meran-Mauls nappe stack consists of three nappes separated by NW to NNW dipping shear zones. The lowermost nappe in the southwest is represented by the Schenna (Scena) unit. It is overlain along the Masul shear zone by a nappe consisting of the Hirzer (Punta Cervina) unit and the Pens (Pennes) unit including Triassic (meta)sediments. Separated by the Fartleis fault the St. Leonhard (San Leonardo) unit forms the uppermost nappe. The aim of this study is to describe the individual units and the separating structural elements more properly, based on new structural, petrological, geothermobarometric and geochronological data and to compare these units to other Austroalpine elements in the vicinity. Sillimanite-bearing paragneiss, minor amphibolite and quartzite as well as a distinct marble layer close to its base characterise the Schenna unit. Further, it contains pegmatite dikes, presumably Permian in age. Amphibolite-facies P-T conditions of c. 0.55 ± 0.15 GPa and 600 ± 100°C are thus correlated with a Permian metamorphic imprint. The Masul shear zone mostly consists of mylonitic paragneiss of the Hirzer unit. It is pre-Alpine in age and probably formed during the Jurassic. For the paragneiss of the Hirzer unit upper greenschist- to amphibolite-facies metamorphic conditions of 0.4-0.50 ± 0.15 GPa and 550 ± 70°C are attributed to the Variscan tectonometamorphic imprint. The whole Pens unit represents a shear zone. Due to the occurrence of Permotriassic (meta)-sediments within this shear zone, it is an Alpine structure, as well as the bordering Fartleis fault. Rb/Sr biotite ages yield sometimes partly reset pre-Alpine age values in the whole Meran-Mauls nappe stack, indicating a pervasive anchizonal to lowermost greenschist-facies metamorphic overprint during the Eoalpine tectonometamorphic event. Tectonostratigraphically the Meran-Mauls nappe stack can be attributed to the Drauzug-Gurktal nappe system. The latter forms the uppermost structural element of the Austroalpine nappe stack and thus only shows a weak Eoalpine metamorphic overprint. With respect to its special lithologic composition the Schenna unit can be correlated with the Tonale unit in the southwest and the Strieden-Komplex in the east.
Meran-Mauls推覆岩堆(奥高山单元/意大利南蒂罗尔)单个推覆层的岩石学和地质年代学调查
Meran-Mauls推覆体是意大利南蒂罗尔(South Tyrol)奥高山构造单元的一部分。在那里,它占据了一个特殊的位置,直接在南阿尔卑斯白云岩压头和陶恩窗口的西部。它位于南阿尔卑斯单元的上盘,位于外亚得里亚海断裂系统的北西倾段,即Meran-Mauls断裂之上。其他两侧均为渐新世—中新世走滑和正断层。根据最近的填图,梅兰-莫尔推覆体由三个推覆体组成,由NW至NNW倾斜剪切带分隔。西南最底推覆体为Schenna (Scena)单元。沿马苏尔剪切带被由Hirzer (Punta Cervina)单元和Pennes (Pennes)单元组成的推覆体覆盖,包括三叠纪(元)沉积物。由Fartleis断层分隔的圣莱昂哈德(圣莱昂纳德)单元形成了最上层的推覆体。本研究的目的是根据新的构造、岩石学、地温压学和地质年代学资料,更恰当地描述单个单元和分离的构造元素,并将这些单元与邻近的其他奥高山元素进行比较。含硅线石的副长岩,少量角闪岩和石英岩,以及靠近其基部的一层明显的大理岩,是Schenna单元的特征。此外,它含有伟晶岩脉,可能是二叠纪时期的。0.55±0.15 GPa和600±100℃的角闪岩相P-T条件与二叠纪变质印记有关。马苏尔剪切带主要由赫泽尔单元糜棱质副长岩组成。它的年龄在前阿尔卑斯山脉,可能形成于侏罗纪。对于Hirzer单元的共生,上绿片岩-角闪岩相的变质条件为0.4-0.50±0.15 GPa和550±70℃,这归因于Variscan构造变质印记。整个Pens单元代表一个剪切区。由于剪切带内发育二叠纪(元)沉积,属于高寒构造,并与Fartleis断裂相邻。在整个默兰-莫尔推覆体中,Rb/Sr黑云母年龄有时会部分重置前阿尔卑斯年龄,表明在始阿尔卑斯构造变质事件期间,普遍存在从周向最下方的绿片岩相变质覆层。在构造地层学上,梅兰-莫尔推覆体可归属于德劳祖格-古尔克塔尔推覆体体系。后者构成了奥阿尔卑斯推覆体的最上层构造元素,因此只表现出弱的始阿尔卑斯变质覆印。由于其特殊的岩性组成,Schenna单元可与西南的Tonale单元和东部的striden - komplex进行对比。
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来源期刊
Austrian Journal of Earth Sciences
Austrian Journal of Earth Sciences Earth and Planetary Sciences-Paleontology
CiteScore
3.10
自引率
0.00%
发文量
0
审稿时长
>12 weeks
期刊介绍: AUSTRIAN JOURNAL OF EARTH SCIENCES is the official journal of the Austrian Geological, Mineralogical and Palaeontological Societies, hosted by a country that is famous for its spectacular mountains that are the birthplace for many geological and mineralogical concepts in modern Earth science. AUSTRIAN JOURNAL OF EARTH SCIENCE focuses on all aspects relevant to the geosciences of the Alps, Bohemian Massif and surrounding areas. Contributions on other regions are welcome if they embed their findings into a conceptual framework that relates the contribution to Alpine-type orogens and Alpine regions in general, and are thus relevant to an international audience. Contributions are subject to peer review and editorial control according to SCI guidelines to ensure that the required standard of scientific excellence is maintained.
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