Schorn Anja, Neubauer Franz, Genser Johann, Bernroider Manfred
Department of Geography and Geology, University of Salzburg, Hellbrunnerstraße 34, 5020 Salzburg, Austria.
Tectonophysics. 2013 Jan 11;583:28-48. doi: 10.1016/j.tecto.2012.10.016.
For the reconstruction of Alpine tectonics of the Eastern Alps, the evaporitic Permian to Lower Triassic Haselgebirge Formation plays a key role in (1) the origin of Haselgebirge bearing nappes, (2) the inclusion of magmatic and metamorphic rocks revealing tectonic processes not preserved in other units, and (3) the debated mode of emplacement of the nappes, namely gravity-driven or tectonic. Within the Moosegg quarry of the central Northern Calcareous Alps gypsum/anhydrite bodies are tectonically mixed with lenses of sedimentary rocks and decimeter- to meter-sized tectonic clasts of plutonic and subvolcanic rocks and rare metamorphics. We examined various types of (1) widespread biotite-diorite, meta-syenite, (2) meta-dolerite and rare ultramafic rocks (serpentinite, pyroxenite) as well as (3) rare metamorphic banded meta-psammitic schists and meta-doleritic blueschists. The apparent Ar/Ar biotite ages from three biotite-diorite, meta-dolerite and meta-doleritic blueschist samples with variable composition and fabrics range from 248 to 270 Ma (e.g., 251.2 ± 1.1 Ma) indicating a Permian age of cooling after magma crystallisation or metamorphism. The chemical composition of biotite-diorite and meta-syenite indicates an alkaline trend interpreted to represent a rift-related magmatic suite. These, as well as Permian to Jurassic sedimentary rocks, were incorporated during Cretaceous nappe emplacement forming the sulphatic Haselgebirge mélange. The scattered Ar/Ar white mica ages of a meta-doleritic blueschist (of N-MORB origin) and banded meta-psammitic schist are ca. 349 and 378 Ma, respectively, proving the Variscan age of pressure-dominated metamorphism. These ages are similar to detrital white mica ages reported from the underlying Rossfeld Formations, indicating a close source-sink relationship. According to our new data, the Haselgebirge bearing nappe was transported over the Lower Cretaceous Rossfeld Formations, which include many clasts derived from the Haselgebirge Formation and its exotic blocks deposited in front of the incoming nappe comprising the Haselgebirge Formation.
对于东阿尔卑斯山的阿尔卑斯构造重建而言，二叠纪至下三叠纪的哈瑟尔山组蒸发岩在以下方面起着关键作用：（1）含哈瑟尔山推覆体的起源；（2）包含揭示其他单元未保存的构造过程的岩浆岩和变质岩；（3）推覆体的就位方式存在争议，即重力驱动还是构造驱动。在北钙质阿尔卑斯山中部的穆斯埃格采石场，石膏/硬石膏体与沉积岩透镜体以及深成岩和次火山岩及罕见变质岩的分米至米级构造碎屑在构造上相互混合。我们研究了各种类型的岩石：（1）广泛分布的黑云母闪长岩、变正长岩；（2）变辉绿岩和罕见的超镁铁岩（蛇纹岩、辉石岩）；以及（3）罕见的变质带状变石英砂岩片岩和变辉绿岩蓝片岩。来自三个成分和结构各异的黑云母闪长岩、变辉绿岩和变辉绿岩蓝片岩样品的表观氩/氩黑云母年龄在248至270 Ma之间（例如，251.2±1.1 Ma），表明岩浆结晶或变质作用后冷却的二叠纪年龄。黑云母闪长岩和变正长岩的化学成分显示出碱性趋势，被解释为代表与裂谷相关的岩浆岩套。这些岩石以及二叠纪至侏罗纪的沉积岩在白垩纪推覆体就位期间被纳入，形成了含硫酸盐的哈瑟尔山混杂岩。一个变辉绿岩蓝片岩（具有N - MORB源）和带状变石英砂岩片岩的分散氩/氩白云母年龄分别约为349和378 Ma，证明了华力西期以压力为主的变质作用年龄。这些年龄与下伏罗斯费尔德组报道的碎屑白云母年龄相似，表明源区与沉积区关系密切。根据我们的新数据，含哈瑟尔山的推覆体是在早白垩世罗斯费尔德组之上运移的，罗斯费尔德组包含许多源自哈瑟尔山组的碎屑及其外来岩块，这些外来岩块沉积在进入的包含哈瑟尔山组的推覆体前方。
