The Grobgneis complex, located in the eastern Austroalpine unit of the Eastern Alps, exposes large volumes of pre-Alpine porphyric metagranites, sometimes associated with small gabbroic bodies. To better understand tectonic setting of the metagranites, we carried out detailed geochronological and geochemical investigations on the major part of the porphyric metagranites. LA–ICP–MS zircon U–Pb dating of three metagranites sampled from the Grobgneis complex provides the first reliable evidence for large volumes of Permian plutonism within the pre-Alpine basement of the Lower Austroalpine units. Concordant zircons from three samples yield ages at 272.2 ± 1.2 Ma, 268.6 ± 2.3 Ma and 267.6 ± 2.9 Ma interpreted to date the emplacement of the granite suite. In combination with published ages for other Permian Alpine magmatic bodies, the new U–Pb ages provide evidence of a temporally restricted period of plutonism (“Grobgneis”) in the Raabalpen basement Complex during the Middle Permian. Comparing the investigated basement with that of the West Carpathian basement, we argue that widespread Permian granite magmatism occurred in the Lower Austroalpine units. They belong to the high-K calc-alkaline to shoshonitic S-type series on the base of geochemical data. Zircon Hf isotopic compositions of the Grobgneis metagranites show εHf(t) values of − 4.37 to − 0.6, with TDM2 model ages of 1.31–1.55 Ga, indicating that their protoliths were derived by the recycling of older continental crust. We suggest that the Permian granitic and gabbroic rocks are considered as rifted-related rocks in the Lower Austroalpine units and are contemporaneous with cover sediments.

中文翻译：

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下奥陶高山单元中广泛的二叠纪花岗岩岩浆作用：在东部阿尔卑斯山的二叠纪裂谷的意义

Grobgneis复合体位于东阿尔卑斯山的东奥阿高山单元中，暴露出大量的阿尔卑斯前斑岩变质岩，有时与小型辉长岩体有关。为了更好地了解花岗岩的构造背景，我们对斑岩型花岗岩的主要部分进行了详细的年代学和地球化学研究。LA-ICP-MS从Grobgneis复杂岩中取样的三个变质花岗岩的锆石U-Pb测年提供了第一个可靠的证据，证明了在下奥图高山单元的高山前基底内有大量的二叠纪岩溶作用。从三个样品中得出的一致锆石的年龄分别为272.2±1.2 Ma，268.6±2.3 Ma和267.6±2.9 Ma，这可解释为迄今花岗岩组的位置。结合其他二叠纪高山岩浆体的公布年龄，新的U–Pb年龄提供了中二叠纪Raabalpen基底复合体中的岩浆作用（Grobgneis）在时间上受限制的时期的证据。将调查的地下室与西喀尔巴阡地下室的地下室进行比较，我们认为在下奥陶高山单元中发生了广泛的二叠纪花岗岩岩浆活动。根据地球化学数据，它们属于高钾钙碱性至shoshonitic S型系列。Grobgneis变质岩的锆石Hf同位素组成显示εHf（t）值为-4.37至-0.6，TDM2模型年龄为1.31-1.55 Ga，表明它们的原生质是通过回收旧大陆壳而获得的。我们认为，二叠纪的花岗岩和辉长岩被认为是下奥陶高山单元中与裂谷有关的岩石，并且与盖层沉积物同时存在。