The Alps, as part of the Alpine-Mediterranean Mountain chain, are one of the classical localities for orogenic studies, where the Mesozoic-Cenozoic tectonic evolution is well known, and many classical models have been proposed to explain the tectonic evolution from Mesozoic rifting and breakup to Late Mesozoic-Cenozoic subduction, plate collision, and exhumation. However, the pre-Mesozoic tectonic evolution of the pre-Alpine basement remains poorly known because of the lack of sufficient age data due to complex polyphase deformation and multiple metamorphic overprints. New data from the mainly amphibolite-facies pre-Alpine basement of the Austroalpine mega-unit indicates that this basement is composed of a heterogeneous series of continental units, island arcs, ophiolites, subduction mélanges, accretionary wedges, and seamounts affected by different metamorphic grades. This study presents new results of LA-ICP-MS U-Pb dating and MC-ICP-MS Lu-Hf isotopic tracing of zircons from three key areas of Austroalpine basement, including the: i) Wechsel Gneiss and Waldbach Complexes, and Wechsel Phyllite Unit, (ii) Saualpe-Koralpe-Pohorje, and (iii) Schladming-Seckau areas. We determine the Wechsel Gneiss Complex to be a continental magmatic arc formed during 500–560 Ma in the proximity to a continental block with a ‘memory’ of Late Archean to Early Proterozoic continental crust. The Wechsel Gneiss Complex has U-Pb ages of 2.1 to 2.2 Ga and 2.5 to 2.8 Ga that indicate a close relationship to northern Gondwana, with depleted mantle Hf model ages as old as 3.5 Ga. The Wechsel Phyllite Unit structurally overlying the Wechsel Gneiss Complex has partly different sources, including juvenile crust formed at ca. 530 Ma. In contrast, the Waldbach Complex constantly added new crustal material during the 490–470 Ma period and bears considerably more positive ε_Hf(t) values than the underlying Wechsel Gneiss Complex and gives relatively young, depleted mantle model ages of 700 to 500 Ma. The Waldbach Complex is, therefore, interpreted to be part of a magmatic arc that formed during closure of the Prototethys and was metamorphosed during Variscan orogenic events at ca. 350–330 Ma. The Schladming-Seckau and Wechsel Complexes represent a Cambro-Ordovician magmatic arc system formed by Prototethys subduction processes with the associated Late Neoproterozoic to Early Ordovician ophiolitic Speik complex having formed in its back-arc basin or as Prototethyan lithosphere. The Plankogel Complex and structurally overlying micaschist and amphibolite units represent accreted ocean, ocean island, and continent-derived materials, interpreted to be an accretionary complex formed during the Permo-Triassic closure of the Paleotethys. Many granites of the Austroalpine mega-unit with Permian ages (e.g., porphyric granite called Grobgneiss and other granite gneisses and associated pegmatites) were likely formed in an extensional environment that culminated in the opening of the Middle-Late Triassic Meliata oceanic rift. These granites formed by partial remelting of crust with mainly Middle Proterozoic Hf model ages. Taken all these data together, we find that the Austroalpine basement is heterogeneously composed and includes complexes of different ages, different tectonic evolutionary histories and different remolten sources representing different locations before final accretion. The composite of pre-Alpine complexes in the Austroalpine mega-unit likely assembled not earlier than Late Permian or Early Triassic.

阿尔卑斯山脉作为高山-地中海山脉链的一部分，是造山学研究的经典地点之一，中生代-新生代构造演化是众所周知的，中生代裂谷构造演化被提出许多经典模型来解释。破裂到晚中新生代俯冲、板块碰撞和剥露。然而，由于复杂的多相变形和多次变质叠印，缺乏足够的年龄数据，对前高山基底的前中生代构造演化仍然知之甚少。来自南高山巨型单元的主要角闪岩相前高山基底的新数据表明，该基底由一系列异质的大陆单元、岛弧、蛇绿岩、俯冲混杂岩、增生楔、和受不同变质等级影响的海山。本研究展示了 LA-ICP-MS U-Pb 测年和 MC-ICP-MS Lu-Hf 同位素示踪来自 Austroalpine 基底三个关键区域的锆石的新结果，包括：i) Wechsel 片麻岩和 Waldbach 杂岩，以及 Wechsel 千枚岩单位，(ii) Saualpe-Koralpe-Pohorje 和 (iii) Schladming-Seckau 地区。我们确定 Wechsel 片麻岩杂岩是一个大陆岩浆弧，形成于 500-560 Ma，靠近大陆块，具有晚太古代到早元古代大陆地壳的“记忆”。Wechsel 片麻岩杂岩的 U-Pb 年龄为 2.1 至 2.2 Ga 和 2.5 至 2.8 Ga，表明与冈瓦纳大陆北部关系密切，耗尽地幔 Hf 模型年龄高达 3.5 Ga。Wechsel 千枚岩单元在结构上覆盖在 Wechsel 片麻岩杂岩上有部分不同的来源，包括在大约形成的幼壳。530 马。相比之下，瓦尔德巴赫杂岩在 490 至 470 Ma 期间不断增加新的地壳物质，并具有明显更高的正 ε_高频(t) 值比下面的 Wechsel 片麻岩杂岩值高，并给出了年龄为 700 至 500 Ma 的相对年轻、耗尽的地幔模型。因此，Waldbach 杂岩被解释为岩浆弧的一部分，该岩浆弧在 Prototethys 闭合期间形成，并在大约 20 年的 Variscan 造山事件期间变形。350–330 毫安。Schladming-Seckau 和 Wechsel 杂岩代表了一个寒武纪-奥陶纪岩浆弧系统，由原特提斯俯冲过程形成，相关的晚新元古代至早奥陶世蛇绿岩 Speik 杂岩在其弧后盆地或原始岩石圈中形成。Plankogel Complex 和结构上覆盖的云母片岩和角闪岩单元代表了增生的海洋、海洋岛和大陆衍生的材料，解释为在古特提斯二叠纪-三叠纪闭合期间形成的增生杂岩。具有二叠纪时代的南高山巨型单元的许多花岗岩（例如，称为 Grobgneiss 的斑状花岗岩和其他花岗岩片麻岩和相关伟晶岩）可能形成于伸展环境中，最终导致中-晚三叠世 Meliata 海洋裂谷的开放。这些花岗岩由地壳部分重熔形成，主要具有中元古代Hf模型年龄。综合所有这些数据，我们发现南高山基底是异质组成的，包括不同时代、不同构造演化历史和代表最终增生前不同位置的不同重熔源的复合体。