Monazite dating in metapelites is an emerging method to investigate polymetamorphic areas. A protocol for Th–U–Pb dating of monazite by electron microprobe was adopted for a JEOL JXA-8530F. It was applied to the Variscan and Early-Alpine metamorphic Austroalpine Oetztal-Stubai Complex (OSC). In the Alpeiner Valley in the Stubai region, the Schrankogel complex is the eastern succession of the Central Metabasite Zone. In this part, metabasites are alternating with metapelites. In 4 samples from micaschist lenses, dominantly Carboniferous monazite isochrone ages at 335 ± 4 Ma, 320 ± 4 Ma; 319 ± 4 Ma and 319 ± 4 Ma were obtained. The micaschist samples with diverse modal compositions and variable bulk rock Ca contents of calculated assay, display distinct monazite microstructures, as quantified by automated SEM-MLA (mineral liberation analysis) routines. Clusters of small monazite could indicate new crystallization and yielded isochrones at 313 and 304 Ma. In contrast, corona structures of apatite and allanite around large monazites with isochrones between 350 and 315 Ma suggest a decomposition during decreasing temperature. Garnets in metapelitic assemblages display growth zonations with low pyrope contents in the cores and pyrope-rich rims. A prograde metamorphism with high pressure amphibolite-facies peak conditions at ~ 12 kbar and ~ 680 °C, and a post Pmax path with decompression to 4 kbar and 640–600 °C was estimated from the micaschists and from zoned Ca-amphiboles in retrogressed amphibolitized eclogites. The P–T path entered the monazite stability field during the decompression. This signals a Carboniferous age of the metamorphism. A minor population in one sample is composed of sporadic Permian single monazite ages. A Cretaceous monazite population is lacking. In the wide parts of the Austroalpine basement with Carboniferous-to-Cretaceous mica mixing ages, monazite age populations allow to discriminate a distinct Permian metamorphic event.

中文翻译：

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Oetztal-Stubai情结（Alpeiner谷，Stubai）中含独居石石榴石云母的电子微探针岩石年代学。

变质岩中的独居石定年法是研究多变质区域的新兴方法。JEOL JXA-8530F通过电子探针对独居石进行Th–U–Pb定年的协议。它被应用于瓦里斯坎和早期高山变质的奥特高山阿尔卑斯山脉的厄茨塔尔-舒巴泰复合体（OSC）。在Stubai地区的Alpeiner山谷中，Schrankogel复合体是Central Metabasite Zone的东部演替。在这一部分中，变质岩与变质岩交替发生。在来自云母片的4个样品中，主要石炭纪独居石异位酮年龄为335±4 Ma，320±4 Ma；获得了319±4 Ma和319±4 Ma。云母样品具有不同的模态组成和计算的测定中可变的大块岩石钙含量，显示出独特的独居石微结构，如通过自动SEM-MLA（矿物解放分析）程序所量化。小独居石的团簇可能表明新的结晶，并在313Ma和304Ma处产生了等时线。相反，大独居石周围磷灰石和尿囊石的电晕结构（等时线在350至315 Ma之间）表明在温度降低期间分解。异生组合中的石榴石显示出生长带，其核心和富烟酒的轮缘中的烟酒含量低。从云母和逆行带状钙闪石估计，在〜12 kbar和〜680°C的高压闪石岩相峰条件下，会发生前向变质作用，在减压至4 kbar和640–600°C时，Pmax后路径会解压缩。闪石化的榴辉岩。减压过程中，PT路径进入独居石稳定性场。这标志着变质的石炭纪。一个样本中的少数群体由零星的二叠纪单独居年龄组成。缺少白垩纪独居石种群。在石炭纪至白垩纪云母混合年龄的奥拓高山基底的大部分地区，独居石年龄种群可以区分明显的二叠纪变质事件。