The Theodul-Glacier-Unit (TGU) is a 100 m thick and 2 km long slab of pre-Alpine schist, gneiss and mafic rocks tectonically emplaced in the eclogite-facies Zermatt-Saas meta-ophiolite nappe (ZSU). The meta-sedimentary rocks occur mostly as garnet-phengite schists with locally cm-sized garnet porphyroblasts. The metavolcanic basic rocks are present as variably retrogressed eclogites showing a continental basalt signature and contain abundant zircon, which is unusual for basalts. The zircons dated with the U–Pb system yield an upper intercept age of 295 ± 16 Ma and a lower intercept age of 145 ± 34 Ma. The early Permian age is interpreted to represent the age of high-grade granulite facies metamorphism, evidence of which is also preserved in the cores of garnet porphyroblasts of the Grt-Ph schists. The lower intercept age corresponds to the time of continental breakup and the initiation of the Tethys in the Mid-Jurassic; these events may have created the TGU as an extensional allochton. Eclogite facies metamorphism recorded by the TGU rocks occurred during Alpine subduction at 57 Ma, the Lu–Hf age of TGU eclogite garnets. The TGU reached a depth of about 53 km at P–T conditions of 1.7 GPa and 520 °C derived from both, eclogite and Grt-Ph schist. This is in contrast to the ZSU surrounding the TGU with a reported subduction depth of more than 80 km at 43 Ma. It is proposed here that TGU and ZSU were subducted separately out of sequence. After juxtaposition of the two units during late Alpine thrusting and folding forming the present day geometry of nappes in the Zermatt-Saas region both units were progressively metamorphosed to about 650 MPa and 470 °C. This late prograde metamorphism at 34 Ma produced oligoclase + magnesio-hornblende in the matrix of Grt-Ph schists and eclogites. The derived TGU data document a complete Wilson Cycle.

中文翻译：

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Theodul冰川单元，位于西阿尔卑斯山采尔马特-萨斯山脉的高山蛇绿岩中的前高山岩石板

Theodul-Glacier-Unit（TGU）是一块100 m厚，2 km长的平板，由阿尔卑斯山前的片岩，片麻岩和镁铁质岩石构造地包裹在白云岩相Zermatt-Saas蛇绿岩推覆层中。准沉积岩多为石榴石-片岩片岩，局部有厘米大小的石榴石成斑细胞。中等火山岩基岩以变质的榴辉岩存在，表现出大陆玄武岩的特征，并含有丰富的锆石，这对于玄武岩而言是罕见的。用U–Pb系统标定日期的锆石产生的上限年龄为295±16 Ma，下限的年龄为145±34 Ma。二叠纪早期被解释为代表了高级花岗石相变质的年龄，Grt-Ph片岩的石榴石成岩细胞的核心中也保留了这一证据。较低的截距年龄对应于大陆分裂和侏罗纪中期特提斯开始的时间。这些事件可能已将TGU创建为延伸性异位线。TGU岩石记录的榴辉岩相变质发生在TGU榴辉岩石榴石Lu-Hf年龄57 Ma的高山俯冲过程中。在1.7 GPa和520°C的P–T条件下，从榴辉岩和Grt-Ph片岩得到的TGU达到了约53 km的深度。这与TSU周围的ZSU形成对比，后者在43 Ma的俯冲深度超过80 km。在此建议将TGU和ZSU顺序分包。在阿尔卑斯山晚期推挤和折叠过程中将两个单元并置后，形成了采尔马特-萨斯地区当前尿布的几何形状，两个单元逐渐变形至约650 MPa和470°C。在34 Ma处这种晚期的晚期变质作用在Grt-Ph片岩和榴辉岩的基质中产生了寡糖+镁红角闪石。导出的TGU数据记录了完整的Wilson周期。