In this contribution, we highlight the importance of in‐situ monazite geochronology linked to P−T modelling for identification of timescales of metamorphic processes. Barrovian‐type micaschists, migmatites and augengneiss from the Gumburanjun dome in the southeastern extremity of the Gianbul dome, NW Himalaya, have been studied in order to correlate the early stages of Himalayan metamorphism at different crustal levels and infer the timing of anatexis. P−T−t paths are constrained through combined pseudosection modelling and in‐situ and in‐mount monazite and xenotime laser ablation–split‐stream inductively coupled plasma‐mass spectrometry. Petrography and garnet zoning combined with pseudosection modelling show that garnet‐staurolite schists record burial from ~530 to 560°C and 5.5 kbar to ~630 to 660°C and 7 kbar; staurolite‐kyanite schists from ~530 to 560°C and 5 kbar to ~670 to 680°C and 7−9 kbar; and garnet‐kyanite migmatites from 540−570°C and 5 kbar to ~680 to 750°C and 7−10 kbar, probably also to >750°C and >9 kbar above the muscovite stability field. The decompression paths of garnet‐staurolite schists indicate cooling on decompression, while garnet rim chemistry and local sillimanite growth point to a stage of re‐equilibration at ~600 to 670°C and 4−6 kbar in some of the staurolite‐kyanite schists, and at ~670 to 700°C and 6 kbar in garnet‐kyanite migmatites. Some of the staurolite‐kyanite schists and garnet‐kyanite migmatites also contain andalusite or andalusite‐cordierite. Monazite and xenotime were analysed in thin sections in garnet, staurolite and kyanite, and in the matrix; and in mounts. BSE images and compositional maps of monazite (xenotime was too small) show variable internal structures from homogeneous through patchy zoning with embayed to sharp boundaries. Two groups of samples can be identified on the basis of the presence or absence of c. 44 − 37 Ma ages. The first group of samples—two garnet‐staurolite schists—recorded only c. 31 − 27 Ma ages in porphyroblasts and no c. 40 Ma ages. The second group (samples of staurolite‐kyanite schist, garnet‐kyanite migmatites, augengneiss) have both the older, c. 44 − 37 Ma monazite ages in porphyroblasts and younger ages down to c. 22 Ma. These significantly different ranges of ages from porphyroblasts of 44−37 Ma, and 31−27 Ma, are interpreted as the duration of prograde P−T paths in Eocene and Oligocene, and indicate diachronous two‐stage burial of rocks. Early migmatization occurred at 38 Ma. The c. 29 Ma is interpreted as the time when rocks from the lower and middle crustal levels were partially exhumed and came in to contact with rocks that were downgoing at this time. Localized monazite recrystallization is as young as 26−24 Ma. The youngest ages of 23−22 Ma are related to leucogranite emplacement.

中文翻译：

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岩相喜马拉雅山西北部岩石年代学揭示的始新世辉辉岩形成和历时埋葬

在这方面的贡献，我们强调的重要性原位挂独居石年代学研究-对-叔建模变质过程的时间尺度的鉴定。对Gianbul圆顶东南端喜马拉雅山Gumburanjun圆顶中的Barrovian型云母，游岩和奥金尼属进行了研究，目的是关联不同地壳水平上喜马拉雅变质的早期阶段，并推断出Anatexis的时间。通过组合伪截面建模和原位约束Pt路径以及山中独居石和xenotime激光烧蚀分流电感耦合等离子体质谱法。岩石学和石榴石分区与伪剖面模拟相结合，表明石榴石-堇青石片岩记录的埋藏温度为〜530至560°C和5.5 kbar至〜630至660°C和7 kbar。星形石-蓝晶石片岩在〜530至560°C和5 kbar的片岩中延伸至〜670至680°C和7−9 kbar的片岩; 从540-570°C和5 kbar到约680至750°C和7-10 kbar的石榴石-蓝晶石辉辉岩，也可能在白云母稳定场以上达到> 750°C和> 9 kbar。石榴石-堇青石片岩的减压路径表明降温有所降温，而石榴石-蓝晶石片岩的石榴石边缘化学和局部硅线石生长指向约600至670°C和4-6 kbar的重新平衡阶段，石榴石-蓝晶石辉石中的温度约为670至700°C，压力为6 kbar。某些辉石-蓝晶石片岩和石榴石-蓝晶石辉晶岩也含有红柱石或红柱石-堇青石。在石榴石，星形石和蓝晶石以及基质中，薄片和独居石分别进行了分析。和在坐骑。BSE图像和独居石的成分图（xenotime太小）显示出内部结构从均质到斑驳的带状区域，并带有隐蔽的边界。可以根据是否存在 BSE图像和独居石的成分图（xenotime太小）显示出内部结构从均质到斑驳的带状区域，并带有隐蔽的边界。可以根据是否存在 BSE图像和独居石的成分图（xenotime太小）显示出内部结构从均质到斑驳的带状区域，并带有隐蔽的边界。可以根据是否存在c。44-37岁。第一组样品（两个石榴石-辉石片岩）仅记录c。在成花细胞中年龄为31 − 27 Ma，无c。40 Ma年龄。第二组（十字石-蓝晶石片岩，石榴石蓝晶石混合岩样品，augengneiss）同时具有较旧的，Ç。在成岩细胞中年龄为44 − 37 Ma独居石，年龄低至c。22马。这些显著不同于44-37马，和31-27麻斑晶年龄范围，被解释为的顺行的持续时间对叔在始新世和渐新路径，并指示岩穿时两个阶段的埋葬。早期迁移发生在38 Ma。该ç。29 Ma被解释为下部和中地壳层的岩石被部分挖出并与此时正在下降的岩石接触的时间。独居石的局部重结晶年龄为26-24 Ma。23-22 Ma的最小年龄与白云石镶嵌有关。