We studied monazite behaviour in UHP diamond-bearing gneiss from Saxnäs in the Seve Nappe Complex of the Scandinavian Caledonides (Petrík et al., 2019). Although the rock has been reequilibrated under granulite facies and partial melting conditions, the UHP stage is recorded by the presence of diamond. Microdiamonds occur in situ as inclusions in garnet, kyanite and zircon, either as single-crystal or polyphase inclusions with Fe-Mg carbonates, rutile and CO 2 . Two garnet types have been recognised: dominant Grt I with inclusions of diamond found mostly in the garnet rims, which suggests that originally the bulk of Grt I grew at UHP conditions. Grt II, forming small crystals, overgrowths on, or domains within Grt I originated by dehydration melting reactions involving breakdown of phengite and clinopyroxene during decompression. Monazite occurs in the rims of Grt I close to microdiamond, where garnet shows the highest pyrope content and a secondary peak of yttrium. Such a position indicates thermally activated diffusion under high temperature at the end of prograde metamorphism. Based on such textural relations, we argue that monazite formed at UHP conditions.

中文翻译：

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含钻石片麻岩变质演化过程中的独居石行为：来自斯堪的纳维亚 Caledonides Seve Nappe Complex 的案例研究

我们研究了斯堪的纳维亚 Caledonides 的 Seve Nappe Complex 的 Saxnäs 含 UHP 金刚石片麻岩中的独居石行为（Petrík 等人，2019 年）。尽管岩石在麻粒岩相和部分熔融条件下重新平衡，但钻石的存在记录了超高压阶段。微金刚石作为石榴石、蓝晶石和锆石中的包裹体就地出现，可以是单晶包裹体，也可以是含铁镁碳酸盐、金红石和 CO 2 的多相包裹体。已识别出两种石榴石类型：主要的 Grt I，主要在石榴石边缘发现钻石内含物，这表明 Grt I 的大部分最初是在 UHP 条件下生长的。Grt II，形成小晶体、过度生长或 Grt I 内的域，起源于脱水熔融反应，涉及减压过程中菱镁矿和斜辉石的分解。独居石出现在 Grt I 靠近微金刚石的边缘，其中石榴石显示出最高的辉石含量和钇的次要峰。这样的位置表明在顺行变质结束时高温下的热激活扩散。基于这种结构关系，我们认为独居石是在 UHP 条件下形成的。