Abstract—

The paper presents data on phase relations in garnet-bearing carbonatite from the Tromsø Nappe, Norway. The carbonatite matrix consists of calcite–dolomite carbonate with three generations of garnet inclusions (up to 15–20%). The relics of the primary garnets (Grt₁) are depleted (<10^–2 wt %) in the rare earth elements (REE). The garnet of the second and third generations (Grt_2–3) is anomalously enriched (up to 10–15 wt %) in the light REE (LREE), and the carbonates are depleted in these elements. The distribution of REE between the garnet and carbonate indicates the absence of equilibrium. The melting of the carbonatite at T = 950–1400°C, P = 4.0 GPa showed that the “dry” solidus temperature is 1150°C, and the liquidus temperature is >1300°C. In the experiment with H₂O + CO₂ fluid, the solidus and liquidus temperatures are ≤950 and 1250°C, respectively. The subsolidus association is calcite, garnet, clinopyroxene, biotite, and accessory minerals: apatite, ilmenite, rutile, and titanite. The garnet and carbonatite melt occur in reaction relationships, as is evident from the garnet zoning with a decrease in the FeO and increase in the MgO, CaO, TiO₂, and LREE concentrations. The geological setting, phase relationships, and experimental data indicate that the garnet-bearing carbonatites in the Tromsø area were formed in relation to the carbonatization and melting of upper mantle material at high pressures during the collision of the Baltica and Laurentia plates in the course of the Caledonian orogenesis, with subsequent intrusion and crystallization of silicate–carbonate magmas.

中文翻译：

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挪威 Tromsø Nappe 含石榴石碳酸岩的岩石成因

摘要-

该论文提供了挪威特罗姆瑟纳佩带石榴石碳酸岩的相关系数据。碳酸岩基质由方解石-白云石碳酸盐和三代石榴石包裹体（高达 15-20%）组成。原生石榴石 ( Grt ₁ )的遗迹中稀土元素 (REE)已耗尽 (<10 ^–2 wt %)。第二代和第三代石榴石（Grt _2-3）异常富集（高达 10-15 wt %）轻稀土（LREE），而碳酸盐中这些元素贫乏。石榴石和碳酸盐之间 REE 的分布表明不存在平衡。碳酸岩在T = 950–1400°C 时的熔化，P= 4.0 GPa 表明“干”固相线温度为 1150°C，液相线温度 >1300°C。在H ₂ O + CO ₂流体的实验中，固相线温度和液相线温度分别≤950℃和1250℃。亚固相组合是方解石、石榴石、斜辉石、黑云母和副矿物：磷灰石、钛铁矿、金红石和钛石。石榴石和碳酸岩熔体以反应关系发生，从石榴石分带可以看出，FeO 减少，MgO、CaO、TiO _{2 增加}, 和 LREE 浓度。地质背景、相关系和实验数据表明，特罗姆瑟地区含石榴石碳酸岩的形成与波罗的海板块和劳伦蒂亚板块碰撞过程中上地幔物质在高压下碳化和熔融有关。加里东造山作用，随后硅酸盐-碳酸盐岩浆侵入和结晶。