Magma-carbonate interaction is an increasingly recognised process occurring at active volcanoes worldwide, with implications for the magmatic evolution of the host volcanic systems, their eruptive behaviour, volcanic CO₂ budgets, and economic mineralisation. Abundant calc-silicate skarn xenoliths are found at Merapi volcano, Indonesia. We identify two distinct xenolith types: magmatic skarn xenoliths, which contain evidence of formation within the magma, and exoskarn xenoliths, which more likely represent fragments of crystalline metamorphosed wall-rocks. The magmatic skarn xenoliths comprise distinct compositional and mineralogical zones with abundant Ca-enriched glass (up to 10 wt% relative to lava groundmass), mineralogically dominated by clinopyroxene (En_15-43Fs_14-36Wo_41-51) + plagioclase (An_37-100) ± magnetite in the outer zones towards the lava contact and by wollastonite ± clinopyroxene (En_17-38Fs_8-34Wo_49-59) ± plagioclase (An_46-100) ± garnet (Grs_0-65Adr_24-75Sch_0-76) ± quartz in the xenolith cores. These zones are controlled by Ca transfer from the limestone protolith to the magma and by transfer of magma-derived elements in the opposite direction. In contrast, the exoskarn xenoliths are unzoned and essentially glass-free, representing equilibration at sub-solidus conditions. The major mineral assemblage in the exoskarn xenoliths is wollastonite + garnet (Grs_73-97Adr_3-24) + Ca-Al-rich clinopyroxene (CaTs_0-38) + anorthite ± quartz, with variable amounts of either quartz or melilite (Geh_42-91) + spinel. Thermobarometric calculations, fluid inclusion microthermometry and newly calibrated oxybarometry based on Fe³⁺/ΣFe in clinopyroxene indicate magmatic skarn xenolith formation conditions of ∼850 ± 45 °C, < 100 MPa and at an oxygen fugacity between the NNO and HM buffer. The exoskarn xenoliths, in turn, formed at 510-910 °C under oxygen fugacity conditions between NNO and air. These high oxygen fugacities are likely imposed by the large volumes of CO₂ liberated from the carbonate. Halogen and sulphur-rich mineral phases in the xenoliths testify to the infiltration by a magmatic brine. In some xenoliths this is associated with the precipitation of copper-bearing mineral phases by sulphur dissociation into sulphide and sulphate, indicating potential mineralisation in the skarn system below Merapi. Compositions of many xenolith clinopyroxene and plagioclase crystals overlap with that of magmatic minerals, suggesting that the crystal cargo in Merapi magmas may contain a larger proportion of skarn-derived xenocrysts than previously recognised. Assessment of xenolith formation timescales demonstrates that magma-carbonate interaction and associated CO₂ release could affect eruption intensity, as recently suggested for Merapi and similar carbonate-hosted volcanoes elsewhere.

中文翻译：

---

默拉皮火山（印度尼西亚）的钙硅酸盐异岩中记录的岩浆碳酸盐相互作用的岩浆和交代作用

岩浆与碳酸盐的相互作用是世界各地活跃火山中日益被认可的过程，对宿主火山系统的岩浆演化，其喷发行为，火山CO ₂预算以及经济矿化具有影响。在印度尼西亚默拉比火山发现了丰富的钙硅酸盐矽卡岩异岩。我们确定了两种不同的异岩体类型：岩浆矽卡岩异岩体（其中包含岩浆内形成的证据）和外骨骼异岩体（更可能代表结晶变质壁岩的碎片）。岩浆矽卡岩异岩包含独特的成分和矿物学带，富含丰富的富含钙的玻璃（相对于熔岩地基质量最高可达10 wt％），矿物学上由斜_ino石占主导地位（En _15-43 Fs _14-36Wo _41-51）+斜长石（An _37-100）±在外部区域朝向熔岩接触的磁铁矿和硅灰石±斜辉石（En _17-38 Fs _8-34 Wo _49-59）±斜长石（An _46-100）异种岩芯中的±石榴石（Grs _0-65 Adr _24-75 Sch _0-76）±石英。这些区域受Ca从石灰岩原生岩到岩浆的转移以及岩浆衍生元素向相反方向的转移的控制。相比之下，外骨骼的异种石没有分区，并且基本上没有玻璃，表示在亚固相线条件下达到平衡。外生异种岩中的主要矿物组合是硅灰石+石榴石（Grs_73-97 Adr _3-24）+富含Ca-Al的亚斜辉石（CaTs _0-38）+钙长石±石英，石英或莫来石（Geh _42-91）+尖晶石的含量可变。热比重法的计算，流体夹杂物显微热法和基于斜发py中Fe ³⁺ /ΣFe的新校准的氧压法表明岩浆矽卡岩异岩体形成条件约为850±45°C，<100 MPa，并且在NNO和HM缓冲液之间为氧逸度。反过来，在NNO和空气之间的氧逸度条件下，外骨骼异物在510-910°C下形成。大量的CO ₂可能导致这些高氧气逸度从碳酸盐中释放出来。异种岩中的卤素和富含硫的矿物相证明了岩浆盐水的渗透。在某些异岩中，这与含硫铜分解成硫化物和硫酸盐而导致含铜矿物相的沉淀有关，这表明在默拉皮以下的矽卡岩体系中可能存在矿化作用。许多异种的斜生辉石和斜长石晶体的成分与岩浆矿物的成分重叠，这表明默拉比岩浆中的晶体货物可能含有比以前所认识的更大的矽卡岩型异晶。异岩形成时间尺度的评估表明，岩浆-碳酸盐相互作用和相关的CO ₂ 释放可能会影响喷发强度，正如最近对默拉皮（Merapi）和其他地方类似的碳酸盐岩火山所建议的那样。