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首页> 外文期刊>Contributions to Mineralogy and Petrology >Amphibole perspective to unravel pre-eruptive processes and conditions in volcanic plumbing systems beneath intermediate arc volcanoes: a case study from Ciomadul volcano (SE Carpathians)
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Amphibole perspective to unravel pre-eruptive processes and conditions in volcanic plumbing systems beneath intermediate arc volcanoes: a case study from Ciomadul volcano (SE Carpathians)

机译：角闪石透视揭示中弧火山下火山管道系统的喷发前过程和条件：以Ciomadul火山为例（SE喀尔巴阡山脉）

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Ciomadul is the youngest volcano in the Car-pathian-Pannonian region produced crystal-rich high-K dacites that contain abundant amphibole phenocrysts. The amphiboles in the studied dacites are characterized by large variety of zoning patterns, textures, and a wide range of compositions (e.g., 6.4-15 wt% Al_2O_3, 79-821 ppm Sr) often in thin-section scale and even in single crystals. Two amphibole populations were observed in the dacite: low-Al hornblendes represent a cold (<800 °C) silicic crystal mush, whereas the high-Al pargasites crystallized in a hot (>900 °C) mafic magma. Amphibole thermobarometry suggests that the silicic crystal mush was stored in an upper crustal storage (~ 8-12 km). This was also the place where the erupted dacitic magma was formed during the remo-bilization of upper crustal silicic crystal mush body by hot mafic magma indicated by simple-zoned and composite amphiboles. This includes reheating (by ~200 °C) and partial remelting of different parts of the crystal mush followed by intensive crystallization of the second mineral population (including pargasites). Breakdown textures of amphiboles imply that they were formed by reheating in case of hornblendes, suggesting that pre-eruptive heating and mixing could take place within days or weeks before the eruption. The decompression rim of pargasites suggests around 12 days of magma ascent in the conduit. Several arc volcanoes produce mixed intermediate magmas with similar bimodal amphibole cargo as the Ciomadul, but in our dacite the two amphibole population can be found even in a single crystal (composite amphiboles). Our study indicates that high-Al pargasites form as a second generation in these magmas after the mafic replenishment into a silicic capture zone; thus, they cannot unambiguously indicate a deeper mafic storage zone beneath these volcanoes. The simple-zoned and composite amphiboles provide direct evidence that significant compositional variations of amphiboles do not necessarily mean variation in the pressure of crystallization even if the Al-tschermak substitution can be recognized, suggesting that amphibole barometers that consider only amphibole composition may often yield unrealistic pressure variation.
机译：Ciomadul是喀尔巴阡山脉-Pannonian地区最年轻的火山，出产富含晶体的高K Dacites，其中含有丰富的角闪石。所研究的dacit中的闪石的特征通常在于薄片状甚至单晶，其特征在于多种多样的分区模式，纹理和广泛的组成（例如6.4-15 wt％Al_2O_3、79-821 ppm Sr） 。在da石中观察到两个闪石种群：低铝角混纺物代表冷（<800°C）的硅质结晶糊状物，而高铝方解石则在热（> 900°C）的镁铁质岩浆中结晶。闪石热压法表明，硅质结晶糊状物储存在上地壳储存物中（〜8-12 km）。这也是在上地壳硅质晶体糊状体通过简单分区和复合闪石指示的热镁铁质岩浆的再活化过程中形成喷出的岩浆岩的地方。这包括重新加热（约200°C）和使晶体糊状物的不同部分部分重熔，然后对第二种矿物质（包括方解石）进行密集结晶。闪石的分解质地暗示它们是在角horn的情况下通过重新加热而形成的，这表明喷发前的加热和混合可能在喷发前几天或几周内发生。方解石的减压边缘表明导管中约有12天的岩浆上升。几个弧形火山产生混合的中间岩浆，具有与Ciomadul类似的双峰闪石货，但在我们的dacite中，即使在单晶（复合闪石）中也可以找到两个闪石。我们的研究表明，在镁铁质补充到硅质捕获区之后，这些岩浆中形成了高铝的方解石第二​​代。因此，它们不能明确指示这些火山下方有较深的铁镁质储藏区。简单区域的和合成的闪石提供了直接的证据，即即使可以识别Al-tschermak取代，闪石的重大组成变化也不一定意味着结晶压力的变化，这表明仅考虑闪石成分的闪石晴雨表可能经常产生不现实的现象。压力变化。

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