Interaction between magma and carbonate plays a pivotal role in volcanic systems, yet its impact on magma transport properties remains inadequately explored. This study presents novel viscosity data on a leucite-bearing phonotephritic melt from the 472 CE Pollena eruption (Vesuvius, Italy), doped with varying amounts of CaO and CaO + MgO. The compositions match the chemistry of melt inclusions and interstitial glasses from skarns at Vesuvius, which have been interpreted as related to mixing of magma with different amounts of CaO and MgO derived from the host carbonates (limestone and dolostone). Viscosity measurements were conducted at both high (1150–1400 °C) and low temperatures (640–760 °C) by concentric cylinder viscometry, differential scanning calorimetry, and micropenetration methods. Through an integrated approach which combines Brillouin and Raman spectroscopy with the aforementioned techniques, we accurately predict the viscosity changes induced by magma‑carbonate interaction and identify the formation of nanoheterogeneities during low-temperature viscosity measurements. Notably, viscosity models from the literature fail to accurately reproduce our experimental data set at both high and low temperature. In the high-temperature regime, the addition of CaO induces a remarkable viscosity decrease, surpassing that produced by CaO + MgO addition. Furthermore, our findings reveal a significant viscosity/temperature crossover resulting from the addition of CaO and CaO + MgO to the melt phase. Undoped melt exhibits a higher viscosity compared to doped melts above 750 °C, with an inverse trend observed below this temperature threshold. Such rheological constraints may affect the mobility and mixing capability of melts exposed to different levels of carbonate assimilation.

中文翻译：

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碳酸盐同化和纳米异质性对维苏威火山辉石熔体粘度的影响


岩浆和碳酸盐之间的相互作用在火山系统中起着关键作用，但其对岩浆输送特性的影响仍未得到充分探讨。本研究提供了公元 472 年 Pollena 喷发（意大利维苏威火山）中含白铁矿的含白铁矿的光辉石熔体的新粘度数据，掺杂了不同量的 CaO 和 CaO + MgO。这些成分与维苏威火山矽卡岩的熔融包裹体和间隙玻璃的化学性质相匹配，它们被解释为与岩浆与来自主碳酸盐岩（石灰石和白云石）的不同数量的 CaO 和 MgO 的混合有关。在高温 （1150–1400 °C） 和低温 （640–760 °C） 下，通过同心圆筒粘度计、差示扫描量热法和微穿透法进行粘度测量。通过将布里渊光谱和拉曼光谱与上述技术相结合的综合方法，我们准确预测了岩浆-碳酸盐相互作用引起的粘度变化，并确定了低温粘度测量过程中纳米异质性的形成。值得注意的是，文献中的粘度模型无法准确再现我们在高温和低温下的实验数据集。在高温条件下，CaO 的添加导致粘度显着降低，超过了 CaO + MgO 添加产生的粘度。此外，我们的研究结果揭示了由于在熔融相中添加 CaO 和 CaO + MgO 而导致的显着粘度/温度交叉。与 750 °C 以上的掺杂熔体相比，未掺杂的熔体表现出更高的粘度，低于该温度阈值时观察到相反的趋势。 这种流变学限制可能会影响暴露于不同水平碳酸盐同化的熔体的流动性和混合能力。