In this study the first viscosity measurements in the glass transition range of melts from highly explosive large-volume eruptions from the Colli Albani Volcanic District (CAVD) are presented. The magmas are ultrapotassic, rich in iron and CaO and characterised by a low silica content (< 45 wt%). Melt compositions range from tephri-phonolitic to foiditic. The Colli Albani eruptions appear anomalous since they produced a large volume of erupted material in spite of their silica undersaturated compositions. The viscosity of the Colli Albani melt changes as the melt composition evolves from the original melt to a country-rock contaminated melt to a crystal-bearing melt with a permanent decrease in liquid viscosity. Conventional estimations of viscosities assume these magmas to have a low viscosity. The presented data show that the melt viscosities are higher than expected. Taking into account further chemical or rheological features of a melt, the investigated CAVD melts are not that striking as assumed in comparison with other large-volume eruptions. Consequently, considering the alkaline-earth to alkaline ratio together with the SiO2 content could provide an alternative when comparing large volume eruptions.

中文翻译：

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colli albani 火山区（意大利）熔体的流变学：案例研究

在这项研究中，首次介绍了科利阿尔巴尼火山区 (CAVD) 高爆炸性大体积喷发熔体的玻璃化转变范围内的粘度测量值。岩浆是超钾质的，富含铁和 CaO，其特征是二氧化硅含量低 (< 45 wt%)。熔体成分范围从 tephri-phonolitic 到 foiditic。Colli Albani 喷发显得异常，因为尽管它们的二氧化硅成分不饱和，但它们产生了大量喷发物质。Colli Albani 熔体的粘度随着熔体成分从原始熔体演变为受围岩污染的熔体再到含晶体的熔体而发生变化，液体粘度会永久降低。粘度的常规估计假设这些岩浆具有低粘度。所提供的数据表明熔体粘度高于预期。考虑到熔体的进一步化学或流变学特征，与其他大体积喷发相比，所研究的 CAVD 熔体并不像假设的那样引人注目。因此，在比较大体积喷发时，考虑碱土与碱的比例以及 SiO2 含量可以提供替代方案。