Abstract This paper provides a new parameterization of the temperature and H2O content dependence of the pure liquid viscosities of rhyolitic and dacitic magmas associated with representative volcanic products of the Caxias do Sul and Santa Maria eruptive sequences. The viscosities of silicic volcanic products from the Santa Maria rhyolite (SMr), Caxias do Sul (CSd) and Barros Cassal (BCd) eruptive sequences (Lower Cretaceous volcanism of Parana-Etendeka Large Igneous Province) were measured in the temperature range from ca. 1600 °C to the glass transition (Tg). Anhydrous melt viscosities of representative samples from the main eruptive sequences were determined via concentric cylinder viscometry in the super liquidus regime. The quench products of SMr and CSd were then hydrated using an Internally Heated Pressure Vessel to generate two suites of samples with variable water content of up to 4.41 (CSd) and 5.27 (SMr) wt% as determined by Karl Fischer Titration (KFT). Finally, both anhydrous and hydrous samples were used for micropenetration viscosity measurements near Tg. Both types of samples show a minor amount of Fe-Ti-oxide nanolites identified via Raman spectroscopy, which presence did not substantially interfere with viscosity determinations. Based on the results of the viscosity measurements we parameterized the viscosity dependence as a function of water content using the following Vogel Fulcher Tammann (VFT) expressions accounting for the water and temperature dependence of the viscosity: logη = −4.55 + (10065–176*H2O)/[T-(34.6 + 375.3/(1 + H2O))] for SMr. and logη = −4.55 + (9213–338.1*H2O)/[T-(148.5 + 301.3/(1 + H2O))] for CSd. where η is the viscosity in Pa s, T the absolute temperature and H2O the dissolved water content in wt%. This novel parameterization appears to solve a few inconsistencies associated with the variation of the main descriptive parameters of the effect of H2O, improving the performance of some previous parameterizations. These results are useful for scaling to the conditions extant during ascent and eruption and during flow, emplacement and welding, at temperatures above Tg, for the dacitic and rhyolitic products investigated here.

中文翻译：

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巴拉那岩浆省（巴西南里奥格兰德州）帕尔马斯型岩浆的粘度：对高温硅质火山作用的影响

摘要 本文提供了与 Caxias do Sul 和 Santa Maria 喷发序列的代表性火山产物相关的流纹质和英安质岩浆的纯液体粘度的温度和 H2O 含量依赖性的新参数化。来自 Santa Maria 流纹岩 (SMr)、Caxias do Sul (CSd) 和 Barros Cassal (BCd) 喷发序列（Parana-Etendeka 大型火成岩省的下白垩纪火山）的硅质火山产物的粘度在约 1600 °C 至玻璃化转变 (Tg)。来自主要喷发序列的代表性样品的无水熔体粘度是通过超液相线状态下的同心圆柱粘度测定法确定的。然后使用内加热压力容器将 SMr 和 CSd 的淬火产物水合，以生成两套样品，根据卡尔费休滴定 (KFT) 测定，其含水量高达 4.41 (CSd) 和 5.27 (SMr) wt%。最后，无水和含水样品均用于 Tg 附近的微渗透粘度测量。两种类型的样品都显示出通过拉曼光谱鉴定出的少量 Fe-Ti-氧化物纳米颗粒，其存在基本上不会干扰粘度测定。基于粘度测量的结果，我们使用以下 Vogel Fulcher Tammann (VFT) 表达式将粘度依赖性参数化为水含量的函数，说明粘度对水和温度的依赖性：logη = -4.55 + (10065–176* H2O)/[T-(34.6 + 375.3/(1 + H2O))] 对于 SMr。对于 CSd，logη = -4.55 + (9213–338.1*H2O)/[T-(148.5 + 301.3/(1 + H2O))]。其中 η 是以 Pa s 为单位的粘度，T 是绝对温度，H2O 是以 wt% 为单位的溶解水含量。这种新颖的参数化似乎解决了与 H2O 影响的主要描述参数变化相关的一些不一致问题，提高了一些先前参数化的性能。对于此处研究的英安质和流纹质产品，这些结果对于在高于 Tg 的温度下在上升和喷发期间以及在流动、就位和焊接期间扩展到现有条件是有用的。这种新颖的参数化似乎解决了与 H2O 影响的主要描述参数变化相关的一些不一致问题，提高了一些先前参数化的性能。对于此处研究的英安质和流纹质产品，这些结果对于在高于 Tg 的温度下在上升和喷发期间以及在流动、就位和焊接期间扩展到现有条件是有用的。这种新颖的参数化似乎解决了与 H2O 影响的主要描述参数变化相关的一些不一致问题，提高了一些先前参数化的性能。对于此处研究的英安质和流纹质产品，这些结果对于在高于 Tg 的温度下在上升和喷发期间以及在流动、就位和焊接期间扩展到现有条件是有用的。