Magma ascending from the storage region toward the surface may crystallize small and rapidly-grown crystals, designated as microlites. Upon decompression, the rapid changes of the microlite textures, such as number density and crystal size, directly impact the rheology of the magma in the volcanic conduit, and eventually control the effusive vs. explosive style of the subaerial eruption. This is of prime importance for volcanic risk assessment involving highly viscous silica-rich magmas that are prone to fragmentation. To this aim, we present a theoretical modeling of plagioclase nucleation and growth in rhyolitic-like melts, based on previous decompression experiments. Thus, the modeling is valid for plagioclase crystallization in rhyolitic melts decompressed at 875°C from 200 MPa to final pressures of 50, 75, or 100 MPa, which represents effective undercooling (ΔT_eff) of 110, 80 and 55°C, respectively. Our results of nucleation-rate calculation using the Classical Nucleation Theory (CNT; case of homogeneous nucleation) and values of crystal-melt interfacial energy (σ) either from literature or empirically calculated, strongly disagree with previously-determined experimental nucleation rates. By inverting the CNT calculation using the experimentally-determined nucleation rates, we propose plagioclase-liquid interfacial energies from 0.041 to 0.059 J.m⁻² with ΔT_eff increasing from 55 to 110°C, which is about 2–3 times lower than σ determined empirically and macroscopically. We modeled plagioclase growth rates by atom diffusion in melt (following Fick's second law adapted to multicomponent systems), considering a crystal-melt interface advancing over time (as crystal grows) and a chemically-closed finite reservoir (no component supply). The component limiting plagioclase growth has been determined to be CaO, for which we calculated diffusion coefficients from 10⁻¹⁴ to 10⁻¹⁵ m²/s (conditions of a silicic melt, 875°C, and H₂O saturation pressures from 50 to 100 MPa). The overall good agreement between the model and the experimental growth laws validates diffusion as the main process controlling isothermal decompression-induced plagioclase growth under moderate ΔT_eff < 110°C. Combining both calculations, crystal number density and size, may be relevant to predict plagioclase microlite textures in ascending rhyolitic magmas, which may now be incorporated in conduit flow models to assess the magma rheological behavior that controls eruption dynamics.

从储藏区向表面上升的岩浆可能会使小的且快速生长的晶体结晶，称为微晶。减压后，微岩质地的快速变化（例如数量密度和晶体大小）直接影响火山管道中岩浆的流变性，并最终控制了地下喷发的喷出式与爆炸式。这对于涉及易碎裂的高粘性富含二氧化硅的岩浆的火山风险评估至关重要。为此，我们基于先前的减压实验，提出了斜纹岩样熔体中斜长石成核和生长的理论模型。因此，该模型对于在875°C下从200 MPa减压至最终压力50、75或100 MPa的流纹熔体中斜长石结晶有效。_eff）分别为_110、80和55°C。我们使用经典成核理论（CNT；均相成核的情况）进行成核速率计算的结果以及根据文献或通过经验计算得出的晶体熔体界面能（σ）的值都与先前确定的实验成核速率强烈不同。通过使用实验确定的成核速率反演CNT计算，我们提出了斜边-液相界面能量为0.041至0.059 Jm ^-2，_ΔTeff从55°C升至110°C，大约比凭经验和宏观确定的σ低2-3倍。考虑到晶体-熔体界面随时间推进（随着晶体生长）和化学封闭的有限储层（无组分供应），我们通过原子在熔体中的扩散来模拟斜长石生长速率（遵循适用于多组分系统的菲克第二定律）。确定了限制斜长石生长的成分为CaO，为此我们计算出的扩散系数为10 ^-14至10 ^-15 m ² / s（硅熔液，875°C和H _2的条件O饱和压力为50至100 MPa）。该模型与实验生长规律之间的总体良好一致性验证了扩散是控制中等温度_ΔTeff <110°C时等温减压诱导的斜长石生长的主要过程。结合晶体数量密度和大小的两种计算，可能与预测流纹岩浆上升中斜长石微晶岩的质地有关，现在可以将其合并到导管流模型中，以评估控制喷发动力学的岩浆流变行为。