Abstract
Plagioclase microlites in a magma nucleate and grow in response to melt supersaturation (Δϕplag). The resultant frozen plagioclase crystal size distribution (CSD) preserves the history of decompression pathways (dP/dt). SNGPlag is a numerical model that calculates the equilibrium composition of a decompressing magma and nucleates and grows plagioclase in response to an imposed Δϕplag. Here, we test a new version of SNGPlag calibrated for use with basaltic andesite magmas and model dP/dt for the ca. 12.6 ka Curacautín eruption of Llaima volcano, Chile. Instantaneous nucleation (Nplag) and growth (Gplag) rates of plagioclase were computed using the experimental results of Shea and Hammer (J Volcanol Geotherm Res 260:127–145, 10.1016/j.jvolgeores.2013.04.018, 2013) and used for SNGPlag modeling of basaltic andesite composition. Maximum Nplag of 6.1 × 105 cm h−1 is achieved at a Δϕplag of 44% and the maximum Gplag of 27.4 μm h−1 is achieved at a Δϕplag of 29%. Our modeled log dP/dtavg range from 2.69 ± 0.09 to 6.89 ± 0.96 MPa h−1 (1σ) with an average duration of decompression from 0.87 ± 0.25 to 16.13 ± 0.29 h assuming a starting pressure Pi of 110–150 MPa. These rates are similar to those derived from mafic decompression experiments for other explosive eruptions. Using assumptions for lithostatic pressure gradients (dP/dz), we calculate ascent rates of < 1–6 m s−1. We conducted a second set of Monte Carlo simulations using Pi of 15–30 MPa to investigate the influence of shallower decompression, resulting in log dP/dtavg from 2.86 ± 0.49 to 6.00 ± 0.86 MPa h−1. The dP/dt modeled here is two orders of magnitude lower than those calculated by Valdivia et al. (Bull Volcanol, 10.1007/s00445-021-01514-8, 2022) for the same eruption using a bubble number density meter, and suggests homogeneous nucleation raises dP/dt by orders of magnitude in the shallow conduit. Our modeling further supports the rapid-ascent hypothesis for driving highly explosive mafic eruptions.
Similar content being viewed by others
Introduction
Investigating magma ascent rates
Decompression rate affects eruption style (e.g., Eichelberger et al. 1986; Jaupart and Allegre 1991; Burgisser and Gardner 2005; La Spina et al. 2021; Bamber et al. 2020). As magmas ascend from depth, volatiles exsolve and crystals nucleate and grow in response to changes in pressure (P) and temperature (T). During rapid ascent, bubbles remain coupled to the magma resulting in explosive eruption (Eichelberger et al. 1986; Jaupart and Allegre 1991). Conversely, during slow ascent, bubbles coalesce, resulting in sufficient permeability to degas the melt and thus removes the volatile primer necessary for explosivity and results in effusive eruption (Mangan and Sisson 2000). Crystallization of microlites during decompression increases magma viscosity (Vona et al. 2011; La Spina et al. 2016; Vetere et al. 2021) and may act to either impede the ability of gas to decouple from the magma or enhance coalescence by pushing isolated vesicles together. As such, understanding the rate of magma decompression and therefore ascent rate is important for estimating eruption duration, intensity, and volcano hazards.
Several analytical and experimental methods exist for the investigation of magma decompression rate, each with their own strengths and weaknesses. Bubble and crystal textures provide a record of magma decompression or ascent path (Cashman and Marsh 1988; Blundy and Cashman 2008; Arzilli et al. 2019; Bamber et al. 2020; Marshall et al. 2022a; Valdivia et al. 2022), and thus rocks provide a valuable look into the subsurface evolution of a magma. Crystal size distributions (CSDs) of microlites can be used to approximate crystallization times when a crystal growth rate is assumed (Marsh 1988; Cashman and Marsh 1988; Murch and Cole 2019; Bamber et al. 2020; Valdivia et al. 2022). Although CSDs can be easily measured and their slopes used for interpretation of changing ascent rates, the calculations may be skewed if post-fragmentation crystallization occurs. In addition, CSDs assume constant crystal nucleation and growth rates. More sophisticated investigations involve reproducing measured microlite textures by performing magma decompression experiments (Fig. 1), during which crystal textures evolve in response to an applied perturbation in P and/or T (Geschwind and Rutherford 1995; Hammer and Rutherford 2002; Hammer 2004; Szramek et al. 2006; Castro and Dingwell 2009; Andrews and Gardner 2010; Brugger and Hammer 2010; Shea and Hammer 2013; Waters et al. 2015; Befus and Andrews 2018). Decompression experiments are effective at approximating ascent rates by producing sufficient effective undercooling (ΔTeff) or supersaturation (\(\Delta \phi\)) necessary to drive crystallization, but for the most part only produce time-averaged ascent rates that do not reflect possible changes in ascent rate as a magma nears the surface. Furthermore, conducting decompression experiments can be time-consuming. Mineral breakdown reaction rims (Rutherford and Hill 1993; Browne and Gardner 2006) and compositional zoning (Waters et al. 2015) form in response to the pressure change imposed on a magma during ascent but are not always present. Melt embayments allow for diffusive modeling of elemental loss and thus ascent rates (Liu et al. 2007; Myers et al. 2016, 2018; Barth et al. 2019). Melt inclusions and embayments are, however, not perfect storage containers. Mineral fractures may result in leakage, and diffusion modeling cannot be conducted without knowledge of initial conditions and diffusive boundary conditions. Finally, geophysical observations can be used to monitor seismicity with depth in real time and allows researchers to track magma movement during an eruption (e.g., Moran et al. 2008; Thelen et al. 2008). Most volcanoes, however, are not equipped with extensive geophysical arrays that allow precision monitoring, and geophysical observations may not distinguish between different types of subsurface volcanic activity.
Existing numerical models for magma ascent rate
To circumvent some of the disadvantages of existing experimental and analytical methods for investigating ascent rates, numerical models exist that utilize observations easily collected from rocks. Toramaru (2006) developed a magma ascent rate meter as a function of bubble number density (BND) assuming a single homogeneous nucleation event and constant decompression. Although BNDs indeed reflect changes in volatile supersaturation and decompression, extensive coalescence, multiple nucleation events, highly tortuous bubble networks (e.g., Valdivia et al. 2022), or collapsed foam textures are not representative of original BNDs and will skew ascent rate calculations. The model of Toramaru et al. (2008) uses microlite number densities (MND) to estimate ascent rates and only requires water and groundmass Si content at the point of microlite nucleation as additional inputs. But as Murch and Cole (2019) point out, the model results of Toramaru et al. (2008) are highly influenced by the Si content input, and an error of only 5% in Si content can result in errors in ascent rate calculations as large as 500%. In addition, both models only produce time-averaged ascent rates rather than instantaneous rates over time, and therefore do not adequately model variable ascent rates that occur in nature (e.g., Mastin and Ghiorso 2000; Moran et al. 2008; Thelen et al. 2008). More recent numerical models consider the fluid dynamics of three phase basaltic magmas and disequilibrium crystallization and vesiculation during their ascent (La Spina et al. 2016; Arzilli et al. 2019; La Spina et al. 2021; Bamber et al. 2020).
SNGPlag
Supersaturation Nucleation and Growth of Plagioclase (SNGPlag) is an iterative forward model that calculates time-dependent plagioclase crystallization, the integral of nucleation and growth, within a constant magma composition for a specified pressure–temperature-time (P–T–t) path (Andrews and Befus 2020). Comprehensive descriptions of the model can be found in Befus and Andrews (2018) and Andrews and Befus (2020) and are only summarized here. Specifically, the model tracks the numbers and sizes of plagioclase crystals within a 1 m3 volume of magma. SNGPlag considers nucleation and growth as functions of plagioclase supersaturation (Δϕplag), defined as the difference between the equilibrium volume fraction of plagioclase as determined using MELTS (Gualda et al. 2012; Ghiorso and Gualda 2015) and the modeled volume fraction. SNGPlag uses Δϕplag rather than ΔTeff as the former can be readily determined through time whereas ΔTeff is only known at the onset of decompression. Melt decompression and/or cooling act to increase Δϕplag. Nucleation and growth of plagioclase crystals in response to Δϕplag drive the magma towards equilibrium, with the instantaneous nucleation and growth rates of plagioclase being functions of Δϕplag (Befus and Andrews 2018). SNGPlag allows nucleation and growth to be path-dependent and does not assume constant nucleation and growth rates (Andrews and Befus 2020). SNGPlag can model multiple styles of decompression (e.g., linear, accelerating, paused) to investigate the style of decompression on plagioclase crystallization. Multiple decompression styles may be applied to the same simulation, such as a linear pathway that has a pause during decompression. While SNGPlag cannot provide a unique solution for natural samples, it can describe a limited range of likely decompression rates and paths (Andrews and Befus 2020).
Previous versions of SNGPlag are calibrated for felsic compositions. Here, we extend the calibration of SNGPlag to include basaltic andesite compositions using the experimental results of Shea and Hammer (2013). We then apply an inverse implementation of SNGPlag to the 12.6 ka basaltic andesite Curacautín eruption of Llaima volcano, Chile (Marshall et al. 2022a; Valdivia et al. 2022) to estimate decompression rates necessary to generate ignimbrite-forming mafic eruptions. The results and application of our modeling can be applied to similar mafic volcanic centers to investigate the conditions that result in unusually explosive mafic eruptions.
The Curacautín eruption
The Curacautín eruption occurred at ca. 12.6 ka and resulted in the deposition of the extensive Curacautín ignimbrite (Ci, Marshall et al. 2022a). The Ci is a 4.0–4.5 km3 (dense-rock equivalent) unconsolidated basaltic andesite ignimbrite exposed radially around Llaima that flowed up to 30 km from Llaima (Marshall et al. 2022a; Naranjo and Moreno 2005), though others have mapped the Ci up to 100 km from source (Naranjo and Moreno 1991). The Ci consists of four coarse ash to fine lapilli tuff flow units (Fig. 2, Marshall et al. 2022a). Recent work by Marshall et al. (2022a) and Valdivia et al. (2022) suggests the Ci is the result of fragmentation of a rapidly ascending, non-degassed magma at a low fragmentation threshold. There is no evidence to suggest the explosivity of the Ci eruption was driven by magma-water interaction, though some evidence exists for localized phreatic activity (Marshall et al. 2022a, b).
Methods
Calibration of SNGPlag for basaltic andesite compositions
Previously published versions of SNGPlag (Befus and Andrews 2018; Andrews and Befus 2020) use nucleation and growth rates determined experimentally for the 1991 Pinatubo dacite magma with a rhyolitic melt composition. Application of SNGPlag to the Curacautín eruption necessitates acquiring plagioclase nucleation (Nplag) and growth rates (Gplag) for a basaltic andesite magma. We used the results of single step decompression experiments conducted by Shea and Hammer (2013) on the Mascota basaltic andesite. Their study includes 11 experimental runs (Table 1) with P, T, H2O, and compositional conditions reasonable for the Curacautín eruption (Lohmar 2008; Schindlbeck et al. 2014). Importantly, they report the plagioclase crystallinities, maximum lengths, and volumetric number densities for all runs, thereby enabling calculation of instantaneous nucleation and growth rates.
Determination of instantaneous nucleation and growth rates of plagioclase
We adapted the existing SNGPlag code written in MATLAB to find Nplag and Gplag that best fit the experimental observations of Shea and Hammer (2013). Briefly, we assume that the Nplag and Gplag have functional forms that can be described as log-normal functions of Δϕplag; variation of four different parameters can change the functional form to virtually any arbitrary path (Befus and Andrews 2018). We find the best fit for Nplag and Gplag by running SNGPlag for the known decompression experiments of Shea and Hammer (2013) across an 8-dimensional space (four dimensions for both Nplag and Gplag). This results in 100,000 possible combinations of Nplag and Gplag. Nplag and Gplag were modeled using the R2 high performance computing cluster at Boise State University. The best fit Nplag and Gplag are those that best recover the observed results of Shea and Hammer (2013). Run parameters were taken from Shea and Hammer (2013) with each single-step run discretized into 2,500 P–T–t steps. Nplag and Gplag are calculated at each step as functions of Δϕplag with the form:
where x = b·exp1Δϕplag, Δϕplag = plagioclase supersaturation, and μ, σ, b, and k are fit parameters that describe the specific shape of curves that represent the mean, standard deviation, scaling with respect to Δϕplag, and its maximum value (Befus and Andrews 2018). The input ranges and best fit calibration parameters for Nplag and Gplag are provided in Table 2. Values for μ, σ, and k were randomly sampled from a selected range (Table 2). For our calibration, b was set to 1. SNGPlag accounts for volume interferences ϕint between crystals for a randomly distributed population of crystals by,
where ϕapp is the apparent crystallinity, which is the sum of all crystal sizes and numbers calculated at each step divided by the system volume (1 m3). From this, we obtain the equation,
where plagioclase crystallinity ϕplag is reported with overlapping crystals removed (Andrews and Befus 2020). Finally, uncertainty in NV and σNv is determined by,
where Sn is the characteristic crystal size in a 1 mm2 area (Andrews and Befus 2020). Optimum values for Gplag and Nplag were determined using least squares optimization of the calibration data (Table 2).
During each step of SNGPlag, existing plagioclase grow, and new plagioclase nucleate based upon Gplag, Nplag, and Δϕplag. SNGPlag produces matrices of plagioclase crystal number and size that can be binned and converted into cumulative CSDs. Because SNGPlag calculates volumetric number densities and size distributions by nucleating and growing plagioclase in a 1-m3 model volume, we avoid the uncertainties that result from stereological conversions of 2D data. Use of a 1-m3 model volume to effectively eliminate rounding errors and discrepancies that can occur in smaller volumes with fewer crystals.
Modeling conditions
Modeling the Ci CSDs using the best fit Nplag and Gplag rates requires realistic or plausible values for Pi, Pf, T, dP/dt, and volume fraction phenocrysts. Schindlbeck et al. (2014) calculated Ci crystallization temperatures of ~ 1,110 ± 45 °C using the olivine- and clinopyroxene-liquid thermobarometer of Putirka (2008), water content of 1.4 ± 0.32% using the plagioclase hygrometer of Lange et al. (2009), and storage pressures between 400 and 600 MPa corresponding to depths of up to 18 km, though work by Lohmar (2008) suggests that crystallization occurred at ≤ 7 km. Marshall et al. (2022a) measured phenocryst content of Curacautín pyroclasts from < 1 to ~ 3.5%, and Lohmar (2008) measured up to 7% phenocrysts. Valdivia et al. (2022) estimated dP/dt for the Ci from 0.36 to 2.6 MPa s−1 using the bubble number density decompression rate meter of Toramaru (2006). Finally, experiments by Arzilli et al. (2019) found the conditions required for basaltic magmas to erupt as high explosivity events are temperatures < 1100 °C, syn-eruptive crystal content ≥ 30%, and melt viscosities of 105 Pa s.
Our modeling consisted of 100,000 simulations with initial and final conditions selected in a random Monte Carlo scheme from a range of defined inputs (Table 3). We conducted experiments with Pi between 110 and 150 MPa due to the limited range of experimental pressure data used for SNGPlag calibration. We did not assume a 400–600 MPa Pi because those pressures calculated by Schindlbeck et al. (2014) are total pressure whereas those of SNGPlag are the partial pressure of water (e.g., PH2O). Starting phenocryst content was 5 vol.%. Pf was set to 10–40 MPa. All simulations were run at T = 950–1050 °C; Ti and Tf were allowed to vary independently. We used average dP/dt of 1–1000 MPa h−1 (0.0003–0.3 MPa s−1). 40% of runs were linear decompressions, 30% accelerating, and 30% were two-step decompressions, whereby there was a pause following initial linear decompression and subsequent post-pause decompression was either linear or accelerating. A subset of experiments was declared to “fragment” at a pressure Pfrag of 20–80 MPa during the simulations; these runs had dP/dt of 1–20 MPa h−1 prior to fragmentation and increased to 30–400 MPa h−1 following fragmentation. Runs that fragmented experienced cooling ΔTfrag of up to 60 °C, the upper bound suggested by Mastin and Ghiorso (2001) for adiabatic cooling of an erupting mixture of gas and ash.
Comparison of natural and modeled CSDs
Cumulative CSDs of natural samples describe the number of plagioclase crystals that are larger than each size bin. Using counting statistics, we can convert that size relationship into an uncertainty bound (σCSD) at each size, \(\sigma_{CSD} = \sqrt {{n_{bin} }}\), where nbin is the number of microlite counts per size bin. The upper and lower bounds then define an envelope for natural CSDs (Fig. 3). Therefore, with higher nbin, our uncertainty becomes smaller. Our modeled CSDs therefore have an effective uncertainty of zero as the billions of crystals compose each bin. This is not to say the modeling here is perfect, but rather that uncertainty is orders of magnitude greater in measurements of the natural samples.
Modeling limitations
The experiments of Shea and Hammer (2013) were mostly quenched at higher pressures, with only two experiments decompressed to Pf of 22 and 10 MPa and ΔT > 113 °C (Table 1). Those two experiments produced the highest plagioclase crystallinities of 34.8% and 46.1%, respectively. No experiments have been conducted at conditions where the melt viscosity should be highest. As such, our Nplag and Gplag for very high Δϕplag are extrapolated, although we note that any decompression path other than single-step will have some crystallization prior to reaching lower P, and therefore have a lower Δϕplag than a single step run initially has at the same pressure. SNGPlag does not consider any unique conduit geometries or eruption style (e.g., dike geometry, ring faulting during eruption) that may impact late decompression or ascent dynamics. Shearing along conduit margins is not considered in SNGPlag but has been shown to impact crystallization (Vetere et al. 2021). Nucleation delay inversely correlates with ΔT and may suppress crystallization up to ~ 100 + h at low ΔT (Rusiecka et al. 2020), which could impact CSDs. SNGPlag does not explicitly consider nucleation delay in the crystallization calculations, but low growth rates acting upon small numbers will result in very low numbers of detectable crystals at early times or low ΔT. Finally, the only volatile species considered in our modeling is H2O, although the presence of CO2 or another volatile species should only affect the crystallization of plagioclase insofar as it reduces the partial pressure of H2O.
Results
Instantaneous nucleation and growth rates of plagioclase
Instantaneous Nplag and Gplag curves have similar geometries (Fig. 4). The maximum Nplag of 6.1 × 105 cm−3 h−1 is reached at Δϕplag = 44 vol.%. The maximum Gplag of 27.4 µm h−1 is reached at Δϕplag = 29 vol.%. There is very little Nplag activity at Δϕplag < 10%, but the Gplag of these early crystals is quite high. Nplag and Gplag beyond maximum Δϕplag are extrapolated and may not be representative of nature.
Model results
The large parameter space over which we modeled the Curacautín eruption includes many runs that are physically unrealistic; we applied filters to remove those results. Our filters identified runs that begin and/or end > 10 °C above the plagioclase liquidus and removes them. This reduced the number of model runs from 100,000 to 13,283 (Table 4). Because our decompression rates vary in an exponential fashion, it is not appropriate to compare them in linear space, so we report our average decompression rates as log2 values. For example, three decompression rates of 1, 9, and 80 MPa h−1 would yield a linear average rate of 30 MPa h−1, but a more representative average rate is obtained in log space and yields 9 MPa h−1.
Average Unit 1 dP/dt are 53–93 MPa h−1 for L1, 46–89 MPa h−1 for L4, and 87–95 MPa h−1 for L6 (Figs. 5, 6). Average Unit 2 dP/dt are 62–93 MPa h−1 (L8). Average Unit 3 dP/dt are the slowest at 6–55 MPa h−1 (L10). Conversely, average Unit 4 dP/dt are the fastest at 104–141 MPa h−1 (L18, Table 4). Unit 1 average durations of decompression tavg are between 1.40 and 4.08 h for L1, 2.40–4.69 h for L4, and 1.79–1.96 h for L6. Unit 2 tavg are between 1.69 and 2.02 h (L8). Unit 3 tavg are between 3.56 and 16.13 h (L10). Unit 4 tavg are between 0.87 and 0.96 h (L18, Figs. 5, 6, Table 4).
Discussion
Plagioclase nucleation and growth rates
Nplag and Gplag curves (Fig. 4) for the basaltic andesite Curacautín magma have similar shapes, but very different magnitudes in comparison to those determined for the 1991 Pinatubo dacite (Befus and Andrews 2018). The Curacautín magma reaches a maximum Nplag = 6.1 × 105 cm−3 h−1 at Δϕplag = 44 vol.% which is an order of magnitude lower than the Pinatubo dacite at the same Δϕplag (Fig. 4A). Conversely, the maximum Curacautín Gplag of 27.4 µm h−1 is reached at Δϕplag = 29 vol.%, whereas the 1991 Pinatubo Gplag for the same Δϕplag is 6.0 µm h−1 and does not reach 27.4 µm h−1 until Δϕplag ≲ 52 vol.% (Fig. 4B). Indeed, Gplag is more than an order of magnitude higher in the mafic composition for Δϕplag ≲ 5%. Our modeled Nplag and Gplag suggest that although plagioclase nucleates more than an order of magnitude slower in basaltic andesites than in dacites at similar Δϕplag the growth rate Gplag in the mafic composition is generally an order of magnitude faster. Significantly, the difference in volumetric growth rate is ~ 1000 times greater in the basaltic andesite (the linear growth rate Gplag raised to the third power). That is, a smaller number of crystals are able to more rapidly grow and thus reduce Δϕplag in the mafic magma as compared to more silicic magmas. This explains the predominance of acicular plagioclase microlites commonly observed in the pyroclasts of mafic explosive eruptions (Constantini et al. 2010; Arzilli et al. 2019; Bamber et al. 2020; Rowe et al. 2021; Marshall et al. 2022a).
Decompression rates
Natural plagioclase CSDs for the Ci are concave upward at the finest size bins (Valdivia et al. 2022). Valdivia et al. (2022) divided Ci CSDs into two segments based on linear regression fitting. Using experimentally derived growth rates of 10–4 mm s−1 (Arzilli et al. 2019), 2 × 10–5 mm s−1 (Arzilli et al. 2015), 10–6 mm s−1 (Shea and Hammer 2013), and 10–7 mm s−1 (Arzilli et al. 2015), they calculated timescales of crystallization from 2 s to 1.2 h for the smallest size fraction of plagioclase microlites in CSDs, and 8 s to 5.0 h for the largest size fraction. Here, we use cumulative natural CSDs for fitting to our modeled CSDs to remove downturns at the smallest size fractions observed by Valdivia et al. (2022).
Using the 1% population of isolated Ci vesicles, Valdivia et al. (2022) calculated average dP/dt for the Ci magma of 0.84–1.95 MPa s−1 for Unit 1, 0.36 MPa s−1 for Unit 2, 2.60 MPa s−1 for Unit 3, and 0.55 MPa s−1 for Unit 4 using the BND meter of Toramaru (2006), with a minimum average dP/dt for the Curacautín eruption of 1.4 MPa s−1. Our average modeled dP/dt rates (0.18 × 10–2–3.9 × 10–2 MPa s−1) are approximately two orders of magnitude slower than the rates calculated by Valdivia et al. (2022, Fig. 7, Table 4). The bubble textures investigated by Valdivia et al. (2022) represent two distinct phases of Curacautín magma evolution. The highly tortuous vesicle network of > 99% pore volume is indicative of relatively slow ascent (e.g., Marshall et al. 2022b), whereas the small, isolated vesicles likely formed during an episode of homogeneous nucleation very late in ascent or syn-eruptively at low pressures in the shallow subsurface (Mangan and Sisson 2000) where dP/dt are greatest. Conversely, our average dP/dt modeled with SNGPlag represent pressures from 10 to 150 MPa where rates of decompression begin slow and increase over time (Supplemental Material). Together, our work and that of Valdivia et al. (2022), suggests that decompression (and therefore ascent) rates increase by orders of magnitude at the shallowest conduit depths (Fig. 7) or during fragmentation. Interestingly, the decompression rates modeled here are in agreement with those modeled by La Spina et al. (2021) for highly explosive eruptions, and the decompression rates calculated by Valdivia et al. (2022) are consistent with rates associated with high fountaining (La Spina et al. 2021) and may further support the boiling over eruption model proposed in Marshall et al. (2022a).
The low water content of the Ci melt (1.1 ± 0.32%; Schindlbeck et al. 2014) suggests storage at shallower depths, or water undersaturation. We conducted a second, smaller set of experiments (n = 50,000) at Pi = 15–30 MPa and Pf = 3–10 MPa to investigate crystallization over a shorter decompression window from shallower depths (Table 4). Average dP/dt for Unit 1 are 24–59 MPa h−1 (L1), 34–46 MPa h−1 (L4), and 46–61 MPa h−1 (L6). Unit 2 dP/dt are 66–75 MPa h−1. Unit 3 average dP/dt are 8–61 MPa h−1. Finally, average Unit 4 dP/dt are 74–80 MPa h−1. These rates tend to be slower than those modeled for deeper chamber conditions but are generally within the same order of magnitude (Table 4). Because Schindlbeck et al. (2014) estimated a chamber depth of ~ 18 km for the Curacautín magma, the dP/dt calculated with Pi up to 150 MPa are likely a more reasonable approximation of Curacautín decompression (Fig. 7).
The dP/dt modeled here for the Curacautín magma are similar to dP/dt calculated or estimated for other mafic eruptions using decompression experiments and diffusion modeling, but are orders of magnitude lower than mafic dP/dt calculated from bubble textures (Fig. 8). Homogeneous bubble nucleation events create densely packed networks of bubbles at very shallow depths where rates of dP/dt are highest (Mangan and Sisson 2000), and thus dP/dt determined from bubble textures may only reflect very shallow ascent conditions and not be representative of conditions from deeper in the conduit. Conversely, our modeling here reflects ascent rates integrated over the entire conduit and not just the shallowest depths and likely records more of the decompression history, albeit perhaps not the final, shallowest portions.
Magma ascent rates
Decompression rates do not have the same relationship to ascent rate at all volcanoes. This results from differences in lithostatic or magmastatic pressure gradients at different volcanoes, which is impacted by factors such as crustal thickness, country rock compositions and densities, conduit geometry, and elevation. In addition, particular decompression speedometers may be sensitive to the partial pressure of a particular volatile species, not total pressure (Ptotal); SNGPlag is sensitive to PH2O, which is less than Ptotal when the system is water undersaturated or saturated with a mixed volatile phase. Here, we consider two simplified scenarios to derive first order estimates of magma ascent rate from our modeled decompression rates, and then compare those rates with a calculated lithostatic pressure gradient (dP/dz) for the crust beneath Llaima.
Our first estimate assumes that PH2O = Ptotal and that there is no other volatile species in our system. This of course is an oversimplification as there would be some amount of PCO2 present as well as others volatile species in minor concentrations. If we also assume that a dP/dz = 90 MPa per every 4 km is reasonable for a mix of mafic lavas and granitic plutons (Naranjo and Moreno 2005), then we obtain average Unit 1 ascent rates for the Ci of 0.66 ± 0.67–1.13 ± 0.78 m s−1 for L1, 0.66 ± 0.58–1.10 ± 0.86 m s−1 for L4, and 1.07 ± 0.80–1.17 ± 0.80 m s−1 for L6. Our Unit 2 (L8) average ascent rates are 0.77 ± 0.37–1.14 ± 0.81 m s−1. Unit 3 (L10) average ascent rates are the slowest at 0.08 ± 0.01–0.68 ± 0.58 m s−1. Conversely, Unit 4 (L18) average ascent rates are the fastest at 1.28 ± 0.09–1.74 ± 0.84 m s−1. Due to our assumptions and simplifications, these rates should be considered a minimum (Fig. 9).
Our second calculation combines our modeling parameter space with a chamber depth estimate of 18 km (Schindlbeck et al. 2014). If we assume the Ci magma is water undersaturated, then we can expect the magma resided at a greater depth prior to decompression. Using a maximum Pi during SNGPlag modeling of 120 MPa, we obtain an effective dP/dz in PH2O of 60 MPa per every 9 km. Using these new assumptions, our ascent rates for the Ci magma increase. Average ascent rates for Unit 1 become 2.23 ± 2.27–3.89 ± 2.04 m s−1 (L1), 1.90 ± 1.97–3.72 ± 2.90 m s−1 (L4), and 3.61 ± 2.68–3.96 ± 2.71 m s−1 (L6). Unit 2 average ascent rates are 2.58 ± 1.24–3.86 ± 2.73 m s−1. Unit 3 average ascent rates are 0.27 ± 0.02–2.30 ± 1.97 m s−1. Finally, Unit 4 average ascent rates are 4.31 ± 0.30–5.86 ± 2.85 m s−1. Because this second set of ascent rates assumes the same decompression rates as our first scenario but over a greater depth, they should be considered maximum estimates (Fig. 9).
Finally, Schindlbeck et al. (2014) report a dP/dz at Llaima of ~ 20 MPa km−1 down to the brittle-ductile transition located at ~ 14–15 km. Using their dP/dz, we calculated ascent rates for Unit 1 of 0.63 ± 0.66–1.32 ± 0.90 m s−1, 0.86 ± 0.41–1.29 ± 0.91 m s−1 for Unit 2, 0.09 ± 0.01–0.77 ± 0.66 m s−1 for Unit 3, and 1.44 ± 0.10–1.95 ± 0.95 m s−1 for Unit 4 (Fig. 7). These rates are closer to our lower end approximation. Note that Schindlbeck et al. (2014) estimated a storage depth of 18 km for the Curacautín magma, and thus their dP/dz may be a minimum.
Difficulty of fitting smallest CSD microlites
SNGPlag struggles to fit the smallest crystal sizes in the observed plagioclase CSDs. This may be a result of the tighter 2σ bounds at smaller sizes because the number of crystals exceeding those sizes is large, therefore decreasing the uncertainty allowed in the model fits (Fig. 3). Alternatively, poor fits at small microlite sizes may result from the range of P values reported in the experiments of Shea and Hammer (2013) that we used for calibration of SNGPlag Nplag and Gplag rates (Table 1). The lowest Pf used for calibration are 10 and 22 MPa, but these were only two out of the eleven experiments, whereas the other nine were conducted to 42 ≤ Pf ≤ 100 MPa (Shea and Hammer 2013). Because Nplag and Gplag are not linear with respect to Δϕplag (Fig. 4), they should be higher in experiments conducted at very low P, corresponding to high Δϕplag, although this extrapolation does not account for much high viscosities potentially retarding the nucleation and growth rates. Our modeled Pf and calibration Pf stop at 10 MPa, but natural plagioclase textures likely continue to record shallower conduit conditions. In this scenario, we would expect crystallization of a higher number of smaller plagioclase microlites, which may have produced the densely crystalline Ci pyroclasts (Marshall et al. 2022a, b; Valdivia et al. 2022).
Interpreting the Curacautín eruption
Rapid magma ascent rates are often invoked to explain mafic Plinian and ignimbrite-forming eruptions (Sable et al. 2006, 2009; Vinkler et al. 2012; Arzilli et al. 2019; Bamber et al. 2020; Marshall et al. 2022a; Valdivia et al. 2022). Supersaturation resulting from rapid ascent drives plagioclase nucleation and crystallization. Our modeling here reveals that Nplag in the basaltic andesite Ci is considerably lower than Nplag in dacites, but maximum Gplag of 7.6 × 10–7 cm s−1 is volumetrically up to 1000× greater than dacite Gplag at the same Δϕplag. Our Gplag is one order of magnitude lower than the ~ 3–5 × 10–6 cm s−1 measured by Vetere et al. (2021) during basaltic andesite viscosity experiments. Those authors argue for the importance of shear rate being considered in models of magmatic and volcanic processes, which is not something considered in this version of SNGPlag (Table 2). Indeed, shear rate and its impact on viscosity would impact our Gplag and may help explain conduit processes proposed by Marshall et al. (2022b).
Our modeling here suggests that rapid dP/dt produced the plagioclase microlite textures observed in Ci pyroclasts (Table 3; Marshall et al. 2022a, b; Valdivia et al. 2022). Such extensive crystallization would have increased the magma viscosity to the point that vesicles would begin to distort and wrap around the nucleating and rapidly growing acicular plagioclase. This explains the highly tortuous 99% interconnectivity vesicle population textures identified by Valdivia et al. (2022). Highly tortuous vesicle networks inhibit outgassing, which in turn enhances the overpressure necessary for brittle fragmentation.
The three sets of magma ascent rates we estimated here using different dP/dz reasonable for the South Central Volcanic Zone of Chile offer a first-order look into the ascent rates that drove the Curacautín eruption (Fig. 9). Minimum ascent rates of 0.1–1.7 m s−1 using a dP/dz of 22.5 MPa km−1 are similar to the ascent rates of 0.1–2.0 m s−1 we estimated using the dP/dz of Schindlbeck et al. (2014). Conversely, a dP/dz of 20 MPa per every 3 km yields ascent rates up to 3× faster (Fig. 9).
Unit 1 ascent rates are variable between 0.6 and 1.3 m s−1 and increase slightly to 0.8–1.3 m s−1 in Unit 2. Unit 3 ascent rates drop by an order of magnitude to 0.1–0.8 m s−1 and suggests modulation of the magma flux during the Curacautín eruption. Unit 4 has the fastest magma ascent rate of 1.3–2.0 m s−1 and represents the final pulse of the Ci eruption. Valdivia et al. (2022) calculated vesicle overpressures necessary to fragment the Ci magma between 3.8 and 5.1 MPa. Such a low fragmentation threshold combined with the rapid dP/dt calculated here implies a limited decompression history prior to climatic fragmentation. Because the Ci was produced during a single eruptive event (Marshall et al. 2022a), changes in magma ascent rate did not likely result from changes in shallow magma storage or magma recharge, but rather changes in vesiculation or conduit/vent geometry during eruption. Discriminating between those different parameters is beyond the scope of the current version of SNGPlag.
The rapid Gplag calculated in our modeling would generate acicular plagioclase morphologies that produce highly tortuous vesicle networks that inhibit outgassing. Following fragmentation, decompression and ascent rates of the gas-pyroclast mixture are orders of magnitude greater than the original bulk magma and suggest there is little time between fragmentation and eruption. In the case of the Ci, the time period between fragmentation and eruption likely generated the highly crystalline groundmass of l < 10 μm plagioclase microlites that overprints sutures between fused domains of heterogeneous vesicle textures discussed in Marshall et al. (2022b). These results help elucidate the still poorly understand conduit processes that impact how mafic magmas can erupt as large, explosive events.
Conclusions
Plagioclase nucleation and growth rates, Nplag and Gplag, respectively, differ substantially between mafic and felsic magmas. Those differences can affect eruption style. Modeled maximum Nplag for the 12.6 ka basaltic andesite Curacautín eruption are orders of magnitude lower than those for the 1991 Pinatubo dacite (Fig. 4); Gplag, however, is up to 10× greater in mafic magmas than felsic magmas, resulting in volumetric growth rates ~ 1000× greater in mafic magmas than felsic ones. This result explains the predominately acicular nature of plagioclase microlites in the products of mafic explosive eruptions attributed to rapid ascent rates.
The dP/dt modeled here for the Ci eruption using SNGPlag are between 10–3 and 10–1 MPa s−1 and are similar to dP/dt measured experimentally for similar compositions and known eruption styles (e.g., Arzilli et al. 2019; La Spina et al. 2021; Bamber et al. 2020). We were able to fit the majority of CSD bins to the natural samples. Unlike decompression experiments which must follow some particular decompression pathway(s) (Fig. 1), our modeling applies instantaneous Nplag and Gplag to produce thousands of possible decompression pathways to derive the most likely decompression scenario, and thus reflect the total decompression path of the Ci magma. Our modeled dP/dt are ~ 2 orders of magnitude lower than those calculated by Valdivia et al. (2022) for the same eruption. This difference reflects time-integrated rates recording most of magma decompression and ascent presented here, whereas those of Valdivia et al. (2022) were calculated using the BND meter of Toramaru (2006) on a homogenous nucleation event in the shallow conduit. Importantly, these two sets of dP/dt reveal that decompression (and therefore magma ascent) of the Curacautín magma increased by orders of magnitude following the onset of fragmentation and record the explosive nature of the eruption. In addition, such a dramatic change in ascent rate would have similar impacts on Δϕplag (Fig. 4), resulting in the crystallization of the l < 10 μm population of unbroken plagioclase microlites identified by Marshall et al. (2022b) and may explain the rapid crystallization times Valdivia et al. (2022) calculated from plagioclase CSDs.
Future work is necessary to fully describe the effects of decompression on crystallization and eruption processes described here. Integrating a viscosity component into SNGPlag would allow us to investigate viscosity’s role on ascent dynamics, which has profound impacts on degassing and crystallization and may help explain the textures reported in Marshall et al. (2022b). Plagioclase is not the only crystal phase in many mafic eruptions, and future modeling should consider additional crystal phases such as pyroxenes and olivine in addition to plagioclase. Finally, future decompression experiments conducted to very low Pi (and therefore higher melt viscosity) would enhance the calibration parameter space of SNGPlag and allow for the investigation of crystallization at the shallowest depths of conduits where microlites are likely to crystallize most extensively.
Data availability
Data is available upon request from the authors.
References
Andrews BJ, Befus KS (2020) Supersaturation Nucleation and Growth of Plagioclase: a numerical model of decompression-induced crystallization. Contrib Miner Petrol 175:23. https://doi.org/10.1007/s00410-020-1660-9
Andrews BJ, Gardner JE (2010) Effects of caldera collapse on conduit dimensions and magma decompression rate: an example from the 1800 14C yr BP eruption of Ksudach Volcano, Kamchatka, Russia. J Volcanol Geotherm Res 198:205–216. https://doi.org/10.1016/j.jvolgeores.2010.08.021
Arzilli F, Agostini C, Landi P, Fortunati A, Mancini L, Carroll M (2015) Plagioclase nucleation and growth kinetics in a hydrous basaltic melt by decompression experiments. Contrib Miner Petrol 170:55. https://doi.org/10.1007/s00410-015-1205-9
Arzilli F, La Spina G, Burton MR, Polacci M, Le Gall N, Hartley ME, Di Genova D, Cai B, Vo NT, Bamber EC, Nonni S, Atwood R, Llewellin EW, Brooker RA, Mader HM, Lee PD (2019) Magma fragmentation in highly explosive basaltic eruptions induced by rapid crystallization. Nat Geosci 12:1023–1028. https://doi.org/10.1038/s41561-019-0468-6
Bamber EC, Arzilli F, Polacci M, Hartley ME, Fellowes J, Di Genova D, Chavarría D, Saballos JA, Burton MR (2020) Pre- and syn-eruptive conditions of a basaltic Plinian eruption at Masaya Volcano, Nicaragua: the Masaya Triple Layer (2.1 ka). J Volcanol Geotherm Res 392:106761. https://doi.org/10.1016/j.jvolgeores.2019.106761
Barth A, Newcombe M, Plank T, Gonnermann H, Hajimirza S, Soto GJ, Saballos A, Hauri E (2019) Magma decompression rate correlates with explosivity at basaltic volcanoes—constraints from water diffusion in olivine. J Volcanol Geotherm Res 387:106664. https://doi.org/10.1016/j.jvolgeores.2019.106664
Befus KS, Andrews BJ (2018) Crystal nucleation and growth produced by continuous decompression of Pinatubo magma. Contrib Miner Petrol 173:92. https://doi.org/10.1007/s00410-018-1519-5
Blundy J, Cashman KV (2008) Petrologic reconstruction of magmatic system variables and processes. Rev Miner Geochem 69(1):179–239. https://doi.org/10.2138/rmg.2008.69.6 (In: Putirka KD, Tepley III FJ (eds) Minerals, inclusions and volcanic processes)
Browne B, Gardner JE (2006) The influence of magma ascent path on the texture, mineralogy, and formation of hornblende reaction rims. Earth Planet Sci Lett 246:161–176. https://doi.org/10.1016/j.epsl.2006.05.006
Brugger CR, Hammer JE (2010) Crystal size distribution analysis of plagioclase in experimentally decompressed hydrous rhyodacite magma. Earth Planet Sci Lett 300(3):246–254. https://doi.org/10.1016/j.epsl.2010.09.046
Burgisser A, Gardner JE (2005) Experimental constraints on degassing and permeability in volcanic conduit flow. Bull Volcanol 67:42–56. https://doi.org/10.1007/s00445-004-0359-5
Cashman KV, Marsh BD (1988) Crystal size distribution (CSD) in rocks and the kinetics and dynamics of crystallization II. Makaopuhi Lava Lake. Contrib Miner Petrol 99:292–305. https://doi.org/10.1007/BF00375363
Castro JM, Dingwell DB (2009) Rapid ascent of rhyolitic magma at Chaitén volcano, Chile. Nature 461:780–783. https://doi.org/10.1038/nature08458
Constantini L, Houghton BF, Bonadonna C (2010) Constraints on eruption dynamics of basaltic explosive activity derived from chemical and microtextural study: the example of the Fontana Lapilli Plinian eruption, Nicaragua. J Volcanol Geotherm Res 189:207–224. https://doi.org/10.1016/j.jvolgeores.2009.11.008
Eichelberger JC, Carrigan CR, Westrich HR, Price RH (1986) Non-explosive silicic volcanism. Nature 323:598–602. https://doi.org/10.1038/323598a0
Geschwind C-H, Rutherford MJ (1995) Crystallization of microlites during magma ascent: the fluid mechanics of 1980–1986 eruptions at Mount St. Helens. Bull Volcanol 57:356–370. https://doi.org/10.1007/BF00301293
Ghiorso MS, Gualda GAR (2015) An H2O-CO2 mixed fluid saturated model compatible with rhyolite-MELTS. Contrib Miner Petrol 169:53. https://doi.org/10.1007/s00410-015-1141-8
Gualda GAR, Ghiorso MS, Lemons RV, Carley TL (2012) Rhyolite-MELTS: A modified calibration of MELTS optimized for silica-rich, fluid-bearing magmatic systems. J Petrol 53:875–890. https://doi.org/10.1093/petrology/egr080
Hammer JE (2004) Crystal nucleation in hydrous rhyolite: experimental data applied to classical theory. Am Miner 89(11–12):1673–1679. https://doi.org/10.2138/am-2004-11-1212
Hammer JE, Rutherford MJ (2002) An experimental study of the kinetics of decompression-induced crystallization in silicic melt. J Geophys Res. https://doi.org/10.1029/2001JB000281
Jaupart C, Allegre C (1991) Gas content, eruption rate and instabilities of eruption regime in silicic volcanoes. Earth Planet Sci Lett 102:413–429. https://doi.org/10.1016/0012-821X(91)90032-D
La Spina G, Arzilli F, Llewellin EW, Burton MR, Clark AB, Vitturi MDM, Polacci M, Hartley ME, Di Genova D, Mader HM (2021) Explosivity of basaltic lava fountains is controlled by magma rheology, ascent rate and outgassing. Earth Planet Sci Lett 553:116658. https://doi.org/10.1016/j.epsl.2020.116658
La Spina G, Burton M, de’ Michieli Vitturi M, Arzilli F, (2016) Role of syn-eruptive plagioclase disequilibrium crystallization in basaltic magma ascent dynamics. Nat Commun 7:13402. https://doi.org/10.1038/ncomms13402
Lange RA, Frey HM, Hector J (2009) A thermodynamic model for the plagioclase-liquid hygrometer/thermometer. Am Miner 94:494–506. https://doi.org/10.2138/am.2009.3011
Liu Y, Anderson AT, Wilson CJN (2007) Melt pockets in phenocrysts and decompression rates of silicic magmas before fragmentation. J Geophys Res 112:B06204. https://doi.org/10.1029/2006JB004500
Lohmar S (2008) Petrologia de las ignimbritas Lican y Pucon (volcan Villarrica) y Curacautin (volcan Llaima) en los Andes del sur de Chile. Dissertation, University of Chile
Mangan M, Sisson T (2000) Delayed, disequilibrium degassing in rhyolitic magma: decompression experiments and implications for explosive volcanism. Earth Planet Sci Lett 183:441–455. https://doi.org/10.1016/S0012-821X(00)00299-5
Marsh BD (1988) Crystal size distribution (CSD) in rocks and the kinetics and dynamics of crystallization: I. Theory. Contrib Miner Petrol 99:277–291. https://doi.org/10.1007/BF00375362
Marshall AA, Brand BD, Martínez V, Bowers J, Walker M, Wanless VD, Andrews BJ, Manga M, Valdivia P, Giordano G (2022a) The mafic Curacautín ignimbrite of Llaima volcano, Chile. J Volcanol Geotherm Res 421:107418. https://doi.org/10.1016/j.jvolgeores.2021.107418
Marshall AA, Manga M, Brand BD, Andrews BJ (2022b) Autobrecciation and fusing of mafic magma preceding explosive eruptions. Geology 50(10):1177–1181. https://doi.org/10.1130/G50180.1
Mastin LG, Ghiorso MS (2000) A numerical program for steady-state flow of magma-gas mixtures through vertical eruptive conduits. U.S. Geological Survey Open-File Report 2000–209, p 66. https://doi.org/10.3133/ofr00209
Mastin LG, Ghiorso MS (2001) Adiabatic temperature changes of magma-gas mixtures during ascent and eruption. Contrib Miner Petrol 141:307–321. https://doi.org/10.1007/s004100000210
Moran SC, Malone SD, Qamar AI, Thelen WA, Wright AK, Caplan-Auerbach J (2008) Seismicity associated with renewed dome building at Mount St. Helens, 2004–2005. In: Sherrod DR, Scott WE, Stauffer PH (eds) A Volcano Rekindled: the renewed eruption of Mount St. Helens, 2004–2005. U.S. Geological Survey Professional Paper, vol 1750, pp 27–54. https://doi.org/10.3133/pp17502
Murch AP, Cole PD (2019) Using microlites to gain insights into ascent conditions of differing styles of volcanism at Soufrière Hills Volcano. J Volcanol Geotherm Res 384:221–231. https://doi.org/10.1016/j.jvolgeores.2019.07.022
Myers ML, Wallace PJ, Wilson CJN, Morter BK, Swallow EJ (2016) Prolonged ascent and episodic venting of discrete magma batches at the onset of the Huckleberry Ridge supereruption, Yellowstone. Earth Planet Sci Lett 451:285–297. https://doi.org/10.1016/j.epsl.2016.07.023
Myers ML, Wallace PJ, Wilson CJN, Watkins JM, Liu Y (2018) Ascent rates of rhyolitic magma at the onset of caldera-forming eruptions. Am Miner 103(6):952–965. https://doi.org/10.2138/am-2018-6225
Naranjo JA, Moreno H (2005) Geología del volcán Llaima, Region de la Araucanía. Servicio Nacional de Geología y Minería, Carta Geologíca de Chile, Serie Geología Básica 88:1–33. Escala 1:50,000. https://www.scribd.com/document/385589999/Geologia-Volcan-Llaima-pdf
Naranjo JA, Moreno H (1991) Actividad explosiva postglacial en el volcan Llaima, Andes del Sur (38°45’S). Rev Geol Chile 18(1):69–80. https://doi.org/10.5027/andgeoV18n1-a06
Putirka KD (2008) Thermometers and barometers for volcanic systems. Rev Miner Geochem 69:61–120. https://doi.org/10.2138/rmg.2008.69.3
Rowe MC, Carey RJ, White JDL, Kilgour G, Hughes E, Ellis B, Rosseel J-B, Segovia A (2021) Tarawera 1886: an integrated review of volcanological and geochemical characteristics of complex basaltic eruption. N Z J Geol Geophys. https://doi.org/10.1080/00288306.2021.1914118
Rusiecka MK, Bilodeau M, Baker DR (2020) Quantification of nucleation delay in magmatic systems: experimental and theoretical approach. Contrib Miner Petrol 175:47. https://doi.org/10.1007/s00410-020-01682.4
Rutherford MJ, Hill PM (1993) Magma ascent rates from amphibole breakdown: an experimental study applied to the 1980–1986 Mount St. Helens eruptions. J Geophys Res 98(B11):19667–19684. https://doi.org/10.1029/93JB01613
Sable JE, Houghton BF, Del Carlo P, Coltelli M (2006) Changing conditions of magma ascent and fragmentation during the Etna 122 BC basaltic Plinian eruption: evidence from clast microtextures. J Volcanol Geotherm Res 158:333–354. https://doi.org/10.1016/j.jvolgeores.2006.07.006
Sable JE, Houghton BF, Wilson CJN, Carey RJ (2009) Eruption mechanisms during the climax of the Tarawera 1886 basaltic Plinian eruption inferred from microtextural characteristics of the deposits. In: Thordarson T, Self S, Larsen G, Rowland SK, Hoskuldsson A (eds) Studies in volcanology: the legacy of George Walker, vol 2. Special Publications of IAVCEI, pp 129–154. https://doi.org/10.1144/IAVCEI002.7
Schindlbeck JC, Freundt A, Kutterolf S (2014) Major changes in the post-glacial evolution of magmatic compositions and pre-eruptive conditions at Llaima volcano, Andean Southern Volcanic Zone, Chile. Bull Volcanol 76:830. https://doi.org/10.1007/s00445-014-0830-x
Shea T (2017) Bubble nucleation in magmas: a dominantly heterogeneous process? J Volcanol Geotherm Res 343:155–170. https://doi.org/10.1016/j.jvolgeores.2017.06.025
Shea T, Hammer JE (2013) Kinetics of cooling- and decompression-induced crystallization in hydrous mafic-intermediate magmas. J Volcanol Geotherm Res 260:127–145. https://doi.org/10.1016/j.jvolgeores.2013.04.018
Szramek L, Gardner JE, Larsen J (2006) Degassing and microlite crystallization of basaltic andesite magma erupting at Arenal Volcano, Costa Rica. J Volcanol Geotherm Res 157:182–201. https://doi.org/10.1016/j.jvolgeores.2006.03.039
Thelen WA, Crosson RS, Creagor KC (2008) Absolute and relative locations of earthquakes at Mount St. Helens, Washington, using continuous data: implications for magmatic processes. In: Sherrod DR, Scott WE, Stauffer PH (eds) A Volcano Rekindled: the renewed eruption of Mount St. Helens, 2004–2005. U.S. Geological Survey Professional Paper, vol 1750, pp 71–95. https://doi.org/10.3133/pp17504
Toramaru A (2006) BND (bubble number density) decompression rate meter for explosive volcanic eruptions. J Volcanol Geotherm Res 154:303–316. https://doi.org/10.1016/j.jvolgeores.2006.03.027
Toramaru A, Noguchi S, Oyoshihara S, Tsune A (2008) MND (microlite number density) water exsolution rate meter. J Volcanol Geotherm Res 175(1–2):156–167. https://doi.org/10.1016/j.jvolgeores.2008.03.035
Valdivia P, Marshall AA, Manga M, Brand BD, Huber C (2022) Mafic explosive volcanism at Llaima volcano: 3D X-ray microtomography reconstruction of pyroclasts to constrain shallow conduit processes. Bull Volcanol 84(2). https://doi.org/10.1007/s00445-021-01514-8
Vetere F, Petrelli M, Perugini D, Haselbach S, Morgavi D, Pisello A, Iezzi G, Holtz F (2021) Rheological evolution of eruptible Basaltic-Andesite Magmas under dynamic conditions: the importance of plagioclase growth rates. J Volcanol Geotherm Res 420:107411. https://doi.org/10.1016/j.jvolgeores.2021.107411
Vinkler AP, Cashman KV, Giordano G, Groppelli G (2012) volution of the mafic Villa Senni caldera-forming eruption at Colli Albani volcano, Italy, indicated by textural analysis of juvenile fragments. J Volcanol Geotherm Res 235–236:37–54. https://doi.org/10.1016/j.jvolgeores.2012.03.006
Vona A, Romano C, Dingwell DB, Giordano D (2011) The rheology of crystal-bearing basaltic magmas from Stromboli and Etna. Geochim Cosmochim Acta 75:3214–3236. https://doi.org/10.1016/j.gca.2011.03.031
Waters LE, Andrews BJ, Lange RA (2015) Rapid crystallization of plagioclase phenocrysts in silicic melts during fluid-saturated ascent: phase equilibrium and decompression experiments. J Petrol 56:981–1006. https://doi.org/10.1093/petrology/egv025
Acknowledgements
This work was supported by National Science Foundation EAR grant 1831143 and a Smithsonian Institution Pre-Doctoral Fellowship awarded to AM. The authors would like to thank Mike Ramshaw for his assistance with parallelizing SNGPlag. The content of this manuscript was improved by thoughtful comments from Fabio Arzilli and an anonymous reviewer. We’d also like to thank editor Mark Ghiorso for his handling of the manuscript during peer review.
Author information
Authors and Affiliations
Corresponding author
Ethics declarations
Conflict of interest
The authors declare no competing interests.
Additional information
Communicated by Mark S Ghiorso.
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Supplementary Information
Below is the link to the electronic supplementary material.
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
About this article
Cite this article
Marshall, A.A., Andrews, B.J. Modeling decompression paths in a basaltic andesite magma using the nucleation and growth of plagioclase microlites. Contrib Mineral Petrol 178, 62 (2023). https://doi.org/10.1007/s00410-023-02030-y
Received:
Accepted:
Published:
DOI: https://doi.org/10.1007/s00410-023-02030-y