Magma recharge patterns control eruption styles and magnitudes at Popocatépetl volcano (Mexico)

This work was funded by UK Natural Environment Research Council grant NE/M014584/1, Royal Society (London) Newton International Exchanges grant IE140605, and a Natural History Museum (London) Collection Enhancement Fund, all to C.M. Petrone, and a Janet Watson Scholarship (Imperial College London) to M.F. Mangler.Diffusion chronometry has produced petrological evidence that magma recharge in mafic to intermediate systems can trigger volcanic eruptions within weeks to months. However, less is known about longer-term recharge frequencies and durations priming magma reservoirs for eruptions. We use Fe-Mg diffusion modeling in orthopyroxene to show that the duration, frequency, and timing of pre-eruptive recharge at Popocatépetl volcano (Mexico) vary systematically with eruption style and magnitude. Effusive eruptions are preceded by 9–13 yr of increased recharge activity, compared to 15–100 yr for explosive eruptions. Explosive eruptions also record a higher number of individual recharge episodes priming the plumbing system. The largest explosive eruptions are further distinguished by an ∼1 yr recharge hiatus directly prior to eruption. Our results offer valuable context for the interpretation of ongoing activity at Popocatépetl, and seeking similar correlations at other arc volcanoes may advance eruption forecasting by including constraints on potential eruption size and style.Peer reviewe

Variation of plagioclase shape with size in intermediate magmas : a window into incipient plagioclase crystallisation

This work was funded by UK Natural Environment Research Council grant NE/T000430/1.Volcanic rocks commonly display complex textures acquired both in the magma reservoir and during ascent to the surface. While variations in mineral compositions, sizes and number densities are routinely analysed to reconstruct pre-eruptive magmatic histories, crystal shapes are often assumed to be constant, despite experimental evidence for the sensitivity of crystal habit to magmatic conditions. Here, we develop a new program (ShapeCalc) to calculate 3D shapes from 2D crystal intersection data and apply it to study variations of crystal shape with size for plagioclase microlites (l 5–10 µm) show progressively more tabular habits. Crystal growth modelling and experimental constraints indicate that this trend reflects shape evolution during plagioclase growth, with initial growth as prismatic rods and subsequent preferential overgrowth of the intermediate dimension to form tabular shapes. Because overgrowth of very small crystals can strongly affect the external morphology, plagioclase microlite shapes are dependent on the available growth volume per crystal, which decreases during decompression-driven crystallisation as crystal number density increases. Our proposed growth model suggests that the range of crystal shapes developed in a magma is controlled by the temporal evolution of undercooling and total crystal numbers, i.e., distinct cooling/decompression paths. For example, in cases of slow to moderate magma ascent rates and quasi-continuous nucleation, early-formed crystals grow larger and develop tabular shapes, whereas late-stage nucleation produces smaller, prismatic crystals. In contrast, rapid magma ascent may suppress nucleation entirely or, if stalled at shallow depth, may produce a single nucleation burst associated with tabular crystal shapes. Such variation in crystal shapes have diagnostic value and are also an important factor to consider when constructing CSDs and models involving magma rheology.Peer reviewe

Melt diffusion-moderated crystal growth and its effect on euhedral crystal shapes

Crystal growth is often described as either interface-controlled or diffusion-controlled. Here, we study crystal growth in an intermediate scenario where reaction rates at the crystal-melt interface are similar to the rates of diffusive transport of ions through the melt to the advancing crystal surface. To this end, we experimentally investigated euhedral plagioclase crystal shapes in dry mafic (basaltic) and hydrous silicic (haplodacitic) melts. Aspect ratios and inferred relative growth rates of the 3D short (S) and intermediate (I) crystal dimensions vary significantly between mafic and silicic melts, with δS:δI = 1:6 – 1:20 in basalt and 1:2.5 – 1:8 in hydrous haplodacite. The lower aspect ratios of plagioclase grown in the silicic melt coincide with 10-100x lower melt diffusion rates than in the mafic melt. Using an anisotropic growth model, we show that such differences in melt diffusivity can explain the discrepancy in plagioclase aspect ratios: if interface reaction and melt diffusion rates are of similar magnitude, then the growth of a crystal facet with high interfacial reaction rates may be limited by melt diffusion while another facet of the same crystal with lower interfacial reaction rates may grow uninhibited by melt diffusivity. This selective control of melt diffusion on crystal growth rates results in progressively more equant crystal shapes as diffusivity decreases, consistent with our experimental observations. Importantly, crystals formed in this diffusion-moderated, intermediate growth regime may not show any classical diffusion-controlled growth features. The proposed model was developed for plagioclase microlites, but should be generalisable to all anisotropic microlite growth in volcanic rocks

Elemental diffusion chronostratigraphy:time-integrated insights into the dynamics of plumbing systems

Time-related information of pre-eruptive magmatic processes is locked in the chemical profile of compositionally zoned minerals and can be retrieved by means of elemental diffusion chronometry. However, only the timescale of the outermost rim is commonly resolved, limiting our knowledge of timescales to those directly preceding the eruption. A major obstacle is the need to accurately constrain the temperatures at which diffusion occurred. Elemental diffusion chronostratigraphy can be fully resolved for crystals that have spent their lifetime in hot storage. Under this condition, crystals will be kept at the temperature of the eruptible magma(s), and diffusion timescales approximate the storage of the crystal in question in different melt environments. Hot storage conditions are typical of open-conduit systems in steady state and are driven by the regular supply of fresh hot magmas determining the constant presence of eruptible magma. Fe-Mg interdiffusion in pyroxene crystals from Stromboli and Popocatépetl are used to reconstruct elemental diffusion chronostratigraphies of single crystals and to discuss their implications for magma dynamics. Uncertainties introduced by temperature estimates and other input data, including experimentally derived values for the activation energy E and the pre-exponential factor D0, have large effects on the accuracy of modeled timescales, which need to be evaluated and mitigated. Elemental diffusion chronostratigraphy is an extremely powerful tool for obtaining time-related temporal information on the dynamics and histories of volcanic plumbing systems, providing in-depth knowledge of the magmatic system far beyond late-stage pre-eruptive processes.</p

Elemental Diffusion Chronostratigraphy:Time-Integrated Insights Into the Dynamics of Plumbing Systems

Time-related information of pre-eruptive magmatic processes is locked in the chemical profile of compositionally zoned minerals and can be retrieved by means of elemental diffusion chronometry. However, only the timescale of the outermost rim is commonly resolved, limiting our knowledge of timescales to those directly preceding the eruption. A major obstacle is the need to accurately constrain the temperatures at which diffusion occurred. Elemental diffusion chronostratigraphy can be fully resolved for crystals that have spent their lifetime in hot storage. Under this condition, crystals will be kept at the temperature of the eruptible magma(s), and diffusion timescales approximate the storage of the crystal in question in different melt environments. Hot storage conditions are typical of open-conduit systems in steady state and are driven by the regular supply of fresh hot magmas determining the constant presence of eruptible magma. Fe-Mg interdiffusion in pyroxene crystals from Stromboli and Popocatépetl are used to reconstruct elemental diffusion chronostratigraphies of single crystals and to discuss their implications for magma dynamics. Uncertainties introduced by temperature estimates and other input data, including experimentally derived values for the activation energy E and the pre-exponential factor D 0, have large effects on the accuracy of modeled timescales, which need to be evaluated and mitigated. Elemental diffusion chronostratigraphy is an extremely powerful tool for obtaining time-related temporal information on the dynamics and histories of volcanic plumbing systems, providing in-depth knowledge of the magmatic system far beyond late-stage pre-eruptive processes.</p

Magma recharge patterns control eruption styles and magnitudes at Popocatépetl volcano (Mexico)

Diffusion chronometry has produced petrological evidence that magma recharge in mafic to intermediate systems can trigger volcanic eruptions within weeks to months. However, less is known about longer-term recharge frequencies and durations priming magma reservoirs for eruptions. We use Fe-Mg diffusion modeling in orthopyroxene to show that the duration, frequency, and timing of pre-eruptive recharge at Popocatépetl volcano (Mexico) vary systematically with eruption style and magnitude. Effusive eruptions are preceded by 9–13 yr of increased recharge activity, compared to 15–100 yr for explosive eruptions. Explosive eruptions also record a higher number of individual recharge episodes priming the plumbing system. The largest explosive eruptions are further distinguished by an ∼1 yr recharge hiatus directly prior to eruption. Our results offer valuable context for the interpretation of ongoing activity at Popocatépetl, and seeking similar correlations at other arc volcanoes may advance eruption forecasting by including constraints on potential eruption size and style.</p

Magma recharge patterns control eruption styles and magnitudes at Popocatépetl volcano (Mexico)

Diffusion chronometry has produced petrological evidence that magma recharge in mafic to intermediate systems can trigger volcanic eruptions within weeks to months. However, less is known about longer-term recharge frequencies and durations priming magma reservoirs for eruptions. We use Fe-Mg diffusion modeling in orthopyroxene to show that the duration, frequency, and timing of pre-eruptive recharge at Popocatépetl volcano (Mexico) vary systematically with eruption style and magnitude. Effusive eruptions are preceded by 9–13 yr of increased recharge activity, compared to 15–100 yr for explosive eruptions. Explosive eruptions also record a higher number of individual recharge episodes priming the plumbing system. The largest explosive eruptions are further distinguished by an ~1 yr recharge hiatus directly prior to eruption. Our results offer valuable context for the interpretation of ongoing activity at Popocatépetl, and seeking similar correlations at other arc volcanoes may advance eruption forecasting by including constraints on potential eruption size and style

A Pyroxenic View on Magma Hybridization and Crystallization at Popocatépetl Volcano, Mexico

The Popocatépetl Volcanic Complex (PVC) is an active arc volcano located in central Mexico, 70 km southeast of Mexico City. Current models of the PVC’s plumbing system and magma petrogenesis are largely based on studies of isolated Plinian eruptions over the past 23.5 ka and present-day Vulcanian activity, while voluminous interplinian effusive summit and flank eruptions remain underrepresented. Here, we present a detailed petrological characterization focussed on ortho- and clinopyroxene in five effusive flank eruptions and two Plinian eruptions of the PVC during the last ∼14.1 ka. Texturally and compositionally defined pyroxene populations are used to constrain magmatic temperatures and deconvolve crystallization histories. At least two long-lived, inter-connected magmatic environments (ME) are identified in the mid- to upper crust beneath the PVC: (1) a mafic ME crystallizing high-Mg orthopyroxene + clinopyroxene + Cr-spinel ± sulfide at 1000–1115°C, and (2) an evolved, shallower ME crystallizing plagioclase + low-Mg orthopyroxene + clinopyroxene + Fe-Ti oxides + apatite ± sulfide at long-term storage temperatures of ∼970°C. The architecture of the PVC plumbing system has remained stable throughout the last ∼14.1 ka, and both MEs have sustained above-solidus magma storage temperatures fueled by recharge with hydrous, high-Mg basaltic mantle melts that crystallized fosteritic olivine + Cr-spinel + low-Ca clinopyroxene in the lower- to mid-crust at 1080–1220°C. Lavas and pumices show texturally and compositionally diverse crystal cargoes indicative of frequent magma mixing, with ≤67% of pyroxene crystals originating from the mid- to upper crustal mafic ME, of which ≤74% were stored and diffusively overprinted in the evolved ME for centuries to millenia. Pyroxene crystals of different origins, ages and thermal histories are stored in the evolved ME as a heterogeneous crystal mush that is frequently disrupted, reorganized and replenished by mafic injections. Magma recharge causes melt and crystal hybridization over timescales ranging from near-instantaneous to millenia, which produces the diverse crystal cargo and restricted whole-rock compositions typical for the PVC and many other arc volcanoes. We suggest that hot storage conditions and magma dynamics similar to the PVC may be characteristic for many other arc volcanoes of intermediate sizes and compositions.</p

A Pyroxenic View on Magma Hybridization and Crystallization at Popocatépetl Volcano, Mexico

The Popocatépetl Volcanic Complex (PVC) is an active arc volcano located in central Mexico, 70 km southeast of Mexico City. Current models of the PVC’s plumbing system and magma petrogenesis are largely based on studies of isolated Plinian eruptions over the past 23.5 ka and present-day Vulcanian activity, while voluminous interplinian effusive summit and flank eruptions remain underrepresented. Here, we present a detailed petrological characterization focussed on ortho- and clinopyroxene in five effusive flank eruptions and two Plinian eruptions of the PVC during the last ∼14.1 ka. Texturally and compositionally defined pyroxene populations are used to constrain magmatic temperatures and deconvolve crystallization histories. At least two long-lived, inter-connected magmatic environments (ME) are identified in the mid- to upper crust beneath the PVC: (1) a mafic ME crystallizing high-Mg orthopyroxene + clinopyroxene + Cr-spinel ± sulfide at 1000–1115°C, and (2) an evolved, shallower ME crystallizing plagioclase + low-Mg orthopyroxene + clinopyroxene + Fe-Ti oxides + apatite ± sulfide at long-term storage temperatures of ∼970°C. The architecture of the PVC plumbing system has remained stable throughout the last ∼14.1 ka, and both MEs have sustained above-solidus magma storage temperatures fueled by recharge with hydrous, high-Mg basaltic mantle melts that crystallized fosteritic olivine + Cr-spinel + low-Ca clinopyroxene in the lower- to mid-crust at 1080–1220°C. Lavas and pumices show texturally and compositionally diverse crystal cargoes indicative of frequent magma mixing, with ≤67% of pyroxene crystals originating from the mid- to upper crustal mafic ME, of which ≤74% were stored and diffusively overprinted in the evolved ME for centuries to millenia. Pyroxene crystals of different origins, ages and thermal histories are stored in the evolved ME as a heterogeneous crystal mush that is frequently disrupted, reorganized and replenished by mafic injections. Magma recharge causes melt and crystal hybridization over timescales ranging from near-instantaneous to millenia, which produces the diverse crystal cargo and restricted whole-rock compositions typical for the PVC and many other arc volcanoes. We suggest that hot storage conditions and magma dynamics similar to the PVC may be characteristic for many other arc volcanoes of intermediate sizes and compositions