Chemical variation of clinopyroxene phenocrysts from the trachybasaltic lavas of Mount Etna, Sicily

Duncan, Andy; Preston, R. M. F.

doi:10.1180/minmag.1980.043.330.10

Cited by 19 publications

(13 citation statements)

References 8 publications

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“…9c). The Na-Ca inter-sector constancy is in agreement with previous sector zoning studies on Etnean clinopyroxene (Downes, 1974;Duncan and Preston, 1980) and other volcanic systems globally (Hollister and Gancarz, 1971;Ferguson, 1973;Leung, 1974). In contrast, disequilibrium partitioning of Na into Al-Ti-rich sectors has been reported for clinopyroxenes from Aleutian (Brophy et al, 1999) and Hawaiian (Hammer et al, 2016;Welsch et al, 2016) basalts, where sector zoning was related to rapid crystal growth.…”

Section: Clinopyroxene-melt Equilibrium and Thermobarometry On Sectorsupporting

confidence: 91%

“…A recipe for handling sector-zoned crystals Sector zoning has been broadly documented in clinopyroxene from alkali basalts (Hollister and Gancarz, 1971;Ferguson, 1973;Wass, 1973;Leung, 1974;Downes, 1974;Duncan and Preston, 1980;Shimizu, 1981;Hammer et al, 2016;Welsch et al, 2016) and less commonly in tholeiitic systems (Nakamura, 1973;Neave and Putirka, 2017) and arc settings (Arculus, 1973;Brophy et al, 1999). However, the potential kinetic controls on mineral chemistry have undermined the utility of these crystals for the interpretation of magma histories.…”

Section: Implications For the Interpretation Of Magma Dynamicsmentioning

confidence: 99%

“…Mollo and Hammer, 2017) is always necessary for the crystals to grow to the size of phenocrysts. In natural volcanic rocks, augite crystals often deviate from the frequently assumed 'treering' model and develop sector zoning (Hollister and Gancarz, 1971;Arculus, 1973;Ferguson, 1973;Downes, 1974;Leung, 1974;Dowty, 1976;Duncan and Preston, 1980;Shimizu, 1981;Watson and Liang, 1995;Brophy et al, 1999;Hammer et al, 2016;Welsch et al, 2016;Neave and Putirka, 2017;Mollo and Hammer, 2017;Stock et al, 2018), generating an hourglass form ( Fig. 1).…”

Section: Introductionmentioning

confidence: 99%

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Sector-zoned clinopyroxene as a recorder of magma history, eruption triggers, and ascent rates

Ubide

Mollo

Zhao

et al. 2019

Geochimica et Cosmochimica Acta

137

129

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Sector-zoned clinopyroxene is common in igneous rocks, but has been overlooked in the study of magmatic processes. Whilst concentric zoning is commonly used as a record of physicochemical changes in the melt feeding crystal growth, clinopyroxene is also highly sensitive to crystallisation kinetics. In sector-zoned crystals, the fidelity of compositional changes as recorders of magma history is dubious and the interplay between thermodynamic and kinetic controls remains poorly understood. Here we combine electron probe and laser ablation micro-chemical maps of titanaugite crystals from Mt. Etna (Sicily, Italy) to explore the origin of sector zoning at the major and trace element levels, and its implications for the interpretation of magmatic histories. Elemental maps afford the possibility to revisit sector zoning from a spatially controlled perspective. The most striking observation is a clear decoupling of elements into sectors vs. concentric zones within single crystals. Most notably, Al-Ti enrichments and Si-Mg depletions in the prism sectors {1 0 0}, {1 1 0} and {0 1 0} relative to the hourglass (or basal) sectors {À1 1 1} correlate with enrichments in rare earth elements and highly charged high field strength elements due to cation exchanges driven by kinetic effects. In contrast, transition metals (Cr, Ni, Sc) show little partitioning into sectors and strong enrichments in concentric zones following resorbed surfaces, interpreted as evidence of mafic recharge and magma mixing. Our results document that kinetic partitioning has minor effects on the compositional variations of cations with low charge relative to the ideal charge/radius of the structural site they occupy in the clinopyroxene lattice. We suggest that this may be due to a lower efficiency in charge balance mechanisms compared to highly charged cations. It follows that compatible metals such as Cr can be considered trustworthy recorders of mafic intrusions and eruption triggers even in sector-zoned crystals. We also observe that in alkaline systems where clinopyroxene crystallisation takes place at nearequilibrium conditions, sector zoning should have little effect on Na-Ca partitioning and in turn, on the application of experimentally calibrated thermobarometers. Our data show that whilst non-sector-zoned crystals form under relatively stagnant conditions, sector zoning develops in response to low degrees of undercooling, such as during slow magma ascent. Thus, we propose that the chemistry of sector-zoned crystals can provide information on magma history, eruption triggers, and possibly ascent rates.

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Section: Clinopyroxene-melt Equilibrium and Thermobarometry On Sectorsupporting

confidence: 91%

Section: Implications For the Interpretation Of Magma Dynamicsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Sector-zoned clinopyroxene as a recorder of magma history, eruption triggers, and ascent rates

Ubide

Mollo

Zhao

et al. 2019

Geochimica et Cosmochimica Acta

137

129

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“…This distribution agrees with that observed in sector zoned clinopyroxenes at Mt. Etna (Downes, 1974;Duncan and Preston, 1980;Ubide et al, 2019) and other volcanic systems world-wide (Hollister and Gancarz, 1971;Ferguson, 1973;Leung, 1974). In a recent study on major and trace element zoning of sector zoned clinopyroxene, Ubide et al (2019) demonstrated that sector zoning is strongly dependent on the charge/size of a given cation and its ability to charge-balance the clinopyroxene structure after incorporation of Al 3+ in tetrahedral substitution for Si 4+ .…”

Section: Dynamic Crystallisation Of Clinopyroxene Megacrystssupporting

confidence: 88%

Deep Magma Storage Revealed by Multi-Method Elemental Mapping of Clinopyroxene Megacrysts at Stromboli Volcano

et al. 2019

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The magmatic architecture and physicochemical processes inside volcanoes influence the style and timescale of eruptions. A long-standing challenge in volcanology is to establish the rates and depths of magma storage and the events that trigger eruption. Magma feeder systems are remarkably crystal-rich, and the growth stratigraphy of minerals sampled by erupted magmas can reveal a wealth of information on pre-eruptive processes. Here we combine detailed textural and chemical data acquired on large (>5 mm), euhedral augite megacrysts from Roman era activity (Pizzo scoria cone, 2.4-1.8 ka) at Stromboli (Italy) to investigate the plumbing system prior to the onset of current steady-state activity. Our dataset includes novel laser ablation time-of-flight mass spectrometry (LA-ICP-TOFMS) maps, which rapidly visualise multi-element zoning patterns across entire megacryst sections. The clinopyroxene data are complemented with geochemical constraints on mineral and melt inclusions, and adhering glassy tephra. Megacrysts are sector and oscillatory zoned in trace elements, yet their major element compositions are relatively uniform and in equilibrium with shoshonite-buffered melts. Mild sector zoning documents dynamic crystallisation under conditions of low undercooling during magma residence and growth. Clinopyroxene-melt thermobarometric and hygrometric calibrations, integrated with thermodynamically derived equilibrium equations, accurately track the P-T-H 2 O path of magmas. The refined models return restricted crystallisation depths that are deeper than those reported previously for historical and current eruptions, but consistent with deep clinopyroxene-dominated crystallisation (≥10 km), resembling other water-rich alkaline mafic systems. Megacryst cores are overgrown by oscillatory zoned mantles recording continuous input of magma that failed to trigger eruption. Crystal rims are characterised by a mild increase in compatible transition metals Cr and Ni, and depletion in incompatible elements, indicative of pre-eruptive mafic replenishment and magma mixing. The volcanic system appears to have been dominated by protracted periods of replenishment, convection, Ubide et al. Mapping Clinopyroxene Megacrysts at Stromboli and crystal residence, punctuated by rapid megacryst evacuation and eruption upon arrival of more mafic magma (days-weeks). Since the inception of current steady-state activity, eruption-triggering melts have become appreciably more mafic, suggesting that intrusion of primitive magma may be a key driver of the steady-state regime.

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“…Oscillatory zoning, frequent in Mt. Etna cpx as well as plagioclases (Duncan and Preston 1980;Giacomoni et al 2014), has been attributed to diffusion and nucleation rates and/or to major changes in the physical and/or chemical conditions of the magma. Phemister (1937) first suggested that finer-scale oscillations are manifestations of local disequilibrium, while coarser oscillations arise from extensive chemical or physical changes within the magma body.…”

Section: Magma Feeding Systemmentioning

confidence: 98%

Mt. Etna plumbing system revealed by combined textural, compositional, and thermobarometric studies in clinopyroxenes

Giacomoni

Coltorti

Bryce

et al. 2016

Contrib Mineral Petrol

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International audienceCoupled textural and in situ geochemical studies of clinopyroxene (cpx) phenocrysts, from both historical and recent eruptions of Mt. Etna volcano, provide a means to investigate the processes occurring in the deepest portion of the feeding system (>10 km depth). Five distinct textures were recognized: (1) normal oscillatory zoning, (2) normal zoning with Fe-rich rim, (3) sieve-textured core, (4) reverse oscillatory zoning, and (5) dusty rim. Electron microprobe analyses indicate an almost constant diopside–augite composition, with a slight enrichment in the enstatite for more recent erupted cpx. Core-to-rim compositional profiles, performed along the cpx, reveal distinct compositional characteristics. Normal oscillatory zoning is often characterized by a sharp increase in FeO (Δ ~ 2 wt%) accompanied by a drop in Al2O3 on the outermost 30 μm. Reverse oscillatory zoning, by contrast, exhibits a drop in FeO, Al2O3 (Δ ~ 2 wt%), and a remarkable crystal rim increase in MgO (up to 5 wt%). Similar compositional changes are evident in dusty-textured rims, which are characterized by dissolution edges and overgrowth containing glass pockets and channels. No significant compositional variations have been observed across crystals with sieve-textured cores. Trace element concentrations show enrichments in Sr, La, Zr, and REE, together with a decreasing La/Yb ratio (from ~7 to ~4) in rims of normally zoned crystals. Cpx with reverse zoning and dusty rims has low Sr, La, Zr, and REE contents toward crystal rims. Thermometers and barometers, based on equilibrium cpx-melt pairs, suggest that cpx cores start nucleating at 720 MPa, with the majority of them forming between 600 and 400 MPa but continuing to crystallize until very shallow depths (<100 MPa). Normal oscillatory-zoned phenocrysts surrounded by rims form at pressures shallower than 400 MPa, while reverse zoning and dusty rims occur between 400 and 500 MPa. Coupled petrologic and thermobarometric studies on both clinopyroxenes and plagioclases, associated with detailed textural and in situ geochemical analyses, are promising tools to reconstruct the entire magma ascent path beneath open-system volcanoes. At Mt. Etna, two distinct processes could account for the observed textures: Fe-rich rims in normal oscillatory-zoned crystals can be related to decompression-induced crystallization, while reverse zoning and dusty rims can be produced by mixing with a more basic magma at 400–500 MPa (i.e., ~10 km). Textural features are not restricted to a particular evolutionary phase of the volcano, which suggest that the deep feeding system has not changed significantly since the first alkaline volcanic phase

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Chemical variation of clinopyroxene phenocrysts from the trachybasaltic lavas of Mount Etna, Sicily

Cited by 19 publications

References 8 publications

Sector-zoned clinopyroxene as a recorder of magma history, eruption triggers, and ascent rates

Sector-zoned clinopyroxene as a recorder of magma history, eruption triggers, and ascent rates

Deep Magma Storage Revealed by Multi-Method Elemental Mapping of Clinopyroxene Megacrysts at Stromboli Volcano

Mt. Etna plumbing system revealed by combined textural, compositional, and thermobarometric studies in clinopyroxenes

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