Hybrid magma generation preceding Plinian silicic eruptions at Hekla, Iceland: evidence from mineralogy and chemistry of two zoned deposits

2007 ◽  
Vol 144 (4) ◽  
pp. 643-659 ◽  
Author(s):  
GUDRUN SVERRISDOTTIR
Keyword(s):  
Basaltic Andesite ◽  
Surface Composition ◽  
Magma Mixing ◽  
Major And Trace Elements ◽  
Silicic Magma ◽  
Compositional Variation ◽  
Rhyolitic Magma ◽  
Partial Melt ◽  
Dyke Injection ◽  
Reverse Zoning

Hekla is a Holocene volcanic ridge in southern Iceland, which is notable for the link between repose periods and the composition of the first-erupted magma. The two largest explosive silicic eruptions, H4 and H3, erupted about 4200 and 3000 years ago. Airfall deposits from these eruptions were sampled in detail and analysed for major and trace elements, along with microprobe analyses of minerals and glasses. Both deposits show compositional variation ranging from 72 % to 56 % SiO2, with mineralogical evidence of equilibrium crystallization in the early erupted rhyolitic component but disequilibrium in the later erupted basaltic andesite component. The eruptions started with production of rhyolitic magma followed by dacitic to basaltic andesite magma. Sparse crystallization of the intermediate magma and predominant reverse zoning of minerals, trending towards a common surface composition, indicate magma mixing between rhyolite and a basaltic andesite end-member. The suggested model involves partial melting of older tholeiitic crust to produce silicic magma, which segregated and accumulated in deep crustal reservoir. Silicic magma eruption is triggered by basaltic andesite dyke injection, with a proportion of the dyke magma contributing to the production and eruption of a mixed hybrid magma. Both the volume of the silicic partial melt, and the proportion of the hybrid magma depend on the pre-eruptive repose time.

scholarly journals Compositional Variation of Eudialyte-Group Minerals from the Lovozero and Ilímaussaq Complexes and on the Origin of Peralkaline Systems

Minerals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 548
Author(s):  
Lia N. Kogarko ◽  
Troels F. D. Nielsen
Keyword(s):  
Linear Trend ◽  
Major And Trace Elements ◽  
High Tech ◽  
Compositional Variation ◽  
Elemental Distribution ◽  
Magma Chambers ◽  
Eudialyte Group ◽  
System A ◽  
Distribution Of Elements ◽  
World Class

The Lovozero complex, Kola peninsula, Russia and the Ilímaussaq complex in Southwest Greenland are the largest known layered peralkaline intrusive complexes. Both host world-class deposits rich in REE and other high-tech elements. Both complexes expose spectacular layering with horizons rich in eudialyte group minerals (EGM). We present a detailed study of the composition and cryptic variations in cumulus EGM from Lovozero and a comparison with EGM from Ilímaussaq to further our understanding of peralkaline magma chambers processes. The geochemical signatures of Lovozero and Ilímaussaq EGM are distinct. In Lovozero EGMs are clearly enriched in Na + K, Mn, Ti, Sr and poorer Fe compared to EGM from Ilímaussaq, whereas the contents of ΣREE + Y and Cl are comparable. Ilímaussaq EGMs are depleted in Sr and Eu, which points to plagioclase fractionation and an olivine basaltic parent. The absence of negative Sr and Eu anomalies suggest a melanephelinitic parent for Lovozero. In Lovozero the cumulus EGMs shows decrease in Fe/Mn, Ti, Nb, Sr, Ba and all HREE up the magmatic layering, while REE + Y and Cl contents increase. In Lovozero EGM spectra show only a weak enrichment in LREE relative to HREE. The data demonstrates a systematic stratigraphic variation in major and trace elements compositions of liquidus EGM in the Eudialyte Complex, the latest and uppermost part of Lovozero. The distribution of elements follows a broadly linear trend. Despite intersample variations, the absence of abrupt changes in the trends suggests continuous crystallization and accumulation in the magma chamber. The crystallization was controlled by elemental distribution between EGM and coexisting melt during gravitational accumulation of crystals and/or mushes in a closed system. A different pattern is noted in the Ilimaussaq Complex. The elemental trends have variable steepness up the magmatic succession especially in the uppermost zones of the Complex. The differences between the two complexes are suggested to be related dynamics of the crystallization and accumulation processes in the magma chambers, such as arrival of new liquidus phases and redistributions by mush melts.

scholarly journals Extreme isotopic heterogeneity in Samoan clinopyroxenes constrains sediment recycling

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Jenna V. Adams ◽  
Matthew G. Jackson ◽  
Frank J. Spera ◽  
Allison A. Price ◽  
Benjamin L. Byerly ◽  
...  
Keyword(s):  
Mantle Source ◽  
Magma Mixing ◽  
Major And Trace Elements ◽  
Mantle Heterogeneity ◽  
Isotopic Data ◽  
Nd Isotopes ◽  
Isotopic Heterogeneity ◽  
Total Variability ◽  
High Silica ◽  
Insight Into

AbstractLavas erupted at hotspot volcanoes provide evidence of mantle heterogeneity. Samoan Island lavas with high 87Sr/86Sr (>0.706) typify a mantle source incorporating ancient subducted sediments. To further characterize this source, we target a single high 87Sr/86Sr lava from Savai’i Island, Samoa for detailed analyses of 87Sr/86Sr and 143Nd/144Nd isotopes and major and trace elements on individual magmatic clinopyroxenes. We show the clinopyroxenes exhibit a remarkable range of 87Sr/86Sr—including the highest observed in an oceanic hotspot lava—encompassing ~30% of the oceanic mantle’s total variability. These new isotopic data, data from other Samoan lavas, and magma mixing calculations are consistent with clinopyroxene 87Sr/86Sr variability resulting from magma mixing between a high silica, high 87Sr/86Sr (up to 0.7316) magma, and a low silica, low 87Sr/86Sr magma. Results provide insight into the composition of magmas derived from a sediment-infiltrated mantle source and document the fate of sediment recycled into Earth’s mantle.

scholarly journals Petrologic Insights into Rift Zone Magmatic Interactions from the 2011 Eruption of Kīlauea Volcano, Hawaiʻi

2019 ◽  
Vol 60 (11) ◽  
pp. 2051-2075
Author(s):  
Brett H Walker ◽  
Michael O Garcia ◽  
Tim R Orr
Keyword(s):  
Trace Element ◽  
Rift Zone ◽  
Magma Mixing ◽  
Major And Trace Elements ◽  
Kilauea Volcano ◽  
The Other ◽  
Least Squares Regression ◽  
Mixing Processes ◽  
Residual Magma ◽  
Kīlauea Volcano

Abstract The high frequency of historical eruptions at Kīlauea Volcano presents an exceptional opportunity to address fundamental questions related to the transport, storage, and interaction of magmas within rift zones. The Nāpau Crater area on Kīlauea’s East Rift Zone (ERZ) experienced nine fissure eruptions within 50 years (1961–2011). Most of the magma intruded during these frequent eruptions remained stored within the rift zone, creating a potential magma mixing depot within the ERZ. The superbly monitored and sampled 2011 eruption (Puʻu ʻŌʻō episode 59) presents an extraordinary opportunity to evaluate magma mixing processes within the ERZ. Whole-rock, glass, and olivine compositions were determined, not only for lava from the 2011 eruption, but also for a new suite of Nāpau Crater area samples from the 1963, 1965, 1968, 1983, and 1997 eruptions, as well as the previously undocumented 1922 eruption. Whole-rock XRF data revealed two geochemically distinct magma batches for episode 59: one less evolved (∼6·6 wt % MgO, 0·46 wt % K2O) than the other (∼6·2 wt % MgO, 0·58 wt % K2O). Episode 59 lava is remarkably aphyric (∼0·1 vol. % phenocrysts), making use of mineralogy to identify parent magma affinities problematic. Linear compositional trends of whole-rock major and trace elements, and reversely zoned olivine crystals indicate episode 59 lavas underwent magma mixing. Least squares regression calculations and plots of major and trace element data, were used to evaluate whether the episode 59 samples are products of mixing summit-derived magma with residual magma from previous Nāpau Crater area eruptions. The regression results and trace element ratios are inconsistent with previously proposed mixing scenarios, but they do support mixing between summit-derived magma and residual magma from the 1983 and 1997 Nāpau Crater area eruptions. These magmas were stored in physically and chemically distinct pods at depths of 1·6–3·0 km prior to mixing with new magma intruded from the summit to produce the episode 59 lava. One pod contained a fractionated equivalent of 1983 lava, and the other a hybrid of compositions similar to 1983 and 1997 lavas. The petrology of episode 59 lava demonstrates that magmas from two previous eruptions (1983 and 1997) were available to mix with magma intruded from the summit region. This study clarifies the pre-eruptive history of the mixed episode 59 lava, and elucidates the evolution of the volcano's magmatic system in a region of frequent eruptions.

Analysis of Experimentally Zoned Crystals to Investigate The Thermo-Chemical Evolution of Magma Reservoirs

2020 ◽  
Author(s):  
Alessandro Musu ◽  
Luca Caricchi ◽  
Diego Perugini ◽  
Rosa Anna Corsaro ◽  
Francesco Vetere ◽  
...  
Keyword(s):  
Inductively Coupled Plasma ◽  
Magma Mixing ◽  
Deformation Gradient ◽  
Major And Trace Elements ◽  
Machine Learning Algorithms ◽  
Concentric Cylinder ◽  
Distribution Maps ◽  
Chemical Zoning ◽  
Magma Reservoirs ◽  
Static Conditions

<p>Magma reservoirs are characterized by thermal and chemical gradients producing large variations of the spatial distribution of the physical properties of the magma they contain. Understanding the pre-eruptive thermal, chemical and physical evolution of magma represents an important step to correctly interpret the signs of an impending eruption. In this framework, the chemical zoning of minerals, which provide us a record of these thermal and chemical perturbations, represents an important tool to reconstruct reservoir dynamics. We study the effect of the competition between changing intensive parameters, element diffusion and mineral growth on the chemical zoning of minerals. We grow chemical zoned minerals at the Petro-Volcanology Research Group of the University of Perugia, using tephra from 2002-03 Mt. Etna eruption as starting material. The zonation in minerals is been forced inside a high-temperature furnace by oscillating the temperature under three different conditions: static conditions, using a controlled deformation gradient (concentric cylinder apparatus) and using a chaotic mixing regime (Chaotic Magma Mixing Device – CMMD). We collect major and trace elements distribution maps on a large number of crystals using Electron Probe Micro Analyzer (EPMA) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), respectively. The data will be analysed using a series of custom built machine learning algorithms to disentangle zoning related to variations of the thermodynamic conditions of crystal growth from the effects of the competition between diffusion and growth. Our data will help deciphering the zoning patterns observed in natural crystals, improve our understanding of magma reservoir dynamics and help the interpretation of monitoring signals in the period preceding a volcanic eruption.</p>

The origin of large zoned ignimbrites: the case of Aso caldera, Japan

2020 ◽  
Author(s):  
Franziska Keller ◽  
Olivier Bachmann ◽  
Nobuo Geshi ◽  
Ayumu Miyakawa
Keyword(s):  
Basaltic Andesite ◽  
Magma Mixing ◽  
Alternative View ◽  
Magma Reservoirs ◽  
Melt Separation ◽  
Storage Zone ◽  
Aso Caldera ◽  
Silicic Magmas ◽  
Crystal Accumulation ◽  
Compatible Elements

<p>Silicic magmas are the most evolved, most viscous and potentially most explosive melts present on Earth. Despite their importance, the processes leading to accumulation of large amounts of silicic magma in the crust are still a matter of debate. Ignimbrite sheets of large caldera forming eruptions are interpreted to be unique snapshots of upper crustal magma reservoirs just prior to eruption and hence represent an exceptional possibility to study pre-eruptive magmatic conditions within silicic reservoirs.</p><p>The Aso System, in Central Kyushu (Japan), is an archetypical example of a multicyclic caldera-forming volcanic edifice; it was built by four catastrophic caldera forming eruptions, with the latest (Aso 4) taking place approximately 90 ka ago. The ignimbrite sheets produced during the Aso eruptions are some of the first ever described compositionally zoned pyroclastic flow deposits and are interpreted to be the result of extensive magma mixing of two compositionally distinct magmas in an upper crustal reservoir.</p><p>Here, we propose an alternative view of the Aso 4 ignimbrite sheets based on re-evaluation of whole rock data combined with mineral and glass geochemistry. The relatively scarce presence of mafic pyroxenes and plagioclases indicate recharge of hot, mafic magmas occurring shortly prior to eruption. However, the large amount of crystal-poor, felsic material in early erupted units in combination with late-erupted, crystal-rich basaltic andesite clasts, which are enriched in compatible elements and rich in compositionally highly evolved minerals, lead to the conclusion that magma mixing alone is not able to explain the complexities observed in Aso 4 deposits. Evidence for crystal accumulation in late erupted basaltic andesite clasts implies the formation of melt-rich lenses within a crystal-rich reservoir due to significant crystal-melt separation. We therefore propose an origin of the compositionally zoned Aso 4 ignimbrite largely by erupting a heterogeneous upper crustal reservoir, consisting of crystal-poor rhyodacitic melt pockets within a cumulate mush. The emptying of this heterogeneous magma storage zone was likely triggered by a recharge event from deeper in the system, initiating partial melting of previously-formed crystals (rejuvenation), mingling/ mixing, pressurization, and finally catastrophic evacuation of the eruptible portions of the subvolcanic reservoir, including parts of the cumulate mush.</p>

scholarly journals The characteristic of acid melts which formed tephra of pleistocene-holocene eruptions of Ichinsky Volcano, Kamchatka (Results of melt inclusions study)

2019 ◽  
Vol 64 (3) ◽  
pp. 237-262
Author(s):  
M. L. Tolstykh ◽  
M. M. Pevzner ◽  
V. B. Naumov ◽  
A. D. Babansky
Keyword(s):  
Trace Elements ◽  
Melt Inclusions ◽  
Magma Mixing ◽  
Major And Trace Elements ◽  
Magmatic System ◽  
Acid Melts

This paper presents the results of a study of melt inclusions in plagioclase, amphibole and pyroxene from Ichinsky volcano’s tephras of different age. Two types of melts have been identified, distinguished by different concentrations of potassium (K2O). Major and trace elements’ composition of these melts indicates that magma mixing was the dominating process in the Ichinsky magmatic system.

scholarly journals MAGMA GENERATION AND MIXING IN THE EARLIEST VOLCANIC CENTRE OF SANTORINI (AKROTIRI PENINSULA). MINERAL CHEMISTRY EVIDENCE FROM THE AKROTIRI PYROCLASTICS

2017 ◽  
Vol 43 (5) ◽  
pp. 2625
Author(s):  
K. Kitsopoulos
Keyword(s):  
Magma Mixing ◽  
Mineral Chemistry ◽  
Silicic Magma ◽  
High Alumina ◽  
Primitive Mantle ◽  
Volcanic Centre ◽  
Magma Generation ◽  
High Alumina Basalt ◽  
Ti Oxides

Santorini is a dominant expression of magma generation and subsequent volcanism in the Meditereanean area, where a calk-alkaline, high-alumina, basalt-andesite-dacite type of volcanism was expressed from eight centres. The volcanics of the Akrotiri peninsula are considered to be the products of the earliest (Pliocene Pleistocene) volcanic centre. The present study has investigated the mineral chemistry of some major pyrogenic phenocrysts, such as plagioclase and Fe-Ti oxides, of the Akrotiri pyroclatics unit, which have undergone a notable zeolitization procedure. The results are compatible with magma mixing mechanism of a primitive mantle derived, saturated, of mafic composition component with silicic magma in shallow crustal depths.

Differentiation in Sheared Granular Magma

2020 ◽  
Author(s):  
Nick Petford ◽  
John Clemens ◽  
Curt Koenders
Keyword(s):  
Magma Mixing ◽  
Shear Zones ◽  
Mineral Chemistry ◽  
Quantitative Model ◽  
Chemical Components ◽  
High Definition ◽  
Volume Increase ◽  
Recent Developments ◽  
Dilatancy Effect ◽  
Reverse Zoning

<p>Recent developments in high definition mineral chemistry at the grain scale are shedding new light on the processes and rates of magma storage, differentiation and eruption. However, the complementary physics and fluid dynamics of magma as a granular material are still based on viscous compaction theory, which may not be relevant in sub-volcanic settings where magma is being deformed by external shear. We present a quantitative model for shear deformation of a crystallised dense magma (>70% solid) with poro-elastic properties where the critical link between the mechanics and associated compositional changes in the melt are governed by dilation (volume increase) of the granular skeleton. Key material parameters governing the dilatancy effect include magma permeability, mush strength, the shear modulus and the contact mechanics and geometry of the granular assemblage. Calculations show that dilation reduces the interstitial fluid (melt) pressure to produce a ‘suction’ effect. At shear strain rates in excess of the tectonic background, deformation-induced melt flow can redistribute chemical components and heat between regions of crystallising magma with contrasting rheological properties, at velocities far in excess of diffusion or buoyancy forces, the latter of course the driving force behind fractional crystallisation and compaction. Unlike static magmas, there is no ‘lock-up’ state above which the interstitial melt cannot percolate. Co-mingling of hotter, indigenous melt has the potential to interrupt (or locally reverse) fractionation trends and produce reverse zoning or resorbtion of crystals, mimicking some of the textural effects attributed to magma mixing. Post-failure instabilities include hydraulic rupture of the mush along shear zones with potential for larger scale extraction and redistribution of evolved melt. A novel feature of congested, sub-volcanic granular magma is that the eruption itself helps drive rapid melt extraction, negating the requirement to first segregate large volumes of evolved melt as a precursor. </p>

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