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  • 1
    Electronic Resource
    Electronic Resource
    Crystal population density in not stationary volcanic systems: estimate of olivine growth rate in basalts of Lanzarote (Canary Islands) (1991)
    Springer
    Mineralogy and petrology 44 (1991), S. 181-196 
    Details
    ISSN: 1438-1168
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Zusammenfassung Wir haben Populations-Dichte-Daten von Melanephelinit bis Olivin-Tholeiit-Laven, die Olivin-Kristalle als erste und oft einzige Phase am Liquidus zeigen, erarbeitet. Die Proben stammen von der Insel Lanzarote, wo große Volumina primitiver BasaltMagmen direkt von einer Ursprungsregion in einer Tiefe von 100-50 km an die Oberfläche kommen. Das Vorkommen von Mantel-Xenolithen weist auf eine minimale Aufstiegsgeschwindigkeit von 1.0 ms−1 hin, und dies entspricht Aufstiegszeiten der Magmen in der Größenordnung von einem Tag. Modale Daten wurden automatisch von digitalisierten Bildern von Dünnschliffen gesammelt. Die räumlichen GrößenverteilungsDichten von Olivin zeigen eine exponentionelle Variation für kleine Kristalle und einen beinahe konstanten Wert für große Kristalle. Dieses Verhaltensteht mit Schwankungen der Nukleations- und Wachstumsraten bei Unterkühlung im Zusammenhang. Parameter, die sich für Olivin-Wachstumsraten ergaben, weisen auf Werte von ungefähr 3 × 10−7 cm s−1 für Unterkühlung von 30°C hin.[/ p]
    Notes: Summary We have collected pupulation density data of melanephelinite to olivine tholeiite lavas showing seriated olivine phenocrysts as the first, and often the only, phase occurring on the liquidus. The samples are from the island of Lanzarote, where large volumes of primitive basaltic magmas reach directly the surface from their source regions at a depth between 100 and 50 km. A minimum ascent speed of 1.0 ms−1, corresponding to times of rise of the magmas in the order of 1 day, was estimated from the occurrence of mantle xenoliths. Modal data have been automatically collected from digitalized images of thin sections. The spatial size distribution densities of olivine show an exponential variation for small crystal dimensions and a nearly constant value for large ones. Theoretical analysis shows that this behaviour can be related to variations of nucleation and growth rate with undercooling. Parameters derived for olivine growth rate equation suggest a growth rate of about 3 x 10−7 cm s−1 for undercooling of about 30°C.[/ p]
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01166962
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  • 2
    Electronic Resource
    Electronic Resource
    Effects of magma storage and ascent on the kinetics of crystal growth (1994)
    Springer
    Contributions to mineralogy and petrology 115 (1994), S. 402-414 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The size distributions of crystals of olivine, plagioclase and oxides of the 1991/93 eruption at Mt. Etna (Italy) are analyzed. The simultaneous collection of this information for different minerals gives precious insight into the cooling history of lavas. Three distinct episodes are detectable: a storage of the magma in a deep reservoir, characterized by nearly constant and low nucleation and growth rates (near to equilibrium); an ascent phase, with an ever increasing nucleation rate related to volatile exsolution; and finally a quenching phase. In addition to geochemical and geophysical evidence, the similarity of the crystal size distributions of the present eruption with those of previous ones of this century makes it possible to exclude that crystal size distributions of Etnean lavas are due to mixing of different populations. This strongly suggests that the main features of the volcano feeding system have not changed despite observed variations in the magma output rates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00320974
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  • 3
    Electronic Resource
    Electronic Resource
    A model of the Phlegraean Fields magma chamber in the last 10,500 years (1984)
    Springer
    Bulletin of volcanology 47 (1984), S. 349-358 
    Details
    ISSN: 1432-0819
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Volcanological and petrological data suggest that the Phlegraean Fields volcanic activity has been fed, at least in the last 10,500 years, by a not-refilled magma chamber where trachytic residual liquids were produced by fractionation of a trachybasaltic magma. Using estimated volumes of the erupted products andP–T data obtained through petrological studies, a conductive thermal model of the chamber was built up in order to estimate its past and present size. Results suggest a volume decrease from approximately 14 to 1.4 km3 of the trachybasaltic magma in 10,500 years. Trachytic liquid would also be present in the chamber in a minimum amount of 0.4 km3. The model allowed some insights on the petrogenesis of the Phlegraean trachytes, suggesting that they were erupted as liquids because thermally buffered within the magma chamber.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01961566
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  • 4
    Electronic Resource
    Electronic Resource
    Compositional variation in the 1983 and other recent Etnean lavas: Insights on the shallow feeding system (1984)
    Springer
    Bulletin of volcanology 47 (1984), S. 995-1007 
    Details
    ISSN: 1432-0819
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract A systematic petrographic and chemical study of chronologically ordered lava samples collected during the 1983 Etna eruption, has shown minor fluctuating variations in crystallinity and chemistry, apparently correlated with variations in the rate of effusion. Comparison with the compositional variations observed in the lavas emitted during the 1971–1983 period, has revealed a repeated evolutional tendency suggesting a small size shallow storage system periodically refilled, as in 1983, by more primitive magma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01952357
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  • 5
    Electronic Resource
    Electronic Resource
    Phenocryst/matrix trace-element partition coefficients for hawaiite-trachyte lavas from the Ellittico volcanic sequence (Mt. Etna, Sicily, Italy) (1998)
    Springer
    Mineralogy and petrology 64 (1998), S. 65-88 
    Details
    ISSN: 1438-1168
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Zusammenfassung Ein Satz von Phänokristall/Matrix Verteilungs-Koeffizienten für bis zu 29 Spurenelemente wurde mittels ICP-MS Analytik in hawaiitischen bis trachytischen Laven der Ellittico Abfolge (Ätna-System, Sizilien) erhalten. Die Verteilungs-Koeffizienten wurden für Plagioklas, Klinopyroxen, Olivin, Kaersutit und Ti-Magnetit bestimmt. Diese Phasen, zusammen mit Apatit (in dieser Arbeit nicht analysiert), stellen die fraktionierende Assoziation von festen Bestandteilen in alkalischen Magmen, die das vulkanische System des Ätna versorgen, dar. Der Datensatz ist ein erster Versuch die Verteilung von Spurenelementen zwischen Festphasen und Schmelze für Magmen des Ätna zu charakterisieren und kann ebenso nutzbringend auf andere Gebiete mit alkalischem Vulkanismus angewandt werden. Die Verteilungs-Koeffizienten werden hier benützt, um das Ausmaß der Inkompatibilität von 29 Spurenelementen zu erfassen, und das Ausmaß der Differentiationsprozesse und der vorherrschenden SauerstoffFugazität der Ellittico-Magmen zu bestimmen.
    Notes: Summary A set of phenocryst/matrix partition coefficients was obtained for up to 29 trace elements (ICP-MS analyses) in hawaiite to trachyte lavas from the Ellittico volcanic sequence (Mt. Etna system, Sicily). Partition coefficients were determined for plagioclase, clinopyroxene, olivine, kaersutite and Ti-magnetite. These phases, along with apatite (not analysed in this work), constitute the common fractionating solid assemblage of alkaline magmas feeding Mt. Etna volcanic system. The obtained data set forms the first attempt to characterise the solid/melt trace-element partitioning for Etnean magmas, and can be usefully applied in other sites of alkaline volcanism. The partition coefficients are here used to define the scale of incompatibility of 29 trace elements and to asses the extent of differentiation processes and the prevailing oxygen fugacity of Ellittico magmas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01226564
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  • 6
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    Metasomatism induced by alkaline magma in the upper mantle of northern Victoria Land (Antarctica): an experimental approach (2008)
    In:  Geological Society Special Publication 293: 279-302.
    Details
    Publication Date: 2008-01-25
    Description: Magma generation in the Ross Sea system is related to partial melting of strongly metasomatized mantle sources where amphibole most probably plays a crucial role. In this context, metasomatism induced by a mela-nephelinite melt in lithospheric mantle of the Mt. Melbourne Volcanic Province (northern Victoria Land (NVL), Antarctica) was investigated experimentally studying the effects of melt interaction with lherzolite at 1.52.0 GPa and T=9751300 {degrees}C, and wehrlite at 1.0 GPa and T=10501250 {degrees}C. The experiments were designed to induce melt infiltration into the ultramafic rocks. The observed modifications in minerals are compared with those found in mantle xenoliths from NVL. The effects of metasomatic modifications are evaluated on the basis of run temperature, distance from the infiltrating melt and the diffusion rates of chemical components. Both in lherzolite and wehrlite, clinopyroxene exhibits large compositional variations ranging from primary diopside to high-MgCr(Na) augitic and omphacitic clinopyroxenes in lherzolite, and to low-Mg and high-TiAlFeNa augites in wehrlite. Olivine (in wehrlite) and spinel (in lherzolite) are also compositionally modified: the former shows enrichment in Fe and the latter displays a higher Cr/(Cr+Al) ratio. The systematic variations in mineral compositions imply modifications of the chemistry of the infiltrating melt as recorded by the glass veinlets and patches observed in some charges. In experiments involving wehrlite paragenesis, the glass composition approaches that of melt patches associated with both amphibole-free and amphibole-bearing natural samples, and is related to olivine + clinopyroxene crystallization coupled with primary clinopyroxene dissolution at the contact between the metasomatizing melt and the solid matrix. Even if amphibole crystallization was not attained in the experiments, we were able to explain the occurrence of amphibole in the natural system considering that in this case a hot metasomatizing melt infiltrates a cooler matrix.
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  • 7
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    Metasomatism of the upper mantle beneath the Hyblean Plateau (Sicily): evidence from pyroxenes and glass in peridotite xenoliths (2008)
    In:  Geological Society Special Publication 293: 197-221.
    Details
    Publication Date: 2008-01-25
    Description: Coarse-grained, protogranular spinel peridotite xenoliths in the Upper Miocene Valle Guffari diatreme display a complex history for the shallow mantle underneath the Hyblean Plateau (SE Sicily). The mineral assemblage and composition (olivine Fo8991, orthopyroxene En8891, Cr-diopside En4849Fs46Wo4548, Cr-rich spinel with cr-number=2539) record at least one depletion event caused by melt extraction, followed by metasomatic enrichment. One of these samples (HYB40) hosts a fresh glass vein. Rare earth elements (REE) in clinopyroxenes from these peridotites show three patterns: (1) light REE-enriched (Lan/Ybn=717); (2) spoon-shaped (Lan/Ybn=1820; Lan/Smn=2134; Smn/Ybn〈1); (3) nearly flat (Lan/Ybn [~]3). Whole-rock and clinopyroxene trace elements indicate that these patterns are associated with more or less complete equilibration with at least two distinct metasomatic melts: an alkaline silicate melt resembling the host basalt and a hawaiitic melt (for peridotite HYB40). PT estimates yield 0.91.2 GPa and 8701050 {degrees}C, suggesting that refertilization by metasomatizing melts occurred at the CrustMantle boundary or just below. In addition, the PT data coincide with the palaeogeotherm reported by an earlier worker that is consistent with a high geothermal gradient. However, this thermal regime does not fit with the occurrence of an active mantle plume beneath the Hyblean area because of the deduced mantle potential temperatures, which are almost 200{degrees}C lower than those typical for a mantle plume. fO2 calculation gives a redox state above the fayalitemagnetitequartz buffer FMQ (up to +1.7 {Delta}log units) related to melt-driven metasomatism.
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  • 8
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    Thermal Evolution of the Lithosphere in a Rift Environment as Inferred from the Geochemistry of Mantle Cumulates, Northern Victoria Land, Antarctica (2011)
    Oxford University Press
    Details
    Publication Date: 2011-03-29
    Description: Among the abundant mantle xenoliths carried by the Cenozoic alkaline basalts of northern Victoria Land, Antarctica, we have studied a suite of clinopyroxene-rich cumulates collected at Browning Pass (Mt. Melbourne Volcanic Province), ranging in composition from wehrlites to clinopyroxenites. Clinopyroxenes belonging to both the Cr-diopside (wehrlites) and Al-augite series (ol-clinopyroxenites and clinopyroxenites) all show convex-upward REE patterns. Modal and cryptic metasomatism has variably affected the xenoliths, accounting for amphibole replacement of clinopyroxene and/or selective enrichment in incompatible elements. Chemical features, along with O–Sr–Nd isotopic data, indicate that both the parental magmas and the metasomatizing melts are related to the Cenozoic magmatic activity and imply the role of at least two mantle components with distinct isotopic fingerprints. The positive covariation between 18 O olivine and the amount of modal olivine, and between 18 O olivine and olivine Fo content, suggest that during the fractionation of olivine and pyroxene, the parent magma experienced a change in O-isotope composition; a low- 18 O melt component was not only added to the minerals during the metasomatic event but was also involved in the genesis of the parental melts. The Browning Pass cumulates are used to constrain the origin of the Antarctic Cenozoic magmatism from a heterogeneous mantle source whose depleted end-member is inferred to be the local lithospheric mantle, whereas the enriched end-member is represented by early metasomatic veins or domains emplaced into the depleted mantle during an amagmatic phase of rifting at the beginning of Ross Sea opening. Thermobarometric analysis of the process shows that the respective contribution to magma generation of the two end-members is related to the change of local thermal regime induced by an ‘edge effect’ in the mantle circulation at the lithospheric step between the thick East Antarctic craton and the thinned Ross Sea crust.
    Print ISSN: 0022-3530
    Electronic ISSN: 1460-2415
    Topics: Geosciences
    Published by Oxford University Press
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  • 9
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    Geothermometric study of Cr-spinels of peridotite mantle xenoliths from northern Victoria Land (Antarctica) (2014)
    Mineralogical Society of America
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    Publication Date: 2014-04-02
    Description: The crystal chemistry of Cr-spinels included in spinel peridotite mantle xenoliths from Baker Rocks and Greene Point (northern Victoria Land, Antarctica) has been studied by single-crystal structure refinement and electron microprobe analysis. All crystals are characterized by a dominance of Al Cr substitution with minor evidences of Mg Fe 2+ substitution and pertain to the Mg-rich portion of the spinel sensu stricto-chromite join. The two groups of samples, Baker Rocks (BR) and Greene Point (GP), show distinct degree of cation order with the inversion parameter ranging from 0.17 to 0.20 for BR spinels and from 0.06 to 0.13 for GP crystals. Closure temperatures, computed by a geothermometer based on the M Al+ T Mg T Al+ M Mg intracrystalline exchange, range from 883 to 911 °C for BR spinels and from 592 to 675 °C for GP spinels. We show that this difference is due to the higher concentration in Fe 3+ in GP spinels that enabled a faster kinetics of the intracrystalline cation ordering reaction, allowing the GP spinels to reach a higher degree of cation ordering and then lower closure temperatures.
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
    Published by Mineralogical Society of America
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  • 10
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    An improved clinopyroxene-based hygrometer for Etnean magmas and implications for eruption triggering mechanisms (2016)
    Mineralogical Society of America
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    Publication Date: 2016-12-02
    Description: We have refined the clinopyroxene-based hygrometer published by Armienti et al. (2013) for a better quantitative understanding of the role of H 2 O in the differentiation of Etnean magmas. The original calibration data set has been significantly improved by including several experimental clinopyroxene compositions that closely reproduce those found in natural Etnean products. To verify the accuracy of the model, some randomly selected experimental clinopyroxene compositions external to the calibration data set have been used as test data. Through a statistic algorithm based on the Mallows’ C P criterion, we also check that all model parameters do not cause data overfitting, or systematic error. The application of the refined hygrometer to the Mt. Etna 2011–2013 lava fountains indicates that most of the decreases in H 2 O content occur at P 〈 100 MPa, in agreement with melt inclusion data suggesting abundant H 2 O degassing at shallow crustal levels during magma ascent in the conduit and eruption to the surface.
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
    Published by Mineralogical Society of America
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