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A study of melt inclusions at Vulcano (Aeolian Islands, Italy): insights on the primitive magmas and on the volcanic feeding system 总被引：5，自引：0，他引：5
A. Gioncada R. Clocchiatti A. Sbrana P. Bottazzi D. Massare L. Ottolini 《Bulletin of Volcanology》1998,60(4):286-306
This work presents the results of a microthermometric and EPMA-SIMS study of melt inclusions in phenocrysts of rocks of the
shoshonitic eruptive complex of Vulcano (Aeolian Islands, Italy). Different primitive magmas related to two different evolutionary
series, an older one (50–25 ka) and a younger one (15 ka to 1890 A.D.), were identified as melt inclusions in olivine Fo88–91 crystals. Both are characterized by high Ca/Al ratio and present very similar Rb/Sr, B/Be and patterns of trace elements,
with Nb and Ti anomalies typical of a subduction zone. The two basalts present the same temperature of crystallization (1180±20 °C)
and similar volatile abundances. The H2O, S and Cl contents are relatively high, whereas magmatic CO2 concentrations are very low, probably due to CO2 loss before low-pressure crystallization and entrapment of melt inclusions. The mineral chemistry of the basaltic assemblages
and the high Ca/Al ratio of melt inclusions indicate an origin from a depleted, metasomatized clinopyroxene-rich peridotitic
mantle. The younger primitive melt is characterized with respect to the older one by higher K2O and incompatible element abundances, by lower Zr/Nb and La/Nb, and by higher Ba/Rb and LREE enrichment. A different degree
of partial melting of the same source can explain the chemical differences between the two magmas. However, some anomalies
in Sr, Rb and K contents suggest either a slightly different source for the two magmas or differing extents of crustal contamination.
Low-pressure degassing and cooling of the basaltic magmas produce shoshonitic liquids. The melt inclusions indicate evolutionary
paths via fractional crystallization, leading to trachytic compositions during the older activity and to rhyolitic compositions
during the recent one. The bulk-rock compositions record a more complex history than do the melt inclusions, due to the syneruptive
mixing processes commonly affecting the magmas erupted at Vulcano. The composition and temperature data on melt inclusions
suggest that in the older period of activity several shallow magmatic reservoirs existed; in the younger one a relatively
homogeneous feeding system is active. The shallow magmatic reservoir feeding the recent eruptive activity probably has a vertical
configuration, with basaltic magma in the deeper zones and differentiated magmas in shallower, low-volume, dike-like reservoirs.
Received: 11 March 1998 / Accepted: 14 July 1998 相似文献
2.
Pinarelli Laura Gioncada Anna Capaccioni Bruno Vaselli Orlando Downes Hilary 《Mineralogy and Petrology》2019,113(1):39-60
Mineralogy and Petrology - Vulcano is part of the Aeolian volcanic arc in the southern Tyrrhenian Sea. Its products were emplaced through multiple episodes of edifice building and collapse since... 相似文献
3.
A. Gioncada R. Mazzuoli M. Bisson M. T. Pareschi 《Journal of Volcanology and Geothermal Research》2003,122(3-4):191-220
Over the last 42 ka, volcanic activity at Lipari Island (Aeolian Arc, Italy) produced lava domes, flows and pyroclastic deposits with rhyolitic composition, showing in many cases evidence of magma mixing such as latitic enclaves and banding. In this same period, on nearby Vulcano Island, similar rhyolitic lava domes, pyroclastic products and lava flows, ranging in composition from shoshonite to rhyolite, were erupted. As a whole, the post-42 ka products of Lipari and Vulcano show geochemical variations with time, which are well correlated between the two islands and may correspond to a modification of the primary magmas. The rhyolitic products are similar to each other in their major elements composition, but differ in their trace element abundances (e.g. La ranging from 40 to 78 ppm for SiO2 close to 75 wt%). Their isotopic composition is variable, too. The 87Sr/86Sr (0.704723–0.705992) and 143Nd/144Nd (0.512575–0.512526) ranges partially overlap those of the more mafic products (latites), having 87Sr/86Sr from 0.7044 to 0.7047 and 143Nd/144Nd from 0.512672 to 0.512615. 206Pb/204Pb is 19.390–19.450 in latites and 19.350–19.380 in rhyolites. Crystal fractionation and crustal assimilation processes of andesitic to latitic melts, showing an increasing content in incompatible elements in time, may explain the genesis of the different rhyolitic magmas. The rocks of the local crustal basement assimilated may correspond to lithotypes present in the Calabrian Arc. Mixing and mingling processes between latitic and rhyolitic magmas that are not genetically related occur during most of the eruptions. The alignment of vents related to the volcanic activity of the last 40 ka corresponds to the NNW–SSE Tindari–Letojanni strike-slip fault and to the correlated N–S extensional fault system. The mafic magmas erupted along these different directions display evidence of an evolution at different PH2O conditions. This suggests that the Tindari–Letojanni fault played a relevant role in the ascent, storage and diversification of magmas during the recent volcanic activity. 相似文献
4.
Geologic model of the magmatichydrothermal system of vulcano (Aeolian Islands, Italy) 总被引：1，自引：0，他引：1
Summary This paper presents a model of the active magmatic-hydrothermal (high-sulfidation) system of La Fossa volcano, based on mineralogical and geochemical studies of hydrothermal alteration on the surface and in the subsoil (geothermal wells and lithic clasts from explosive eruptions).The main engine of this system is represented by the shallow magmatic feeding system of La Fossa, which produces substantial degassing of volatiles (H2O, S, Cl). The introduction of magmatic fluids into the conduit system causes high temperature recrystallisation and metasomatism of the volcanic and sub-volcanic rocks. Lateraly to the volcanic conduits, the magmatic fluids undergo a primary neutralization, forming neutral low permeability hydrothermal zones. During their rise to the surface, the magmatic vapours may condense in groundwater, forming acid solutions that react with rocks to form superficial hydrothermal alteration. Silicic, advanced argillic and intermediate argillic alteration facies develop. This reflects the progressive neutralisation of extremely acid fluids. High contents of trace elements, like TI and Bi, supporting evidence for magmatic fluid transport, were found close to the high temperature fumaroles (up to 500°Q in the silicic alteration zone of La Fossa.
Ein geologisches Modell des magmatisch-hydrothermalen Systems von Vulcano, Aeolische Inseln, Italien
Zusammenfassung Diese Arbeit stellt ein Modell für das aktive magmatisch-hydrothermale (highsulfidation) System des La Fossa Vulkans vor. Dieses beruht auf mineralogischen und geochemischen Studien der hydrothermalen Umwandlung an der Oberfläche und im Untergrund (geothermale Bohrungen und lithische Klasten von explosiven Eruptionen). Als Energiequelle fungiert das seichte magmatische Zufuhrsystem von La Fossa, das signifikante Entgasung volatiler Phasen (H2O, S, HCl) mit sich bringt. Das Eindringen magmatischer Fluide in die Zufuhrkanäle verursacht Rekristallisation und Metasomatose der vulkanischen und subvulkanischen Gesteine bei hohen Temperaturen. In lateralen Bereichen der vulkanischen Zufuhrkanäle erfahren die magmatischen Fluide eine primäre Neutralisation, wobei neutrale hydrothermale Zonen niedriger Permeabilität entstehen. Während des Aufstiegs an die Oberfläche können die magmatischen Fluide im Grundwasser kondensiert werden, wobei sie saure Lösungen bilden, die wiederum mit den Gesteinen reagieren und zu Hydrothermalalteration führen. Dabei entstehen silizische, fortgeschrittene argillische und intermediäre agillische Umwandlungsfazies. Dies entspricht der zunehmenden Neutralisation extrem saurer Fluide. Hohe Gehalte an Spurenelementen, wie TI und Bi können als zusätzliche Hinweise für magmatischen Fluidtransport gesehen werden, sie treten in der Nähe der HochTemperatur-Fumarolen (bis 500'C) in der silizischen Alterationszone von La Fossa auf.相似文献
5.
The historic Breccia di Commenda (BC) explosive eruption of Vulcano (Aeolian Islands, Italy) opened with a phase that generated a gray fine ash layer dispersed to the northwest (phase 1). The eruption continued with a dilute pyroclastic density current (PDC) that was dispersed to the east, followed by the emplacement of radially distributed, topographically controlled PDC deposits (phase 2). The last phase of the eruption produced a sequence of accretionary lapilli and gray fine ash dispersed toward the southeast (phase 3). The most impressive feature of the BC is its high lithic/juvenile clast ratio and the yellow color of the deposits of phase 2. Lithic fragments are mainly hydrothermally altered rocks, in the silicic and advanced argillic facies. Juvenile fragments, ranging from 20?% to 40?% by volume, are mainly confined to the ash component of the deposits and comprise rhyolitic to trachyandesite, poorly to non-vesicular fragments. The fine ash fraction of the deposits is richer in S, Cu, Zn, Pb, and As than the BC juvenile lapilli and bombs, and also the juvenile components of other La Fossa units, suggesting that the BC formed in the presence of an anomalously high amount of S and metals. Sulfur and metals may have been carried as aerosols by chloride- and sulfate-bearing micro-crystals, derived from the condensation of magmatic gas in the eruptive cloud. The high content of hydrothermally altered lithic clasts in the deposits suggests that explosions involved the fluid-saturated hydrothermally altered rocks residing in the conduit zone. However, the presence of a juvenile component in the deposits supports the idea that this explosion may have been triggered by the ascent of new magma. We categorize this eruption as magmatic-hydrothermal to emphasize that in this type of phreatomagmatic eruption the external water was an active hydrothermal system. Rock magnetic temperatures of non-altered lava lithic fragments indicate a uniform deposit temperature for the PDC deposits of between 200 and 260?°C, with a maximum at 280?°C. These homogeneous, relatively low temperatures are consistent with the idea that the phase 2 explosions involved the expansion of abundant steam from the flashing of the hydrothermal system. In addition, recent paleomagnetic dating of the BC provides an age of between 1000 and 1200?AD, younger than that reported in the previously published data, suggesting that previous interpretations and the recent history of La Fossa and Mt. Pilato require re-evaluation. 相似文献
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R. Clocchiatti A. Del Moro A. Gioncada J. L. Joron M. Mosbah L. Pinarelli A. Sbrana 《Bulletin of Volcanology》1994,56(6-7):466-486
The magmatic system feeding the last eruption of the volcano La Fossa, Vulcano Island, Italy was studied. The petrogenetic mechanisms controlling the differentiation of erupted rocks were investigated through petrography, mineral chemistry, major, trace and rare earth element and Sr, Nd and Pb isotopic geochemistry. In addition, melt inclusion and fluid inclusion data were collected on both juvenile material and xenolithic partially melted metamorphic clasts to quantify the P-T conditions of the magma chamber feeding the eruption. A regular and continuous chemical zoning has been highlighted: rhyolites are the first erupted products, followed by trachytes and latites, whereas rhyolitic compositions were also found in the upper part of the sequence. The chemical and isotopic composition of the rhyolites indicates that they originated by fractional crystallization from latitic magmas plus the assimilation of crustal material; the trachytes represent hybrid magmas resulting from the mixing of latites and rhyolites, contaminated in the shallow magmatic system. The erupted products, primarily compositionally zoned from latites to rhyolites, are heterogeneous due to syn-eruptive mingling. The occurrence of magmacrust interaction processes, evidenced by isotopic variations (87Sr/86Sr=0.70474±3 to 0.70511±3; 143Nd/144Nd=0.512550±6 to 0.512614±8; 206Pb/204Pb=19.318–19.489; 207Pb/204Pb=15.642–15.782; 208Pb/204Pb=39.175–39.613), is confirmed by the presence of partially melted metamorphic xenoliths, with 87Sr/86Sr=0.71633±6 to 0.72505±2 and 143Nd/144Nd=0.51229±7, in rhyolites and trachytes. AFC calculations indicate a few percentage contribution of crustal material to the differentiating magmas. Thermometric measurements on melt inclusions indicate that the crystallization temperatures of the latites and trachytes were in the range of 1050–1100° C, whereas the temperature of the rhyolites appears to have been around 1000°C at the time of the eruption. Compositional data on melt inclusions reveal that the magmas involved in the eruption contained about 1–1.5 wt.% dissolved H2O in pre-eruptive conditions. Secondary fluid inclusions found in metamorphic xenoliths give low equilibration pressure data (30–60 MPa), giving the location of the higher portions of the chamber at around 1500–2000 m of depth. 相似文献
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Pantelleria Island, located in the Sicily Channel Rift Zone (Italy), is the type locality for the peralkaline rhyolitic rocks called pantellerites. In the last 50 ka, after the large Green Tuff caldera-forming eruption, volcanic activity at Pantelleria has consisted of effusive and explosive eruptions mostly vented inside and along the rim of the caldera and producing silicic lava flows, lava domes and poorly dispersed pantelleritic pumice fall deposits. Basaltic cinder cones and lava flows are only present outside the caldera in the NW sector of the island. The most recent basaltic (Cuddie Rosse, ～ 20 ka) and pantelleritic (Cuddia Randazzo and Cuddia del Gallo, ～ 6 ka) pyroclastic products were sampled to investigate magmatic volatile contents through the study of melt inclusions.The melt inclusions in pyroxene and olivine phenocrysts of Cuddie Rosse scoriae have an alkali basalt composition. The dissolved volatiles comprise 0.9–1.6 wt.% H2O, several hundred ppm of CO2, 1600–2000 ppm of sulphur and 500–900 ppm of chlorine. The water–carbon dioxide couple gives a confining pressure ～ 2 kbar prior to the eruption. This result indicates that episodes of magma ponding and crystallization occurred in the upper crust prior to eruption. The melt inclusions in feldspar, fayalite and aenigmatite phenocrysts of Cuddia del Gallo and Cuddia Randazzo pumice have a pantelleritic composition (Agpaitic Indices 1.3–2.1), up to 4.4 wt.% H2O, 8700 ppm Cl, 6000 ppm F, and CO2 below the detection limit. Sulphur averaging 420 ppm has been measured in Cuddia Randazzo melt inclusions. These data indicate relatively high volatile contents for these low-energy Strombolian-type eruptions. Melt inclusions in Cuddia del Gallo pumice show the most evolved composition (Agpaitic Indices 2–2.1) and the highest volatile content, in agreement with fluid saturation conditions in the magma chamber prior to the eruption. This implies a confining pressure of ～ 1 kbar for the top of the pantelleritic reservoir. The composition of melt inclusions and mineralogical assemblage of Cuddia Randazzo pumice indicate that it has a lower evolutionary degree (Agpaitic Indices 1.3–1.8) and lower pre-eruptive Cl and H2O contents than Cuddia del Gallo pumice. An increase in pressure due to the exsolution of volatiles in the upper part of the pantelleritic reservoir may have triggered the Cuddia del Gallo explosive eruption. Evidence of widespread pre-eruptive mingling between trachytes and pantellerites suggests that the intrusion of trachytic magma into the pantelleritic reservoir likely played a major role in destabilizing the magma system just prior to the Cuddia Randazzo event. 相似文献
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