排序方式： 共有9条查询结果，搜索用时 93 毫秒
1
1.
Gianfilippo?De AstisEmail author Lucia?Pappalardo Monica?Piochi 《Bulletin of Volcanology》2004,66(7):622-641
New stratigraphic, major- and trace-element, and Sr-, Nd- and Pb- isotopic data on volcanic deposits older than 14 ka from the island of Procida, Italy, are presented and compared with published analyses from the rest of the Phlegraean Volcanic District (PVD). Procida rocks range in composition from basalt to shoshonite and trachyte and show
87Sr/86Sr, 143Nd/144Nd, 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios varying within the ranges 0.70523–0.70678, 0.512539–0.512630, 18.99–19.29, 15.67–15.69 and 39.10–39.39, respectively. The presence of a compositional gap in the range SiO2=54–59 wt % is evidence of magma bimodality, and suggests that the feeding magmatic system was formed by at least two different reservoirs located at different depths. Geochemical and isotopic variations with increasing differentiation can be explained by fractional crystallization mechanisms, that in some cases were associated with crustal contamination that occurred in both deeper and shallower reservoirs; the most evolved magmas formed in the shallower one. Mixing/mingling processes also occurred. The variation of isotopic composition through time observed both for Procida and for Campi Flegrei and Ischia rocks is evidence of strong affinity between magmas that erupted on the entire PVD until about 40 ka. This indicates that they share a common origin and a common plumbing system. Most of the PVD eruptive centers active until about 40 ka lie within a NE-SW-oriented volcano-tectonic belt extending from the southeastern part of Ischia, through Procida and Torregaveta volcano to the northeastern sector of the present Campi Flegrei caldera. This not only indicates the existence of a link between regional structures and volcanism in the area, but also suggests that PVD magma genesis and evolution were strongly regulated by extensional tectonics. In the last 40 ka the mafic rocks erupted along this extensional structure – from Torregaveta and the islands of Ischia and Procida – indicate that it still represents an important crustal discontinuity that focuses mantle-derived magmas. Procida trachybasalts are enriched in large ion lithophile elements (LILE) and light and middle rare earth elements (LREE and MREE), and show slight negative anomalies in the high field strength elements (HFSE) relative to average MORB. A slight depletion in HREE is present. Trace element and isotope systematics can be referred to a lithospheric mantle source. The lithospheric mantle source carries intra-plate and slab-derived components, the latter probably inherited from a previous subduction event. 相似文献
2.
3.
G. Orsi M. Piochi L. Campajola A. D'Onofrio L. Gialanella F. Terrasi 《Journal of Volcanology and Geothermal Research》1996,71(2-4)
The chronology of the most significant eruptions at the island of Ischia in the last 5000 years has been studied by means of Accelerator Mass Spectrometry to obtain 14C data. The results are in good agreement with stratigraphical and archeological constraints. This allows interpretation of the measured dates as ages of the eruptions which produced the deposits overlying or incorporating the sampled paleosols and charcoal fragments, respectively. These ages define the timing of volcanism in the last 5000 years, suggesting that the recent volcanic activity at Ischia is characterized by periods of very intense volcanism alternating to periods of quiescence. This timing of the volcanism is correlated with the behaviour of the magmatic system and dynamics of resurgence of the Mt. Epomeo block. 相似文献
4.
Magma ascent and eruptive processes from textural and compositional features of Monte Nuovo pyroclastic products, Campi Flegrei, Italy 总被引：1，自引：0，他引：1
Geochemical and textural studies were carried out on alkaline products of the AD 1538 Monte Nuovo eruption. Due to the integration of the volcanological study with eyewitness reports, the dynamics and timing of each phase of the eruption and the volume of emitted magmas are known in detail. On this basis, unique in Campi Flegrei, the relations between magma chamber mechanisms, eruptive styles, magma ascent dynamics and volatile exsolution processes have been explored. Glass and phenocryst compositions indicate that the erupted magma has a homogeneous phono-trachytic composition. Textures and compositions of phenocrysts indicate that they crystallised at equilibrium with the melt in the magma chamber, likely as a mushy boundary layer along the chamber wall, where the temperature was below the liquidus temperature of the crystal free-chamber core. The estimated crystallisation temperature is 850±40°C. The magma phase relations in Petrogenys Residua System suggest that phenocryst crystallisation occurred at
between 100 and 200 MPa, corresponding to depths ranging from 3 to 8 km. The microlite composition and their close genetic relations with vesicles indicate that groundmass crystallisation occurred during the eruption as a consequence of magma degassing and vesiculation induced by decompression during its ascent toward the surface. Crystal size distributions reveal that microlites grew in two stages of undercooling that we define as: (1) magma migration onset upward from the chamber and (2) magma rising through the conduit to the surface, possibly lasting tens of days and few days, respectively. These results provide information on the physical conditions that characterise pre- and syn-eruptive processes, which may be useful in order to define eruptive scenarios and to evaluate short-term precursors. Furthermore, the collected data provide for the first time information on degassing-induced crystallisation during the eruption of a highly evolved alkaline magma.Editorial responsibility: M. Carroll 相似文献
5.
Francesca?ForniEmail author Eleonora?Petricca Olivier?Bachmann Silvio?Mollo Gianfilippo?De Astis Monica?Piochi 《Contributions to Mineralogy and Petrology》2018,173(6):45
Understanding the mechanisms responsible for the generation of chemical gradients in high-volume ignimbrites is key to retrieve information on the processes that control the maturation and eruption of large silicic magmatic reservoirs. Over the last 60 ky, two large ignimbrites showing remarkable zoning were emplaced during caldera-forming eruptions at Campi Flegrei (i.e., Campanian Ignimbrite, CI, ~?39 ka and Neapolitan Yellow Tuff, NYT, ~?15 ka). While the CI displays linear compositional, thermal and crystallinity gradients, the NYT is a more complex ignimbrite characterized by crystal-poor magmas ranging in composition from trachy-andesites to phonolites. By combining major and trace element compositions of matrix glasses and mineral phases from juvenile clasts located at different stratigraphic heights along the NYT pyroclastic sequence, we interpret such compositional gradients as the result of mixing/mingling between three different magmas: (1) a resident evolved magma showing geochemical characteristics of a melt extracted from a cumulate mush dominated by clinopyroxene, plagioclase and oxides with minor sanidine and biotite; (2) a hotter and more mafic magma from recharge providing high-An plagioclase and high-Mg clinopyroxene crystals and (3) a compositionally intermediate magma derived from remelting of low temperature mineral phases (i.e., sanidine and biotite) within the cumulate crystal mush. We suggest that the presence of a refractory crystal mush, as documented by the occurrence of abundant crystal clots containing clinopyroxene, plagioclase and oxides, is the main reason for the lack of erupted crystal-rich material in the NYT. A comparison between the NYT and the CI, characterized by both crystal-poor extracted melts and crystal-rich magmas representing remobilized portions of a “mature” (i.e., sanidine dominated) cumulate residue, allows evaluation of the capability of crystal mushes of becoming eruptible upon recharge. 相似文献
6.
M. Piochi C. R. J. Kilburn M. A. Di Vito A. Mormone A. Tramelli C. Troise G. De Natale 《International Journal of Earth Sciences》2014,103(2):401-421
The Campi Flegrei caldera in southern Italy is one of the greatest geohazard areas on Earth. Evidence of an active magmatic and geothermal system is provided by ongoing ground uplift, with volcano-tectonic and long-period (LP) seismicity, the persistent degassing of ~1500 tonnes of CO2 per day, the presence of hot fumaroles at temperatures of 90–150 °C, brine-rich aquifers (with total dissolved solids up to 33 g l?1) and high thermal gradients in the crust (with temperatures reaching 420 °C at 3,050 m b.s.l.). Since the 1940s, more than 100 exploratory boreholes have been drilled in the area to depths of 80–3,100 m by the Azienda Geologica Italiana Petroli (AGIP) and the Società Anonima Forze Endogene Napoletane (SAFEN). To date, however, no systematic reanalysis of the drilling data has been carried out, and the buried volcanic structure has not been updated using the most recent scientific results and previous findings. By integrating unpublished data from the AGIP and SAFEN reports with published information from geological, volcanological, petrological, petrophysical and geophysical studies, this paper presents an improved picture of the Campi Flegrei caldera that will be useful for volcanic hazard assessment and mitigation in the Naples area and for future research planning. The results suggest that intra-caldera activity has been influenced by how the magmatic system at depths greater than about 4 km has determined the transfer of magma, volatiles, and heat to the overlying geothermal system and, ultimately, to the surface. In particular, intriguing is that the most volcanically active central-eastern sector of the caldera, which is subject to intense bradyseismic ground movement and gas emission, coincides with a structurally delimited subsurface rock volume characterized by an uprising of the 100 °C isotherm, a deep water supply to the shallower aquifer, the early disappearance of secondary calcite, LP seismicity and high seismic S-wave attenuation. In this area, we also document evidence of repeated injection at depths of c. 1.5–3.0 km of isolated and small-volume batches of magma, where occurred their crystallization and degassing. Shallow intrusions and degassing of magma are thus identified as two of the key processes that drive unrest in Campi Flegrei. 相似文献
7.
Mormone Angela Ghiara Maria Rosaria Balassone Giuseppina Piochi Monica Lonis Roberto Rossi Manuela 《Mineralogy and Petrology》2018,112(6):767-788
Mineralogy and Petrology - The island of Sardinia (Italy) presents some of the most interesting zeolite ores in Europe, most of which are associated with old pyroclastic deposits. In particular,... 相似文献
8.
9.
New major and trace element analyses and Sr-isotope determinations of rocks from Mt. Somma–Vesuvius volcano produced from 25 ky BP to 1944 AD are part of an extensive database documenting the geochemical evolution of this classic region. Volcanic rocks include silica undersaturated, potassic and ultrapotassic lavas and tephras characterized by variable mineralogy and different crystal abundance, as well as by wide ranges of trace element contents and a wide span of initial Sr-isotopic compositions. Both the degree of undersaturation in silica and the crystal content increase through time, being higher in rocks produced after the eruption at 472 AD (Pollena eruption). Compositional variations have been generally thought to reflect contributions from diverse types of mantle and crust. Magma mixing is commonly invoked as a fundamental process affecting the magmas, in addition to crystal fractionation. Our assessment of geochemical and Sr-isotopic data indicates that compositional variability also reflects the influence of crustal contamination during magma evolution during upward migration to shallow crustal levels and/or by entrapment of crystal mush generated during previous magma storage in the crust. Using a variant of the assimilation fractional crystallization model (Energy Conservation–Assimilation Fractional Crystallization; [Spera and Bohrson, 2001. Energy-constrained open-system magmatic processes I: General model and energy-constrained assimilation and fractional crystallization (EC–AFC) formulation. J. Petrol. 999–1018]; [Bohrson, W.A. and Spera, F.J., 2001. Energy-constrained open-system magmatic process II: application of energy-constrained assimilation–fractional crystallization (EC–AFC) model to magmatic systems. J. Petrol. 1019–1041]) we estimated the contributions from the crust and suggest that contamination by carbonate rocks that underlie the volcano (2 km down to 9–10 km) is a fundamental process controlling magma compositions at Mt. Somma–Vesuvius in the last 8 ky BP. Contamination in the mid- to upper crust occurred repeatedly, after the magma chamber waxed with influx of new mantle- and crustal-derived magmas and fluids, and waned as a result of magma withdrawal and production of large and energetic plinian and subplinian eruptions. 相似文献
1