Persistent polybaric rests of calc-alkaline magmas at Stromboli volcano, Italy: pressure data from fluid inclusions in restitic quartzite nodules. (Articolo in rivista)

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  • Persistent polybaric rests of calc-alkaline magmas at Stromboli volcano, Italy: pressure data from fluid inclusions in restitic quartzite nodules. (Articolo in rivista) (literal)
Anno
  • 2003-01-01T00:00:00+01:00 (literal)
Alternative label
  • VAGGELLI G.1, FRANCALANCI L.1-2, RUGGIERI G.3, TESTI S.2 (2003)
    Persistent polybaric rests of calc-alkaline magmas at Stromboli volcano, Italy: pressure data from fluid inclusions in restitic quartzite nodules.
    in Bulletin of volcanology (Print)
    (literal)
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  • VAGGELLI G.1, FRANCALANCI L.1-2, RUGGIERI G.3, TESTI S.2 (literal)
Pagina inizio
  • 385 (literal)
Pagina fine
  • 404 (literal)
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  • This paper is devoted to researchers working in the field of volcanic hazard and provides an interesting contribution to the understanding of magmatic progesses. The densities and relative pressure/depth data suggest that the reequilibration process occurred at pressure between 3.5 and 2 kbar. The highest pressure value probably indicate the minimum depth of provenance (about 9-10km) of quartz nodules. This reequilibration process occurring in a wide pressure range suggest that the calcalkaline magma with the included nodules either stood shortly in a thick magma reservoir or crossed slowly a wide conduit. A second magma rest is supposed to occurr at pressure lower than 1-1.5 kbar. No pressure/depth differences seem to occur between Strombolicchio and Paleostromboli II periods indicating the same plumbing system for the calcalkaline magmas of Stromboli. (literal)
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  • 65 (literal)
Rivista
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  • Impact factor 1,484 (literal)
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  • A fluid inclusions study has been performed on quartz nodules hosted by calc-alkaline lavas of both Strombolicchio (200 ky) and Paleostromboli II (60 ky) period. The quartz grains contain four types of fluid inclusions distinguished on the basis both of fluid type and textural/phase relationships at room temperature. Microthermometric experiments were performed on both Type I and II CO2 inclusions. A pure CO2 system is supposed for both types. The microthermometric data may be summarized as follow: - Type I CO2 inclusions homogenise to liquid or as critical conditions between 21.0 °C and 31 °C. - The ThL histogram shows a continuum distribution with a distinct peak at about ThL=29-30 °C. - Type II inclusions homogenise to vapour. - The ThV histogram for secondary Type II inclusions show a continuum distribution from 13.5 to 30.5 °C with a maximum peak of frequency at 28-29 °C. - No difference of Th distribution seem to occur between Strombolicchio and Paleostromboli II samples. The results obtained on Stromboli confirm and better constrain the hypothesis, based on chemical and petrological data, of the existence of two magma chambers at different depths within the crust.Recognition of the polybaric evolution of the Stromboli magmas also represents an important contribution to our understanding of the magma evolution and emplacement system. (literal)
Note
  • ISI Web of Science (WOS) (literal)
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  • 1) C.N.R. – Istituto di Geoscienze e Georisorse, Sezione di Firenze, Via La Pira, 4, I-50121, Firenze, Italy; 2) Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Via La Pira, 4, I-50121, Firenze, Italy; 3) C.N.R., Istituto di Geoscienze e Georisorse, Via Moruzzi, 1, I-56124, Pisa, Italy. (literal)
Titolo
  • Persistent polybaric rests of calc-alkaline magmas at Stromboli volcano, Italy: pressure data from fluid inclusions in restitic quartzite nodules. (literal)
Abstract
  • A fluid inclusion study has been performed on quartzite nodules hosted by calc-alkaline lavas of both the Strombolicchio (200 ka) and Paleostromboli II (60 ka) periods. The nodules are mainly composed of quartz crystals with subordinate plagioclase and K-feldspar. Small interstitial minerals such as plagioclase, K-feldspar, clinopyroxene, biotite, and quartz are also found, together with glass. Muscovite, epidote and zircon occur as accessory minerals. Different quartzite nodules occur: (1) equigranular polygonal granoblastic quartzite nodules forming a polygonal texture with clear triple points; (2) inequigranular polygonal granoblastic quartzite nodules; (3) breakup nodules with strongly resorbed quartz. These quartzites are restites from partial melting, involving felsic crustal rocks at the magma/wall rock contact. Restitic quartz re-crystallises at variable and generally high temperatures, leading to the formation of quartzites with different textures. Quartz grains contain five types of fluid inclusions distinguished on the basis of both fluid type and textural/phase relationships at room temperature. Type I are two-phase (liquid+vapour) CO2-rich fluid inclusions. They are primary and subordinately pseudosecondary in origin and have undergone re-equilibration processes. Type II mono-phase/two-phase (vapour/liquid+vapour) CO2–rich fluid inclusions are the most common, and, based on their spatial distribution and shape, they can be divided into two sub-classes: Type IIa and Type IIb. Type II inclusions are secondary or pseudosecondary and they are assumed to have formed after decrepitation of Type I inclusions and cracking of the host quartz. Type III inclusions are mono-phase (vapour), they possibly contain CO2 at very low density and surround the inner rims of quartz grains. Type IV two-phase silicate-melt inclusions contain glass ± CO2–rich fluid. Some of them are cogenetic with Type II inclusions. Finally, Type V aqueous two-phase (liquid+vapour) fluid inclusions are both vapour-rich and liquid-rich aqueous inclusions. Microthermometric experiments were performed on both Type I and II inclusions. Type I inclusions homogenise to liquid between 20 °C and 30.5 °C. Type IIa inclusions homogenise to vapour in the 24 to 30 °C range, with a maximum peak of frequency at 29 °C. Type IIb inclusions also homogenise to vapour between 14 °C and 25 °C. There appears to be no difference in homogenisation temperature distribution between the Strombolicchio and Paleostromboli II samples. The trapping pressures of the fluid inclusions have been obtained by combining the microthermometric data of the Strombolicchio and Paleostromboli II samples with the pressure-temperature-volume (i.e. density) characteristics for a pure CO2 system. The data on the early inclusions (Type I) suggest an important magma rest at a pressure of about 290 MPa (i.e. about 11 km depth). Type IIa CO2 inclusions suggest that a second magma rest occurred at a pressure of about 100 MPa (i.e. about 3.5 km depth), while Type IIb inclusions were trapped later at a shallower depth during the final magma upwelling. No pressure/depth differences seem to occur between the Strombolicchio and Paleostromboli II periods, indicating the same polybaric rests for the calc-alkaline magmas of Stromboli, despite their significantly different ages. This persistence in magma stagnation conditions from 200 ka to 60 ka suggests a similar plumbing system for the present-day Strombolian activity. (literal)
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