MAGMA MIXING AND CONVECTIVE COMPOSITIONAL LAYERING WITHIN THE VESUVIUS MAGMA CHAMBER

被引:122
作者
CIVETTA, L
GALATI, R
SANTACROCE, R
机构
[1] Dipartimento di Geofisica e Vulcanologia, Università di Napoli, Napoli, I-80138
[2] Departimento di Scienze della Terra, Università di Pisa, I-56100
[3] Istituto Internazionale di Vulcanologia, CNR, Catania, I-95129
关键词
D O I
10.1007/BF00414525
中图分类号
P [天文学、地球科学];
学科分类号
07 ;
摘要
The pumice-fall deposits of the last two Plinian eruptions of Vesuvius - A.D. 79 "Pompei" and 3700 B.P. "Avellino" - show a marked vertical compositional variation from white phonolite at the base to grey tephritic phonolite at the top. In both Avellino and Pompei sequences a compositional gap separates white from grey pumice. Grey and white pumice have distinct Sr and Nd isotopic compositions (grey pumice: Sr-87/ Sr-86 = 0.70749-56, Nd-143/Nd-144 = 0.512507 for Pompei; 0.70760-69, 0.512504 for Avellino; white pumice: 0.70757-78 for Pompei; 0.70729-42 for Avellino). K-feldspar separated from both grey and white pumice has, in all cases, a "white" Sr-87/Sr-86 ratio (0.70766-79 for Pompei, 0.70728-33 for Avellino). The observed variations are interpreted as reflecting a pre-eruptive zonation of the magma chamber. Although mineralogical evidence of interaction between magma and calcareous country rocks exists in both eruptions, crustal contamination has not significantly modified the isotopic signatures of the erupted products. Petrographic and isotopic evidence of syneruptive magma mingling occur in Pompei grey pumice as well as in Avellino white and grey pumice, but they do not fully explain all the observed geochemical and isotopic variations. These variations are related to the complex refilling history of the magmatic system and result by fractional crystallization and mixing processes acting within the magma chamber. Preliminary data from other Plinian and subplinian eruptions of the Somma-Vesuvius point out the repetitive behaviour of Sr-87/Sr-86 variation in the last 25 000 years, hence suggesting a single magma chamber and continuity of the feeding system.
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页码:287 / 300
页数:14
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共 35 条
  • [1] Arno V., Principe C., Rosi M., Santacroce R., Sbrana A., Sheridan M.F., Eruptive history, Somma-Vesuvius, pp. 53-103, (1987)
  • [2] Bacon C.R., Druitt T.H., Compositional evolution of the zoned calcalkaline magma chamber of Mount Mazama, Crater Lake, Oregon, Contrib Mineral Petrol, 98, pp. 224-256, (1988)
  • [3] Barberi F., Innocenti F., Lirer L., Munno R., Pescatore T., Santacroce R., The Campanian Ignimbrite: a major prehistoric eruption in the Neapolitan area (Italy), Bull Volcanol, 41, pp. 1-22, (1978)
  • [4] Barberi F., Bizouard H., Clocchiatti R., Metrich N., Santacroce R., Sbrana A., The Somma-Vesuvius magma chamber: a petrological and volcanological approach, Bull Volcanol, 44, pp. 295-315, (1981)
  • [5] Barberi F., Leoni L., Metamorphic carbonate ejecta from Vesuvius Plinian eruptions: evidence of the occurrence of shallow magma chamber, Bulletin Volcanologique, 43, pp. 107-120, (1980)
  • [6] Barberi F., Cioni R., Rosi M., Santacroce R., Sbrana A., Vecci R., Magmatic and phreatomagmatic phases in explosive eruptions of Vesuvius as deduced by grain-size and compositional analysis of pyroclastic deposits, J Volcanol Geothermal Res, 38, pp. 287-307, (1989)
  • [7] Belkin H.E., De Vivo B., Roedder E., Cortini M., Fluid inclusion geobarometry from ejected Mt. Somma-Vesuvius nodules, Amer Mineral, 70, pp. 288-303, (1985)
  • [8] Carey S., Sigurdsson H., Temporal variations in column heigh and magma discharge rate during the 79 a.d. eruption of Vesuvius, Geol Soc Am Bull, 99, pp. 303-314, (1987)
  • [9] Cortini M., Hermes O.D., Sr isotopic evidence for a multi source origin of the potassic magmas in the Neapolitan area, Contrib Mineral Petrol, 77, pp. 47-55, (1981)
  • [10] Delibrias G., Di Paolo G.M., Rosi M., Santacroce R., La storia vulcanica del complesso vulcanico ricostruita dalle succressioni piroclastiche del Monte Somma, Rend Soc It Mineral Petrol, 35, pp. 411-438, (1979)