Publication Date:
2019-03-26
Description:
We present and discuss temperatures, major and trace element gas geochemistry, radiogenic isotopes (Pb, Sr)
and the first Zn isotope data of fumarole condensates and altered rocks from the Vulcano fumarolic field. The
fumaroles of the La Fossa cone, sampled on 5th May 2015, have temperatures ranging between 233 and 427 °C.
They plot compositionally on the mixing trend between the magmatic and hydrothermal end-members defined
by previous studies, but are strongly displaced towards the hydrothermal component. Correlations of radiogenic
(Sr, Pb) and stable isotopes of Zn with δ13CCO2 and several trace elements of the fumarolic acid condensates
support mixing between the above mentioned distinct (magmatic and hydrothermal) fluids. The magmatic endmember
has a less radiogenic Sr (87Sr/86Sr ~0.7045) and heavier Zn isotope composition (δ66Zn ~0.3‰). The
hydrothermal fluid end-member has a more radiogenic 87Sr/86Sr signature (〉 0.7055), which could be due to
leaching of radiogenic Sr from the crystalline basement rocks or reflect seawater Sr. It is also characterized by
lighter Zn isotope composition (δ66Zn 〈 −0.3), most likely reflecting equilibrium fractionation of Zn isotopes
during precipitation of sphalerite (ZnS) from the hydrothermal fluid. Nonetheless, some scatter in the correlation
trends suggests either the involvement of additional (subordinate) source(s) or temporal variations in isotopic
and chemical compositions of the two above end-members.
Pb isotope compositions of the fumaroles sampled in this study show a shift towards less radiogenic values
compared to pre-2001 fumaroles. This could indicate either a change in the hydrothermal circulation pattern
(leading to leaching of rocks with different isotopic compositions) or the involvement of a new, isotopically
distinct, magmatic fluid.
The alteration zones around the fumarole vents are also characterized by systematic correlations of Pb and Zn
isotopes with major and trace elements. We interpret these as the result of the addition onto the substratum
volcanic rock of Pb and Zn from the fumaroles. Zn isotope signatures of the alteration zones are significantly
heavier than those of the corresponding fumaroles (δ66Zn=0.3–1.6) probably due to equilibrium fractionation
occurring during sphalerite precipitation at the vent discharge
Description:
Published
Description:
153-171
Description:
4V. Processi pre-eruttivi
Description:
JCR Journal
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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