Historic activity of mt. Vesuvius: major elements and volatile constituents of primary melts
Abstract
Mt. Vesuvius experienced a three-century long period of semi-persistent activity, after the 1631 eruption and is presently in a phase of rest. During this period, several eruptions displayed composite style since they started with lava effusions and evolved towards explosive activity (lava fountains, phreatomagmatic explosions and occasionally steady columns). The tephrostratigraphic sequence of post-1631 activity is well reconstructed [1] on the basis of historical chronicles and field investigations, whereas information about the feeding system is still weak. We have selected samples related to energetic lava fountain activity that occurred during the 1794, 1822 and 1872 composite-style eruptions for investigating the deep feeding systems of Mt. Vesuvius, during the 1631--1944 period. We present data on melt inclusions and their host olivines. Major elements, S, Cl and F were obtained using the electron microprobe (SX50, Camparis), CO_2 and H_2O by Fourier Transform InfraRed spectroscopy. Carbon was also analysed by nuclear reaction 12C(d,p)13C. The magma batches emitted during the 1794, 1822 and 1872 eruptions brought to the surface primitive olivines (Fo90.4-88.5) containing spinel (Cr/(Cr+Al) = 0.77--0.75). Their inclusions attest of crystallization at high pressure from K-rich (HK) parental magmas with K_2O varying from 4.3 to 6.0, high K_2O/H_2O (up to 2.4), Cl/H_2O (up to 0.25), Cl/F (up to 3) ratios, and H_2O content systematically high and variable from 2.3 to 4.9 wt.%. The most primitive compositions are recorded in melt inclusions from the oldest samples (1794 and 1822 eruptions). We propose a rather rapid transfer of HK-melts carrying olivine crystals from depth. This process is only detectable by the means of melt inclusions in Fo-rich olivines phenocrysts occurring only in the deposits related to the most powerful episodes of lava fountains while the whole rocks are cumulative with respect to clinopyroxene (± leucite). These new data, in addition to those from the 1944 and 1906 samples [2], demonstrate that deep-seated magma batches are systematically involved in most energetic phases of the recent eruptions of Mt Vesuvius. The calculated total fluid pressures fit with the crustal structures deduced from the seismic records [3]. However, our model does not match with a widely laterally extended magmatic sill. References [1] Arrighi et al., 2001; [2] Marianelli et al., 1999, Bull. Volcanol. 61, 48-63; [3] Auger et al., 2001, Science, 294, 1510-1512
- Publication:
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EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....8410C