Publikationsdatum:
2021-02-10
Beschreibung:
The 2007 caldera-forming eruption of Piton de la Fournaise (PdF)
erupted the largest volume of magma (210 Mm3)recorded at this volcano in at least three centuries. Major and trace element and Sr^Nd isotope data for bulk-rocks, groundmasses and olivine phenocrysts
have been combined with melt inclusion data (major, trace and volatile elements) to track magma evolution over the whole eruptive sequence. We show that each eruptive phase had a distinctive
geochemical and petrological signature and that caldera collapse on
5 April was preceded by a marked shift in bulk magma composition
and crystal content and size. Aphyric basalt erupted at the beginning
of the sequence (February 2007) had relatively high Sr isotope ratio
(87Sr/86Sr ¼ 0·70420^0·704180) and low Nd isotopic ratio(143Nd/144Nd ¼ 0·51285^0·51286). Olivine-basalts extruded on2^5 April just before caldera collapse are less enriched in radiogenic
Sr (87Sr/86Sr ¼ 0·70412^0·70416), but characterized by the same
Nd isotopic composition. This magma is interpreted as a new deep
input, which pressurized the shallow PdF plumbing system and
triggered the 2007 activity. Post-collapse oceanite lavas represent the
main volume of magma extruded in 2007. Their bulk-rocks and
groundmasses have 87Sr/86Sr (0·70418) intermediate between
those of February and 5 April, and similar to those of the March
2007 and 2001^2006 lavas.We show that the Steady State Basalts
(SSB) commonly erupted at PdF are hybrid melts, which result from multistep mixing between ‘alkaline’and ‘transitional’end-members. Our results lead us to propose a new model of the PdF plumbing
system to reconcile the petrological, geochemical and geophysical observations: (1) the shallow portion (above sea level) of the PdF plumbing system hosts several small sills, in which magma experiences variable degrees of degassing, cooling and crystallization; (2) oceanite lavas result from the withdrawal of shallow harrisitic
mushes stored at low pressures (548 MPa; 51800^2400 m depth) below both the volcano summit and its eastern flank; (3) water degassing plays a major role in fast magma crystallization at shallow
depths. Multistep ascent and periodic extrusion of the shallow magmas is promoted by injections of deeper and hotter basaltic magma, containing up to 1·3 wt % H2O and 1630 ppm S. In 2007, the new deep input was the ultimate source of the large excess in sulfur degassing detected by satellites. Lateral draining and intrusion
of magma below the eastern flank of the volcano are the cause of major volcano deformation, flank sliding and summit caldera collapse.
Beschreibung:
Published
Beschreibung:
1287-1315
Beschreibung:
2V. Struttura e sistema di alimentazione dei vulcani
Beschreibung:
3V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanici
Beschreibung:
4V. Processi pre-eruttivi
Beschreibung:
6A. Geochimica per l'ambiente e geologia medica
Beschreibung:
JCR Journal
Schlagwort(e):
Piton de la Fournaise
;
plumbing system
;
magma reservoir
;
caldera collapse
;
melt inclusions
;
volatile budget
;
isotope geochemistry
;
basalt
Repository-Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Materialart:
article
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