Publication Date:
2020-06-17
Description:
Petrological and geochemical (major element, trace element, Sr–Nd isotope) data for recent (〈5 kyr
old) basalts that sporadically erupt on the western flank of Piton de la Fournaise (PdF), one of the
most active volcanoes on Earth, allow the tracking of magma transfer and evolution from mantle to
crustal depths. In the western peripheral area of PdF we document the broadly synchronous eruptions
of (1) primitive olivine and olivine–clinopyroxene transitional basalts with tholeiitic affinity
30 that are closely associated in space with (2) transitional olivine basalts with alkaline affinity, and (3)
hybrid lavas, intermediate between the ‘alkaline’ and the ‘tholeiitic’ end-members. The composition
of the latter overlaps with that of the lavas frequently erupted from the conduit system feeding
the main summit cone. AlphaMELTS modelling, and fluid inclusion and clinopyroxene barometry,
constrain the conditions of magma storage at 10–30 km, and the ascent of magma from the upper
35 mantle to the shallow crustal plumbing system. Variable degrees of mantle melting, together with
minor source heterogeneity and contamination with cumulate-derived partial melts, contribute to
the diversity of PdF magmas. However, all these processes do not represent the dominant factors
that produce the large variability we found in major element composition. Indeed, the composition
of basalts erupted from PdF peripheral centers is strongly controlled by polybaric olivine–clinopyr-
40 oxene fractionation at pressures higher than 3 kbar. Crystal textures and geochemical modelling
suggest that fast magma ascent is critical to prevent clinopyroxene dissolution. Conversely, longlasting
magma stagnation promotes pyroxene resorption and magma differentiation. ‘Central’
eruptions occurring close to the PdF summit cone emit variably more evolved melts, which result
from olivine–clinopyroxene–plagioclase differentiation at intermediate–shallow pressure (〈3 kbar
and in most cases 〈1 kbar). Deep and extensive magma mixing before injection into the crustal
magma conduit system, located below the summit region, results in the apparent homogeneity of
basalts erupted from the central area. As regards ‘peripheral’ eruptions, deep-seated stagnation of
basaltic melts and differentiation at the mantle–crust transition zone (c. 4 kbar) produces a range of
5 magma compositions. We demonstrate that rapid magma ascent from deep-seated reservoirs can
bypass the central plumbing system. The eruptions of these magmas both in the central area and
on the densely populated flanks have major consequences in terms of volcanic hazard at PdF.
Description:
Published
Description:
1717–1752
Description:
2V. Struttura e sistema di alimentazione dei vulcani
Description:
JCR Journal
Keywords:
transitional basalts
;
clinopyroxene crystallization and resorption
;
mantle–crust underplating
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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