Publication Date:
2020-10-29
Description:
Turrialba volcano lies in the southern sector of the Central American Volcanic Front (CAVF) in Costa Rica. The
geochemistry of major and trace elements, and Sr and Nd isotopes of a selected suite of volcanic rocks ranging
in composition from basaltic andesite to dacite and belonging to the last 10 ka of activity of Turrialba volcano
is described, together with the He-, Ne-, and Ar-isotope compositions of fluid inclusions hosted in olivine and
pyroxene crystals. Most of the variability in the rock chemistry is consistentwith typical trends of fractional crystallization,
but there is an outlying group of andesites that displays an adakite-like composition (with a consistent
depletion in high-field-strength elements and a marked enrichment in Sr) and low 3He/4He ratios (7.0–7.2 Ra).
The trace-element composition of these rocks is typical of subduction-related magmas influenced by an OIB-like
component at the source associated with the subduction of the Galapagos seamounts. The 87Sr/86Sr
(0.703612–0.703678) and 143Nd/144Nd (0.512960–0.512984) ratios of the bulk rocks vary within narrowranges,
and are among the least-radiogenic isotope signatures of the CAVF volcanoes. The 3He/4He ratios measured in
fluid inclusions hosted in olivine crystals (up to 8.1 Ra) are among the highest for the CAVF, and indicate that radiogenic
4He from fluids derived fromthe subducting slab contribute negligibly to the mantle wedge. The difference
in He isotopes between most of studied rocks and those showing adakite-like features reasonably reflects
two distinct components in the local mantle: (1) a MORB-like component, characterized by the highest
He-isotope ratios (7.8–8.1 Ra), and (2) an OIB-like component, characterized by lower He-isotope ratios
(7.0–7.2 Ra), coming from the subduction of the Galapagos seamounts. An overview at the regional scale indicates
that high He-isotope ratios are peculiar to the two extreme sectors of the CAVF (Costa Rica to the south
and Guatemala to the north), whereas in the central sector (Nicaragua) the magma source is probably contaminated
by slab fluids.
For the past few years Turrialba volcano has been in a volcanic unrest phase that has included a series of explosions,
the most recent of which occurred between October 2014 and May 2015. The volcano is subject to an ongoing
safety alert due to the possibility of a magmatic eruption. One of the crucial questions to be addressed is the
kind of eruption that can be expected, and hence what type of magma is likely to be involved. The high 3He/4He
ratios (7.8–8.0 Ra) measured during 2011 at high-temperature fumaroles of Turrialba craters are comparable to
those measured in fluid inclusions of basaltic andesites that erupted in 1864–1866, suggesting that the magma
currently feeding the shallow plumbing system has similar geochemical characteristics to the most recently
erupted magma.
Description:
Published
Description:
319-335
Description:
1V. Storia e struttura dei sistemi vulcanici
Description:
2V. Dinamiche di unrest e scenari pre-eruttivi
Description:
JCR Journal
Description:
restricted
Keywords:
Turrialba
;
3He/4He ratio
;
Fluid inclusions
;
Adakite
;
MORB mantle
;
OIB mantle
;
04. Solid Earth::04.04. Geology::04.04.05. Mineralogy and petrology
;
04. Solid Earth::04.04. Geology::04.04.07. Rock geochemistry
;
04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry
;
04. Solid Earth::04.08. Volcanology::04.08.01. Gases
;
04. Solid Earth::04.08. Volcanology::04.08.05. Volcanic rocks
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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