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Origin of the {sup 238}U-{sup 230}Th disequilibrium in magmas from subduction zones: the Arenal example; Origine du desequilibre {sup 238}U-{sup 230}TH dans les magmas des zones de subduction: exemple de l`Arenal

Abstract

The existence in some volcanic products of strong excess of {sup 238}U with respect to {sup 230}Th is one of the characteristics of volcanic arc magmas. These excesses are generally attributed to fluid additions inside mantellic sources before magma segregation, differentiation and eruption. These fluids should be linked to the dehydration of the subducted rocks. These hypotheses are essentially based on correlations between {sup 10}Be, {sup 87}Sr anomalies, Ba/La ratios and on the distribution of volcanic centers with respect to the subduction zone. Recent studies suggest an evolution of the composition of volcanic sources in Central America from a depleted mantle type (MORB) in the North (Nicaragua) to a less transformed enriched type (OIB) in the South (Costa Rica). The Arenal volcano belongs to a transition zone between these two types. The preliminary study of trace elements and {sup 238}U-{sup 230}Th disequilibria in recent volcanic products (1968-1993) indicates a more complex situation. At least two different mantle sources were successively involved characterized by different Th/La and La/Yb ratios and very different to the OIB type. Also most lavas are in equilibrium with {sup 238}U/{sup 232}Th ratios of about 1.2 to 1.3. However, in eruptive cycle, some lavas are characterized by  More>>
Authors:
Villemant, B [1] 
  1. Paris-6 Univ., 75 (France)
Publication Date:
Dec 31, 1996
Product Type:
Technical Report
Report Number:
SGF-BSV-39
Reference Number:
SCA: 540230; PA: AIX-29:010134; EDB-98:062388; SN: 98001937625
Resource Relation:
Other Information: DN: 2 refs.; PBD: 1996; Related Information: Is Part Of Volcanology Section Bulletin. French Geologic Society; Boudon, G. [I.P.G.P. - Observatoire Volcanologique, 75 - Paris (France)]; Gourgaud, A. [Universite Blaise Pascal, 63 - Clermont Ferrand (France)]; Soler, E. [Universite Paris 6, Paris (France)]; PB: 20 p.; Bulletin de la Section de Volcanologie. Societe Geologique de France
Subject:
54 ENVIRONMENTAL SCIENCES; COSTA RICA; EARTH MANTLE; GEOCHEMISTRY; ISOTOPE RATIO; LAVA; MAGMA; RARE EARTHS; ROCK-FLUID INTERACTIONS; THORIUM 230; THORIUM 232; URANIUM 238; VOLCANOES
OSTI ID:
607175
Research Organizations:
Institut de Physique du Globe de Paris (IPGP), 75 - Paris (France). Observatoire volcanologique
Country of Origin:
France
Language:
French
Other Identifying Numbers:
Other: ON: DE98611651; TRN: FR9703435010134
Availability:
INIS; OSTI as DE98611651
Submitting Site:
FRN
Size:
pp. 8
Announcement Date:
Jun 17, 1998

Citation Formats

Villemant, B. Origin of the {sup 238}U-{sup 230}Th disequilibrium in magmas from subduction zones: the Arenal example; Origine du desequilibre {sup 238}U-{sup 230}TH dans les magmas des zones de subduction: exemple de l`Arenal. France: N. p., 1996. Web.
Villemant, B. Origin of the {sup 238}U-{sup 230}Th disequilibrium in magmas from subduction zones: the Arenal example; Origine du desequilibre {sup 238}U-{sup 230}TH dans les magmas des zones de subduction: exemple de l`Arenal. France.
Villemant, B. 1996. "Origin of the {sup 238}U-{sup 230}Th disequilibrium in magmas from subduction zones: the Arenal example; Origine du desequilibre {sup 238}U-{sup 230}TH dans les magmas des zones de subduction: exemple de l`Arenal." France.
@misc{etde_607175,
title = {Origin of the {sup 238}U-{sup 230}Th disequilibrium in magmas from subduction zones: the Arenal example; Origine du desequilibre {sup 238}U-{sup 230}TH dans les magmas des zones de subduction: exemple de l`Arenal}
author = {Villemant, B}
abstractNote = {The existence in some volcanic products of strong excess of {sup 238}U with respect to {sup 230}Th is one of the characteristics of volcanic arc magmas. These excesses are generally attributed to fluid additions inside mantellic sources before magma segregation, differentiation and eruption. These fluids should be linked to the dehydration of the subducted rocks. These hypotheses are essentially based on correlations between {sup 10}Be, {sup 87}Sr anomalies, Ba/La ratios and on the distribution of volcanic centers with respect to the subduction zone. Recent studies suggest an evolution of the composition of volcanic sources in Central America from a depleted mantle type (MORB) in the North (Nicaragua) to a less transformed enriched type (OIB) in the South (Costa Rica). The Arenal volcano belongs to a transition zone between these two types. The preliminary study of trace elements and {sup 238}U-{sup 230}Th disequilibria in recent volcanic products (1968-1993) indicates a more complex situation. At least two different mantle sources were successively involved characterized by different Th/La and La/Yb ratios and very different to the OIB type. Also most lavas are in equilibrium with {sup 238}U/{sup 232}Th ratios of about 1.2 to 1.3. However, in eruptive cycle, some lavas are characterized by a strong {sup 238}U excess with respect to {sup 230}Th with cannot be linked to the sources, even when modified by fluids in depth. These results are interpreted in terms of heterogeneities of mantle sources and low depths late interactions with hydrothermal fluids during eruptions. Abstract only. (J.S.). 2 refs.}
place = {France}
year = {1996}
month = {Dec}
}