Volatile transport during the crystallization of anatectic melts: Oxygen, boron and hydrogen stable isotope study on the metamorphic complex of Naxos, Greece

Détails

ID Serval
serval:BIB_6A95BA567D57
Type
Article: article d'un périodique ou d'un magazine.
Collection
Publications
Institution
Titre
Volatile transport during the crystallization of anatectic melts: Oxygen, boron and hydrogen stable isotope study on the metamorphic complex of Naxos, Greece
Périodique
Geochimica et Cosmochimica Acta
Auteur⸱e⸱s
Matthews A., Putlitz B., Hamiel Y., Hervig R.L.
ISSN-L
0016-7037
Statut éditorial
Publié
Date de publication
2003
Peer-reviewed
Oui
Volume
67
Pages
3145-3163
Langue
anglais
Notes
ISI:000185111200005
Résumé
Crystallization of anatectic melts in high-temperature metamorphic
terrains releases volatile-rich magmas that can be transported into
adjacent lithologies. This study addresses the variations in the oxygen,
boron and hydrogen isotopic composition of aplite-pegmatite dikes that
formed during the crystallization of anatectic melts in regional
high-temperature metamorphism on the island of Naxos, Greece, and
propagated upward into the overlying sequences of metamorphic schist.
The transport distance of these dikes was increased through a
significant horizontal component of travel that was imposed by
contemporaneous low-angle extensional shearing. Laser fluorination
oxygen isotope analyses of quartz, tourmaline, garnet, and biotite
mineral separates from the aplite-pegmatite dikes show a progressive
rise in delta(18)O values with increasing distance from the core. Oxygen
isotope fractionations among quartz, tourmaline, and garnet show
temperature variations from > 700degreesC down to similar to400degreesC.
This range is considered to reflect isotopic fractionation beginning
with crystallization at high temperatures in water-undersaturated
conditions and then evolving through lower temperature crystallization
and retrograde sub-solidus exchange. Two processes are examined for the
cause of the progressive increase in delta(18)O values: (1)
heterogeneous delta(18)O sources and (2) fluid-rock exchange between the
aplite/pegmatite magmas and their host rock. Although the former process
cannot be ruled out, there is as yet no evidence in the exposed
sequences on Naxos for the presence of a suitable high delta(18)O magma
source. In contrast, a tendency for the delta(18)O of quartz in the
aplite/pegmatite dikes to approach that of the quartz in the metamorphic
rock suggests that fluid-rock exchange with the host rock may
potentially be an important process. Advection of fluid into the magma
is examined based on Darcian fluid flow into an initially
water-undersaturated buoyantly propagating aplitic dike magma. It is
shown that such advective flow could only account for part of the
O-18-enrichment, unless it were amplified by repeated injection of magma
pulses, fluid recycling, and deformation-assisted post-crystallization
exchange. The mechanism is, however, adequate to account for hydrogen
isotope equilibration between dike and host rock. In contrast,
variations in the delta(11)B values of tourmalines suggest that
B-11/B-10 fractionation during crystallization and/or magma degassing
was the major control of boron geochemistry rather than fluid-rock
interaction and that the boron isotopic system was decoupled from that
of oxygen. Copyright (C) 2003 Elsevier Ltd.
Création de la notice
24/09/2012 18:17
Dernière modification de la notice
20/08/2019 14:25
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