Fluid-saturated subsolidus experiments from 2.0 to 6.5 GPa, and from 680 to 800degreesC have been performed on three model peridotites in the system Na2O-CaO-FeO-MgO-Al2O3-SiO2-H2O (NCFMASH). Amphibole and chlorite coexist up to 2.4 GPa, 700degreesC. Chlorite persists to 4.2 GPa at 680degreesC. Starting from 4.8 GPa, 680degreesC a 10 Angstrom phase structure replaces chlorite in all compositions. The 10 Angstrom phase structure contains significant Al2O3 (up to 10.53 wt %) deviating from the MgO-SiO2-H2O 10 Angstrom phase (MSH 10 Angstrom phase). A mixed layered structure (chlorite-MSH 10 Angstrom phase) is proposed to account for aluminium observed. In the Tinaquillo lherzolite amphibole breakdown occurs via the reaction amphibole + olivine +/- H2O = clinopyroxene + orthopyroxene + chlorite. Thermal stability of chlorite (chlorite + orthopyroxene = forsterite + garnet + H2O) is shifted towards lower temperatures, compared with the system MASH. Furthermore, the chlorite thermal breakdown is also related to the degenerate reaction chlorite + clinopyroxene = olivine + garnet(+/- orthopyroxene) + H2O. Chlorite and the Al-10 Angstrom phase structure contribute significantly to the water budget in subduction zones in the depth range relevant for arc magmatism, whereas amphibole-related fluid release is restricted to the forearc region. Chlorite and Al-10 Angstrom phase breakdowns might explain the occurrence of a double seismic zone by dehydration embrittlement.

Experimentally determined phase relations in hydrous peridotites to 6.5 GPa and their consequences on the dynamics of subduction zones / P. Fumagalli, S. Poli. - In: JOURNAL OF PETROLOGY. - ISSN 0022-3530. - 46:3(2005), pp. 555-578.

Experimentally determined phase relations in hydrous peridotites to 6.5 GPa and their consequences on the dynamics of subduction zones

P. Fumagalli
Primo
;
S. Poli
Ultimo
2005

Abstract

Fluid-saturated subsolidus experiments from 2.0 to 6.5 GPa, and from 680 to 800degreesC have been performed on three model peridotites in the system Na2O-CaO-FeO-MgO-Al2O3-SiO2-H2O (NCFMASH). Amphibole and chlorite coexist up to 2.4 GPa, 700degreesC. Chlorite persists to 4.2 GPa at 680degreesC. Starting from 4.8 GPa, 680degreesC a 10 Angstrom phase structure replaces chlorite in all compositions. The 10 Angstrom phase structure contains significant Al2O3 (up to 10.53 wt %) deviating from the MgO-SiO2-H2O 10 Angstrom phase (MSH 10 Angstrom phase). A mixed layered structure (chlorite-MSH 10 Angstrom phase) is proposed to account for aluminium observed. In the Tinaquillo lherzolite amphibole breakdown occurs via the reaction amphibole + olivine +/- H2O = clinopyroxene + orthopyroxene + chlorite. Thermal stability of chlorite (chlorite + orthopyroxene = forsterite + garnet + H2O) is shifted towards lower temperatures, compared with the system MASH. Furthermore, the chlorite thermal breakdown is also related to the degenerate reaction chlorite + clinopyroxene = olivine + garnet(+/- orthopyroxene) + H2O. Chlorite and the Al-10 Angstrom phase structure contribute significantly to the water budget in subduction zones in the depth range relevant for arc magmatism, whereas amphibole-related fluid release is restricted to the forearc region. Chlorite and Al-10 Angstrom phase breakdowns might explain the occurrence of a double seismic zone by dehydration embrittlement.
English
Amphibole; Chlorite; High pressure; Peridotites; Subduction zones
Settore GEO/07 - Petrologia e Petrografia
Articolo
Sì, ma tipo non specificato
2005
Clarendon Press
46
3
555
578
Periodico con rilevanza internazionale
ISI:000227133100005
info:eu-repo/semantics/article
Experimentally determined phase relations in hydrous peridotites to 6.5 GPa and their consequences on the dynamics of subduction zones / P. Fumagalli, S. Poli. - In: JOURNAL OF PETROLOGY. - ISSN 0022-3530. - 46:3(2005), pp. 555-578.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/5750
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