Preserved near ultrahigh-pressure melt from continental crust subducted to mantle depths

Remnants of hydrous melt formed at mantle depths have been identified and characterized within high-pressure leucogranulites of the Orlica-Snieznik Dome (Bohemian Massif, central Europe). They occur as nanogranites in garnet formed via partial melting of granitoids during the Variscan orogeny. Melt...

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Bibliographic Details
Published in:Geology (Boulder) 2015-05, Vol.43 (5), p.447-450
Main Authors: Ferrero, Silvio, Wunder, Bernd, Walczak, Katarzyna, O'Brien, Patrick J, Ziemann, Martin A
Format: Article
Language:English
Subjects:
Bohemian Massif
Central Europe
continental crust
crust
Europe
Evolution
experimental studies
Geology
granites
granulites
homogenization
igneous and metamorphic rocks
igneous rocks
laboratory studies
leucogranulite
mantle
Melting
metamorphic rocks
nanogranites
Orlica-Snieznik Dome
P-T conditions
partial melting
Petrology
plate tectonics
plutonic rocks
Pressure
Rheology
Rocks
Snieznik
subduction
ultrahigh pressure
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Summary:Remnants of hydrous melt formed at mantle depths have been identified and characterized within high-pressure leucogranulites of the Orlica-Snieznik Dome (Bohemian Massif, central Europe). They occur as nanogranites in garnet formed via partial melting of granitoids during the Variscan orogeny. Melt composition and H2O content have been investigated in situ after experimental re-homogenization of the nanogranites, and are consistent with melts produced experimentally from crustal lithologies at mantle depths. This is the first geochemical study of melt inclusions from natural crustal rocks equilibrated close to the stability field of coesite, shedding light on how continental crust melts during deep subduction. Whereas decompressional melting is commonly invoked for deeply subducted crustal lithologies, melting occurred near or at the metamorphic peak pressure in the Orlica-Snieznik granulites. Melting of deeply subducted crustal rocks significantly modifies the rheology and thus promotes fast exhumation: this process has a critical influence on the geodynamic evolution of subduction-collision orogens as well as crustal differentiation at depth.
ISSN:0091-7613
1943-2682
DOI:10.1130/G36534.1