High temperature – low pressure metamorphism during subduction of Neo-Tethys beneath the Iranian plate: evidence for mafic migmatite formation in the Alvand complex (western Iran)

Subduction of Neo-Tethys oceanic lithosphere beneath the Iranian plate during the Mesozoic formed several igneous bodies of ultramafic to intermediate and felsic composition. Intrusion of these magmas into a regional metamorphic sequence (the Sanandaj-Sirjan Zone) caused partial melting and formatio...

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Bibliographic Details
Published in:Mineralogy and petrology 2020-12, Vol.114 (6), p.539-557
Main Authors: Saki, Adel, Miri, Mirmohammad, Oberhänsli, Roland
Format: Article
Language:English
Subjects:
Asthenosphere
Biotite
Composition
Earth and Environmental Science
Earth Sciences
Gabbro
Geochemistry
Granite
High temperature
Inorganic Chemistry
Isotopes
Lava
Lithosphere
Low pressure
Magma
Melting
Mesozoic
Metamorphism
Mineralogy
Ocean circulation
Oceanic crust
Olivine
Original Paper
Paleoceanography
Phase diagrams
Plagioclase
Rocks
Solidus
Subduction
Temperature
Upwelling
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Summary:Subduction of Neo-Tethys oceanic lithosphere beneath the Iranian plate during the Mesozoic formed several igneous bodies of ultramafic to intermediate and felsic composition. Intrusion of these magmas into a regional metamorphic sequence (the Sanandaj-Sirjan Zone) caused partial melting and formation of migmatites with meta-pelitic protoliths. The Alvand complex (west Iran) is a unique area comprising migmatites of both mafic and pelitic protoliths. In this area, the gabbroic rocks contain veins of leucosome at their contact with pyroxenite and olivine gabbro. These leucosomes are geochemically and mineralogically different from leucosomes of the meta-pelitic migmatites and clearly show properties of I-type granites. Microscopic observations and whole rock compositions of the mafic migmatite leucosomes show that migmatization occurred through partial melting of biotite, hornblende and plagioclase. Thermobarometric calculations indicate 800 °C and 3.7 kbar for partial melting, although phase diagram modeling demonstrates that the presence of water could decrease the solidus temperature by about 40 °C. Our results suggest an asthenospheric magma upwelling as the source of heat for partial melting of the gabbroic rock during subduction of Neo-Tethys oceanic crust under the western edge of the Iranian plate. The present study also reveals relationships between migmatization and formation of S- and I -type granites in the area.
ISSN:0930-0708
1438-1168
DOI:10.1007/s00710-020-00721-z