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| Titel |
Four flavours of orogenic plateau magmatism: what's melting beneath the Turkish-Iranian Plateau? |
| VerfasserIn |
Iain Neill, Mark Allen, Monireh Kheirkhah, Khachatur Meliksetian, Lars Kaislaniemi, Jeroen van Hunen |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250092074
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| Publikation (Nr.) |
 EGU/EGU2014-6400.pdf |
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| Zusammenfassung |
| Orogenic plateaux are first order topographic features of the continents, occurring in collision
zones such as Tibet and Andean-style continental arcs. Plateaux are sites of abundant
mantle-derived magmatism, but there is little understanding of its geodynamic cause in spite
of widespread assumptions that slab break-off or lithospheric thinning are controlling
factors.
Late Cenozoic magmatism is distributed 100s of km from the Arabia-Eurasia suture zone
across the modern Turkish-Iranian Plateau (TIP) in the countries of Armenia, Iran, Turkey
and adjacent areas. There is huge compositional variation. Here we document four varieties
of recent TIP magmas and argue their occurrence is controlled by: geographic location,
prior fertilisation of the lithospheric mantle, lithospheric thickness, temperature and
stability, and asthenospheric convection. (1) Close to the original Arabia-Eurasia
suture in Eastern Turkey, slab break-off is likely to have occurred at ~10 Myr, and
the lithosphere is presently thin (45-50 km) with little or no mantle lithosphere
present. Magmatism is mostly calk-alkaline, sourced from the asthenosphere or any
remaining mantle lithosphere, and is affected by crustal contamination. (2) In the
Lesser Caucasus up to ~500 km from the suture, magmatism is more alkaline, less
contaminated and is derived from subduction-modified lithospheric mantle. (3) Close
to the suture in Iran, the lithosphere has thickened to >200 km during collision.
Magmatism is volumetrically limited and derived almost exclusively from the lithospheric
mantle, with highly enriched alkaline or ultrapotassic compositions. Unlike the Lesser
Caucasus, there is little or no magmatism in the Iranian desert up to 500 km from the
suture. (4) Beyond ~500 km from the suture zone, magmatism is sparse and varies
in composition: dominantly OIB-like in Eastern Iran, alkaline but arc-like in the
Alborz, and more felsic above the relatively thick (~55 km) crust of the Greater
Caucasus.
Magmatism in (1) is plausibly caused by asthenospheric upwelling following slab
breakoff, whereas magmatism in (2) is dominated by melting of the base of the still-present
lithospheric mantle during convective removal or asthenospheric upwelling. Magmatism in
(3) is probably triggered by decomposition of hydrous phases within the lithosphere, whereas
those in (4) have various triggers: OIB-like magmas may relate to local delamination or
thin-spots, more arc-like magmas may be due to lithospheric thickening in the Alborz and
Greater Caucasus. Geochemical and geodynamic modelling suggest that at ~500 km
distance from the suture there is a cut-off, at which asthenosphere stirring (due to slab
break-off) ceases to be an effective cause of decompression melting, small-scale
lithospheric delamination and convection. The relative scarcity of magmatism in
Western and Central Iran is good evidence that the mantle beneath this region is not
being stirred by delamination processes: there is otherwise little difference in the
previous Tethyan subduction histories of Iran and Eastern Turkey. Overall, there is no
single trigger or source of magmatism beneath the TIP, but two processes appear
to dominate: melting due to dehydration of the lithosphere as it is thickened or
convectively removed, and decompression melting of upwelling asthenosphere. |
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