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Small-volume melts of lithospheric mantle during continental collision : late Cenozoic lavas of Mahabad, NW Iran.

Kheirkhah, M. and Neill, I. and Allen, M.B. and Ajdari, K. (2013) 'Small-volume melts of lithospheric mantle during continental collision : late Cenozoic lavas of Mahabad, NW Iran.', Journal of Asian earth sciences., 74 . pp. 37-49.

Abstract

Basanites and alkali basalts from Mahabad in the West Azerbaijan province of Iran are part of a widespread series of Late Miocene–Quaternary mantle-derived magmas erupted within the Turkish–Iranian orogenic plateau, itself part of the active Arabia–Eurasia collision zone. New elemental and Sr–Nd isotopic results are combined with geophysical and geological constraints to suggest that these lavas formed predominantly by small degrees of partial melting of the thick (≫100 km) Eurasian lithospheric mantle within the garnet facies. Samples are highly enriched in large ion lithophile elements (LILE) and the light rare earth elements (LREE), up to 600 times chondritic values. They mostly possess negative primitive mantle-normalised Rb, K, Nb–Ta, Zr–Hf and Ti anomalies, with an overall signature that indicates a mantle source metasomatised by fluids or melts derived from crust during continental collision or the Tethyan oceanic subduction that preceded it. Sr–Nd isotopic values are similar to other Quaternary centres in NW Iran; 87Sr/86Sr is slightly depleted with respect to Bulk Silicate Earth, at ∼0.7045, and 143Nd/144Nd is slightly enriched, at ∼0.5127. Crustal contamination does not appear to be an important process in the chemistry of these samples. Possible triggers for melting may include: breakdown of hydrous phases during lithospheric thickening; hydration of the mantle lithosphere by underthrusting of the Arabian passive margin; small-scale sub-lithospheric convection due to a significant thickness gradient in the Zagros lithosphere. Such processes may account for small-volume syn-collisional mantle-derived magmatism elsewhere in regions of thick lithosphere where recent slab break-off or lithospheric delamination cannot be proven.

Item Type:Article
Keywords:Lithosphere, Iran, Basalt, Geochemistry, Melting.
Full text:(AM) Accepted Manuscript
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Status:Peer-reviewed
Publisher Web site:http://dx.doi.org/10.1016/j.jseaes.2013.06.002
Publisher statement:NOTICE: this is the author’s version of a work that was accepted for publication in Journal of Asian Earth Sciences. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Asian Earth Sciences, 74, 2013, 10.1016/j.jseaes.2013.06.002.
Date accepted:No date available
Date deposited:12 June 2014
Date of first online publication:September 2013
Date first made open access:No date available

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