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Petrogenesis of mafic collision zone magmatism : the Armenian sector of the Turkish-Iranian Plateau.

Neill, I. and Meliksetian, K. and Allen, M.B. and Navasardyan, G. and Kuiper, K. (2015) 'Petrogenesis of mafic collision zone magmatism : the Armenian sector of the Turkish-Iranian Plateau.', Chemical geology., 403 . pp. 24-41.

Abstract

The Turkish–Iranian Plateau grew after the Middle Miocene following the initial Paleogene Arabia–Eurasia collision. Authors attribute uplift to break-off of the southern Neo-Tethys slab beneath the Bitlis–Zagros Suture at ~ 15–10 Ma, coupled with continued plate convergence and regional crustal shortening. Since this time there has been an upsurge in mantle-derived collision magmatism over large parts of NW Iran, Eastern Anatolia and the Lesser Caucasus, potentially hundreds of kilometres from the site of southern Neo-Tethys slab break-off, > 10 Myr after the proposed break-off event. Whole rock elemental and Sr–Nd–Pb–Hf isotope data are presented for < 3 Ma trachy-basalt to trachy-basaltic andesite lavas erupted in Armenia in the South Caucasus. Samples formed by < 5% melting of fertile subduction-modified spinel-facies lithospheric mantle, and few display elemental or isotopic evidence for contamination by the 45-km thick Mesozoic–Paleogene arc crust or South Armenian Block continental crust. Recent magmatic activity in Armenia may not be a direct consequence of southern Neo-Tethys slab break-off 300–450 km away, beneath the Bitlis Suture. Late Miocene break-off of a second (northern Neo-Tethys) slab beneath the Pontide Arc may have allowed asthenospheric upwelling over a wider area than was affected by southern Neo-Tethyan break-off. However, whole-scale delamination of mantle lithosphere is ruled out due to the modest degrees of partial melting, a lack of asthenospheric components and limited crustal involvement in magmatism. Small-scale sub-lithospheric convection may be complementary to break-off, causing localised removal of lithospheric mantle and aiding the occurrence of melting for a significant time interval after the break-off event(s). Collision magmas such as those in Armenia represent mantle-derived additions to continental crust, enriched in incompatible elements but with Th/La ratios ≤ 0.2, much lower than those calculated for continental crust (0.25–0.3). Collision magmatism in Turkic-style orogens must be balanced by infra-crustal recycling and delamination to produce bulk continental crust.

Item Type:Article
Keywords:Arabia–Eurasia collision, Armenia, Continental crust, Orogenic plateau, Radiogenic isotopes, Sub-lithospheric convection
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Status:Peer-reviewed
Publisher Web site:http://dx.doi.org/10.1016/j.chemgeo.2015.03.013
Publisher statement:© 2015 The Authors. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Date accepted:12 March 2015
Date deposited:02 April 2015
Date of first online publication:2015
Date first made open access:No date available

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