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Gabbroic-dioritic dykes from the Sanandaj-Sirjan Zone; windows on Jurassic and Eocene geodynamic processes in the Zagros Orogen, western Iran

Reza Deevsalar, Ryuichi Shinjo, Kuo-Lung Wang, Hadi Yeganehfar and Iain Neill
Gabbroic-dioritic dykes from the Sanandaj-Sirjan Zone; windows on Jurassic and Eocene geodynamic processes in the Zagros Orogen, western Iran
Journal of the Geological Society of London (June 2018) 175 (6): 915-933

Abstract

The Sanandaj-Sirjan Zone (SaSiZ) is a magmatic terrane within the Zagros Orogen, western Iran, marking the Tethyan suture zone between the Afro-Arabian Plate and the Central Iran Micro-Continent. Mafic-intermediate dyke swarms with Middle Jurassic (Group-1: hornblende gabbro and diorite) and Late Eocene (Group-2: hornblende-pyroxene gabbro) ages are recognized in the Malayer-Boroujerd Plutonic Complex of the northern SaSiZ. Group-1 dykes have elemental and isotopic signatures consistent with melting of a mantle source modified during Neo-Tethyan subduction. Some Group-1 magmas evolved to intermediate compositions through assimilation and fractional crystallization. Group-2 dykes have within-plate trace element geochemical signatures, modelled as deriving from low-degree melting of asthenospheric mantle without a subduction influence. Published models postulate either a Cretaceous-Eocene Neo-Tethyan flat-slab scenario, or a Latest Cretaceous-Palaeogene Neo-Tethyan break-off event beneath the SaSiZ. Such models do not reconcile with the Late Eocene presence of within-plate magmatism in westernmost Iran, very close to the Zagros Suture. We argue that a period of flat-slab subduction concluded with sub-parallel subduction of a Neo-Tethyan ridge to the trench. The resulting slab break-off event in the Late Eocene is responsible for generation of the distinct Mesopotamia and Zagros slabs in mantle tomography models. Break-off was followed by small volume within-plate type magmatism before short-lived re-establishment of Tethyan subduction prior to the final Arabia-Eurasia collision. Supplementary material: Field photographs, photomicrographs, additional geochemical plots, descriptions of analytical methods and tables of geochemical modelling parameters are available at https://doi.org/10.6084/m9.figshare.c.4126196.


ISSN: 0016-7649
EISSN: 2041-479X
Coden: JGSLAS
Serial Title: Journal of the Geological Society of London
Serial Volume: 175
Serial Issue: 6
Title: Gabbroic-dioritic dykes from the Sanandaj-Sirjan Zone; windows on Jurassic and Eocene geodynamic processes in the Zagros Orogen, western Iran
Affiliation: Tarbiat Modares University, Department of Geology, Tehran, Iran
Pages: 915-933
Published: 20180612
Text Language: English
Publisher: Geological Society of London, London, United Kingdom
References: 85
Accession Number: 2018-062886
Categories: Igneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 5 tables, geol. sketch map
N34°00'00" - N37°00'00", E40°00'00" - E50°00'00"
Secondary Affiliation: University of the Ryukyus, JPN, JapanAcademia Sinica, TWN, TaiwanPayame Noor University, IRN, IranUniversity of Glasgow, GBR, United Kingdom
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data from The Geological Society, London, London, United Kingdom
Update Code: 201834
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