Contributions to Mineralogy and Petrology, Volume (173), No (81), Year (2018-10) , Pages (80-103)

Title : ( Geochemical and geochronological evidence for a Middle Permian oceanic plateau fragment in the Paleo-Tethyan suture zone of NE Iran )

Authors: Gültekin Topuz , Ernst Hegner , Seyed Massoud Homam , Lukas Ackerman , Jörg A. Pfänder , Hadi Karimi ,

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Abstract

The mafic–ultramafic Fariman complex in northeastern Iran has been interpreted as a Paleo-Tethyan ophiolitic fragment with subduction- and plume-related characteristics as well as a basin deposit on an active continental margin. Contributing to this issue, we present geochemical, geochronological, and mineralogical data for transitional and tholeiitic basalts. Thermodynamic modeling suggests picritic parental magmas with 16–21 wt% MgO formed at plume-like mantle potential temperatures of ca. 1460–1600 °C. Rare pyroxene spinifex textures and skeletal to feather-like clinopyroxene attest to crystallization from undercooled magma and high cooling rates. Chromium numbers and TiO2 concentrations in spinel are similar to those in intraplate basalts. 40Ar–39Ar dating of magmatic hornblende yielded a plateau age of 276 ± 4 Ma (2σ). Transitional basalt with OIB-like trace element characteristics is the predominant rock-type; less frequent are tholeiitic basalts with mildly LREE depleted patterns and picrites with intermediate trace element characteristics. All samples show MORB-OIB like Pb/Ce, Th/La, and Th/Nb ratios which preclude subduction-modified mantle sources and felsic crustal material. Tholeiitic basalts and related olivine cumulate rocks show MORB-like initial εNd values of + 9.4 to + 6.2 which define a mixing line with the data for the transitional basalts (εNd ca. + 2.6). Initial 187Os/188Os ratios of 0.124–0.293 support mixed sources with a high proportion of recycled mafic crust in the transitional basalts. High concentrations of highly siderophile elements are in agreement with the high mantle potential temperatures and inferred high-melting degrees. It is argued that the Fariman complex originated by melting of a mantle plume component as represented by the OIB-like transitional basalt and entrained asthenosphere predominant in the MORB-like tholeiites. Two lines of evidence such as association of the Fariman complex with pelagic to neritic sedimentary rocks and the tectonic position at the boundary of two continental blocks defined by ophiolites and accretionary complexes of different ages suggest formation in an oceanic domain. Thus, we interpret it as a fragment of an oceanic plateau, which escaped subduction and was accreted as exotic block in the Paleo-Tethyan suture zone.

Keywords

, Picrite · Nd and Os isotopes · Geochemistry · Mantle plume · Oceanic plateau · Paleo, Tethys · The Mashhad– Fariman complex · Iran
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@article{paperid:1070105,
author = {Gültekin Topuz and Ernst Hegner and Homam, Seyed Massoud and Lukas Ackerman and Jörg A. Pfänder and Karimi, Hadi},
title = {Geochemical and geochronological evidence for a Middle Permian oceanic plateau fragment in the Paleo-Tethyan suture zone of NE Iran},
journal = {Contributions to Mineralogy and Petrology},
year = {2018},
volume = {173},
number = {81},
month = {October},
issn = {0010-7999},
pages = {80--103},
numpages = {23},
keywords = {Picrite · Nd and Os isotopes · Geochemistry · Mantle plume · Oceanic plateau · Paleo-Tethys · The Mashhad– Fariman complex · Iran},
}

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%0 Journal Article
%T Geochemical and geochronological evidence for a Middle Permian oceanic plateau fragment in the Paleo-Tethyan suture zone of NE Iran
%A Gültekin Topuz
%A Ernst Hegner
%A Homam, Seyed Massoud
%A Lukas Ackerman
%A Jörg A. Pfänder
%A Karimi, Hadi
%J Contributions to Mineralogy and Petrology
%@ 0010-7999
%D 2018

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