Tectonic significance of Triassic mafic rocks in the June Complex, Sanandaj–Sirjan zone, Iran

This study concentrates on the petrological and geochemical investigation of mafic rocks embedded within the voluminous Triassic June Complex of the central Sanandaj–Sirjan zone (Iran), which are crucial to reconstruct the geodynamics of the Neotethyan passive margin. The Triassic mafic rocks are al...

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Bibliographic Details
Published in:Swiss Journal of geosciences 2018-04, Vol.111 (1-2), p.13-33
Main Authors: Shakerardakani, Farzaneh, Neubauer, Franz, Liu, Xiaoming, Bernroider, Manfred, Monfaredi, Behzad, von Quadt, Albrecht
Format: Article
Language:English
Subjects:
Alkalies
Alkalis
Basalt
Contamination
Crystallization
Depletion
Earth and Environmental Science
Earth Sciences
Enrichment
Field strength
Fractional crystallization
Fractionation
Geochemistry
Geodynamics
Geology
Isotopes
Lava
Liquids
Magma
Magnesium oxide
Mantle
Niobium
Olivine
Passive margins
Plagioclase
Ratios
Rock
Rocks
Silica
Silicon dioxide
Tectonics
Tectonophysics
Triassic
Zirconium
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Summary:This study concentrates on the petrological and geochemical investigation of mafic rocks embedded within the voluminous Triassic June Complex of the central Sanandaj–Sirjan zone (Iran), which are crucial to reconstruct the geodynamics of the Neotethyan passive margin. The Triassic mafic rocks are alkaline to sub-alkaline basalts, containing 43.36–49.09 wt% SiO 2 , 5.19–20.61 wt% MgO and 0.66–4.59 wt% total alkalis. Based on MgO concentrations, the mafic rocks fall into two groups: cumulates (Mg# = 51.61–58.94) and isotropic basaltic liquids (Mg# = 24.54–42.66). In all samples, the chondrite-normalized REE patterns show enrichment of light REEs with variable (La/Yb) N ratios ranging from 2.48 to 9.00, which confirm their amalgamated OIB-like and E-MORB-like signatures. Enrichment in large-ion lithophile elements and depletion in high field strength elements (HFSE) relative to the primitive mantle further support this interpretation. No samples point to crustal contamination, all having undergone fractionation of olivine + clinopyroxene + plagioclase. Nevertheless, elemental data suggest that the substantial variations in (La/Sm) PM and Zr/Nb ratios can be explained by variable degrees of partial melting rather than fractional crystallization from a common parental magma. The high (Nb/Yb) PM ratio in the alkaline mafic rocks points to the mixing of magmas from enriched and depleted mantle sources. Abundant OIB alkaline basalts and rare E-MORB appear to be linked to the drifting stage on the northern passive margin of the Neotethys Ocean.
ISSN:1661-8726
1661-8734
DOI:10.1007/s00015-017-0281-4