Mineral chemical composition and geodynamic significance of peridotites from Nain ophiolite, central Iran

Javad Mehdipour Ghazi*, Mohssen Moazzen, Mohammad Rahgoshay, Hadi Shafaii Moghadam

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

32 Citations (Scopus)

Abstract

The peridotites from north of the town of Nain in central Iran consist of clinopyroxene-bearing harzburgite and lherzolite with small lenses of dunite and chromitite pods. The lherzolite contains aluminous spinel with a Cr number (Cr# = Cr/[Cr + Al]) of 0.17. The Cr number of spinels in harzburgite and chromitite is 0.38-0.42 and 0.62, respectively. This shows that the lherzolite and harzburgite resulted from <18% of partial melting of the source materials. The estimated temperature is 1100 ± 200 °C for peridotites, the estimated pressure is <15 ± 2.3 kbar for harzburgites and >16 ± 2.3 kbar for lherzolites and estimated fo2 is 10-1±0.5 for peridotites. Discriminant geochemical diagrams based on mineral chemistry of harzburgites indicate a supra-subduction zone (SSZ) to mid-oceanic ridge (MOR) setting for these rocks. On the basis of their Cr#, the harzburgite and lherzolite spinels are analogous to those from abyssal peridotites and oceanic ophiolites, whereas the chromites in the chromitite (on the basis of Cr# and boninitic nature of parental melts) resemble those from SSZ ophiolitic sequences. Therefore, the Nain ophiolite complex most likely originated in an oceanic crust related to supra-subduction zone, i.e. back arc basin. Field observations and mineral chemistry of the Nain peridotites, indicating the suture between the central Iran micro-continent (CIM) block and the Sanandaj-Sirjan zone, show that these peridotites mark the site of the Nain-Baft seaway, which opened with a slow rate of ocean-floor spreading behind the Mesozoic arc of the Sanandaj-Sirjan zone as a result of change of Neo Tethyan subduction régime during middle Cretaceous.

Original languageEnglish
Pages (from-to)261-270
Number of pages10
JournalJournal of Geodynamics
Volume49
Issue number5
DOIs
Publication statusPublished - May 2010
Externally publishedYes

Keywords

  • Back arc basin
  • Mineral chemistry
  • Nain ophiolite
  • Peridotite
  • Spreading rate

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