Sabzevar Ophiolite, NE Iran: progress from embryonic oceanic lithosphere into magmatic arc constrained by new isotopic and geochemical data

Hadi Shafaii Moghadam*, Fernando Corfu, Massimo Chiaradia, Robert J. Stern, Ghasem Ghorbani

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

40 Citations (Scopus)

Abstract

The poorly known Sabzevar-Torbat-e-Heydarieh ophiolite belt (STOB) covers a large region in NE Iran, over 400km E-W and almost 200km N-S. The Sabzevar mantle sequence includes harzburgite, lherzolite, dunite and chromitite. Spinel Cr# (100Cr/(Cr+Al)) in harzburgites and lherzolites ranges from 44 to 47 and 24 to 26 respectively. The crustal sequence of the Sabzevar ophiolite is dominated by supra-subduction zone (SSZ)-type volcanic as well as plutonic rocks with minor Oceanic Island Basalt (OIB)-like pillowed and massive lavas. The ophiolite is covered by Late Campanian to Early Maastrichtian (~75-68Ma) pelagic sediments and four plagiogranites yield zircon U-Pb ages of 99.9, 98.4, 90.2 and 77.8 Ma, indicating that the sequence evolved over a considerable period of time. Most Sabzevar ophiolitic magmatic rocks are enriched in Large Ion Lithophile Elements (LILEs) and depleted in High Field Strength Elements (HFSEs), similar to SSZ-type magmatic rocks. They (except OIB-type lavas) have higher Th/Yb and plot far away from mantle array and are similar to arc-related rocks. Subordinate OIB-type lavas show Nb-Ta enrichment with high Light Rare Earth Elements (LREE)/Heavy Rare Earth Elements (HREE) ratio, suggesting a plume or subcontinental lithosphere signature in their source. The ophiolitic rocks have positive εNd (t) values (+5.4 to +8.3) and most have high 207Pb/204Pb, indicating a significant contribution of subducted sediments to their mantle source. The geochemical and Sr-Nd-Pb isotope characteristics suggest that the Sabzevar magmatic rocks originated from a Mid-Ocean Ridge Basalt (MORB)-type mantle source metasomatized by fluids or melts from subducted sediments, implying an SSZ environment. We suggest that the Sabzevar ophiolites formed in an embryonic oceanic arc basin between the Lut Block to the south and east and the Binalud mountains (Turan block) to the north, and that this small oceanic arc basin existed from at least mid-Cretaceous times. Intraoceanic subduction began before the Albian (100-113 Ma) and was responsible for generating Sabzevar SSZ-related magmas, ultimately forming a magmatic arc between the Sabzevar ophiolites to the north and the Cheshmeshir and Torbat-e-Heydarieh ophiolites to the south-southeast.

Original languageEnglish
Pages (from-to)224-241
Number of pages18
JournalLithos
Volume210-211
DOIs
Publication statusPublished - 1 Dec 2014
Externally publishedYes

Keywords

  • Iran
  • Late cretaceous
  • Radiogenic isotopes
  • Sabzevar ophiolite
  • Supra-subduction zone
  • U-Pb zircon

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