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Journal of the Geological Society; 2009; v. 166; issue.1; p. 53-69;
DOI: 10.1144/0016-76492008-022
© 2009 Geological Society of London

Research Article

The Eocene bimodal Piranshahr massif of the Sanandaj–Sirjan Zone, NW Iran: a marker of the end of the collision in the Zagros orogen

S.A. Mazhari1, F. Bea2, S. Amini1, J. Ghalamghash3, J.F. Molina2, P. Montero2, J.H. Scarrow2 & I.S. Williams4

1 Department of Geology, Tarbiat Moallem University, 49 Mofatteh Avenue, Tehran 15614, Iran
2 Department of Mineralogy and Petrology, Fuentenueva Campus, University of Granada, 18002 Granada, Spain
3 Geological Survey of Iran, PO Box 13185-1494, Tehran, Iran
4 Research School of Earth Sciences, The Australian National University, Canberra ACT2 0200, Australia

*Corresponding author: (e-mail: fbea{at}ugr.es)

The bimodal Piranshahr massif is composed of coeval but geochemically unrelated mafic (40.7 ± 0.2 Ma zircon U–Pb sensitive high-resolution ion microprobe (SHRIMP) age) and A-type felsic rocks (41 ± 0.5 Ma Rb–Sr and 41.3 ± 0.8 Ma zircon U–Pb SHRIMP age). The mafic rocks consist of two geochemical types of gabbros that derived from different magmas. The more abundant gabbros are moderately alkaline, have ratios of large ion lithophile elements to REE and high field strength elements to REE similar to those of intraplate mantle magmas, 87Sr/86Sr41 Ma {approx} 0.7036 and {varepsilon}(Nd)41 Ma {approx} +7.2. The less abundant gabbros have calc-alkaline affinities, 87Sr/86Sr41 Ma {approx} 0.7043 and {varepsilon}(Nd)41 Ma {approx} +4.78. Felsic rocks are metaluminous A2-type annite–fayalite–hedenbergite, hypersolvus, leucocratic, coarse-grained agpaitic syenites, pulaskites and granites, with 87Sr/86Sr41 Ma {approx} 0.7048 and {varepsilon}(Nd)41 Ma {approx} +3.6–4.5. Syenites, pulaskites and granites are genetically related. Pulaskites probably represent alkali-enriched water-rich residual melts from which an F-rich vapour phase was later separated. Granites were probably generated during open-system processes, in which F-rich hydrous alkaline fluids released from the syenites acted upon pre-existing felsic rocks. The c. 41 Ma age of the post-collisional Piranshahr massif indicates that the related collision probably occurred at 50–60 Ma (i.e. Late Palaeocene or Early Eocene), thus resolving a much debated question.





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M. B. Allen
Discussion on the Eocene bimodal Piranshahr massif of the Sanadaj-Sirjan Zone, West Iran: a marker of the end of collision in the Zagros orogen: Journal, Vol. 166, 2009, pp. 53-69
Journal of the Geological Society, 2009; 166: 981 - 982.
[Full Text] [PDF]

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F. Bea, J.H. Scarrow, S.A. Mazhari, J.F. Molina, P. Montero, S. Amini, and J. Ghalamghash
Reply to discussion on the Eocene bimodal Piranshahr massif of the Sanadaj-Sirjan Zone, West Iran: a marker of the end of collision in the Zagros orogen: Journal, Vol. 166, 2009, pp. 53-69
Journal of the Geological Society, 2009; 166: 983 - 984.
[Full Text] [PDF]