Paleozoic Tensional Intraplate Magmatism and Mantle Evolution in Central Iran Zone: Geochemistry, Nd-Sr Isotope Data of Lamprophyres

Abstract

A Permian-Triassic lamprophyric magmatism has developed as dyke and subvolcanic intrusions in the northeast of Isfahan Province, in Central Iran, where is so-called the Chahriseh-Bagherabad area. These rocks mainly consist of olivine, pyroxene, amphibole, and biotite as major minerals and apatite, biotite, muscovite, and opaque as minor minerals with porphyritic texture and with felsic xenoliths and xenocrysts. The Chahriseh-Bagherabad lamprophyres (CBL) magma has undergone significant crustal contamination and fractional crystallization. Based on whole rock geochemistry, these rocks belong to alkaline lamprophyres, derived from a low degree (less than 5%) partial melting of an amphibole-garnet lherzolite mantle and enriched by the lithospheric mantle in the source region. Their ⁸⁷Sr/⁸⁶Sr (0.70435–0.70696) and ¹⁴³Nd/¹⁴⁴Nd (0.51260–0.51276) values were supported by an enriched mantle source of the EMІI-type that has been contaminated by the continental upper crust. Thus, the CBL samples are alkaline rock formed by tensional intraplate magmatism in a Paleo-Tethyan subduction zone in the lower Paleozoic to late Permian in which metasomatism and mantle enrichment occurred. The lamprophyres magmas ascend due to tensional stress during rotation and displacement of the central-eastern Iranian microcontinent.