A post-ophiolitic plutonism record in the Central-East Iranian Microcontinent: Evidence for Pre-Eocene age of Neo-Tethys subduction

Abstract

The Eocene Kalut-e-Ghandehari (KG) pluton, located in the Central Eastern Iranian Microcontinent (CEIM), intrudes the Ashin Mesozoic ophiolite and Middle Eocene volcanic rocks. Petrographic and geochemical analyses reveal a calc-alkaline, metaluminous intermediate to mafic composition ranging from gabbro to monzonite. The rocks exhibit characteristic REE and HFSE patterns indicative of subduction-related magmatism. The KG pluton is composed of plagioclase (An = 34–60 %), Alkali-feldspar (Or = 70.8–96.1 %), diopside (Mg# = 0.71–0.90), phlogopite (Fe# = 0.3), and opaque minerals. Geochemical evidence (e.g., enrichment of LREE, LILE (e.g., Cs, Ba, Rb, Th, U), Zr, and Hf; depletion of HREE, Ti, Nb, and Ta, and Y) suggests partial melting of a lithospheric spinel lherzolite that had been previously enriched by an earlier subduction event. The geochemical similarities of parental magmas of the KG pluton and the Soheyl-e-Pakuh pluton (located in the neighboring ophiolite of Nain) indicate that both derive from a subduction-induced partial melting of a mantle peridotite. However, their magma sources temporality and spatially are in accord with eastern and western Neo-Tethys subduction-related magmatisms, respectively. Thus, the cross-cutting relationships between the pluton and the Ashin ophiolite, combined with geochronological data, support a pre-Upper Eocene closure of the eastern Neotethys oceanic crust. This finding provides valuable insights into the Cenozoic tectonic evolution of the Central Iran.