The composite Triassic\u2013Eocene Poshteh pluton, eastern Iran, an Eo-Cimmerian element south of the main Paleotethys suture

Shahryar Mahmoudi,Fernando Corfu

doi:10.1007/s00531-022-02165-6

Shahryar Mahmoudi, Fernando Corfu

Open Access

https://doi.org/10.1007/s00531-022-02165-6

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Abstract

The composite Poshteh Pluton, at the northeastern margin of the Central Iranian Microplate near Taybad in eastern Iran, is positioned at a critical tectonic junction, south of the inferred main Paleotethys suture and along the major regional Doruneh Fault system. It consists of two distinct intrusions. Quartz monzonite is dated in this study by zircon U–Pb ID-TIMS to 215.8 ± 0.5 Ma, an age that coincides with the time of closure of the Paleotethys during the late collisional stages of the Eo-Cimmerian Orogeny. It is geochemically very similar to coeval plutons present along and north of the Paleotethys suture, where they intruded Carboniferous-Permian arc sequences, ophiolites and flysch. The Poshteh quartz monzonite is located south of the suture in a position similar to the Anarak and related complexes further west, which previously have been interpreted as reflecting Mesozoic and Cenozoic disruption of the Eo-Cimmerian Orogen by extensional and transtensional processes. The Triassic quartz monzonite was subsequently invaded by granite at 41.23 ± 0.31 Ma. The emplacement was in part structurally controlled by the Doruneh Fault system and associated to hydrothermal alteration and Fe mineralization. The granite is thus a coeval member of a widespread late Eocene to Oligocene plutonic suite in the region, and likely the result of delamination and melting of the subcontinental lithosphere.

Highlights

Eastern Iran consists of a complex collage of tectonic elements
The first in the Paleozoic, ending with the Triassic Eo-Cimmerian Orogeny, and the second in the Cenozoic corresponding to the Alpine Orogeny (e.g. Stöcklin 1977; Berberian and King 1981; Sengör 1984; Besse et al 1998; Golonka 2004; Zanchi et al 2009a)
The Poshteh area near Taybad, at the northeastern margin of the Central Iranian Microplate (CIM), contains a fragment of the Eo-Cimmerian Orogen marked by late tectonic quartz monzonite (G1), which intruded at 215.8 ± 0.5 Ma during the collisional stage of the orogeny after closing of the Paleotethys

Summary

Introduction

Eastern Iran consists of a complex collage of tectonic elements. It includes late Precambrian to early Paleozoic terranes, derived from northern Gondwana, and variously affected, and eventually welded together, by two major orogenic cycles. South of Fariman and west of Torbat Jam a series of basement units have been upthrust through the Cenozoic cover These units include the Sibak Complex of Ediacaran metamorphic and intrusive rocks, locally cut by Ordovician gabbro (Ranjbar Moghadam et al 2018), in addition to fragments of Devonian, Permian and Triassic units. Based on regional considerations it was interpreted by Ternet et al (1980) to be late Precambrian, but presently there is no direct evidence that would permit to verify this hypothesis Another fault-bounded metasedimentary package further south contains sparse fossils indicating a Devonian age, but the sequence is lithologically different from that at Poshteh (Ternet et al 1980). Plotting was done with the program Isoplot (Ludwig 2009)

TR-103

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