Ordovician of the Anarak Region : implications in understanding Early Palaeozoic history of Central Iran

Abstract

The Pol-e Khavand area south-east of the town of Anarak preserves important clues for understanding geological evolution of Central Iran during the Palaeozoic. New observations confirm the non-conformable relationship between Doshakh metamorphites and overlying unmetamorphosed Lower Palaeozoic sediments, suggesting accretion of the volcanic arc in front of the Yazd block sometime in the late Cambrian to early Ordovician. The newly introduced volcano-sedimentary Polekhavand Formation preserves evidence of a ?Late Cambrian to Early Ordovician post-collisional bimodal volcanism and related extensional regime in the Pol-e Khavand area during that time. The Middle to Upper Ordovician interval of the studied succession is assigned to the newly introduced Chahgonbad Formation. The Darriwilian age of the base of this lithostratigraphical unit is demonstrated by the brachiopods Tritoechia and Yangtzeella which co-occur with a diverse a cephalopod assemblage. The low diversity fauna including brachiopods Hibernodonta sp., Hindella sp., Rostricellula cf. ambigena and trilobites Vietnamia cf. teichmulleri suggest a Katian age for the upper part of the unit. There is insufficient evidence for the existence of the hypothetical Palaeo Tethys suture zone south of the Pol-e Khavand area.