Toye-Darvar A-type granitoid, southwest of Damghan: Constraints on the Paleotethyan extensional basin of Lower Paleozoic’s in Alborz

Toye-Darvar granitoidic pluton is located in southwest of Damghan, in the southern flanke of eastern Alborz structural zone. Despite of its uniform appearance in the field, this pluton is composed of a rock with a wide range of composition including of diorite, monzodiorite, monzonite, quartzmonzonite and granodiorite with monzonite-quartzmonzonite prevalence. Based on the field observations, this pluton intruded in the Bayandor, Soltaniyeh, Zagoon and Laloon formations with the Late Precambrian-Cambrian age and not found in Jirood Formation, in opposite of pervious reports, then its age isn’t Late Devonian. Absence of contact metamorphism indicates the fluid deficence and relatively dry nature of magma, smal size of pluton and diapiric ascent of the magma in a cold solid state in shallow depths of the crust. Existence of Fe-Mn oxide-hydroxides, fluorite, barite, zinc and lead viens in the country rocks, prevalence of hypersolvous-subsolvous reaction fine grain granular textures (perthitic, myrmekitic, graphic and granophyric), alkaline nature of magma, LILE and incompatible elements enrichment, high contents of HFSE in comparision to the other granitoids, low CaO and MgO contents, high FeOt/MgO ratio (prevalence of iron rich mineralogy), high Ga/Al ratio and plotting the samples in the A-type granitoid fields in geochemical discriminat diagrams, all suggest that this pluton is A1 sub-type granitoids (related to intraplate rifting magmatism). Different evidences indicate a close relationships between Toye-Darvar granitoidic pluton and Lower Paleozoic rifting magmatism (Ordovician-Silurian time) in the Gondwanian uniform platform of Iran in relation to initiation of the opening of the paleotethys ocean that reported from different localities in Iran, particularly in Alborz and Central Iran, and the other adjacent countries.