Geochemistry and Sr-Nd isotopic characteristics of ferroan-magnesian metaluminous granites of the NW Sanandaj-Sirjan zone, Iran: granite formation in a compressional-extensional setting during Late Jurassic time

The Almogholagh-Dehgolan region is in the North Sanandaj-Sirjan zone of NW Iran. The granites of the region are metaluminous and display geochemical and textural characteristics of transitional granites between ferroan (A-type) and I-type granites. In geotectonic discrimination diagrams, the Almogholagh-Dehgolan granites plot mainly in the fields of within-plate granites and volcanic arc granites. With the exception of the Qalaylan granites, parts of other granites resemble A(2)-type granites. Granites of the Qalaylan intrusive body have petrographic and geochemical features close to I-type granites and are not A-type. Primary mantle and chondrite-normalized spider diagrams show enrichments in light rare earth elements relative to heavy rare earth elements. For an age of 150 Ma, the initial Sr-87/Sr-86 and Nd-143/Nd-144 ratios vary from 0.702769 to 0.706545 and from 0.512431 to 0.512558, respectively. Epsilon Nd values vary in a relatively limited range between -0.3 and +2.2, which corresponds to a mixed mantle-crustal source. On the basis of new geochemical and isotopic data, we suggest a geodynamic model involving partial melting of lower crustal rocks with the contribution of mantle magmas in a weakly extensional tectonic setting for the generation of the A-type granites of the region. The occurrence of ferroan (A-type) granites in this region of the Sanandaj-Sirjan zone indicates the existence of a partly extensional tectonic environment in a mainly compressional subduction-related regime in Late Jurassic time.

Automated summary

The Almogholagh-Dehgolan region in NW Iran is characterized by metaluminous granites with transitional characteristics between ferroan (A-type) and I-type granites. These granites are mainly categorized as within-plate granites and volcanic arc granites on geotectonic discrimination diagrams. The Qalaylan granites exhibit features similar to I-type granites, while other granites resemble A(2)-type granites. Geochemical and isotopic data suggest a geodynamic model involving partial melting of lower crustal rocks and mantle magmas in a weakly extensional tectonic setting for the generation of A-type granites in this region.