Geochemical and Nd-Sr Isotopic Compositions of Hypabyssal Adakites in the Torud-Ahmad Abad Magmatic Belt, Northern Central Iran Zone: Analysis of Petrogenesis and Geodynamic Implications

Eocene intermediate to felsic subvolcanic rocks of the Torud-Ahmad Abad magmatic belt (TAMB), in northern part Central Iran zone, are exposed between Torud and Ahmad regions South-Southeast Shahrood. These igneous include hypabyssal dacite, trachyte, andesite, trachy-andesite, basaltic andesite; they mainly composed phenocrysts microcrystalline groundmass pyroxene, amphibole, plagioclase, with minor biotite titanomagnetite; form domal structures (plugs stocks), dikes, sills that intruded into Neoproterozoic cogenetic volcano-sedimentary sequences. Based on isotopic analysis these acidic rocks, initial ratios 143Nd/144Nd range from 0.512 775 893 87Sr/86Sr 0.703 746 0.705 314, quite positive εNd(i) values +3.69 +6.00. They enriched light rare earth elements large ion lithophile depleted heavy high-field strength elements, SiO2 content is (52–62) wt.%, Na2O >3 Al2O3 >16 Yb <1.8 ppm, Y <18 ppm. geological, geochemical, Sr Nd data consistent adakitic signatures originating by partial melting subducted Neo-Tethys oceanic slab (Sabzevar branch) lithospheric suprasubduction zone mantle. The mantle typifying rapidly emplaced (slab (high-silica adakite) (low-silica melts) together their locally voluminous extent evidences support a extensional geodynamic setting; evidence an evolution local transpression Late this convergent margin arc environment rifting (basalts adakites) towards submarine conditions Neogene.