سازوكار شكل گيري باتوليت گرانيتوييدي زاهدان، جنوب شرق ايران

The evolution mechanismʹs of Zahedan granitoidic batholith

: Ellipsoidal huge granitoidic batholiths of Zahedan, with NW-SE trending, located in south of this city which is intruded in low metamorphosed Eocene flysches (eastern Iran flysch zone). This batholith has two compositional terms: an extensive intermediate-acid term includes diorite - granodiorite with igneous source (I- type origin) and a low extent crustal and hybrid origin acidic term (H-type) mostly contains biotite-granite. The intermediate-acid I-type term has calc-alkaline and metaluminous nature, enrichment in LREE and LILE and depletion in HREE and HFSE. The negative anomalies in HFSE and positive anomalies in LREE, LILE and especially Pb revealed an igneous mantle origin, especially the role of Sistan subducted oceanic crust and its overlaying mantle wedge in the genesis of this batholith. Also, the role of the continental crust (flysch and greywack metasediments) in contamination of magma has been proved. In addition, the same evidences indicate a calc- alkaline, peraluminous nature, a crustal (resulted from partial melting of flysches and greywacks) and an hybrid origin (mixing of the differentiated part of I-type magma with the anatectic crustal acidic melt) for acidic biotite granite term. Present day 87Sr/86Sr ratios of three samples of this batholith vary from 0.7049 to 0.7065 and their initial 87Sr/86Sr ratios range from 0.7045 to 0.7047 with average 0.7046, verifies these different sources. These data confirm an I-type magmatic origin (melting of mantle or lower crust) for the diorites-granodiorites. Discriminative tectonic diagrams also indicate a volcanic arc granitoids setting (VAG) for this batholith. Andesitic-dacitic dikes with same composition to intermediate-acid I-type term occur in this batholith and its metamorphosed host rocks. These dikes are comagmatic with I-type partʹs of the pluton and show a syn-to late relations with formation and intrusion of the pluton.