METALUMINOUS SUB-ALKALINE GRANITOIDS FROM THE TAKAB AREA, NW IRAN

The Paleoproterozoic Takab complex is composed of a variety of metamorphic rocks including granulites, amphibolites, gneisses, mafic migmatites and meta-ultramafics, which are intruded by the Cenozoic intrusions of granitoids. The granitoids are mainly granodiorite, Qtz-monzodiorite, monzonite and Qtz-diorite. Chemically the granitoids show a low alumina saturation index (ASI), low concentration of SiO₂ and high FeO, MgO and CaO contents which are typical features for I-type granitoids. Field evidence, petrology and geochemical features lead to propose that the investigated granitoid suites are generated from melting of a crustal source connected to the associated mafic migmatites in the area. High concentrations of CaO, MgO and FeOt and low K₂O/Na₂O values, classify the source of the granitoids as metabasites. Basalts, amphibolites and rarely greywackes are protoliths for the magma generation in the Takab area.

The granitoids show main affinities as syn-collisinal granitoids (syn-COLG). Volcanic arc feature in some samples are most likely related to the features inherited from previous arc-related protoliths.

Magmatic crystallisation pressure and temperature for the quartz-diorite and the granodiorite are estimated to be P~8kbar, T~850^oC and P~5kbar, T~790^oC, respectively. Subsolidus conditions are consistent with temperatures of ~600^oC and ~620^oC, and pressures of ~6kbar and ~3.5kbar for the quartz-diorite and the granodiorite, respectively. The responsible magmatic activity in the Takab area occurred in relation to the subduction of the Neo-Tethys during Tertiary during the Alpine Orogeny. Although the accurate timing of collision between the Arabian plate and the Iranian block and associated magmatic activity are highly controversial, recent studies based on structural and metamorphic data suggest that continental collision occurred during Oligocene (see Agard et al. 2005). Widespread Neogene volcanic activities related to the extensional phase of the Alpine orogeny and U/Pb data from the migmatites evidence the Oligocene as the collision time in the Takab area (Hajialioghli, 2007).

References

AGARD, P. OMRANI, J., JOLIVET, L. & MOUTHEREAU, F. 2005. Convergence history

across Zagros (Iran):Constraints from collisional and earlier deformation. International journal of Earth Sciences 94, 401–419.

HAJIALIOGHLI, R. 2007. Petrological investigations on calc-silicate and metabasic rocks

from the Takht-e-Soleyman complex-Northeastern Takab area (Western Iran). unpublished PhD. Thesis. University of Tabriz, 190p.