Petrology
Gholamreza Tajbakhsh
Abstract
Mafic dyke swarms of the Zarigan granitoid in the north of Bafq have intruded the Lower Cambrian volcanic-sedimentary sequence of central Iran. These dykes are lithologically classified as gabbro-diorite and alkali gabbro. The alkaline gabbros are younger and penetrate higher horizons. Geochemically, ...
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Mafic dyke swarms of the Zarigan granitoid in the north of Bafq have intruded the Lower Cambrian volcanic-sedimentary sequence of central Iran. These dykes are lithologically classified as gabbro-diorite and alkali gabbro. The alkaline gabbros are younger and penetrate higher horizons. Geochemically, gabbro-diorites have a tholeiitic to transitional nature with enrichment of LILE, HREE and depletion of Nb and Ta elements. By contrast, alkali gabbros have the sodic alkaline nature, exhibiting Nb-Ta enrichment and high LREE/HREE ratio. Gabbro-diorite magmas are derived from partial melting of sub-continental lithospheric mantle affected by subduction components in equilibrium with spinel lherzolite. On the other hand, the alkali gabbros originate from greater depth and lower partial melting of enriched asthenospheric mantle in equilibrium with garnet lherzolite. These dykes are formed in an intra-arc extension setting associated with subduction of the continental margin. Geometry and mechanism of motion of Posht-e-Badam and Kuh Banan basement faults caused an anticlockwise rotation, crustal fracturing, lithospheric thinning, and stenosphere upwelling of these two faults bounded block.
Gholamreza Tajbakhsh; M. H. Emami; H. Moine Vaziri; N. Rashidnejad Omran
Abstract
Hashtsar ultramafic – mafic intrusive complex is located at about 20 km east of the Kaleybar in the eastern AzerbaijanProvince. This alkaline ring complex is formed by the penetrative of undersaturated and oversaturated different magmatic phases with Late Eocene to Oligocene – Miocene ages. ...
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Hashtsar ultramafic – mafic intrusive complex is located at about 20 km east of the Kaleybar in the eastern AzerbaijanProvince. This alkaline ring complex is formed by the penetrative of undersaturated and oversaturated different magmatic phases with Late Eocene to Oligocene – Miocene ages. Petrographical studies show that this massive consists of three main phases. The first phase is composed of magnetite mela alkali pyroxenite, plagioclase bearing alkali pyroxenite and mela alkali gabbro with coarse grained gabbroic dykes. The second phase consists of the nepheline bearing leuco gabbro - diorite to nepheline monzodiorite and nepheline monzonite, and the third phase is syenite with quartz - monzosyenite to granite with calk-alkaline affinity. Geochemical studies indicate that undersaturated phases are intensively enriched in trace elements, especially in LILE and LREE. These magmas have generated from the parental magma with a potassic alkaline affinity from a metasomatic mantle. The different rocks types of undersaturated phases were produced by the liquid immiscibility, crystal fractionation and accumulation processes. The calc-alkaline magma of the third phase is probably resulted from the lower crust melting due to penetrative of first and secondary phases. Particular and ring emplacement of this complex is concluded by the eruption and discharge of huge and zoned magma chamber, after the caldera subsidence such as, volcanic string of Majid Abad formation in the Hashtsar region.
