M Fadaeian; A Jahangiri; M Moayyed
Abstract
The study area is located in the Ardabil province and in the north east of Meshkinshahr city.More than 200 small and large Eocene age dykes have outcrops in this area with basaltic, tephritic, andesitic and trachy andesit composition. Clinopyroxene, plagioclase, analcime and sometimes coarse olivine ...
Read More
The study area is located in the Ardabil province and in the north east of Meshkinshahr city.More than 200 small and large Eocene age dykes have outcrops in this area with basaltic, tephritic, andesitic and trachy andesit composition. Clinopyroxene, plagioclase, analcime and sometimes coarse olivine crystals are present in these rocks. Mineral chemistry studies suggested that clinopyroxene type in rocks is Diopside type. Existence of normal and reverse zoning in clinopyroxens deduces differentiation were effective factors on evolution of the rocks. Enriched elements Ti, Al, Na, and K of pyroxene core to the rim of the effect of metasomatism to in these rocks. Tectonomagmatic diagrams and compare the chemical composition of study area clinopyroxenes with other tectonic environment suggested that characteristics of alkaline rocks related to volcanic arc. According to geotermobarometric studies clinopyroxenes in study rocks formed at temperature 1150-1200ºC and pressure of 7-14 Kbars. The depth for generation of magma between 55-65 Km and average 60 Km estimated for these rocks.
M Poosti; M Fadaeian
Abstract
The study area is located in the Ardabil province and in the north of Meshkin shahr town. A large part of the areais formed of Eocene igneous rocks. These rocks include basaltic andesite, basalt, tephrite and occasionally analcimite. They are silica saturated or relatively saturated. ...
Read More
The study area is located in the Ardabil province and in the north of Meshkin shahr town. A large part of the areais formed of Eocene igneous rocks. These rocks include basaltic andesite, basalt, tephrite and occasionally analcimite. They are silica saturated or relatively saturated. According to tectonomagmatic diagrams, the original setting of the parental magma was a volcanic arc and subduction zone. The negative anomalies of Nb, the high ratio of LILE/HFSE, the high mounts of Al2O3& P2O5, the low titanium contents, and the degree of partial melting of the metasomatized upper mantle, strengthens the subduction related processes for the formation of the primary magma (alkali olivine basalt). Petrographic evidences suggest that the primary magma is mixed with crustal materials. The chemical composition of rocks, according to geochemical diagrams, is shoshonitic. These rocks may have been formed by the subduction of the oceanic crust of Neoteties during the Mesozoic and early Cenozoic periods. Releasing fluids exerted from the subducting slab, metasomatism of the lithospheric mantle and subsequently the appropriate conditions for melting of the metasomatized mantle, all led to the formation of potassic magmatism and finally, generation of magma with a shoshonitic nature found its way to the surface under the influence of an extension phase and complex fault systems.
