Petrology of Chenask intrusive rocks in the eastern Qazvin, central Alborz: An explanation for Eocene magmatism in an extensional basin related to syn-collisional setting

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Abstract

The Chenasak intrusives are located in eastern Qazvin, western end of the central Alborz. These intrusives consist of granular-textured intermediate menzonite and syenite rocks with mineralogy mainly consisting of plagioclase, potassium feldspar, amphibole, and biotite with varying volume percentages. U-Pb zircon dating data indicate that the menzonite and syenite have approximately the same ages of 41.8±0.5 and 41.2±0.6 Ma, respectively. These rocks have high-potassium calc-alkaline to shoshonite geochemical characteristics and are enriched in large ionic radius elements (LILE) and light rare earth elements (LREE) and depleted in high field strength elements (HFSE) and heavy rare earth elements (HREE), indicating magmas formed in the subduction zone. Whole-rock Nd-Sr isotope ratios indicate that the ɛNd and 87Sr/86Sr values of these rocks vary from +0.5 to +1.2 and 0.70483 to 0.70648. Whole-rock chemistry and isotopic data indicate that the magma forming the menzonite and syenite was formed by the crystalline fractionation of the primary melt derived from the metasomatized mantle in a tensile basin formed by the rollback of the subducting plate during the collision of the Iran and Arabia plates.

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History

  • Receive Date: 02 October 2024
  • Revise Date: 16 December 2024
  • Accept Date: 18 December 2024

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