From Jurassic rifting to Cretaceous subduction in NW Iranian Azerbaijan: geochronological and geochemical signals from granitoids

• Published in: Contributions to mineralogy and petrology Vol. 173; no. 12; pp. 1 - 16
• Main Authors: Lechmann, Anna, Burg, Jean-Pierre, Ulmer, Peter, Mohammadi, Ali, Guillong, Marcel, Faridi, Mohammad
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.12.2018; Springer; Springer Nature B.V
• Subjects: Analysis; Cretaceous; Dikes; Earth; Earth and Environmental Science; Earth Sciences; Embankments; Geochemistry; Geochronology; Geochronometry; Geology; Isotopes; Jurassic; Lava; Lithosphere; Magma; Magmatism; Mantle; Mineral Resources; Mineralogy; Ocean basins; Original Paper; Petrology; Precambrian; Radiometric dating; Rifting; Rock intrusions; Rocks; Rocks, Igneous; Sedimentation; Subduction; Subduction (geology); Trace elements; Volcanic rocks; Zircon; Zirconium; Iran; Azerbaijan; Cretaceous subduction; NW Iran; Granitoids; Jurassic rifting; Zircon geochronology
• ISSN: 0010-7999; 1432-0967
• DOI: 10.1007/s00410-018-1532-8

Previous interpretations of a Jurassic subduction in Iran were based on trace element classification diagrams for granitoids, but their reliability is questionable, underscored by modern examples of continental break-up zones such as the Baja California. We present new field observations, bulk rock geochemistry, Sr and Nd isotope analyses and U–Pb zircon geochronology to assess the age and tectonic setting of previously undated intermediate to felsic magmatic rocks cropping out in the Precambrian basement of NW Iranian Azerbaijan. The geochronology revealed an uneven distribution in space and time: Late Jurassic (159–154 Ma) intrusions and dikes are alkaline to calc-alkaline. Their melt source is mantle dominated with a distinct continental contribution disclosed by radiogenic isotopes and abundant inherited zircon cores. Mid-Cretaceous (112–96 Ma) plutonic bodies and associated volcanic rocks occur only to the east of the major Siah Cheshmeh–Khoy Fault. They have geochemical signatures typical of a metasomatized mantle. In consistence with the sedimentation history of the area, our new interpretation attributes the Late Jurassic magmatism to thinning of a continental lithosphere in a rift-related setting. Mid-Cretaceous magmatism was produced by oceanic subduction beneath the Central Iran continent. We interpret the 40-Ma age gap between the two magmatic episodes as the time of opening of the oceanic basin witnessed by the Khoy ophiolite in the study area.