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Petrogenesis and geodynamic evolution of the Kajan Neogene subvolcanic rocks, Nain, Central Iran

Golkaram, Shirin, Rashidnejad–Omran, Nematollah, Azizi, Hossein, Asahara, Yoshihiro, Buchs, David ORCID:, McDonald, Iain ORCID: and Santos, José Francisco 2016. Petrogenesis and geodynamic evolution of the Kajan Neogene subvolcanic rocks, Nain, Central Iran. Chemie der Erde - Geochemistry 76 (4) , pp. 567-578. 10.1016/j.chemer.2016.08.007

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Kajan subvolcanic rocks in the Urumieh–Dokhtar magmatic arc (UDMA), Central Iran, form a Late Miocene-Pliocene shallow-level intrusion. These subvolcanics correspond to a variety of intermediate and felsic rocks, comprising quartz diorite, quartz monzodiorite, tonalite and granite. These lithologies are medium-K calc-alkaline, with SiO2 (wt.%) varying from 52% (wt.%) to 75 (wt.%). The major element chemical data also show that MgO, CaO, TiO2, P2O5, MnO, Al2O3 and Fe2O3 define linear trends with negative slopes against SiO2, whilst Na2O and K2O are positively correlated with silica. Contents of incompatible trace elements (e.g. Ba, Rb, Nb, La and Zr) become higher with increasing SiO2, whereas Sr shows an opposite behaviour. Chondrite-normalized multi-element patterns show enrichment in LILE relative to HFSE and troughs in Nb, P and Ti. These observations are typical of subduction related magmas that formed in an active continental margin. The Kajan rocks show a strong affinity with calc-alkaline arc magmas, confirmed by REE fractionation (LaN/YbN = 4.5–6.4) with moderate HREE fractionation (SmN/YbN = 1.08–1.57). The negative Eu anomaly (Eu/Eu* <1), the low to moderate Sr content (< 400 ppm) and the Dy/Yb values reflect plagioclase and hornblende (+- clinopyroxene) fractionation from a calc-alkaline melt Whole–rock Sr and Nd isotope analyses show that the 87Sr/86Sr initial ratios vary from 0.704432 to 0.705989, and the 143Nd/144Nd initial ratios go from 0.512722 to 0.512813. All the studied samples have similar Sr-Nd isotopes, indicating an origin from a similar source, with granite samples that has more radiogenic Sr and low radiogenic Nd isotopes, suggesting a minor interaction with upper crust during magma ascent. The Kajan subvolcanic rocks plot within the depleted mantle quadrant of the conventional Sr-Nd isotope diagram, a compositional region corresponding to mantle-derived igneous rocks.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Environmental Sciences
Subjects: Q Science > Q Science (General)
Uncontrolled Keywords: Urumieh–Dokhtar magmatic arc (UDMA); Magma differentiation; Sr and Nd isotope ratios; Calc-alkaline magmas
Publisher: Elsevier
ISSN: 0009-2819
Date of First Compliant Deposit: 28 September 2016
Date of Acceptance: 29 August 2016
Last Modified: 06 Nov 2023 20:41

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