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Geochronology and geochemistry of exotic blocks of Cadomian crust from the salt diapirs of SE Zagros: the Chah-Banu example

Asadi Sarshar, Maryam; Moghadam, Hadi Shafaii; Griffin, William L.; Santos, Jose F.; Stern, Robert J.; Ottley, Chris J.; Sarkarinejad, Khalil; Sepidbar, Fatemeh; O’Reilly, Sue Y.

Geochronology and geochemistry of exotic blocks of Cadomian crust from the salt diapirs of SE Zagros: the Chah-Banu example Thumbnail


Authors

Maryam Asadi Sarshar

Hadi Shafaii Moghadam

William L. Griffin

Jose F. Santos

Robert J. Stern

Khalil Sarkarinejad

Fatemeh Sepidbar

Sue Y. O’Reilly



Abstract

Cadomian calc-alkaline I-type and within-plate A-type igneous rocks are widespread in the crust of Iran where they are ascribed to a convergent margin associated with the southward subduction of Prototethyan oceanic lithosphere beneath N Gondwana. These rocks are found as unmetamorphosed magmatic rocks and their metamorphic equivalents (mafic to felsic gneisses) could have been generated in both Cadomian arcs and associated rear-arcs. Nearly all these exposures also contain metamorphosed metasediments, whereas Cadomian igneous rocks of central Iran are associated with thick sequences of unmetamorphosed terrigenous rocks. In the Zagros Fold-Thrust belt of S Iran, salt diapirs contain abundant xenoliths of Cadomian igneous and sedimentary rocks in association with evaporites, dolomites, carbonates, and banded iron-salt deposits. This paper presents new zircon U-Pb and geochemical-isotopic data from igneous clasts in the Chah-Banu salt diapir in SE Zagros. Petrographic and geochemical data indicate two different types of rock clasts; calc-alkaline, I-type dacites-rhyolites, and arc-related to E-MORB-OIB-like gabbros, basalts, and dolerites. New zircon U-Pb ages show that dacites formed at 538.2 ± 2.2 Ma, whereas gabbros show ages of 539.0 ± 1.8 Ma. Zircons from dacites have negative εHf(t) values of – 1.1 to – 8.3. In contrast, zircons from gabbros have higher εHf(t) values of +4.5 to +8.5, indicating crystallization from mantle-derived juvenile magmas. Bulk rock Nd-Sr isotopic data (e.g. ɛNd(t) = +0.3 to +4.0 and 87Sr/86Sr(i) = 0.7059 to 0.70848) for gabbros, dolerites, and basalts confirm that these rocks originated from a mantle source similar to enriched parts of the subcontinental lithospheric mantle, whereas dacites and rhyolites (with εNd(t) = −3.4 to −4.1 and 87Sr/86Sr(i) = 0.70806 to 0.70907) show strong interaction with, and/or re-melting of older continental crust. We suggest that the bimodal calc-alkaline and E-MORB-OIB-like magmatic rocks in salt diapirs as well as associated evaporites and sedimentary rocks formed in a retro-arc rifted basin behind the Cadomian magmatic arc.

Citation

Asadi Sarshar, M., Moghadam, H. S., Griffin, W. L., Santos, J. F., Stern, R. J., Ottley, C. J., …O’Reilly, S. Y. (2022). Geochronology and geochemistry of exotic blocks of Cadomian crust from the salt diapirs of SE Zagros: the Chah-Banu example. International Geology Review, 64(10), 1409-1430. https://doi.org/10.1080/00206814.2020.1787236

Journal Article Type Article
Acceptance Date Jun 22, 2020
Online Publication Date Jul 13, 2020
Publication Date 2022
Deposit Date Jul 30, 2020
Publicly Available Date Mar 28, 2024
Journal International Geology Review
Print ISSN 0020-6814
Electronic ISSN 1938-2839
Publisher Taylor and Francis Group
Peer Reviewed Peer Reviewed
Volume 64
Issue 10
Pages 1409-1430
DOI https://doi.org/10.1080/00206814.2020.1787236

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