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.

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., Sarkarinejad, K., Sepidbar, F., & 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: Jul 13, 2021
• 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
• Public URL: https://durham-repository.worktribe.com/output/1265185