Lahroud, a Paleo-Tethys Remnant in Northwestern Iran: Implications for Geochemistry, Radioisotope Geochronology, and Tectonic Setting

Abstract

—The Lahroud Ophiolite in northwestern Iran contains extensive zones of Paleozoic ophiolite as remnants of the Paleo-Tethys oceanic crust. The principal rock units are gabbro overlain by pillow basalt, which is intruded by granites and interbedded with pelagic sedimentary units including radiolarian cherts. Geochemistry and radioisotope studies, supported by Nd, Sm, Sr, and Pb isotope data, indicate that the Lahroud Ophiolite originates from a within-plate basaltic mantle source. The isotope studies show that the basalts are derived from Indian-type oceanic mantle sources. The radiogenic data indicate the involvement of subduction-related terrigenous materials in the source magma. All the rocks are geochemically cogenetic and were generated by fractionation of a melt with a composition of average E-MORB with a calc-alkaline signature. Two 40Ar/39Ar ages, 343 ± 3 Ma for muscovite minerals and 187.7 ± 7.7 Ma for glasses, suggest that metamorphic and basaltic rocks formed during the Late Paleozoic to Early Jurassic, respectively. Microfossil studies show the presence of Paleozoic biostratigraphy. The crystallization process and rifting into the oceanic crust in the Lahroud Ophiolite probably began in the Carboniferous, with volcanic activity continuing during the Late Triassic.

A Jurassic volcanic passive margin in Iran and Turkey

“…Due to the time progression of Jurassic intrusions in the central SaSZ and bimodal magmatism, a propagating continental rift was suggested for the C-SaSZ . In this discussion, we (Bozorg Seghinsara et al, 2017;Çimen, 2020;Doaee et al, 2020;Dokuz et al, 2010;Dokuz & Sünnetçi, 2019;Eyuboglu et al, 2016;Galoyan et al, 2018;Genç et al, 2010;Günay et al, 2019;Lechmann et al, 2018;Şen, 2007) and mafic parts of the Early Jurassic ophiolites (Sarifakioğlu et al, 2009;Topuz, Göçmengil, et al, 2013;Uysal, Ersoy, et al, 2015) Eurasia (Alavi, 1991;Zanchi et al, 2009;Karimpour et al, 2010;Hassanpour, 2021;Okay and Şahintürk, 1997). Others consider southward subduction of Palaeotethys beneath northern Turkey continued into Jurassic time to form a back-arc basin in the Sakarya Zone (Dokuz et al, 2010;Genç et al, 2010;Kandemir & Yilmaz, 2009;Karsli et al, 2017;Maffione & van Hinsbergen, 2018;Sengör & Yilmaz, 1981).…”

“…Palaeotethys is generally accepted to have formed in Permo‐Triassic time on the north side of Iran and Turkey. Some researchers accept that Palaeotethys subducted northward beneath Eurasia (Alavi, 1991; Zanchi et al, 2009; Karimpour et al, 2010; Hassanpour, 2021; Okay and Şahintürk, 1997). Others consider southward subduction of Palaeotethys beneath northern Turkey continued into Jurassic time to form a back‐arc basin in the Sakarya Zone (Dokuz et al, 2010; Genç et al, 2010; Kandemir & Yilmaz, 2009; Karsli et al, 2017; Maffione & van Hinsbergen, 2018; Sengör & Yilmaz, 1981).…”