Early Mesozoic sedimentary‒tectonic evolution of the Central-East Iranian Microcontinent: Evidence from a provenance study of the Nakhlak Group

Abstract

In Central Iran, the mixed siliciclastic-carbonate Nakhlak Group of Triassic age is commonly seen to have a Cimmerian affinity, although it shows considerable resemblances with the Triassic Aghdarband Group in far northeastern Iran, east of Kopeh-Dagh area, with Eurasian affinity. The Nakhlak Group is composed of the Alam (Late Olenekian-Anisian), Baqoroq (Late Anisian-?Early Ladinian), and Ashin (Ladinian-?Early Carnian) formations consisting mainly of volcanoclastic sandstone and shale and fossiliferous limestone. The Baqoroq Formation contains also metamorphic detritus. Sandstone petrofacies reflect the detrital evolution from active volcanism to growing orogen and again active volcanism. Textural and modal analyses of volcanic lithic fragments from the Alam Formation reflect the eruption style and magma composition of a felsic to intermediate syn-sedimentary arc activity. The

Permian–Triassic magmatism in response to Palaeotethys subduction and pre-Late Triassic arrival of northeast Gondwana-derived continental fragments at the southern Eurasian margin: Detrital zircon evidence from Triassic sandstones of Central Iran

“…Such subdivision has already been recognized by Alavi et al (1997). The lower part comprises first-cycle sedimentary and volcanic material as well as some recycled metamorphic basement (Hashemi Azizi et al, 2018a). The upper part comprises less sedimentary and volcanic material and is chiefly composed of low-grade metamorphic detritus (Zanchi et al, 2009b;Hashemi Azizi et al, 2018a).…”

“…Petrographic analysis of thin sections (i.e. modal analysis via point counting) revealed that most of the sandstone samples from the Alam Formation include dominantly volcanic detritus mainly represented by lithic fragments and single phenocrysts such as volcanic quartz grains and feldspars (Hashemi Azizi et al, 2018a). The average total quartz-feldspar-lithic fragment ratio is Qt21.6:F38.7:L39.7 (Hashemi Azizi et al, 2018a).…”

“…The lower part comprises first-cycle sedimentary and volcanic material as well as some recycled metamorphic basement (Hashemi Azizi et al, 2018a). The upper part comprises less sedimentary and volcanic material and is chiefly composed of low-grade metamorphic detritus (Zanchi et al, 2009b;Hashemi Azizi et al, 2018a). Baqoroq Formation sandstones have an average total quartz-feldspar-lithic fragment ratio of Qt45:F19.7:L35.3 (Hashemi Azizi et al, 2018a).…”

“…Limestone and shale beds are fossiliferous and contain remains of, for example, ammonoids, bivalves and crinoids, suggesting a Ladinian-?Early Carnian age (Tozer, 1972;Vaziri and Fürsich, 2007;Balini et al, 2009). Sedimentary structures characteristic for Bouma sequences (Bouma, 1962) and Nereites ichnofacies suggest that the Ashin Formation was deposited by distal turbidity currents (Hashemi Azizi et al, 2018a). Petrographic analysis of thin sections showed the Ashin Formation sandstones contain chiefly K-feldspar and volcanic detritus as well as some fossil fragments (Hashemi Azizi et al, 2018a).…”

“…Sedimentary structures characteristic for Bouma sequences (Bouma, 1962) and Nereites ichnofacies suggest that the Ashin Formation was deposited by distal turbidity currents (Hashemi Azizi et al, 2018a). Petrographic analysis of thin sections showed the Ashin Formation sandstones contain chiefly K-feldspar and volcanic detritus as well as some fossil fragments (Hashemi Azizi et al, 2018a). The average total quartz-feldspar-lithic fragment ratio is Qt35:F46.5:L18.5 (Hashemi Azizi et al, 2018a).…”