provenance of siliciclastic Baqoroq Formation, Central Iran, based on petrography and geochemistry: Implication for the evolution of active margin of south Eurasia

Abstract

A mixed siliciclastic-carbonate sequences of the Triassic Nakhlak Group in Central Iran has a unique lithology, but appears some similarities with the Agh-Darband Group in northeastern Iran. Nakhlak Group is composed of three formations: the Alam Formation which is a marine sequence of mixed siliciclastic-carbonate rocks with turbiditic affinity; the Baqoroq Formation is conglomerate sequence with sandstone and shale intercalations composed of volcaniclastic, metamorphic, and carbonate grains; and the Ashin Formation which is a thin bedded shale and sandstone sequence accompanied with limestone intercalations with open marine trace fossils and turbidite sedimentary structures. Petrographic evidences of the Baqoroq Formation diagnosed three main lithologies including carbonate pebbles which are most-likely originated from the Alam Formation, low grade metamorphic rocks that are probably derived from the Anarak Metamorphic Complex(?) and volcaniclastic materials from syn-sedimentary volcanic activities. Petrofacies study revealed three detrital modes of sandstone including litharenite, feldspathic litharenite and lithic arkose. Chemical index of alteration calculated from major oxide elements showed medium grade chemical alteration. Geochemical analysis shows felsic igneous parent rocks and palaeo-tectonic situation of magmatic arc in an active continental margin, which could be in connection with magmatic activities in southern Eurasian active margin. In general, all data and information confirmed that depositional basin of the Agh-Darband back-arc basin at the southern Eurasian active margin as depositional environment for the Nakhlak Group. Later the Nakhlak Group detached from the Turan plate and attached to the Cimmerian block and moved to the present day position by rotation of Central Iranian Microcontinent.

Keywords

• Baqoroq
• Triassic
• Central Iran
• geochemistry
• provenance