The Sanandaj-Sirjan zone of the Zagros orogenic belt is bordered to the northeast by the Urumieh-Dokhtar magmatic assemblage or the “Urmiah-Dukhtar” of Schroeder (1944) and to the southwest by the Zagros folded-thrust belt (Alavi, 2004). These petrographic and geochemical data are then used to shed light on the origin and tectonic setting of these rocks, particularly in relation to the initiation of Neotethys subduction. Apart from a few age determinations (Sabzehei et al., 1970, Valizadeh and Cantagrel, 1975) and field reports (Sabzehei and Berberian, 1973, Berberian and Nogol, 1974, Sabzehei, 1974, Berberian and Berberian, 1981), no detailed studies have been carried out on any of the Mesozoic plutonic rocks in the Sanandaj-Sirjan zone.Īccordingly, this contribution reports on petrographic, whole-rock geochemical and Sm–Nd isotope characteristics of the Siah-kuh granitoid stock (a probably Upper Triassic intrusion) in the southeastern part of the Sanandaj-Sirjan zone (Fig. They appear to have been generated extensively along and above the early Mesozoic subduction zone of the Sanandaj-Sirjan zone. The distribution of Mesozoic plutonic bodies in Iran is mostly restricted to regions close to the eventual active plate margins marked by ophiolitic-melange belts (Fig. The northwest–southeast trending Sanandaj-Sirjan zone (Stocklin, 1968 or the Zagros imbricate zone in Alavi, 1994) consists of Paleozoic-Triassic metamorphic rocks that are overlain by Phanerozoic shallow water sedimentary rocks of a passive continental margin and intruded by large-scale Mesozoic plutons ranging from gabbro to granite. This orogenic belt has been proposed to have resulted from the opening and subduction of the Neotethyan oceanic realm and subsequent oblique collision of Afro-Arabia (Gondwana) with the Iranian microcontinent in the Late Cretaceous–Early Tertiary (Berberian and King, 1981, Alavi, 1994, Alavi, 2004, Mohajjel and Fergussen, 2000). The Zagros orogenic belt of Iran consists of three parallel tectonic subdivisions from northwest to southeast: (1) the Urumieh-Dokhtar magmatic assemblage, (2) the Sanandaj-Sirjan zone (SSZ) and (3) the Zagros folded-thrust belt (Alavi, 2004) (Fig. Dehydration of subducted oceanic crust and partial melting of mantle wedge caused partial melting of subcontinental lithosphere, which resulted in the formation of metasomatised and enriched mafic arc magmas, at variable water fugacity and led to the formation of the Siah-kuh granitoid rocks. The onset of subduction of the Neotethys oceanic crust beneath the Central Iranian microcontinent in Triassic time could have accounted for the continental arc volcanism. These geochemical data suggest that the Siah-Kuh granitoid stock has characterisitics of metaluminous to slightly peraluminous, calc-alkaline, I-type granite formed in a volcanic arc setting. Nd isotope analyses of the Siah-Kuh granitoids yield an “errorchron” age of 199 ± 30 Ma (MSWD = 1.30), consistent with the field relationships and give Nd model ages ( T DM) from 0.81 to 1.64 Ga and εNd( T) values from +1.81 to +2.45 at 200 Ma. Alkali granites with the highest (La/Yb) N values and pronounced negative Eu anomalies are more differentiated products.
Granodiorites with the least fractionated HREE and a general absence of Eu anomalies suggest the involvement of plagioclase and absence of garnet during the melting processes. The chondrite normalized REE patterns are characterized by moderate LREE enrichment and unfractionated HREE. The Siah-Kuh granitoid rocks are characterized by enrichment in large ion lithophile elements (LILE) such as Rb, Ba, K, Ce and depletion in high field strength elements (HFSE) such as Y, Nb and Zr. It also contains a number of mafic enclaves of different sizes and is intruded by alkali granite and granophyre dikes along with monzonitic and a few dioritic dikes. The Siah-Kuh granitoid stock consists mainly of coarse to medium grained leucogranodiorite, leucomonzogranite and alkali granite with subordinate syenite. The Siah-Kuh stock intrudes Lower Paleozoic amphibolites of the Abshur metamorphic complex and Upper Devonian-Lower Carboniferous greenschists of the Sargaz metamorphic complex.
#FARSI ROZE SIAH PART 99 SERIES#
The Upper Triassic Siah-Kuh granitoid stock is part of a series of Triassic-Cretaceous intrusions in the Phanerozoic Sanandaj-Sirjan zone in the Zagros orogenic belt, south-central Iran.
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