Post-collisional polycyclic plutonism from the Zagros hinterland: the Shaivar Dagh plutonic complex, Alborz belt, Iran

Abstract

-The petrological and geochronological study of the Cenozoic Shaivar Dagh composite intrusion in the Alborz Mountain belt (NW Iran) reveals important clues to decipher complex relations between magmatic and tectonic processes in the central sectors of the Tethyan (Alpine-Himalayan) orogenic belt. This pluton is formed by intrusion at different times of two main magmatic cycles. The older (Cycle 1) is formed by calc-alkaline silicic rocks, which range in composition from diorites to granodiorites and biotite granites, with abundant mafic microgranular enclaves. The younger cycle (Cycle 2) is formed by K-rich monzodiorite and monzonite of marked shoshonitic affinity. The latter form the larger volumes of the exposed plutonic rocks in the studied complex. Zircon geochronology (laser ablation ICP-MS analyses) gives a concordia age of 30.8 ± 2.1 Ma for the calc-alkaline rocks (Cycle 1) and a range from 23.3 ± 0.5 to 25.1 ± 0.9 Ma for the shoshonitic association (Cycle 2). Major and trace element relations strongly support distinct origins for each magmatic cycle. Rocks of Cycle 1 have all the characteristic features of active continental margins. Shoshonitic rocks (Cycle 2) define two continuous fractionation trends: one departing from a K-rich basaltic composition and the other from an intermediate, K-rich composition. A metasomatized-mantle origin for the two shoshonitic series of Cycle 2 is proposed on the basis of comparisons with experimental data. The origin of the calc-alkaline series is more controversial but it can be attributed to processes in the suprasubduction mantle wedge related to the incorporation of subducted mélanges in the form of silicic cold plumes. A time sequence can be established for the processes responsible of the generation of the two magmatic cycles: first a calc-alkaline cycle typical of active continental margins, and second a K-rich cycle formed by monzonites and monzodiorites. This sequence precludes the younger potassic magmas as precursors of the older calc-alkaline series. By contrast, the older calc-alkaline magmas may represent the metasomatic agents that modified the mantle wedge during the last stages of subduction and cooked a fertile mantle region for late potassic magmatism after continental collision.

Geochemistry and geochronology of thevolcano-plutonic rocks associated with the Glojehepithermal gold mineralization, NW Iran

“…In contrast, volcanic and plutonic rocks found in the western section of the Alborz Magmatic Belt are highly mineralized. This mineralization is related to numerous granitoid bodies with calc-alkaline to shoshonitic affinity [4,10,[33][34][35][36][37] The Precambrian metamorphic unit consists of schist, phyllite, and felsic rocks. Cambrian strata include dolomitic marble and phyllite, discordantly overlying the Precambrian metamorphic rocks.…”

Fluid Inclusion Investigations of the Masjed Daghi Copper-Gold Porphyry-Epithermal Mineralization, East Azerbaijan Province, NW Iran

“…The most important plutonic rocks in the region that host most of copper, gold, and molybdenum mineralizations at the both banks of Araxes River belong to the intrusive rocks of Gharadagh. Unlike most of the known porphyry deposits of Iran which are situated in the Urmia-Dokhtar zone, the northwestern ore deposits of Iran are located in the Alborz-Pontides zone that continue to northeast of Turkey, and Lesser Caucasus [9]. The porphyry and epithermal deposits of Agarat, Paraghachai, and Kajaran in Armenia [10] …”

Geochemistry, Sr–Nd–Pb isotopes and geochronology of amphibole- and mica-bearing lamprophyres in northwestern Iran: Implications for mantle wedge heterogeneity in a palaeo-subduction zone

“…Two main Cenozoic magmatic arcs are found, namely the Urumieh-Dokhtar magmatic arc and the Alborz magmatic belt, which overlap partially in northwestern Iran. Magmatism started during Cretaceous times but voluminous magmatic bodies formed from late Tertiary until Quaternary (e.g., Dilek et al, 2009;Aghazadeh et al, 2011).…”