Mafic–intermediate plutonic rocks of the Salmas area, northwestern Iran: their source and petrogenesis significance

Abstract

The Salmas area, in the northernmost part of the Sanandaj-Sirjan zone of Iran, contains a crystalline mafic-intermediate complex that intrudes into the Precambrian metamorphic basement complex and is composed of gabbroic and gabbrodiorite cumulates and fine-grained non-cumulate gabbronorites and diorites. These rocks have fine-to coarse-grained texture and are mainly composed of plagioclase, pyroxenes, and amphibole. Major element geochemistry indicates that the pluton has a low-K with tholeiitic affinity. Variations of major and trace elements on Harker diagrams, including negative correlations MgO, Fe 2 O 3 , CaO, and Co and positive correlations Na 2 O, K 2 O, Rb, Ba, and La, with increasing SiO 2 and chondrite-normalized REE patterns, suggest that fractional crystallization of gabbroic rocks could have played a significant role in the formation of evolved rocks. The chondrite-normalized REE patterns are not fractionated (La N /Lu N = 1.3-5.4) and display strong Eu anomalies (Eu/Eu * = 1.15-1.76) in cumulate rocks, which we attributed to cumulus plagioclase. Sr and Nd isotopic ratios vary from 0.704698 to 0.705866 and from 0.512548 to 0.512703, respectively. Gabbronorites with high 143 Nd/ 144 Nd ratios, low 87 Sr/ 86 Sr ratios, and high MgO, Ni, and Cr contents indicate that they were generated from relatively primitive magmas. We used petrogenetic modelling to constrain sources. Trace element ratio modelling indicates that the gabbroic rocks were generated from a spinel-peridotite source via 5-20% degrees of fractional melting at a depth of ∼52 km. Major and REE modelling shows that the diorites are the products of fractional crystallization of gabbronorites.

The Neotethyan Sanandaj‐Sirjan zone of Iran as an archetype for passive margin‐arc transitions

“…Farther northwest, a group of shallow plutons to the south of Urumieh have yielded K‐Ar ages from 110 Ma to 76 Ma [ Ghalamghash et al ., , ] (Table ). In the northernmost SSA near Salmas, mafic to intermediate and felsic plutons intrude Early Cretaceous strata, are overlain by early Tertiary strata, and are presumably Late Cretaceous in age but are as yet undated radiometrically [ Ghaffari et al ., ].…”

Magma mixing/mingling in Salmas granodiorite, NW Iran: evidence from mafic microgranular enclaves

“…The plutons cropping out in the North part of the SSZ (i.e., Qorveh, Urumieh, Alvand, Saqez, Malayer-Boroujerd) are generally formed during the Mesozoic (Torkian et al 2008;Ghalamghash et al 2009;Shahbazi et al 2010;Arian et al 2011;Deevsalar et al 2014). Based on the timing of similar plutonic rocks in the SSZ (Ghaffari et al 2013), emplacement of Salmas pluton could have occurred during Cretaceous. The mixed rocks (granodiorites) cover an area of approximately 20 km 2 and are exposed at the contact of granitic and maficintermediate stocks which all of them are emplaced into Precambrian metamorphic complex (Khodabandeh et al 2002;Ghaffari 2008;Ghaffari et al 2013).…”

“…Based on the timing of similar plutonic rocks in the SSZ (Ghaffari et al 2013), emplacement of Salmas pluton could have occurred during Cretaceous. The mixed rocks (granodiorites) cover an area of approximately 20 km 2 and are exposed at the contact of granitic and maficintermediate stocks which all of them are emplaced into Precambrian metamorphic complex (Khodabandeh et al 2002;Ghaffari 2008;Ghaffari et al 2013). Marble, recrystallized limestone and a skarn zone have developed at the contact of mafic-intermediate rocks with the limestone which is a common phenomenon in North West of Iran (Mollaei et al 2009;Mollai et al 2014).…”

“…Ghaffari et al (2013) show that the diorites are evolved via crystal fractionation of mafic magmas (gabbroic rocks) which are products of melting of spinel-peridotite source. The produced dioritic melts underplate the crust-mantle boundary.…”

“…Minor/ accessory minerals include apatite, zircon, subhedral titanite, and Fe-Ti oxides. The mafic-intermediate rocks consist of plagioclase, clinopyroxene (diopside to augite), ortopyroxene (hyperstene), amphibole, biotite, Fe-Ti oxides, and accessory apatite and zircon (Ghaffari et al 2013).…”