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The Zagros Orogen formed during the Cenozoic collision of Arabia with Eurasia and resulted in the closure of the Neo‐Tethys Ocean. Collision was preceded by a complicated tectonic history involving Pan‐African orogenesis, Late Palaeozoic rifting and the formation of Neo‐Tethys, and subsequent Mesozoic convergence on the northern margin of the ocean contemporaneous with ophiolite obduction on its southern margin. The Sanandaj–Sirjan Zone (SaSZ) is a metamorphic belt within the Zagros Orogen of Gondwanan provenance. U–Pb zircon geochronology has revealed the presence of Pan‐African igneous and metamorphic basement complexes, in addition to minor late Palaeozoic plutons and abundant Jurassic plutonic rocks. This study presents a LA‐ICP‐MS U–Pb apatite age of 440.7 ± 3.7 Ma from a gabbroic body on the central north‐eastern margin of the SaSZ (Nodoushan region). Based on petrography and geochemistry, en route fractional crystallization of ascending magma was an important process in the evolution of the intrusive rocks. Geochemical characteristics imply that the south‐west Nodoushan alkaline gabbroic magma was originated from the asthenospheric mantle source, whereas the high ratios of (La/Yb)N and (Dy/Yb)N are related to the low degree of partial melting from the garnet‐bearing mantle source. Enrichment pattern of Nb, Ta, and Ti and depletion of Rb, Th, and Y are similar to the OIB pattern and intraplate alkaline magmatic rocks. High εNd(t) values (+1.29 to +1.50), low initial Sr isotopic ratios (0.703679–0.704098), and trace element ratios (e.g., Nb/La, Ce/Pb, Ba/Nb, and Th/Nb) indicate that crustal contamination was insignificant in its petrogenesis. The petrogenesis of the Nodoushan alkaline gabbroic rocks could be related to the presence of extensional phase, upwelling and decompressional melting of asthenospheric mantle in the rift basin which was associated with the opening of the Paleo‐Tethys Ocean in Late Ordovician to Silurian times. [ABSTRACT FROM AUTHOR]

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, Fe2O3, CaO, and Co and positive correlations Na2O, K2O, Rb, Ba, and La, with increasing SiO2and 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 (LaN/LuN= 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 high143Nd/144Nd ratios, low87Sr/86Sr 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. [ABSTRACT FROM AUTHOR]