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The continental crust of Iran is dominated by abundant calc-alkaline and alkaline plutonic and volcanic rocks and by rifted basins filled with mostly terrigenous sedimentary rocks that formed at a Late Ediacaran to Cambrian extensional convergent plate margin along the northern margin of Gondwana. Here we present new zircon U–Pb age, geochemical, and isotopic data from plutonic (granite-granodiorite) and metamorphic (gneiss) rocks in the Kariznou region of NE Iran to provide insights into the nature of the Cadomian convergent margin of Iran. Geochemical data indicate calc-alkaline signatures, characterized by strong depletions in Nb, Ta, P, and Ti and arc-like trace element patterns. New zircon U–Pb ages show that calc-alkaline granitoids and granitic gneiss formed at ~564 to 537 Ma and 538 Ma, respectively. Bulk rock Sr-Nd isotopic data of calc-alkaline rocks have εNd(t) = –5.42 to −5.53 and −6.93 to −7.43 for granite and gneiss, respectively. The gneisses show stronger interaction with and/or re-melting of older continental crust than do granitic rocks. We interpret Kariznou magmatic rocks as forming in association with strong extension accompanied by crustal assimilation. Extension initiated ~570 Ma with the deposition of Late Ediacaran sediments, and magmatism began at 545–535 Ma, generating calc-alkaline magmas. The tectonomagmatic evolution of the Kariznou region encapsulates the prolonged transition of Cadomian Iran from a strongly extensional convergent margin, possibly as a result of oblique oceanic subduction and slab roll-back of the subducting Proto-Tethys oceanic lithosphere, culminating in the formation of an Early Palaeozoic passive margin on the northern side of Gondwana. [ABSTRACT FROM AUTHOR]

Several Mesozoic ophiolites in Iran formed in response to Late Cretaceous subduction initiation. Here we review the geology, petrography, mineralogy and geochemistry of mantle rocks from the Nain, Neyriz, Khoy, Esfandagheh and Fannuj ophiolites. They are remnants of Neo-Tethys ocean lithosphere formed during subduction initiation and were emplaced onto the southern flank of Eurasia. Most show SSZ-type geochemical affinity. We summarize the composition of mantle sections from these five representatives, which comprise lherzolites and harzburgites with minor dunite lenses and sometimes chromitites. Spinels in lherzolite from all regions are characterized by low chromium number [Cr# = Cr/(Al + Cr)] of 0.09 to 0.56 and plot in the abyssal peridotite field, whereas spinel in harzburgite and dunite-chromitite have Cr# of 0.41 to 0.73 and 0.45 to 0.86, respectively, showing geochemical affinities with forearc peridotites and boninites, respectively. Lherzolites and harzburgites have low rare earth element (REE) contents and experienced around 15% and 25% partial melting, respectively. Ophiolitic peridotites from the Nain (inner Zagros ophiolitic belt), Khoy, and Neyriz (outer Zagros ophiolitic belt) complexes are depleted in light REE and show flat heavy REE patterns. By contrast, peridotites from the Fannuj (Makran ophiolitic zone) and Esfandagheh (outer Zagros ophiolitic belt) complexes are characterized by flatter and U-shaped REE patterns, respectively, similar to those of SSZ peridotites. Based on the compositions of olivine and spinel, we infer that chromitites and their dunite envelopes experienced wider variations in oxygen fugacity (fO2), equilibrium temperatures, and spinel Cr# values than those of the surrounding lherzolites and harzburgites, suggesting interaction between residual mantle harzburgites and H2O-rich and highly oxidized SSZ melts. Lherzolites from all regions and harzburgites of Nain, Neyriz and Fannuj are MOR-type peridotites that plot in the overlapping space of MOR peridotites and were generated in an extensional environment. These are forearc peridotites that were in equilibrium with tholeiitic melts generated during early proto-forearc or back-arc spreading during subduction initiation, whereas spinels of dunites and high-Cr chromitites were in equilibrium with boninitic melts. [ABSTRACT FROM AUTHOR]

Broadly similar Early to Middle Jurassic stratigraphic sequences including bimodal igneous rocks of the Sanandaj–Sirjan Zone of Iran and the Sakarya Zone of Turkey suggest that these formed in a common tectonic setting in an extensional basin that evolved from a terrestrial magmatic rift to a marine shelf and passive continental margin. Whole‐rock chemistry and Sr–Nd isotope signatures indicate derivation of mafic melts from partial melting of the subcontinental lithosphere. Decompression associated with extension led to 5%–30% partial melting of spinel–garnet lherzolite with minor involvement of continental crust, producing tholeiitic to transitional basaltic magma. Extensional basins inverted during the Mid‐Late Jurassic. These relationships suggest the Early to Middle Jurassic formation of a volcanic rifted margin on the SW Eurasian margin, similar to that of offshore Norway. [ABSTRACT FROM AUTHOR]

The eastern Sakarya Zone (SZ), one of the Alpine Himalayan Belt's main components, has complex Mesozoic–Cenozoic geodynamic evolution, which remains controversial. Early-Middle Jurassic volcano-sedimentary successions (Şenköy Formation) extensively outcrops in Gümüşhane region, NE Turkey. It is regarded as a critical unit to understand the Mesozoic tectonic evolution of the eastern Sakarya Zone. One of the Şenköy Formation's predominant units is sandstone succession, preserving implications for paleoenvironmental conditions and tectono-sedimentary development of Neotethys Ocean. Thus, a combined analysis of comprehensive petrography, whole-rock major, trace and rare earth element data is carried out on the sandstones, which are well constrained as late Sinemurian- Pliensbachian. The sandstones are mainly arkosic to lithic arenites in lithology showing poor textural maturities. They are mostly represented by relatively high ICV, low CIA, high K2O/Al2O3, Fe2O3+ MgO, TiO2, Th/U, pronounced negative Eu anomaly, enriched LREEs, elevated GdN/YbN, low Ce/Ce*, Ni/Co, La/V and Zr/Ti. The petrographic and geochemical characteristics imply that the sediments may have experienced relatively low chemical weathering processes and slight reworking and recycling processes with a short transport distance before deposition in the basin. Early Jurassic sandstone successions were interpreted as a transgressive series, showing a predominantly open sea environment with oxidizing paleoenvironmental conditions. The sandstone samples' paleoenvironment is likely to be located along the southern margin of the arc and the Neotethyan basin to the south. The extensional and trans-extensional tectonic regime might have played an essential role in controlling the basin's isolated-half graben and/or asymmetric geometry, leading to changes in the provenance of studied sandstone samples. Thus, the geochemical signature differences are probably associated with basement-related proximal origins and minor effects of the multi-phases petrogenesis that experienced different source to sink processes. Early Jurassic sandstones were probably derived from multi-genetic source rocks, including (i) granite and (ii) metamorphic rocks. Our new data has also indicated that other source rocks can include mafic to felsic volcanic succession. The possible provenance for granitic pluton and metamorphic rocks can be provided by the Hercynian heterogenetic crystalline basement widespread throughout the SZ. However, mafic to felsic volcanic rock source is likely to be associated with the pre-Early Jurassic nearby volcanic-arc, which is rarely recorded in the eastern SZ. The source rock signatures may imply a close genetic link with ancient magmatic-arc generation due to the southward subduction of Palaeotethys. [ABSTRACT FROM AUTHOR]