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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]

Eocene igneous rocks along the Gangdese belt in southern Tibetan Plateau are important for understanding the India–Eurasia collision and Tibetan Plateau uplift. These magmatic rocks are widely considered to be related to roll-back or break-off of the Neotethyan slab during northward subduction. However, Eocene rhyolites in the northwestern Gangdese belt (SW Qiangtang margin) do not fit either the rollback or breakoff models. This paper investigates these Early Eocene lavas and compares them with contemporaneous igneous rocks along the Gangdese belt via detailed field observations, petrology, zircon geochronology, zircon Lu–Hf isotopes and whole-rock geochemistry. These felsic lavas form large outcrops in western Tibet and have two zircon U–Pb ages of 54.71 ± 0.14 Ma and 54.74 ± 0.27 Ma. They have high SiO2 and alkali contents, FeO*/MgO, and Ga/Al ratios as well as strongly negative Eu anomalies and slightly positive zircon εHf(t) values (+2.5 to +4.4). Both Ti-in-zircon and Zr saturation thermometers confirm high magmatic temperatures (~900°C). They are ferroan, A-type rhyolites. Furthermore, the distinctive low εHf(t) values imply that these rhyolites are likely partial melting products of the southwestern Qiangtang Terrane. The lithosphere in this region undergone long-term shortening and thickening since 80–95 Ma. Pre-thickened lithosphere may be a prerequisite for the Early Eocene delamination, and the simultaneous inducement is a far-field tectonic effect from the India–Eurasia collision. We suggest that: (1) India collided with Eurasia before 55 Ma and triggered delamination to form the Shiquanhe A-type rhyolites on the southwestern Qiangtang margin thereafter; and (2) tectonic stresses related to India–Eurasia collision during the Eocene were transmitted efficiently over large distances. [ABSTRACT FROM AUTHOR]

The M 6.5 earthquake that occurred in the Monte Cristo Range near Mina, Nevada on 15 May 2020 was exceptionally well-recorded with both seismic and geodetic instrumentation. The arid nature of the region also facilitated detailed ground mapping of the surface rupture. Here we integrate several independent data sets to illustrate the educational and research opportunities afforded by these rich data sets. We construct a series of models for slip at depth that are consistent with the satellite-derived geodetic data, the distribution of aftershocks, and the mapped surface rupture. We also show that the modelled depth of maximum slip is in good agreement with heat flow and laboratory data on quartz rheology defining the depth of the brittle-ductile transition. The Monte Cristo Range earthquake also suggests new approaches to seismic hazard assessment may be required for earthquakes in rapidly evolving tectonic regions such as the Walker Lane and Eastern California shear zone. [ABSTRACT FROM AUTHOR]

Deposits of semi-gemstones tourmaline, beryl, and garnet associated with Jurassic granites are found in the northern Sanandaj–Sirjan Zone (SaSZ) of western Iran, defining a belt that can be traced for about 400 km. Granitic magmas strongly interacted with or were derived from melts of continental crust and/or sediments. Based on morphologies, size, mineral assemblage, and contact relationships with host granite and associated metamorphic aureoles, these deposits are categorized into six types: (1) garnet in skarns, (2) tourmaline, beryl, and garnet in pegmatite and aplitic dikes, (3) disseminations and patches of tourmaline in leucogranites, (4) quartz-tourmaline veins in granite, (5) tourmaline and garnet in metamorphic aureoles, and (6) tourmaline orbicules in aplite. Tourmalines are mostly schorl and dravite, and garnets are mostly almandine, spessartine, and grossular. Tourmaline, beryl, and garnet from pegmatites in the contact aureole of Jurassic granites reflect segregations of Be, B, Mn, and Al bearing melts from the Jurassic peraluminous granites. Quartz-tourmaline veins and hydrothermal garnets in skarns reflect fluids exsolved from the surrounding metasediment and pegmatite melt. In contrast, tourmaline patches and orbicules developed from boron-rich aqueous fluids exsolved from cooling granitic magma. Distribution of semi-gemstones in the SaSZ shows that these are mostly related to pegmatites associated with Jurassic granitic intrusions. Mineral equilibrium considerations indicate that SaSZ semi-gemstones crystallized at P = 3.5–7.5 kbar (11.5–25 km deep) and temperatures of 550–650°C. SaSZ pegmatites fall in the muscovite (MS) and MS-rare element classes. They are Lithium Cesium Tantalum (LCT)-type pegmatites. Fluids responsible for gem mineralization were exsolved from cooling granite bodies and released by metamorphosed sediments. Further studies are needed to better understand the northern Sanandaj–Sirjan tourmaline–garnet–beryl semi-gemstone Province. [ABSTRACT FROM AUTHOR]

Cadomian calc-alkaline I-type and within-plate A-type igneous rocks are widespread in the crust of Iran where they are ascribed to a convergent margin associated with the southward subduction of Prototethyan oceanic lithosphere beneath N Gondwana. These rocks are found as unmetamorphosed magmatic rocks and their metamorphic equivalents (mafic to felsic gneisses) could have been generated in both Cadomian arcs and associated rear-arcs. Nearly all these exposures also contain metamorphosed metasediments, whereas Cadomian igneous rocks of central Iran are associated with thick sequences of unmetamorphosed terrigenous rocks. In the Zagros Fold-Thrust belt of S Iran, salt diapirs contain abundant xenoliths of Cadomian igneous and sedimentary rocks in association with evaporites, dolomites, carbonates, and banded iron-salt deposits. This paper presents new zircon U-Pb and geochemical-isotopic data from igneous clasts in the Chah-Banu salt diapir in SE Zagros. Petrographic and geochemical data indicate two different types of rock clasts; calc-alkaline, I-type dacites-rhyolites, and arc-related to E-MORB-OIB-like gabbros, basalts, and dolerites. New zircon U-Pb ages show that dacites formed at 538.2 ± 2.2 Ma, whereas gabbros show ages of 539.0 ± 1.8 Ma. Zircons from dacites have negative εHf(t) values of – 1.1 to – 8.3. In contrast, zircons from gabbros have higher εHf(t) values of +4.5 to +8.5, indicating crystallization from mantle-derived juvenile magmas. Bulk rock Nd-Sr isotopic data (e.g. ɛNd(t) = +0.3 to +4.0 and 87Sr/86Sr(i) = 0.7059 to 0.70848) for gabbros, dolerites, and basalts confirm that these rocks originated from a mantle source similar to enriched parts of the subcontinental lithospheric mantle, whereas dacites and rhyolites (with εNd(t) = −3.4 to −4.1 and 87Sr/86Sr(i) = 0.70806 to 0.70907) show strong interaction with, and/or re-melting of older continental crust. We suggest that the bimodal calc-alkaline and E-MORB-OIB-like magmatic rocks in salt diapirs as well as associated evaporites and sedimentary rocks formed in a retro-arc rifted basin behind the Cadomian magmatic arc. [ABSTRACT FROM AUTHOR]

Garnets show wide ranges of chemical compositions and are key minerals for reconstructing the thermodynamic evolution of metamorphic terranes. The properties of garnets – including Mohs hardness ~7, lack of cleavage, vitreous luster and multiple colors – also makes them useful as semi-gemstones. Garnets are widespread accessory minerals in igneous and metamorphic rocks of western and southern Iran and are especially abundant in skarns and regional metamorphic rocks. 45 garnet deposits of western and southern Iran show six associations: (1) skarn (35 locations); (2) peraluminous granitoid and rhyolite (4 locations); (3) alkaline granite (1 location); (4) metamorphic rocks (3 locations); and (5) ophiolites (2 locations). Distinct garnet compositions are found in each association: mostly grossular-andradite in skarn, Ti-andradite in alkaline granite, almandine in peraluminous granite and volcanic rocks, almandine-grossular in metamorphic rocks and andradite- uvarovite associated with ophiolites. Western and southern Iran garnets are mostly related to skarns around Cenozoic granitoid intrusions. Ti-rich garnet formed at the expense of clinopyroxenites in alkaline igneous complexes due to alkaline metasomatism. These associations are useful for understanding garnet semi-gemstone deposits in western and southern Iran. [ABSTRACT FROM AUTHOR]

Late Eocene – Oligocene volcanic rocks in the eastern Saveh region of the Urumieh-Dokhtar magmatic arc (UDMA) are representative of Paleogene magmatic activity in Iran. They show a wide range of silica-undersaturated to silica-oversaturated compositions, from basalt-trachy basalt and tephri-phonolite to trachyte-latite. Whole rock chemical compositions define a continuous assemblage of mafic and felsic rocks in terms of SiO2 (46.3 to 71.1 wt.%), Al2O3 (12.5–19.2 wt.%), K2O (2.06–12.23 wt.%) and TiO2 (0.41–1.75 wt.%) contents, Mg number (6.8–51) and K2O/Na2O ratios (0.53–30.2). Abundances of rare earth elements in the tephri-phonolite group are much higher than in the trachyte-latite and basalt-trachy basalt groups. Elevated contents of large ion lithophile elements such as Ba (191–7311 ppm) and Pb (6.49–118 ppm) as well as depletions in high field strength elements such as Nb (2.43–40.6 ppm), Ta (0.15–2.24 ppm), Zr (40.8–258 ppm) and TiO2 (0.40–1.77 wt.%) characterize these rocks. Initial ratios of 87Sr/86Sr from 0.7046 to 0.7074 and ɛNd(t) from +0.9 to +3.3 show that these were derived from parental magma extracted from partial melting of metasomatized mantle, namely amphibole- and/or phlogopite-bearing peridotite. Fractionation of feldspar, clinopyroxene, amphibole and phlogopite, and minor contamination with upper crust was responsible for the large variation of the rock types observed. We explain contemporaneous late Eocene – Oligocene calc-alkaline and high-K magmatic activity in the UDMA as due to the partial melting of both hot metasomatized asthenospheric and subcontinental lithospheric mantle in an extensional tectonic regime. This extensional regime probably developed due to the rollback of the subducted Neo-Tethys oceanic plate. [ABSTRACT FROM AUTHOR]

We address the growing controversy about the tectonic setting in which Jurassic magmatism of Iran occurred: arc or continental rift. In the Ghorveh area of the northern Sanandaj Sirjan zone (SaSZ), the Ghalayan metabasites are interlayered with marble and schist and locally cut by acidic dikes. Zircon U-Pb dating of the metabasitic rocks shows that these crystallized at ca. 145–144 Ma ago in the Late Jurassic (Tithonian). This complex was metamorphosed in the lower greenschist facies, however, some protolithic structures such as pillow lava and primary minerals are preserved. The metabasites are tholeiites with low SiO2 (45.6–50.5 wt.%), moderate Al2O3 (11.3–17.0 wt.%), and high TiO2 (0.7–2.9 wt.%) and Fe2O3 (9.4–14.1 wt.%). The Ghalayan metabasites are enriched in Light rare earth elements (LREEs) without significant Nb, Ta, Pb, Sr and Ba anomalies, similar to modern continental intra-plate tholeiitic basalts such as Afar and East African rifts. The Ghalaylan metabasites show wide ranges for 87Sr/86Sr(i) (0.7039–0.7077) and positive εNd(t) values (+0.1 to +4.6). These isotopic compositions are similar to those expected for slightly depleted subcontinental lithospheric mantle sources. Independently built discrimination diagrams indicate an intra-continental rifting regime for the source of Jurassic metabasites in the northern SaSZ. Geochemical and tectonic evidence suggests that rifting or a mantle plume was responsible for volcanic activity in the Upper Jurassic SaSZ. Considering the variation of ages of basaltic volcanism along the SaSZ, we suggest that Ghalayan basaltic magmatism reflected a submarine volcano that formed as part of the late stage continental rift, similar to Afar in the East African Rift system. Our results indicate that an extensional tectonic regime dominated SaSZ tectonics in the Middle to Late Jurassic. [ABSTRACT FROM AUTHOR]

The Baneh plutonic complex is situated in the Zagros suture zone of northwest Iran between the Arabian and Eurasian plates. This complex is divided into granite and appinite groups. Zircon U- Pb dating shows that granites crystallized 41-38 million years ago but appinites experience more protracted magmatic evolution, from at 52 to 38 Ma. Whole-rock chemical compositions show significant major and trace element variations between the two lithologies. Granitic rocks are more evolved, with high contents of SiO2 (62.4-77.0 wt%), low contents of TiO2 (0.25 wt%), MgO (0.05-1.57 wt%), and Fe2O3 (0.40-4.06 wt%) and high contents of Na2O + K2O (≈10 wt%). In contrast, appinites have low contents of SiO2 (51.0-57.0 wt%) and K2O (<2.1 wt%) and high Fe2O3 (6.4-9.35 wt%), MgO (2.0-9.9 wt%), and Mg number (Mg# = 35-76). The concentration of rare earth elements in the appinites is higher than in granitic rocks, making it difficult to form granites solely by fractionation of appinite magma. (87Sr/86Sr)i and εNd(40 Ma) in both groups are similar, from 0.7045 to 0.7061 and -1.2 to +2.6, except for a primitive gabbroic dike with εNd(40 Ma) = +9.9. Appinites show mainly typical I-type characteristics, but granites have some S-type characteristics. The sigmoidal shape of the Baneh pluton and its emplacement into deformed Cretaceous shales and limestone showing kink bands, asymmetric and recumbent folds in a broad contact zone, with pervasive ductile to brittle structures in both host rocks and intrusion, indicate that magma emplacement was controlled by a transpressional tectonic regime, perhaps developed during early stages in the collision of Arabia and Eurasian plates. [ABSTRACT FROM AUTHOR]

Ultramafic portions of ophiolitic fragments in the Arabian–Nubian Shield (ANS) show pervasive carbonate alteration forming various degrees of carbonated serpentinites and listvenitic rocks. Notwithstanding the extent of the alteration, little is known about the processes that caused it, the source of the CO2or the conditions of alteration. This study investigates the mineralogy, stable (O, C) and radiogenic (Sr) isotope composition, and geochemistry of suites of variably carbonate altered ultramafics from the Meatiq area of the Central Eastern Desert (CED) of Egypt. The samples investigated include least-altered lizardite (Lz) serpentinites, antigorite (Atg) serpentinites and listvenitic rocks with associated carbonate and quartz veins. The C, O and Sr isotopes of the vein samples cluster between −8.1‰ and −6.8‰ for δ13C, +6.4‰ and +10.5‰ for δ18O, and87Sr/86Sr of 0.7028–0.70344, and plot within the depleted mantle compositional field. The serpentinites isotopic compositions plot on a mixing trend between the depleted-mantle and sedimentary carbonate fields. The carbonate veins contain abundant carbonic (CO2±CH4±N2) and aqueous-carbonic (H2O-NaCl-CO2±CH4±N2) low salinity fluid, with trapping conditions of 270–300°C and 0.7–1.1 kbar. The serpentinites are enriched in Au, As, S and other fluid-mobile elements relative to primitive and depleted mantle. The extensively carbonated Atg-serpentinites contain significantly lower concentrations of these elements than the Lz-serpentinites suggesting that they were depleted during carbonate alteration. Fluid inclusion and stable isotope compositions of Au deposits in the CED are similar to those from the carbonate veins investigated in the study and we suggest that carbonation of ANS ophiolitic rocks due to influx of mantle-derived CO2-bearing fluids caused break down of Au-bearing minerals such as pentlandite, releasing Au and S to the hydrothermal fluids that later formed the Au-deposits. This is the first time that gold has been observed to be remobilized from rocks during the lizardite–antigorite transition. [ABSTRACT FROM PUBLISHER]

Whether or not magmatic arcs evolve compositionally with time and the processes responsible remain controversial. Resolution of this question requires the reconstruction of arc geochemical evolution at the level of a discrete arc system. Here, we address this problem using the well-studied Central American Volcanic Arc System (CAVAS) as an example. Geochemical and isotopic data were compiled for 1031 samples of lavas and intrusive rocks from the ~1100 km-long segment of oceanic CAVAS (Panama, Costa Rica, Nicaragua) built on thickened oceanic crust over its 75 million year lifespan. We used available age constraints to subdivide this data set into six magmatic phases: 75–39 Ma (Phase I or PI); 35–16 Ma (PII); 16–6 Ma (PIII); 6–3 Ma (PIV); 5.9–0.01 Ma (PVa arc alkaline and PVb adakitic); and 2.6–0 Ma (PVI, Quaternary to modern magmatism, predominantly ≪ 1 Ma). To correct for magmatic fractionation, selected major and trace element abundances were linearly regressed to 55 wt.% SiO2. The most striking observation is the overall evolution of the CAVAS to more incompatible element enriched and ultimately continental-like compositions with time, although magmatic evolution took on a more regional character in the youngest rocks, with magmatic rocks of Nicaragua becoming increasingly distinguishable from those of Costa Rica and Panama with time. Models entailing progressive arc magmatic enrichment are generally supported by the CAVAS record. Progressive enrichment of the oceanic CAVAS with time reflects changes in mantle wedge composition and decreased melting due to arc crust thickening, which was kick-started by the involvement of enriched plume mantle in the formation of the CAVAS. Progressive crustal thickening and associated changes in the sub-arc thermal regime resulted in decreasing degrees of partial melting over time, which allowed for progressive enrichment of the CAVAS and ultimately the production of continental-like crust in Panama and Costa Rica by ~16–10 Ma. [ABSTRACT FROM AUTHOR]