Central Iranian Microcontinent Research Articles

Neoproterozoic-Early Cambrian Northern Chah-Farsakh Cu-Zn VMS-type deposit, Iran: Constraints from geology, geochemistry, fluid inclusions and geodynamic

Northern Chah-Farsakh is the first seafloor VMS described in the Torud-Chahshirin metallogenic belt of Iran. The deposit is hosted by Neoproterozoic-Early Cambrian mafic (basaltic andesitic)-siliciclastic rocks in volcano-sedimentary basin. The evolution of the ore-bearing basin is governed by the Proto-Tethys Oceanic crust subduction beneath the Central Iranian microcontinent. Three ore facies can be distinguished based on the ore textures studies: stringer zone ore facies, massive-replacement ore facies, bedded ore and distal facies. Pyrite, chalcopyrite, magnetite and sphalerite are the main minerals, together with minor amounts of pyrrhotite, bornite, tetrahedrite and tennantite. Textures include laminated, banded, replacement, massive, and vein-veinlet texture. There is a distinct metal zonation in the massive sulfide orebody; Gold, Ag, and Zn contents increase vertically from the stringer to the bedded ore facies; Cu and Co increase in the massive ore facies, and Pb is highest in the stringer zone. Ore mineralization in the Northern Chah-Farsakh deposit has emplaced in two stages. The fine-grained ore bands (stage 1) which are intricately interlayered with host rock beds, exhibit sedimentary structure such as laminae and bedding are consistent with a syn-sedimentary origin. Coarser-grained stage 2 ores have massive and vein-veinlet textures that are considered to form by replacement during sub-seafloor fluid flow. Based on SEM-EDS analysis, significant compositional variations were observed in the Py-1b grains. Py-1b is enriched in Pb compared to Py-1a. The elemental distribution map shows that the chalcopyrite (Cpy-2) minerals in Northern Chah-Farsakh deposit do not have variable composition and are homogeneous. Fluid inclusions in quartz minerals rom the footwall stringer zone have trapping temperatures between 203 and 500 °C with salinities (3.39–16 wt% NaCl equiv.) higher than modern seawater. Fluid inclusion studies suggest that the ore-forming fluids were derived from seawater. High level of Se in the massive ore facies of the Northern Chah-Farsakh supports the formation of mineralization from a high-temperature hydrothermal fluid. The Northern Chah-Farsakh Cu-Zn VMS deposit typify the mafic-siliciclastic type (Besshi-type), where the majority of the host stratigraphy is composed of a mafic flow-volcaniclastics and sedimentary rocks.

Apatite U–Pb geochronology and whole rock, Sr–Nd–Pb isotopic geochemistry of XV mafic‐ultramafic intrusion, Bafq, Central Iran: Implications for petrogenesis and tectonic setting

AbstractThe XV mafic‐ultramafic intrusion is located in the western part of the Posht‐e‐Badam Block (PBB) within the Central Iranian Micro‐Continent (CIMC). Petrographically, the intrusion is composed of gabbro and pyroxenite. Apatite U–Pb dating has established the crystallization age of this intrusion to be 363 ± 67 Ma. The XV intrusive rocks are tholeiitic to slightly calc‐alkaline in nature and are characterized by an enrichment of large ion lithophile elements (LILE) and light rare earth elements (LREE) relative to high field strength elements (HFSE) and Heavy Rare Earth Elements (HREE), respectively. The major oxide elements display continuous trends relative to SiO2. The 87Sr/86Sr(i) ratios range from 0.7045 to 0.7056, and the εNd(i) values range from 2.63 to 3.30. In addition, the 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios exhibit a narrow range, varying from 18.68 to 18.70, 15.67 to 15.71, and 38.84 to 38.99, respectively. The geochemical and isotopic characteristics suggest that the parental magma was derived from a Sub‐ Continental Lithospheric Mantle (SCLM) that was modified by oceanic slab‐derived components. The locations of the XV intrusive rocks in εNd(i) versus TDM (Ga) and Nb/La versus discrimination diagrams further support this conclusion. Fractional crystallization is identified as the dominant process influencing the formation of distinct lithological units within the XV intrusive rocks. Our newly presented isotopic and geochronological data, when considered in the regional context, suggest that the XV intrusive rocks were formed in an extensional tectonic setting. In this scenario, upwelling from the asthenospheric mantle induced heating, leading to the melting of previously subduction‐modified SCLM. Comparative analysis with previously published ages indicates that extensional magmatism in the PBB continued into the Middle Paleozoic.

Kinematic analyses of the asymmetric boudins in the Tutak area within the Zagros hinterland fold-and-thrust belt, Iran

Exhumation of the Tutak gneiss dome occurred in a transpressional regime between the Arabian plate and the Central Iranian microcontinent. The Tutak gneiss dome is located in the eastern part of the basement-involved Zagros hinterland fold-and-thrust belt. This dome consists of exhumed middle crust including the Tutak and Sourian metamorphic complexes, which are lied on its core and edges, respectively. Integrated structural, microstructural, and flow vorticity analyses in quartzo-feldspathic mylonites and well-developed asymmetrical boudins provide significant information regarding the kinematic characteristics coeval with the Tutak gneiss dome development. Asymmetrical boudins have been used as potential shear sense markers throughout the mantle of the Tutak gneiss dome. The deformed quarzitic layers within the slate belt host domino and shear-band boudins, demonstrating both sinistral and dextral shear senses. The mean vorticity number (Wm) was estimated from the quartzo-feldspathic mylonites and asymmetric boudins. Using the hyperbolic distribution (HD) and the RXZ strain ratio/quartz c-axis fabric (RXZ/β) methods. The estimated Wms from the HD method and quartz c-axis patterns are 0.69 to 0.82 and 0.6 to 0.92, respectively, suggesting a combination of 41% to 72% simple- and 28% to 59% pure-shear components. The close match confirms that asymmetric boudins can be a good strain estimator. The estimated deformation temperature (528.33 ± 50 °C) from the opening angles (OAs) of quartz c-axes suggests amphibolite facies conditions. Our results show that the Tutak gneiss dome developed under sub-simple shear conditions, which stretched and shortened the dome parallel and orthogonal to the transpressional boundaries, respectively.

U-Pb geochronology and geochemistry of the Torud igneous rocks: Implications for post-collision Eocene magmatism in northeast Iran

New geochemical and U-Pb isotopic data from the Torud volcanic and subvolcanic rocks and their associated dikes exposed along the southern margin of the Sabzevar-Torud zone provide new evidence for Early-Middle Eocene, post-collision magmatism in northeast Iran. The 52–46 Ma (late Ypresian-Lutetian) U-Pb age interval of zircons separated from these rocks confirm the paleontological age of nummulite-bearing limestone interlayers. Inherited zircons separated from these igneous rocks have a much wider range of U-Pb ages that include Archean, Paleoproterozoic, Mesoproterozoic, Carboniferous, Permian, Triassic, Middle Jurassic, and Late Cretaceous. Most volcanics and subvolcanic rocks display high-K calcalkaline and shoshonitic trends. Distinct crystal fractionation patterns of the volcanic and subvolcanic rocks suggest magmatic differentiation in separate magma chambers. The studied rocks, depleted in the HFSE and enriched in the LILE, display nearly homogeneous isotopic Sr (0.7039–0.7055) and Nd (0.5126–0.5129) ratios and positive ɛNd values (0.08–0.56) indicating partial melting from an enriched lithospheric mantle source that was slightly contaminated with crustal material. Fluids, especially those released from the subducted slab, affected the composition of the source for the studied rocks. The magmatism occurred in the Torud area after the Late Cretaceous-Paleocene collision of the Central Iran microcontinent and Binalud-Kopeh-Dagh blocks and the Early-Middle Eocene break-off of the subducted slab.

Quaternary deformation patterns in East–Central Iran, constrained by coseismic–postseismic displacements of the 2017 Hojedk triplet earthquake in the Kerman Province

The Central Iranian Microcontinent (CIM) in east-central Iran is located north of the active Arabia–Eurasia collision zone. Here, we report on the structure, deformation patterns, and earthquake occurrences along the dextral Lakar–Kuh and Godar fault systems in the CIM. The geometry of these fault systems marks a major restraining bend responsible for surface and rock uplift in the Plio–Pleistocene that produced the Mian Kuh mountain range. The 2017 Hojedk triplet earthquake (Mw = 5.8–6.0) occurred in the Mian Kuh Range. Sentinel–1 A Interferometer Synthetic Aperture Radar (InSAR) images (descending and ascending) were used to extract the coseismic displacements associated with the earthquake and its aftershocks. The results indicate a maximum displacement of ∼20 cm, corresponding to hanging wall uplift along the radar Line-of-Sight (LOS) direction. The Geodetic Bayesian Inversion (GBIS) of the coseismic deformation indicates that the causative faults of the Hojedk earthquakes were two reverse faults with NW–SE–strikes and SW–dips, with minor dextral slip components. Given the focal mechanism solutions and the epicenter locations of the triple earthquake sequence, we infer that these faults at the southern termination of the Lakar–Kuh Fault represent two segments (with different dip angles) of a previously unrecognized, blind reverse fault (a splay of the Godar Fault at depth). The Hojedk Earthquake and the geometry and kinematics of its causative faults highlight the strong potential of seismic hazard zones along the strike-slip fault systems in the CIM.

The gabbro-diorite magmatism from the Narm area, western Kuh-e-Sarhangi (Central Iran): Evolution from Eocene magmatic flare up to Miocene asthenosphere upwelling

Geodynamically, the Kashmar-Kerman Tectonic Zone (KKTZ) is one of the most perplexing tectonomagmatic belts of the Central Iran Microcontinent (CIM), comprising two important districts, Bafq and Kuh-e-Sarhangi. The Late Neoproterozoic-Early Cambrian granitoids, metamorphic rocks, and mildly metamorphosed volcansedimentary sequences are the oldest geologic outcrops in the Narm area, which is located in the western part of Kuh-e-Sarhangi. Alkaline gabbro-diorites with relatively high contents of K2O (1.99–3.03 wt%) and Na2O (2.7–5.99 wt%) are among the youngest intrusive rocks in the area, representing a within-plate provenience. These rocks were emplaced into Paleozoic sedimentary units as mafic-intermediate stocks, sills and dykes. Geochemically, these rocks could have resulted directly from partial melting (e.g., FeOT/MgO>1, Nb/La>0.5) with no considerable indication of assimilation with crustal materials (e.g., Ti/Zr > 30, Ti/Y > 200). Assimilation and fractional crystallization cannot account for magma evolution of gabbro-diorite rocks in the Narm area, using rare earth element ratios and geochemical models. There are also some geochemical signatures of an asthenospheric origin for the Narm gabbro-diorite rocks, such as the low ratios of La/Nb (1.5) and La/Ta (22). U–Pb zircon ages show that the Narm gabbro-diorites formed during two major episodes of magmatism in Central Iran: 40.3 ± 0.1 Ma in the Late Eocene (Bartonian) for gabbroic units and 8.04 ± 0.05 and 7.86 ± 0.05 in the late Miocene (Tartonian) for diorite stocks and diorite sills, respectively. Despite a time difference of more than thirty million years, geochemical similarities between the Eocene gabbro rocks and the Miocene diorite from the Narm area are striking. It is proposed that the best scenarios for the west of Kuh-e-Sarhangi mafic-intermediate magmatic pulses along with the deep faults of the Central Iran, are an Eocene magmatic flare up and a Miocene asthenosphere upwelling. Temporally and spatially, these rocks are comparable to the Cenozoic alkaline intrusive rocks of the Bafq region.

The folds and faults kinematic association in Zagros

The Zagros orogenic belt, one of the most prominent and famous collisional belts in the central part of the Alpine-Himalayan orogenic chain, is located between the southern margin of the Central Iranian microcontinent and the northern margin of the Arabian plate. The structural architecture and folds and faults relationships of a significant segment of the south-central part of the Zagros’ hinterland are investigated in this study through stereoscopy of aerial photographs, interpretations of satellite images, consideration of the major ground topographic variations, and field research. This research found that there must have been at least two major deformation events: (1) a ductile phase, which is older than the Eocene, and (2) a semi-brittle deformation stage, which is younger than the early Miocene and is represented by thrusting, folding, and strike-slip faulting. The presence of numerous fault-related folds and fold-accommodation faults in this area demonstrates the close kinematic relationship between folding and faulting. Based on the topographic changes, a major hidden tear fault and a basement hidden back thrust, which play important roles in the architecture of the area, have been suggested.

New Insights into Interpretation of Aeromagnetic Data for Distribution of Igneous Rocks in Central Iran

Abstract —New insights in the aeromagnetic data over the Central Iranian Microcontinent (CIM) have revealed interesting results for future studies and exploration. This work presents the interpretation of different magnetic analyses and the calculated 3D inversion model to provide important insights into the distribution of igneous rocks in the area that may be traced under significant cover. By analyzing several hundred magnetic susceptibility data points and aeromagnetic anomalies of known igneous rocks over the area, it was determined that mafic–ultramafic intrusive rocks generally have a high magnetic susceptibility and produce a strong magnetic response. Intermediate–felsic intrusive rocks have a low magnetic susceptibility and show a smooth gradient variation and commonly regular shape. Volcanic rocks show a wide range of magnetic susceptibility; therefore, the aeromagnetic anomalies are often random or show strong amplitude with high frequency signals and are rapidly eliminated when an upward continuation is applied. Based on the results of analysis of different magnetic maps and 3D inversion of data, and combining this information with known outcropped of igneous rocks, we revealed 1215 concealed intrusive rocks and 528 volcanic rocks in the area. We also renewed the boundaries of tens outcropped igneous rocks. The known and new mapped igneous rocks can be identified as 12 regions (or zones) for intrusive rocks and 4 regions for volcanic rocks. The results indicate that the mafic–ultramafic rocks are mainly located in the Sistan suture zone of eastern Iran along the Nehbandan fault zone. They also show that the many parts of the Lut block as the main structure of CIM have been under magmatic events, so that most of concealed igneous rocks are distributed in the middle and southern part of the Lut block. Volcanic rocks are widespread in the southeastern and northern parts of the area such as the Urumieh-Dokhtar Magmatic Arc, North Lut, and Bam region.

Biostratigraphy of Baghamshah Formation based on calcareous nannofossils in the Southwest Tabas, Iran

The Tabas Block is part of the Central Iran microcontinent, located between the Lut Block in the East and the Yazd Block in the West. The Baghamshah Formation is the second lithostratigraphic unit from the sedimentary cycle of the Magu Group and the Baghamshah Subgroup in the Jurassic of Tabas Block. This formation is conformably underlaid with the grey pisoidal limestones of the Parvadeh Formation and overlaid with the Pectinid limestones of the Kamar-e-Mehdi Formation (Esfandiar Subgroup). In this research, the biostratigraphy of the Baghamshah Formation in the Rizu and Kamar-e-Mehdi sections, based on calcareous nannofossils, is examined. The thickness of the Baghamshah Formation in the Rizu section is 270 m (mostly including marl and green shales with intercalation of limestones and calcareous sandstones), and in the Kamar-e- Mehdi section is 236 m (composed of gypsiferous marly shales, marl, marly shales and alternation of marl-shale with limestones and calcareous sandstones). According to the taxonomic studies in the Rizu section, 52 species belong to 24 genera, and in the Kamar-e-Mehdi section, 45 species belong to 23 genera of calcareous nannofossils. Based on index calcareous nannofossils, the CC1, CC2, CC3, and CC4 biozones established by Sissinghh in both sections were determined. It is mentioned that CC5 biozone only occur in Kamar-e-Mehdi section. According to the identified biozones, the suggested age of the Baghamshah Formation is early Berriasian–early Hauterivian in the Rizu section, and early Berriasian–late Hauterivian in the Kamar-e-Mehdi section. Keywords: biostratigraphy, Baghamshah, calcareous nannofossils,Tabas, Iran.

Early Cambrian highly fractionated granite, Central Iran: Evidence for drifting of northern Gondwana and the evolution of the Proto-Tethys Ocean

The Zarin granitic body is located in the eastern part of the Yazd Block in the Central Iran microcontinent. The granite has variable granular to mylonitic textures. New zircon U-Pb dating shows that the granitic rocks crystallized at 535–530 Ma. The pluton has high SiO2 abundances (72.1–77.5 wt%), K2O (4.4–6.3 wt%) and low MgO (0.2–0.7 wt%) contents, as well as high K2O/Na2O (1.10–1.97) and A/CNK (molar ratio of Al2O3/(CaO + Na2O + K2O)) 0.9–1.1 ratios, and is dominantly peraluminous. The granite is enriched in light rare earth elements (LREEs) relative to heavy REEs (HREEs), has negative Eu anomalies, and is extremely depleted in Nb, Ba, P, Ta and Ti. It is also characterized by variable but commonly high 87Sr/86Sr(i) (0.7018–0.7093) and negative εNd(i) values of −1.1 to −2.6. The geochemical features indicate that the rocks are highly fractionated I-type granite and have undergone extensive fractional crystallization of hornblende, biotite and feldspar. Results are consistent with melting of an evolved lower crust source during the subduction of the Proto-Tethys Ocean. The emplacement of the Zarin granite is contemporaneous with the extension of a Cadomian continental arc on the north side of Gondwana, that rifted away to create the Rheic Ocean to its south. Cadomian basement rocks in Iran are interpreted as an important link between western and eastern sectors of the Late Proterozoic-Early Paleozoic orogenic belts along the northern side of Gondwana, and the histories of the Rheic, Iapetus and Proto-Tethyan oceans

Geochemistry and petrogenesis of mafic volcanic rocks from Kahak area (Urumieh-Dokhtar magmatic arc)

The Kahak mafic volcanic rocks in the central part of the Urumieh-Dokhtar Magmatic Arc are composed of ‎basalts‏ ‏and‏ ‏basaltic ‎andesite and show sub alkaline to transitional affinity. They are calc-alkaline based on the tholeiitic index (THL). U-‎Pb zircon dating ‎yields almost 60‎‏ ‏‎(Middle Paleocene) and 24 to 19 Ma (Late Oligocene–Early Miocene) for andesitic basalt and basaltic ‎rocks ‎respectively. These rocks ‎are identified by LREE and LILE enrichment and HFSE depletion with relatively negative or without ‎Eu ‎anomalies and E-MORB like ‎pattern in multiple spider diagrams that.attributed to the subduction of the Neotethyan oceanic ‎slab ‎beneath the central Iranian microcontinent. Based on petrography, trace and rare earth elements, and isotopic features, ‎fractional ‎crystallization played a significant role ‎during magma evolution in these rocks. Trace element modeling suggests that the ‎studied mafic ‎rocks were derived by partial melting ‎within the spinel‏ ‏lherzolite mantle. Isotopic ratios also show that they resulted from ‎lithospheric ‎mantle metasomatized by ‎released fluids from subducted slab sediments. The studied samples might have formed in the ‎extensional regime ‎followed ‎by slab rollback and undergone a continental arc to back-arc basin transition during the Paleocene to ‎Miocene. This basin might ‎have ‎been closed in the‏ ‏middle Miocene.

Regional magnetic and gravity structures and distribution of mineral deposits in Central Iran: Implications for mineral exploration

Regional-scale magnetic and gravity data have been enhanced to identify major structures and distinguish geophysical blocks in order to evaluate the distribution of major mineral deposits and prospects in Central Iran. Major structures and coherent magnetic blocks have been defined from magnetic data enhanced using a combination of upward continuation and edge enhancement filters. Broad-scale regional structural architecture and coherent density blocks have been defined from gravity data enhanced using the tilt angle. Crustal thickness was calculated from Bouguer gravity data. Integration of the structures, magnetic, density and depth characteristics derived from the complementary geophysical techniques have been used to correlate and interpret the regional distribution of mineral deposits and occurrences to assist future exploration. Porphyry Cu deposits in the Kerman metallogenic zone are shown to be closely associated with major structures in high magnetic and gravity blocks that are coincident with the Tertiary volcanic units, and in areas where the crustal zone was interpreted to be more than 50 km thick. Pb–Zn deposits in Central Iranian Microcontinent are shown to be spatially associated with major structures, predominantly outside of the high magnetic response blocks, and commonly overlay the low gravity and thick crustal zones. In the north of the study area, one group of Fe deposits display a close correlation to blocks with both a high magnetic and high gravity response. Along strike to the southeast, a second group cluster is seen in an area with a moderate magnetic and a low gravity response.

Slip partitioning and inclined transpression in the Bazargan fold and thrust belt, Central Iran Microcontinent, Kerman area, SE Iran

Inclined transpression can be defined in terms of simultaneous contraction and strike-slip and dip-slip shearing. An example of an upper-crustal inclined transpression zone is exposed at Bazargan area, SE Iran. As with most natural transpression zones, deformation at Bazargan area is heterogeneous, and widespread kinematic strain partitioning has given rise to an irregular distribution of strain components and resulting structures. Based on structural and strati graphical evidence, deformational events are divided into two stages: (1) a Late Triassic event and (2) a Late Cretaceous to Miocene event. A wide range of known structures at the map and outcrop scales show the effect of slip partitioning on the structural evolution of this area during this period. The dynamic analysis based on folds, fault striations and calcite twin data show a NNE-SSW trend for the compressive axes in this area. The results of dynamic analysis reveal that the orientation of the compressive axes did not change during late Triassic to present. Moreover, they show that the structural evolution of the Bazargan area occurred under the effect of continues deformation phases which is related to contraction, dip slip and strike slip component. Furthermore, the results indicate that the evolution of Bazargan area in the south of Tabas block is compatible with an inclined transpression model.

Unravelling metamorphic ages of suture zone rocks from the Sabzevar and Makran areas (Iran): Robust age constraints for the larger Arabia–Eurasian collision zone

AbstractIn this study we establish a time frame for metamorphic processes affecting Neotethyan suture zones at the northern (Sabzevar) and southern (Makran) margin of the Central Iranian Microcontinent. For this purpose, we have applied Rb–Sr and U–Pb geochronology to blueschist‐ and amphibolite facies rocks from these occurrences. So far, no isotopic ages are available for high‐P/low‐T rocks from the Sabzevar area which are exposed in the Govain and Chili mountains near Soltanabad. Three newly dated blueschists from the Govain mountain yielded Rb–Sr ages of 56.52 ± 0.32, 57.20 ± 0.32, and 55.12 ± 0.33 Ma respectively. These ages provide the first unambiguous evidence for late Palaeocene to early Eocene high‐P metamorphism in the Sabzevar zone and confirm the accuracy of earlier age assignments that were derived indirectly. The clearly confirmed age difference between late Palaeocene–early Eocene blueschists of the Govain mountain and kilometre‐scale dismembered HP granulites with Early Cretaceous (Albian) metamorphic ages from outcrops c. 60 km to the west of Soltanabad further corroborates interpretations that these rocks are not related to the same subduction zone complex. The blueschists record closure of an Albian to Late Cretaceous back‐arc basin, whereas the granulites formed due to subduction of older oceanic lithosphere. Uranium–Pb zircon dating of an amphibolite from the Iranshahr region in the Makran Zone yielded an intercept age of 87.8 ± 1.8 Ma and weighted mean age of 88.1 ± 1.7 Ma. Rb–Sr mineral isochrons for seven blueschist‐ and amphibolite facies samples from the same area generated very consistent ages of c. 84 Ma (± <1–3 Ma), regardless of metamorphic grade. The apparent contradiction that rocks recording different P–T conditions have identical metamorphic ages either indicates tectonic mixing of rocks during exhumation that originally had formed at the same time at different depths of the subduction system, or very rapid exhumation so that differences in closure temperatures became indistinguishable. The new data are similar, but much more precise, than previously reported K–Ar ages and suggest that most of the existing data had not been significantly compromised by contamination with extraneous Ar. Potassium–Ar indications for older blueschist‐ and/or amphibolite facies metamorphism (>85 Ma) have not yet been confirmed but can be reconciled with the larger geological frame implying that northward subduction of the Arabian plate beneath the Bajgan–Durkan continental block started shortly after c. 120 Ma.

Strain and vorticity analyses using rotated porphyroclasts in the Tanbour metamorphic rocks: Evidence of transpressional deformation along the Sanandaj-Sirjan metamorphic belt, SW Iran

The Tanbour Metamorphic Complex (TMC) is located within the Sanandaj-Sirjan Metamorphic Belt, SW Iran, along the northeastern margin of the Afro-Arabian plate. Detailed kinematic and strain analyses were combined with vorticity estimates on rocks from the TMC to document patterns and geometry of deformation. The strain parameter measurements including strain ratio in the XZ principal plane of strain ellipsoid (RXZ), strain ellipsoid shape (K) and strain intensity (D), highlight the deformed gneissic rocks in the TMC exhibit constrictional to approximately plane-strain shape of the strain ellipsoids. Several kinematic shear sense indicators including S/C fabrics, mantled porphyroclasts, oblique grain shape, micro-shears with bookshelf geometry and mineral fish show top-to-the-SE sense of shear. The quantitative kinematic analyses highlight that Wk varies between 0.64 and 0.78, implying a general shear flow with 44% < simple shear <58% and 42% < pure shear <57%. The exhumation of TMC is attributed to the exhumation-controlled transpressive tectonic process during oblique convergence between the Afro-Arabian continent and the Central-Iranian microcontinent which started since Upper Cretaceous.

Geochemistry of Rare Earth Element in garnet group minerals in some regional metamorphic complexes - Central Iran Micro-Continent (CIMC)

Geochemistry of Rare Earth Element in garnet group minerals in some regional metamorphic complexes - Central Iran Micro-Continent (CIMC)

Petrogenesis of gabbroic rocks from the Malayer plutonic complex (Sanandaj-Sirjan zone, west Iran)

The Sanandaj-Sirjan zone (SSZ), extending from northwest to southeast of Iran, is a continental arc developed during subduction of the Neotethyan oceanic crust below the Central Iran microcontinent. The Malayer plutonic complex (MPC) is located in northern half of the SSZ and is characterized by the occurrence of subduction-related ultramafic to felsic rocks. Calculated composition of the melts in equilibrium with minerals from the gabbroic rocks were compared with the literature whole rock data from the MPC and from other neighboring complexes in the SSZ. The results showed that the parental melts at the origin of the gabbroic rocks is a high Mg andesite (HMA) with a sanukitoid geochemical affinity originated by a melt-rock reaction process between a felsic melt and ultramafic rocks. This study further confirms that although ultramafic rocks are not commonly found associated with subduction-related rocks, their petrogenetic role cannot be underestimated.

Geochemistry and petrogenesis of Raviz-Shanabad intrusions (SE UDMB): an evidence for Late Eocene magmatism

ABSTRACT The SE segment of the Urumieh-Dokhtar Magmatic Belt (UDMB), known as Dehaj-Sarduieh Magmatic Belt, includes a huge pile of Palaeogene volcano-sedimentary rocks and Eocene to Miocene mafic to felsic intrusions. In the middle of this belt (in Raviz-Shanabad, W Rafsanjan) mafic-intermediate intrusions (as stocks and/or dikes-sills) are abundant and have intruded into the volcano-sedimentary rocks of Dehaj-Sarduieh. The thickness of dikes range from 0.5 to >5 metres and the minimum diameter of the intrusions is ~10 m. These rocks are highly porphyritic and have gabbroic to dioritic composition. Petrographic data indicate that the main rock-forming minerals include plagioclase (labradorite to anorthite based on the new electron microprobe data), pyroxene (augite), and opaque (magnetite and titanomagnetite) minerals, set in a granular groundmass of the same minerals. New zircon U-Pb data show that the age of these rocks is 34.39 ± 0.31 Ma (Late Eocene). These rocks show calc-alkaline characteristics and their geochemical signatures are compatible with arcs with a derivation from subduction zones. Estimated temperature and pressure from Clinopyroxene of these rocks suggest a temperature in the range of 1050° to 1150°C and a pressure of >2 kbar. These data show the formation depth of these intrusions should be ~18 km. Initial 87Sr/86Sr ratio for these rocks varies from 0.70403 to 0.70409, whereas 143Nd/144Nd isotope ratio changes between 0.5128 and 0.5129, corresponding to εNd(i) values of +3.5 to +6.6. These geochemical and isotopic evidences show that the melts originated by 5% partial melting of amphibole spinel peridotite mantle source. Petrographic observations as well as mineral chemistry and isotopic studies indicate that assimilation-fractional crystallization (AFC) has probably played a dominant role in the evolution of the Raviz-Shanabad intrusions. We suggest these intrusions formed as a part of the Late Eocene high-flux magmatism in SE segment of the UDMB in an active continental margin, which was related to the subduction of Neo-Tethys oceanic lithosphere beneath the Central Iranian microcontinent.

The age and geochemistry of the Bardkish syenite, northwest Iran: Syenite formation during Neo‐Tethyan subduction

AbstractSHRIMP U–Pb dating of zircon from two representative samples of the Bardkish syenitic pluton, Urumieh plutonic complex, northwestern Iran, yielded a Late Cretaceous weighted mean 206Pb/238U age of 91.1 ±0.8 Ma (Turonian). The pluton is characterized by high K2O content, Ti–Nb–Ta depletion, enrichment in light rare earth elements and large ion lithophile elements compared to high field strength element, Mg‐rich biotite and calcic amphibole, suggesting a shoshonitic affinity. Geochemical features of the Bardkish syenite are consistent with derivation by fractional crystallization of initial mafic parent magmas. It is most likely that primary magma of the syenite originated from a metasomatized subcontinental lithospheric mantle source with minor crustal component, and underwent a fractional crystallization process during its emplacement. The estimates of trapping pressures and temperatures suggest that crystallization began at the middle crustal level (less than 11 km) near 700–730 °C. The generation of the Bardkish syenite could be related to the subduction of Neo‐Tethyan oceanic crust beneath the Central Iranian microcontinent and it possibly marks a major magmatic episode prior to the final closure of the Neo‐Tethyan ocean in northwest Iran.

Geochemistry and mineral chemistry of gabbroic rocks from Horjand of Kerman province, Southeast of Iran: Implications for rifting along the northeastern margin of Gondwana

The Horjand area is part of the Kashmar-Kerman tectonic zone in the Central Iranian block, where the oldest continental crust of Iran can be found. Mafic igneous rocks associated with sedimentary units (gypsum, shale, limestone, dolomite and sandstone) belong to the magmatism of the Late Neoproterozoic–Early Cambrian Desu Series. Based on petrographic studies, the mafic igneous rocks comprise medium to coarse gabbro, micro-gabbro and hornblende-gabbro. The rocks mainly consist of plagioclase, olivine, clinopyroxene, biotite, amphibole and Fe-Ti oxides. The gabbroic rocks have a variable compositional range, with SiO2 (44.6–52.9 wt. %), MgO (2.94–13.83 %), CaO (5.56–15.23 wt. %) and TiO2 (1.19–2.68 wt. %) contents. Petrographic evidence and geochemical data suggest that fractional crystallization has played an important role in the evolution of the ascending magma of the gabbroic rocks. The chemical composition of the minerals is similar to those of gabbroic rocks that were formed in a non-orogenic environment. The crystallization of clinopyroxene of gabbros mainly occurred under temperatures ranging from 1045 to 1216 °C. The geochemical characteristics and mineral compositions of the gabbros show that the samples predominantly have alkaline to minor tholeiitic affinities. During magma ascent, crustal contamination was minor or absent. Rare earth element modeling demonstrates that the magma of the Horjand gabbros was produced from 10 to 15 percent partial melting of a spinel-garnet lherzolite mantle source. Chondrite-normalized rare earth element (REE) patterns are LREE-enriched with (La/Yb)N of 4.50-12.82. Both normalized REE and trace-element spidergrams are similar to patterns of HIMU-OIB (high mu (μ = U/Pb)-ocean island basalt) or intraplate alkaline magmatic rocks. The gabbros geochemically display an intra-plate tectonomagmatic setting without subduction geochemical characteristics. Based on the available data and mineral chemical composition the development of the Horjand gabbroic rocks could be related to an extensional phase, with upwelling melting of the asthenospheric mantle in the continental rift resulting in alkaline magmatism of Late Neoproterozoic–Early Cambrian age, in the Central Iranian micro-continent.