Iraqi Zagros Research Articles

Cretaceous Limestone Dolomitization and Argument of Its Mg2+ Sources: Exampling the Bekhme and Qamchuqa Formations in the Zagros Collision Belt

This study unveils new considerations regarding the dolomitization of the Bekhme and Qamchuqa formations (BQFs), two reefal Cretaceous units in the Iraqi Zagros collisional belt. Previous studies proposed the dolomitization of these formations due to the ascent of Mg-rich hydrothermal solutions through deep faults but lacked substantial supporting evidence. This paper present new considerations suggesting that the dolomitization of the BQFs resulted from the Cretaceous environmental conditions and basin paleogeographic setting of the platform on which these formations were deposited. To justify this consideration, seven proofs presented. First is the occurrence of dolomite as vast layers extending tens of kilometers laterally and bounded between limestone beds, which resemble a strata-bound occurrence. Second is the absence of vertical selective dolomitization such as, hydrothermal mineralization, vertical dolomite dykes, hydrothermal vents, tubes, or zones. Third is the barrenness of most of the fault surfaces and their surrounding rocks with selective dolomitization. Fourth is the sharp boundary between the dolomite and limestone layers, indicating a sudden environmental change from lagoon to reef or forereef. Fifth is the record of dolomitization in the sediments reworked by bioturbation, evident in thalassinoides burrows. Sixth is the succession of BQFs underlain by limestone and green marl devoid of dolomitization and hydrothermal upward movement. Seventh is the contradictory notion of hydrothermal dolomitization among the most recent study published in the Science journal which atributed dolomitization to normal temperate on earth surface. In the present study, the source of the Mg is argued and its presence is attributed to the warmth of the Arabian platform (plate) near the equator during the Cretaceous period. Another source is the connection of the Arabian platform with the Neo-Tethys Sea, which was the locus of Mg-rich mafic volcanism in the form of arcs and mid-oceanic ridge topography, which supplied a voluminous amount of Mg to the Arabian carbonate platform through ocean currents.

Problemy ophiolitów Zagros i ciał bazaltowych, przykłady z Regionu Kurdystanu, północny Irak

In the Iraqi Zagros, there are ten ophiolites and basaltic bodies, the famous ones are Penjween, Mawat, Bulfat and Peshashan Ophiolite complexes in addition to basaltic bodies such as Kata Rash, Avroman, Gercus, Chalki, and Hamrin basaltic bodies. The present study describes more than 12 significant problems concerning the previous assigning of the bodies as igneous rocks. These problems are observable in the field, laboratory, and in most previous works of literature that oppose the magmatic origin of these bodies. Our study explicated all aspects of each problem and clarified how the problems contradict magmatic crystallization and aid the sedimentary origin of these claimed igneous bodies. Finally, the interpretations of all the problems were collected as conjugate pieces of evidence for appraisal of the new origin of all igneous bodies in the Iraqi and Iranian Zagros belt. The outcomes consider the ophiolitic and basaltic rocks metamorphosed volcaniclastic sandstones (greywackes or mafic sandstone). These sandstones belong to fresh or metamorphosed greywackes of stratigraphic units of the Paleocene-Eocene Walash Formation (as distal facies) and Kata Rash Conglomerate (as proximal facies) which were previously considered volcanic rocks. These sediments are sourced originally from Urumeiah-Dokhtur Magmatic Arc (ADMA) and deposited inside Neo-Tethys, present Sanandaji-Sirjan Zone (SSZ), during the Jurassic-Early Cretaceous. Later, the sediments were metamorphosed and uplifted during the Paleocene and deposited inside the Iraqi Zagros belt by turbidity currents inside the Zagros Foreland basin. These ideas are shown in detail by tectonic and paleogeographic models.

Gabbroic Rocks in Mawat Ophiolite Complex, NE Iraq: Geochemical Constraints on their Tectonogenesis

The Mawat Ophiolite Complex located in north-eastern Iraq represents part of the Iraqi Zagros Suture Zone, located at the border between the Arabian-Iranian plates. It consists of peridotite, gabbro, subvolcanic sheeted dykes and volcanic pillow lava. The geochemical signatures of the gabbro show a significant variation in major elements concentration, low concentrations of TiO2 (0.06-0.36 wt.%), Na2O (0.44-0.98 wt.%), K2O (0.024-0.48 wt.%), P2O5 (0.002-0.009 wt.%) and moderate variations in SiO2 (46.13-53.77 wt.%) with wide ranges and high concentration of Al2O3 (13.87-22.18 wt.%), Fe2O3 (0.04-2.95 wt.%), FeO (2.68-8.76 wt.%), MgO (8.09-14.28 wt.%) and CaO (11.08-17.04 wt.%). The flat REE patterns of the present rocks represent island arc tholeiite (IAT) tectonics and a subduction-related environment. The main features of the magma generated in the supra subduction zone are the enrichment of LILEs and depletion of the HFSEs and the strong negative Nb anomaly. Geochemical evidence indicates that the tholeiitic gabbros were generated in an arc-related tectonic setting. The tectonomagmatic diagrams for gabbros and the very low Ti content propose that the gabbroic rocks of Mawat Ophiolite have island arc tholeiitic (IAT) and possibly boninitic affinities which have a related to the supra-subduction zone (SSZ).

Metamorphic Evolution of the Bulfat Belt (NE-Iraq): Evidence from 40Ar/39Ar Age Spectrum Measurements

The Bulfat Ophiolite Complex (upper allochthonous thrust sheet) which represents a part of the Iraqi Zagros Suture Zone is situated at the boundary between the Arabian Plate and the Iranian Microplate. We have examined the metamorphic and cooling history of metapelitic rocks of Bulfat Complex using the whole-rocks 40Ar/39Ar age determination. The results of four samples match to the definition of the plateau and revealed to 40Ar/ 39Ar age of 42.4 ±0.5 Ma (sample 1), 32.9 ±0.8 Ma (sample 2), 44.3 ±0.8 Ma (sample 3), and 43 .6 ±1.5 Ma (sample 5). However, samples 4 and 6 yielded an age range between 35- 40 Ma and 40- 50 Ma respectively. Generally, plateau ages (32.9-50 Ma) are identical and considered reliable, but the presence of excess argon (40Ar) remains possible in samples (e.g., sample 6) having initial40 Ar/36Ar ratios higher than the present atmospheric 40 Ar/36Ar = 295.5. The excess argon is derived from the mantle by plumes of mafic magmas into the earth crust and/ or released from minerals and rocks during metamorphic processes. Bulfat Complex is subjected to two metamorphic events: the earlier regional occurred during the period Albian-Cenomanian (97-105 Ma) and associated with the intraoceanic infant supra-subduction zone. The later thermal metamorphism overprinted the previous one, and took place due to the intrusion of igneous body pre – 50 Ma age. This igneous activity is considered one of the multi-event magmatism that happened along the Zagros Fold-Thrust Belt during the period from Upper Cretaceous and Mid – Late Miocene. It seems evident that the thermal metamorphic slice of Bulfat Complex (Gemo-Qandil Sequence) represents a part of the oceanic slab that has been subducted beneath the Iranian microplate. This event probably forming the last evolved episode of island arc system ended with the final closure of Neo-Tethys and the collision between the Arabian Plate and Iranian Microplate occurred at Mid-late Miocene.

Effect of Tectonostratigraphic Units in Evolving Aqra Anticline Model

In the current study, a tectonic model for the structure of Aqra Anticline was proposed. The model was dependent on the rock properties, stratigraphic relationships and thickness variations as well as, the model was correlated with other previous studies. The study area is located within the Iraqi Zagros fold/ thrust belt (ZFTB) which represents the northeastern margin of the Arabian Plate. Stratigraphically, the anticline comprises of formations that are deposited between Early Cretaceous to Pliocene periods. These formations are the Sarmord, Qamchuqa, Aqra, Kolosh/Khurmala, Gercus, Pila Spi, Fat'ha, Injana, and the Makdadiya formations. they were deposited during four Tectonostratigraphic Megasequences (TMS). The older TMS contains formations that were deposited prior the development of the Zagros Foreland Basin, whereas the formations of other three Megasequences were deposited within Zagros Foreland Basin. During those times, the foreland basin was divided into three distinct parts. these are fore deep, bulge, and fore-bulge, which were discriminated via listric faults, which played as normal and reverse displacements after and before ophiolite obduction. Some contributions to the tectonostratigraphic model of the area are adopted. They are stages of basin development, determining the time of extension period of the listric faults and detecting the tectonic inversion of these faults. This model is described within the compressional tectonic framework between the Arabian and Eurasian plates.

Variation of the Anticlines Vergency in the Iraqi Zagros Folds Belt and Its Tectonic Indications

Folds of northern Iraq are considered integral part for the Western Zagros Fold – Thrust Belt. The growth of these folds was due to inversion displacement on inherited listric faults. This research deal with the relationship between the folds vergency and the faults that propagated folds, where that the dip of the back limb (gentle limb) for the fold is parallel to the thrust fault surface that propagated the fold, and the vergency of the fold determined by the forelimb (steep limb) situation. As a results, the folds of the high folded zone and of the western part of the low folded zone showed suture ( N and NE) vergency and foreland (S and SW) vergency, while the eastern part of the low fold zone showed foreland (S and SW) vergency only. The appearance of the suture and foreland vergency within the high folds considered as indication to the high tectonic development conformable with the location of these folds in the Iraqi Zagros Fold Belt, while the appearance of the suture and foreland vergency in the western part of the low folded zone attributed to the more tectonic development of this part in comparison with the eastern part of the zone that there folds appeared foreland vergencies only, or to the influence of the evaporite beds for Fatha formation in this part.

U–Pb geochronology and Hf isotope data from the Late Cretaceous Mawat ophiolite, NE Iraq

The Mawat ophiolite, NE Iraq, is one of the Neo-Tethyan ophiolites within the Iraqi Zagros orogen. It consists of many metre-to kilometre-sized tectonic slices of serpentinized dunite, peridotite, gabbro, basaltic rocks and associated oceanic metasediments. Felsic intrusions crosscut the ophiolite. We present U–Pb zircon and monazite ages and Hf zircon isotopes from two crosscutting felsic dykes and a gabbro from the mantle section of the ophiolite. Zircons from the felsic dykes contain spongy domains and xenotime and monazite inclusions. They give ages from 222 to 46 Ma. The age range is interpreted to be caused by secondary processes such as radiogenic Pb mobility and Pb loss. The monazite age of 94.6 ± 1.2 Ma is considered to give a crystallisation age of the felsic dykes. The gabbro zircons give ages between 81 to 38 Ma of which the two oldest grains give the weighted average age of 81.2 ± 2.5 Ma which we interpret to be the crystallisation age of the gabbro. The zircon initial εHf values in the felsic dykes are negative (averages -2.7 and -3.1) while they in the gabbro are positive (average + 3.5), indicating that the felsic magma comes from an older source while the mafic magma comes from a juvenile one. Two mafic units of different ages were identified: the older unit is cut by the 95 Ma felsic dykes and the younger one is represented by the 81 Ma gabbro located within a thrust zone. The youngest ages of 40 Ma are considered to be related to crustal extension.

Overview of the tectonic evolution of the Iraqi Zagros thrust zone: Sixty million years of Neotethyan ocean subduction

The world’s largest ongoing collisional orogeny is the Europe Alps–Himalayan–SE Asian belt and is a natural laboratory to understand many processes that have shaped the continents. Due to political instability and conflict throughout this millennium, the Iraq (Kurdish) sector of the Zagros mountain chain is the least studied part of this orogenic system. In Iraq, the Zagros contains the suture between the Arabian subcontinent to the south and west and the Iranian edge of the Eurasian continent to the north and east. The suture zone is marked by several allochthons of Neotethyan ophiolitic and volcanic arc assemblages that were obducted onto the Arabian margin. New geochronological data, including SHRIMP U-Pb zircon, integrated with whole rock geochemistry, indicates that both Cretaceous (˜96 Ma) and Cenozoic (˜40 Ma) assemblages are present. The relationships between these units are complicated, thus some Cretaceous arc rocks were intruded by Cenozoic arc rocks, and out-of-sequence thrusting has interleaved and juxtaposed assemblages of different ages. Ongoing wrench faulting since continental collision at ˜14 Ma has further complicated the pattern of lithotectonic units, particularly those that were obducted out of the Neotethyan realm. The new data indicate that the Iraqi sector of Neotethys was not ‘quiet’ in the Cretaceous, but contains fragments of arcs of that age, contiguous with those along strike in Turkey, Iran and the Himalayas.

The tectonic evolution of the Dras arc complex along the Indus Suture Zone, western Himalaya: Implications for the Neo-Tethys Ocean geodynamics

In this study we present new whole-rock geochemical data on the Dras arc complex exposed along the Dras–Kargil National Highway, western Ladakh. This complex forms a part of the Indus Suture Zone, which is a major tectonic unit extending along the Himalaya from the Pakistan in the west to the Tibet in the east. The Dras arc complex is dominated by mafic volcanics, with subordinate gabbros at the base exposed near Kargil. The Dras volcanics have augite and plagioclase phenocrysts embedded in a groundmass of plagioclase and pyroxene with porphyritic, intergranular and ophitic textural relationships. Also chlorite and epidote are present as secondary mineral assemblage in these volcanics. Plagioclase and pyroxene are the dominant mineral assemblage in the Kargil gabbro, with minor amounts of oxides and relict olivine. These rock types are characterized by ophitic textures and are devoid of any secondary mineral assemblage when compared to the mafic volcanics, which have suffered greenschist metamorphism. Geochemically, the Dras volcanics and the Kargil gabbros are classified as sub-alkaline tholeiites and show a compositional variation from basalt to basaltic andesite. On a Nb/Yb vs. Th/Yb diagram, they fall within the compositional field of arc-related rocks. NMORB-normalized multi-element patterns shows enrichment in large ion lithophile elements (e.g., Rb, Ba, Th, U, K and Pb) and light rare earth elements (LREE), but a depletion in high field strength elements (e.g., Nb, P, Zr and Ti), which supports a subduction-related origin. Lower Ba/La and La/Yb ratios indicate contribution from fluid fluxing, rather than slab melts to the mantle wedge. The Dras volcanics show similar geochemical trends to volcanic arc rocks from the Nidar and the Spongtang ophiolite complex of the Ladakh Himalaya as well as the Hasanbag and Kata Rush arc rocks from the Iraqi Zagros Suture, having similar age relationships in the context of the Neo-Tethys Ocean.

Clues to inferred different thrust-related fold models and thin-thick skinned tectonics within a single folded structure in Iraqi Zagros, Kurdistan region

The Maqloub–BardaRash structure is situated at the Low Folded Zone within the NW of the Zagros fold-thrust belt in the Iraqi Kurdistan region. One of the main goals of this work is to reveal the variation in the fold architecture and fault shape with depth to build a plausible fold model, as well as to explain the kinematic evolution of the Maqloub–BardaRash structure. The middle part of the anticlinal hinge line of the studied structure shows deviation and anticlockwise rotation. This character is ascribed to the presence of a north-south trending left-lateral strike-slip fault. This fault is considered to be a deep-seated basement fault that likely caused segmentation of Maqloub–BardaRash structure into two parts: the northwestern Maqloub structure which exhibits a normal asymmetry and the southeastern BardaRash structure with a reverse asymmetry. The balanced cross sections based on the top of Middle Miocene Fatha Formation from the studied structures displays a maximum total horizontal shortening of 14% for the Maqloub structure and 9.89% for the BardaRash segment at the same stratigraphic level. Through the Maqloub section, the thrust-related shortening increases downsection, whereas the fold-related shortening increases upsection. Whereas along BardaRash section, the fold-related shortening smaller irregular variations at different stratigraphic levels are evidenced. The Maqloub segment is interpreted as a fault-propagation fold, but the BardaRash segment is interpreted as a faulted detachment fold based on the geometrical analysis of deformed models. Based on the resulting deformed geometries from the balanced cross sections, the propagation of the Maqloub segment is associated with the activation of an underlying basement fault, whereas the BardaRash segment is decoupled along the Triassic ductile sequence. The structural characterization of two different models of the fault-related deformation along the individual Maqloub–BardaRash folded structure will enhance accurate well position of the crestal reservoir.

Provenance of the Walash-Naopurdan back-arc–arc clastic sequences in the Iraqi Zagros Suture Zone

Marine clastic rocks occurring in the Walash and Naopurdan Groups in the Hasanbag and Qalander areas, Kurdistan region, Iraqi Zagros Suture Zone, are lithic arenites with high proportions of volcanic rock fragments. Geochemical classification of the Eocene Walash and Oligocene Naopurdan clastic rocks indicates that they were mainly derived from associated sub-alkaline basalt and andesitic basalt in back-arc and island arc tectonic settings. Major and trace element geochemical data reveal that the Naopurdan samples are chemically less mature than the Walash samples and both were subjected to moderate weathering. The seaway in the southern Neotethys Ocean was shallow during both Eocene and Oligocene permitting mixing of sediment from the volcanic arcs with sediment derived from the Arabian continental margin. The Walash and Naopurdan clastic rocks enhance an earlier tectonic model of the Zagros Suture Zone with their deposition occurring during the Eocene Walash calc-alkaline back-arc magmatism and Early Oligocene Naopurdan island arc magmatism in the final stages of intra-oceanic subduction before the Miocene closure and obduction of the Neotethys basin.

Zircon U–Pb ages and geochemistry of Devonian A-type granites in the Iraqi Zagros Suture Zone (Damamna area): New evidence for magmatic activity related to the Hercynian orogeny

The Damamna granite (DG) is located in the Shalair Valley area in northeast Iraq within the Sanandaj Sirjan Zone (SSZ). The zircon U–Pb ages for the DG rocks are 364–372Ma, indicating crystallization of the granitic body. The DG rocks are A-type granites, hypersolvus and peraluminous. They are enriched in SiO2, alkalis, Ga/Al, Ga, Zr and Rb/Sr and depleted in CaO, MgO, Sr, P, and Ti. These rocks show steep REE patterns, with LREE enrichment relative to HREE ((La/Yb)N=5.7–42.5) and pronounced negative Eu anomalies reflecting feldspar fractionation. The geochemical characteristics and relationships suggest that the DG rocks are anorogenic and were emplaced in an extensional tectonic regime having an OIB-like magma affinity. The DG rocks are characterized by low Y/Nb ratios (0.2–1.5) and positive εNd (371Ma) values (+1.6 to +4.2), which indicate a mantle origin. In the Y/Nb–Yb/Ta diagram, the DG rocks plot in the A1-type granite field, with slightly higher Y/Nb values and a tendency of transitioning from A1 to the nearby A2 field, which possibly indicates a slight crustal contamination effect. The isotopic and geochemical data suggest that a combination of enriched mantle source magma with crustal contamination and fractional crystallization contributed to the generation of the magma for the DG. The geochemical and geochronological results for the DG rocks in the SSZ suggest an extensional zone that probably represents an early stage of Neo-Tethys opening during the Late Devonian or earlier, and this was associated with the Hercynian orogeny and tectono-magmatic activity in northern Arabia and northwestern Iran.

The intra-oceanic Cretaceous (~ 108 Ma) Kata–Rash arc fragment in the Kurdistan segment of Iraqi Zagros suture zone: Implications for Neotethys evolution and closure

The Kata–Rash arc fragment is an allochthonous thrust-bound body situated near Penjween, 100km northeast of Sulymannia city, Kurdistan Region, within the Iraqi portion of the Zagros suture zone. It forms part of the suprasubduction zone ‘Upper Allochthon’ terranes (designated as the Gimo–Qandil Group), which is dominated by calc-alkaline andesite and basaltic–andesite, rhyodacite to rhyolite, crosscut by granitic, granodioritic, and dioritic dykes. Previously, rocks of the Kata–Rash arc fragment were interpreted as a part of the Eocene Walash volcanic group. However, SHRIMP zircon U–Pb dates on them of 108.1±2.9Ma (Harbar volcanic rocks) and 107.7±1.9Ma (Aulan intrusion) indicate an Albian–Cenomanian age, which is interpreted as the time of igneous crystallisation. The Aulan intrusion zircons have initial εHf values of +8.6±0.2. On a Nb/Yb–Th/Yb diagram, all Kata–Rash samples fall within the compositional field of arc-related rocks, i.e. above the mid-ocean-ridge basalt (MORB)—ocean island basalt (OIB) mantle array. Primitive-mantle-normalised trace-element patterns for the Kata–Rash samples show enrichment in the large ion lithophile elements and depletion in the high-field-strength elements supporting their subduction-related character. Low Ba/La coupled with low La/Yb and Hf/Hf* <1 for the Aulan sample with initial εHf of +8.6±0.2 is interpreted as the magma dominated by contributions from fluid fluxing of the mantle wedge and lesser contributions of low temperature melt from subducted slab sediment, in an oceanic setting. This mechanism can explain the sub-DM initial εHf value, without the need to invoke melting of significantly older (continental) crust in an Andean setting. We interpret the Kata–Rash igneous rocks as a fragment of the Late Cretaceous suprasubduction zone system (named here the Kata–Rash arc) that most likely developed within the Neotethys Ocean rather than at a continental margin. Subsequently during the latest Cretaceous to Paleocene, the arc was accreted to the northern margin of the Arabian plate. The results indicate a >3000km continuity of Cretaceous arc activity (Oman to Cyprus), that consumed Neotethyian oceanic crust between Eurasia and the Gondwanan fragment Arabia.

Petrogenesis of metabasalt rocks in the Bulfat complex, Kurdistan region, Iraqi Zagros Suture Zone

Metabasaltes are exposed in the Bulfat complex north of Qaladeza that is a part of the Northwestern Zagros Suture Zone (NZSZ).Petrographic and geochemical study of metabasaltes have been conducted in order to provide insights into the origin and evolution of magmatism found at Neotethyian subducted plate margins and to determine their protolith nature and geodynamic setting. The whole rock chemistry indicates basalt to andesite composition for the metabasaltes. The geochemical investigation strongly suggests that the metabasaltes are derived from calic alkaline basalt and were emplaced in arc tectonic setting.

Geologic evolution of the Iraqi Zagros, and its influence on the distribution of hydrocarbons in the Kurdistan region

Whereas the vast majority of discovered hydrocarbon reserves in Iraq reside in Cretaceous and Cenozoic reservoirs, numerous oil and gas fields have been discovered recently in deeper Jurassic and Triassic reservoirs in the Kurdistan region of Iraq. This study presents a Middle–Upper Jurassic thermal maturity map for the Kurdistan region of Iraq and demonstrates that regional first-order trends in Jurassic source rock maturity show a close correlation to the spatial distribution of oil gravities within the overlying Jurassic (and Cretaceous) reservoirs. This distribution is consistent with compartmentalization of the active source rock kitchens due to Zagros folding, resulting in relatively short-distance migration and charge of the anticlinal structures from the adjacent synclinal lows. The thermal maturity map confirms relatively low maturity over the Mosul high, where the Cretaceous and Cenozoic section overlying the source rock interval is relatively thin, and increasing maturity to the southeast as the thickness of the Cenozoic foredeep sediments increases toward the depocenter located in the southeastern Iraqi Zagros and the adjacent Iranian Zagros. The correlative trend in oil gravities is exemplified by the recent Jurassic discoveries: low to medium gravity oils (14–27° API) in Shaikan and Atrush to the northwest, light oil (39–47° API) in Mirawa and Bina Bawi, and gas condensate (55° API) in Miran West to the southeast. Understanding thermal maturity patterns and hydrocarbon fluid-type distributions will help to guide risk assessment for remaining prospectivity and future exploration drilling within the Kurdistan region of Iraq.

Corrigendum to the paper titled “Petrogenesis and PGE distribution in the Al- and Cr-rich chromitites of the Qalander ophiolite, northeastern Iraq: Implications for the tectonic environment of the Iraqi Zagros Suture Zone” [Lithos, 202–203, (2014) 21–36

a Department of Applied Geology, College of Science, Kirkuk University, Kirkuk, Iraq b Department of Geology, College of Science, Salahaddin University, Erbil, Iraq c Department of Earth Sciences, College of Science, Dalhousie University, Halifax, Canada d Faculty of Earth Sciences, King Abdulaziz University, Saudi Arabia e Geology Department, Faculty of Science, Helwan University, Cairo, Egypt f Department of Earth Sciences, Kanazawa University, Kanazawa, Japan

Petrogenesis and PGE distribution in the Al- and Cr-rich chromitites of the Qalander ophiolite, northeastern Iraq: Implications for the tectonic environment of the Iraqi Zagros Suture Zone

Abstract The Qalander ophiolite is a small, poorly preserved and incomplete melange-type complex situated within the Eocene–Oligocene Walash–Naopurdan Group in the Iraqi Zagros Suture Zone (IZSZ). It is one of six fragmented ophiolite complexes emplaced in the IZSZ during the Cretaceous and Tertiary. Within the Qalander ophiolite, serpentinized dunite and harzburgite hosts small lens-shaped podiform high-Al (North Qalander) and high-Cr (North Shitna) chromitite bodies. The average range of Cr-, Mg-, and Fe 3 -numbers for North Qalander chromitites is 39–53, 75–77, and 3–5, respectively; meanwhile those for North Shitna chromitites are 78–80, 65–73, and 6–8, respectively. The ranges of Al 2 O 3 wt.% and FeO/MgO for the North Qalander and North Shitna chromitites are 15–15.5 and 0.8–1.0, and 9.0–10.5 and 0.4–1.0, respectively. In addition to pyroxene and olivine, inclusions of laurite, millerite and galena were detected within the chromitites of Qalander ophiolite. The matrix minerals between chromite grains are serpentinized olivine and pyroxene, chlorite, and calcite; grains of magnetite, pyrite and ilmenite are also common accessories. The concentrations of platinum-group elements (PGE) in both varieties are typical for the ophiolitic chromitites, but they show two distinct patterns of PGE enrichment. The high-Cr chromitites have relatively uniform mantle-normalized PGE distribution patterns with a steep slope, positive Ru and negative Pt anomalies, and they show enrichment of PGE and depletion in Pt relative to the average upper mantle. The high-Al chromitites show relatively gently sloping patterns with slight positive Ru and negative Pt anomalies, high iridium-group PGE (IPGE) abundances relative to the high platinum-group PGE (PPGE), and are distinctly enriched in Pt and Pd relative to the upper mantle and the average abundances in the high-Cr chromitites. The differences in the PGE content, geochemistry, rare earth element (REE), mineral chemistry and petrographical characteristics of the chromitites suggests two stages of magmatic activity which were responsible for the chromitite genesis in the region. The first stage involved low degree partial melting of S-saturated peridotite melt that produced high-Al chromitites of MORB affinity, which crystallized in the upper mantle close to the Moho. The second stage involved a high degree partial melting of S-undersaturated boninitic melt that produced high-Cr chromitites of arc affinity and crystallized in a deeper mantle section. The presence of low-Cr MORB-type chromitites with high-Cr boninitic-type chromitites in the same mantle section suggests their formation in aback-arc supra-subduction zone tectonic setting.

Geochemistry and geodynamics of the Mawat mafic complex in the Zagros Suture zone, northeast Iraq

Abstract The Iraqi Zagros Orogenic Belt includes two separate ophiolite belts, which extend along a northwest-southeast trend near the Iranian border. The outer belt shows ophiolite sequences and originated in the oceanic ridge or supra-subduction zone. The inner belt includes the Mawat complex, which is parallel to the outer belt and is separated by the Biston Avoraman block. The Mawat complex with zoning structures includes sedimentary rocks with mafic interbedded lava and tuff, and thick mafic and ultramafic rocks. This complex does not show a typical ophiolite sequences such as those in Penjween and Bulfat. The Mawat complex shows evidence of dynamic deformation during the Late Cretaceous. Geochemical data suggest that basic rocks have high MgO and are significantly depleted in LREE relative to HREE. In addition they show positive ɛ Nd values (+5 to+8) and low 87Sr/86Sr ratios. The occurrence of some OIB type rocks, high Mg basaltic rocks and some intermediate compositions between these two indicate the evolution of the Mawat complex from primary and depleted source mantle. The absence of a typical ophiolite sequence and the presence of good compatibility of the source magma with magma extracted from the mantle plume suggests that a mantle plume from the D″ layer is more consistent as the source of this complex than the oceanic ridge or supra-subduction zone settings. Based on our proposed model the Mawat basin represents an extensional basin formed during the Late Paleozoic to younger along the Arabian passive margin oriented parallel to the Neo-Tethys oceanic ridge or spreading center. The Mawat extensional basin formed without creation of new oceanic basement. During the extension, huge volumes of mafic lava were intruded into this basin. This basin was squeezed between the Arabian Plate and Biston Avoraman block during the Late Cretaceous.

Biostratigraphy of oligocene succession in the High Folded Zone, Sulaimani, Kurdistan region, Northeastern Iraq

Oligocene and Lower Miocene sediments from High Folded Zone of Iraqi Zagros have been studied paleontologically at south of Sulaimaniyah, Kurdistan Region, NE Iraq. The identified fauna are consisted of (25) genera and species of benthonic and (16) species of planktonic foraminifera. The fauna comprises relatively abundant foraminiferal assemblages of moderate diversity. Based on the stratigraphic distribution of these species, two biozones have been recognized which are Nummulites—Rotalia and Globoquadrina dehiscens zones. These biozones indicate that the studied sections of Basara and Khewata are of Late Oligocene-Early Miocene age. Based on the microfossils, it has been found that the age of sediments is equivalent to or represents Anah and Serikagni Formations. Some previous studies described Oligocene rocks (Kirkuk Group) as interior sag basin. In the present study, the occurrence of the group inside High Folded Zone and its rich fauna content are used for the discussion of the sag basin versus normal marine water.

Provenance and tectonic setting of the metapelites deposits in the Bulfat Complex, NE-Iraq

Major and trace elements including rare earth elements (REEs) chemistry of the metapelitic rocks of Bulfat Complex (Iraqi Zagros Suture Zone) indicate their enrichment in large-ion Lithophile, light rare earth (LREE) elements, and relative depletion of high field strength and heavy rare earth (HREE) elements. The linear correlation coefficients between TiO2, K2O, and Al2O3 and total REE reveal that phyllosilicates (e.g., mica) and accessory minerals mainly Ti-bearing phases (e.g., ilmenite) are likely the dominant hosts for REEs. Chondrite-normalized REE patterns typical of continental margin settings with significant enrichment of LREE, prominent negative Eu anomalies, and nearly flat HREE are positively correlated with post-Archean Australian shale (PAAS) and upper continental crust (UCC) patterns. Additionally, their consistent elemental La/Sc, Th/Sc, La/Co, Th/Co, Cr/Th, and Eu/Eu* values suggest that sediments may have been originally derived from an old post-Archean upper continental crust composed chiefly of granitic component. It seems most likely that the felsic source rocks were originated by a process of intra-crustal differentiation such as partial melting and/or fractional crystallization involving fractionation of Ca-plagioclase. The geochemical evidences particularly REEs evaluation show that deposition of clasts occurred in an active continental margin setting during lower–upper Cretaceous period contemporaneous with the igneous activities. It is evident therefore that the clasts source is from the north–northeast side, i.e., from the active margin of Iranian microcontinent (Sanandaj–Sirjan Zone).