Numerical simulations and theoretical analyses predict that forearc ophiolites probably record th... more Numerical simulations and theoretical analyses predict that forearc ophiolites probably record the end of subduction followed by re-initiation. We report here the results of a field study and new geochronological data that enable identification of the Kermanshah forearc basin, SW Iran. This basin is filled with two terrestrial volcaniclastic successions separated by an Upper Cretaceous reef facies limestone. Early Late Cretaceous ocean island basalts, early Eocene incompatible element-enriched mid-ocean ridge basalts/normal-type mid-ocean ridge basalts and late Eocene arc basalts of the basin indicate that Neotethyan subduction ended during the early Late Cretaceous and then re-initiated during the late Eocene. We suggest that the Neotethyan Ocean between the Iranian and Arabian continents consisted of leading and trailing oceanic plates separated by a mid-ocean ridge (MOR). Subduction of the leading plate generated the Jurassic–Early Cretaceous Sanandaj–Sirjan arc, which was ended ...
Numerical simulations and theoretical analyses predict that forearc ophiolites probably record th... more Numerical simulations and theoretical analyses predict that forearc ophiolites probably record the end of subduction followed by re-initiation. We report here the results of a field study and new geochronological data that enable identification of the Kermanshah forearc basin, SW Iran. This basin is filled with two terrestrial volcaniclastic successions separated by an Upper Cretaceous reef facies limestone. Early Late Cretaceous ocean island basalts, early Eocene incompatible element-enriched mid-ocean ridge basalts/normal-type mid-ocean ridge basalts and late Eocene arc basalts of the basin indicate that Neotethyan subduction ended during the early Late Cretaceous and then re-initiated during the late Eocene. We suggest that the Neotethyan Ocean between the Iranian and Arabian continents consisted of leading and trailing oceanic plates separated by a mid-ocean ridge (MOR). Subduction of the leading plate generated the Jurassic–Early Cretaceous Sanandaj–Sirjan arc, which was ended ...
Numerical simulations and theoretical analyses predict that forearc ophiolites probably record th... more Numerical simulations and theoretical analyses predict that forearc ophiolites probably record the end of subduction followed by re-initiation. We report here the results of a field study and new geochronological data that enable identification of the Kermanshah forearc basin, SW Iran. This basin is filled with two terrestrial volcaniclastic successions separated by an Upper Cretaceous reef facies limestone. Early Late Cretaceous ocean island basalts, early Eocene incompatible element-enriched mid-ocean ridge basalts/normal-type mid-ocean ridge basalts and late Eocene arc basalts of the basin indicate that Neotethyan subduction ended during the early Late Cretaceous and then re-initiated during the late Eocene. We suggest that the Neotethyan Ocean between the Iranian and Arabian continents consisted of leading and trailing oceanic plates separated by a mid-ocean ridge (MOR). Subduction of the leading plate generated the Jurassic–Early Cretaceous Sanandaj–Sirjan arc, which was ended by MOR–trench collision. The Zagros late Early Cretaceous forearc ophiolites represent the youngest/hottest segments of the leading plate emplaced during the MOR–trench collision. Subsequently, subduction of the MOR generated the forearc basin and basalts with diverse geochemistry. After c. 60 myr, the cooled trailing plate started to subduct, generating the late Eocene arc basalts. This model has significant implications for investigating and understanding other fossil subduction zones elsewhere in the world. Supplementary material: Supplementary material is available at https://doi.org/10.6084/m9.figshare.c.6086586
Adakitic rocks occur in a variety of tectonic settings and are key to understanding the tectonic ... more Adakitic rocks occur in a variety of tectonic settings and are key to understanding the tectonic evolution and geodynamics of orogenic belts. We investigated latest Oligocene (23.5–22.5 Ma) quartz monzonites and granites from the western segment of the Urumieh–Dokhtar magmatic belt in Iran, which are likely to have formed in response to the early stages of Arabia–Eurasia collision. The studied rocks have the geochemical characteristics of typical adakites, such as high SiO 2 (60.18–68.82 wt%) and Sr (499–793 ppm) contents, low Y (8.90–17.1 ppm) and Yb (0.88–1.58 ppm) contents, and high Sr/Y (26.1‒67.8) and (La/Yb) N (21.9‒32.9) ratios. They have variable K 2 O (3.88–5.09 wt%), MgO (0.44–2.74 wt%; Mg# = 33.7–52.5), Cr (4.27–40.59 ppm), Ni (4.28–35.68 ppm) and Th (9.56–59.59 ppm) contents, and relatively depleted Sr–Nd isotopic compositions [( 87 Sr/ 86 Sr) i = 0.70450–0.70516; ε Nd ( t ) = 2.1–2.7]. These characteristics indicate that the quartz monzonites were derived from the part...
In this research, zircon Hf isotopic ratios from Sungun, Sar Cheshmeh, Meiduk, Darreh Zar and Bon... more In this research, zircon Hf isotopic ratios from Sungun, Sar Cheshmeh, Meiduk, Darreh Zar and Bondar Hoza porphyry mineralized intrusions has been studied. The Hf isotopic ratios in the studied porphyry intrusions are similar and the average of zircon eHf values from Sar Cheshmeh, Meiduk, Darreh Zar, Bondar Hanza and Sungun porphyry intrusions are +8.2, +9.3, +9.2, +10 and +8.6, respectively. Also, the averages of zircon TDMC ages from the Sar Cheshmeh, Sungun, Meiduk, Darreh Zar and Bondar Hanza porphyry intrusions are 573, 550, 502, 510 and 464, respectively. The positive and restricted eHf values in the studied porphyry intrusion zircons along with the lack of inherited zircons shows continental crust did not contribute in the evolution of the porphyry magmas. The eHf in the studied zircons is between depleted mantle and lower crust values with a tendency towards the depleted mantle. According to adakitic nature of studied porphyry intrusions, post collisional tectonomagmatic set...
basaltic rocks in Barzand area (Continue to Kousmalyn basaltic rocks in Iran) show parallel trend... more basaltic rocks in Barzand area (Continue to Kousmalyn basaltic rocks in Iran) show parallel trend with Poshtasar basalt and they have older age according to stratigraphy in comparison with Poshtasar basalts. These basalts whit prismatic structure mostly have mugearitic composition and show hyalomicroporphyritic and glomeroporphyritic textures. The main minerals are Ca-rich plagioclase and diopsidic clinopyroxenes. Leucites generally have been altered to analcime. The parent magma of these rocks has a potassic and shoshonitic nature. In multi- element diagrams Ta, Ti and Nb show depletion and LILE, LREE have enrichment that suggests their primary magma have been originated from a subduction related mantle source. According to radiogenic isotopic ratios, mantle source of Barzand basaltic rocks have been drived from a fertilized mantle source during 0.8 to 0.9 billion years ago. According to initial 87Sr/86Sr (0.70499 ± 0.0004) and initial 143Nd/144Nd ratios (0.5127 ± 0.0004) estimated...
The studied area is located in the SE of Heris (Eastern Azerbaijan province) and the Alborz-Azerb... more The studied area is located in the SE of Heris (Eastern Azerbaijan province) and the Alborz-Azerbaijan structural zone. The Eocene volcanic rocks in the area of under study show various compositions ranging from olivine basalt, hornblende basalt, basaltic andesite and andesite to trachy andesite. The studied basaltic rocks, except for amphibole types, which show calc-alkaline affinity, mainly have shoshonitic and the andesitic rocks are adakitic composition. According to primitive mantle and chondrite normalized spider and REE diagrams, the studied rocks are characterized by LILE and LREE enrichment and pronounced depletion in HFS elements. Based on geochemical data the basaltic rocks have been originated from different degrees partial melting of a heterogeneous lithospheric mantle that metasomatized by subduction agents. The adakitic rocks have been generated from partial melting of thickened potassic mafic lower crust that have been metamorphosed in eclogitic facies.
Abstract The Neotethyan tectonics of the Zagros orogenic belt, SW Iran remains still hotly debate... more Abstract The Neotethyan tectonics of the Zagros orogenic belt, SW Iran remains still hotly debated in comparing with its western counterparts. One major issue concerns the timing and nature of the Sanandaj-Sirjan magmatic-metamorphic belt (SSMB), which is made predominantly of metamorphic rocks and Jurassic to Early Cretaceous large plutonic complexes. The Alvand and Qory are two largest plutonic complexes locating in north-central and southern segments, respectively, of the SSMB. Careful LA-ICP-MS U/Pb analyses of the magmatic zircons from the Alvand plutonic complex reveal a smooth spectra, along which the concordant age increase gradually from 120 to 190 Ma; while that of Qory is step-like consisting of two stages, a Jurassic and a late Early Cretaceous ones, respectively. New geochemical data, combined with zircon Lu/Hf results suggest that (1) the Alvand granitoids mostly resulted from a long-lived, successive injection of juvenile-crust-sourced magma batches without obvious fractionation crystallization (FC); but (2) the two stages granitoids of the Qory complex both generated by FC of juvenile-crust-sourced magmas; and (3) the gabbros of the Alvand complex are geochemically of E-MORB-affinity while those of the Qory complex are typical continental arc mafic rocks. Previously published petrological and 40Ar/39Ar data have identified a broken, Jurassic to Early Cretaceous high-pressure metamorphic belt to the southwest of the SSMB, which likely represents the closed, southeastern equivalent of the northern Neotethyan Ocean, north of the Taurides-Anatolia-Armenia block. Thus, the SSMB in Iran, the Kapan belt in Caucasus, and the Serbo-Macedonian belt in northern Turkey form a huge Jurassic to Early Cretaceous continental margin arc system recording northeastwards subduction of the older Northern Neotethyan Ocean beneath Eurasia. The Albian-Cenomanian ophiolites such as Koy, Kermanshah, and Neyriz in Iran represent the eastern counterpart of the younger Southern Neotethyan Ocean, south of the Taurides-Anatolia-Armenia block. During the subduction of the Old Neotethys, an intraplate transform fault likely opened and generated a slab-window beneath the Alvand region, which provided a constant energy source to steadily heat the low crust. This model satisfactorily interprets the unusual geochronological framework and geochemistry of the Alvand complex.
Numerical simulations and theoretical analyses predict that forearc ophiolites probably record th... more Numerical simulations and theoretical analyses predict that forearc ophiolites probably record the end of subduction followed by re-initiation. We report here the results of a field study and new geochronological data that enable identification of the Kermanshah forearc basin, SW Iran. This basin is filled with two terrestrial volcaniclastic successions separated by an Upper Cretaceous reef facies limestone. Early Late Cretaceous ocean island basalts, early Eocene incompatible element-enriched mid-ocean ridge basalts/normal-type mid-ocean ridge basalts and late Eocene arc basalts of the basin indicate that Neotethyan subduction ended during the early Late Cretaceous and then re-initiated during the late Eocene. We suggest that the Neotethyan Ocean between the Iranian and Arabian continents consisted of leading and trailing oceanic plates separated by a mid-ocean ridge (MOR). Subduction of the leading plate generated the Jurassic–Early Cretaceous Sanandaj–Sirjan arc, which was ended ...
Numerical simulations and theoretical analyses predict that forearc ophiolites probably record th... more Numerical simulations and theoretical analyses predict that forearc ophiolites probably record the end of subduction followed by re-initiation. We report here the results of a field study and new geochronological data that enable identification of the Kermanshah forearc basin, SW Iran. This basin is filled with two terrestrial volcaniclastic successions separated by an Upper Cretaceous reef facies limestone. Early Late Cretaceous ocean island basalts, early Eocene incompatible element-enriched mid-ocean ridge basalts/normal-type mid-ocean ridge basalts and late Eocene arc basalts of the basin indicate that Neotethyan subduction ended during the early Late Cretaceous and then re-initiated during the late Eocene. We suggest that the Neotethyan Ocean between the Iranian and Arabian continents consisted of leading and trailing oceanic plates separated by a mid-ocean ridge (MOR). Subduction of the leading plate generated the Jurassic–Early Cretaceous Sanandaj–Sirjan arc, which was ended ...
Numerical simulations and theoretical analyses predict that forearc ophiolites probably record th... more Numerical simulations and theoretical analyses predict that forearc ophiolites probably record the end of subduction followed by re-initiation. We report here the results of a field study and new geochronological data that enable identification of the Kermanshah forearc basin, SW Iran. This basin is filled with two terrestrial volcaniclastic successions separated by an Upper Cretaceous reef facies limestone. Early Late Cretaceous ocean island basalts, early Eocene incompatible element-enriched mid-ocean ridge basalts/normal-type mid-ocean ridge basalts and late Eocene arc basalts of the basin indicate that Neotethyan subduction ended during the early Late Cretaceous and then re-initiated during the late Eocene. We suggest that the Neotethyan Ocean between the Iranian and Arabian continents consisted of leading and trailing oceanic plates separated by a mid-ocean ridge (MOR). Subduction of the leading plate generated the Jurassic–Early Cretaceous Sanandaj–Sirjan arc, which was ended by MOR–trench collision. The Zagros late Early Cretaceous forearc ophiolites represent the youngest/hottest segments of the leading plate emplaced during the MOR–trench collision. Subsequently, subduction of the MOR generated the forearc basin and basalts with diverse geochemistry. After c. 60 myr, the cooled trailing plate started to subduct, generating the late Eocene arc basalts. This model has significant implications for investigating and understanding other fossil subduction zones elsewhere in the world. Supplementary material: Supplementary material is available at https://doi.org/10.6084/m9.figshare.c.6086586
Adakitic rocks occur in a variety of tectonic settings and are key to understanding the tectonic ... more Adakitic rocks occur in a variety of tectonic settings and are key to understanding the tectonic evolution and geodynamics of orogenic belts. We investigated latest Oligocene (23.5–22.5 Ma) quartz monzonites and granites from the western segment of the Urumieh–Dokhtar magmatic belt in Iran, which are likely to have formed in response to the early stages of Arabia–Eurasia collision. The studied rocks have the geochemical characteristics of typical adakites, such as high SiO 2 (60.18–68.82 wt%) and Sr (499–793 ppm) contents, low Y (8.90–17.1 ppm) and Yb (0.88–1.58 ppm) contents, and high Sr/Y (26.1‒67.8) and (La/Yb) N (21.9‒32.9) ratios. They have variable K 2 O (3.88–5.09 wt%), MgO (0.44–2.74 wt%; Mg# = 33.7–52.5), Cr (4.27–40.59 ppm), Ni (4.28–35.68 ppm) and Th (9.56–59.59 ppm) contents, and relatively depleted Sr–Nd isotopic compositions [( 87 Sr/ 86 Sr) i = 0.70450–0.70516; ε Nd ( t ) = 2.1–2.7]. These characteristics indicate that the quartz monzonites were derived from the part...
In this research, zircon Hf isotopic ratios from Sungun, Sar Cheshmeh, Meiduk, Darreh Zar and Bon... more In this research, zircon Hf isotopic ratios from Sungun, Sar Cheshmeh, Meiduk, Darreh Zar and Bondar Hoza porphyry mineralized intrusions has been studied. The Hf isotopic ratios in the studied porphyry intrusions are similar and the average of zircon eHf values from Sar Cheshmeh, Meiduk, Darreh Zar, Bondar Hanza and Sungun porphyry intrusions are +8.2, +9.3, +9.2, +10 and +8.6, respectively. Also, the averages of zircon TDMC ages from the Sar Cheshmeh, Sungun, Meiduk, Darreh Zar and Bondar Hanza porphyry intrusions are 573, 550, 502, 510 and 464, respectively. The positive and restricted eHf values in the studied porphyry intrusion zircons along with the lack of inherited zircons shows continental crust did not contribute in the evolution of the porphyry magmas. The eHf in the studied zircons is between depleted mantle and lower crust values with a tendency towards the depleted mantle. According to adakitic nature of studied porphyry intrusions, post collisional tectonomagmatic set...
basaltic rocks in Barzand area (Continue to Kousmalyn basaltic rocks in Iran) show parallel trend... more basaltic rocks in Barzand area (Continue to Kousmalyn basaltic rocks in Iran) show parallel trend with Poshtasar basalt and they have older age according to stratigraphy in comparison with Poshtasar basalts. These basalts whit prismatic structure mostly have mugearitic composition and show hyalomicroporphyritic and glomeroporphyritic textures. The main minerals are Ca-rich plagioclase and diopsidic clinopyroxenes. Leucites generally have been altered to analcime. The parent magma of these rocks has a potassic and shoshonitic nature. In multi- element diagrams Ta, Ti and Nb show depletion and LILE, LREE have enrichment that suggests their primary magma have been originated from a subduction related mantle source. According to radiogenic isotopic ratios, mantle source of Barzand basaltic rocks have been drived from a fertilized mantle source during 0.8 to 0.9 billion years ago. According to initial 87Sr/86Sr (0.70499 ± 0.0004) and initial 143Nd/144Nd ratios (0.5127 ± 0.0004) estimated...
The studied area is located in the SE of Heris (Eastern Azerbaijan province) and the Alborz-Azerb... more The studied area is located in the SE of Heris (Eastern Azerbaijan province) and the Alborz-Azerbaijan structural zone. The Eocene volcanic rocks in the area of under study show various compositions ranging from olivine basalt, hornblende basalt, basaltic andesite and andesite to trachy andesite. The studied basaltic rocks, except for amphibole types, which show calc-alkaline affinity, mainly have shoshonitic and the andesitic rocks are adakitic composition. According to primitive mantle and chondrite normalized spider and REE diagrams, the studied rocks are characterized by LILE and LREE enrichment and pronounced depletion in HFS elements. Based on geochemical data the basaltic rocks have been originated from different degrees partial melting of a heterogeneous lithospheric mantle that metasomatized by subduction agents. The adakitic rocks have been generated from partial melting of thickened potassic mafic lower crust that have been metamorphosed in eclogitic facies.
Abstract The Neotethyan tectonics of the Zagros orogenic belt, SW Iran remains still hotly debate... more Abstract The Neotethyan tectonics of the Zagros orogenic belt, SW Iran remains still hotly debated in comparing with its western counterparts. One major issue concerns the timing and nature of the Sanandaj-Sirjan magmatic-metamorphic belt (SSMB), which is made predominantly of metamorphic rocks and Jurassic to Early Cretaceous large plutonic complexes. The Alvand and Qory are two largest plutonic complexes locating in north-central and southern segments, respectively, of the SSMB. Careful LA-ICP-MS U/Pb analyses of the magmatic zircons from the Alvand plutonic complex reveal a smooth spectra, along which the concordant age increase gradually from 120 to 190 Ma; while that of Qory is step-like consisting of two stages, a Jurassic and a late Early Cretaceous ones, respectively. New geochemical data, combined with zircon Lu/Hf results suggest that (1) the Alvand granitoids mostly resulted from a long-lived, successive injection of juvenile-crust-sourced magma batches without obvious fractionation crystallization (FC); but (2) the two stages granitoids of the Qory complex both generated by FC of juvenile-crust-sourced magmas; and (3) the gabbros of the Alvand complex are geochemically of E-MORB-affinity while those of the Qory complex are typical continental arc mafic rocks. Previously published petrological and 40Ar/39Ar data have identified a broken, Jurassic to Early Cretaceous high-pressure metamorphic belt to the southwest of the SSMB, which likely represents the closed, southeastern equivalent of the northern Neotethyan Ocean, north of the Taurides-Anatolia-Armenia block. Thus, the SSMB in Iran, the Kapan belt in Caucasus, and the Serbo-Macedonian belt in northern Turkey form a huge Jurassic to Early Cretaceous continental margin arc system recording northeastwards subduction of the older Northern Neotethyan Ocean beneath Eurasia. The Albian-Cenomanian ophiolites such as Koy, Kermanshah, and Neyriz in Iran represent the eastern counterpart of the younger Southern Neotethyan Ocean, south of the Taurides-Anatolia-Armenia block. During the subduction of the Old Neotethys, an intraplate transform fault likely opened and generated a slab-window beneath the Alvand region, which provided a constant energy source to steadily heat the low crust. This model satisfactorily interprets the unusual geochronological framework and geochemistry of the Alvand complex.
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