Search Results (28)

The Paratethyan South Caspian and Mediterranean Levant basins relate to the significant hydrocarbon provinces of Eurasia. The giant hydrocarbon reserves of the SCB are well-known. Within the LB, so far, only a few commercial gas fields have been found. Both the LB and SCB contain some geological peculiarities. These basins are highly complex tectonically and structurally, requiring a careful, multi-component geological–geophysical analysis. These basins are primarily composed of oceanic crust. The oceanic crust of both the South Caspian and Levant basins formed within the complex Neotethys ocean structure. However, this crust is allochthonous in the Levant Basin (LB) and autochthonous in the South Caspian Basin (SCB). This study presents a comprehensive comparison of numerous tectonic, geodynamic, morphological, sedimentary, and geophysical aspects of these basins. The Levant Basin is located directly above the middle part of the massive, counterclockwise-rotating mantle structure and rotates accordingly in the same direction. To the north of this basin is located the critical latitude 35° of the Earth, with the vast Cyprus Bouguer gravity anomaly. The LB contains the most ancient block of oceanic crust on Earth, which is related to the Kiama paleomagnetic hyperzone. On the western boundary of the SCB, approximately 35% of the world’s mud volcanoes are located; the geological reasons for this are still unclear. The low heat flow values and thick sedimentary layers in both basins provide opportunities to discover commercial hydrocarbon deposits at great depths. The counterclockwise-rotating mantle structure creates an indirect geodynamic influence on the SCB. The lithospheric blocks situated above the eastern branch of the mantle structure trigger a north–northeastward movement of the western segment of the Iranian Plate, which exhibits a complex geometric configuration. Conversely, the movement of the Iranian Plate induced a clockwise rotation of the South Caspian Basin, which lies to the east of the plate. This geodynamic ensemble creates an unstable geodynamic situation in the region. Full article

The Southern Lhasa Terrane, as the southernmost tectonic unit of the Eurasian continent, has long been a focal area in global geoscientific research due to its complex evolutionary history. The Yeba Formation exposed in this terrane comprises an Early–Middle Jurassic volcanic–sedimentary sequence that records multiphase tectonic deformation. This study applies structural analysis to identify three distinct phases of tectonic deformation in the Yeba Formation of the Southern Lhasa Terrane. The D₁ deformation is characterized by brittle–ductile shearing, as evidenced by the development of E-W-trending regional shear foliation (S₁). S₁ planes dip northward at angles of 27–87°, accompanied by steeply plunging stretching lineations (85–105°). Both south- and north-directed shear-rotated porphyroclasts are observed in the hanging wall. ⁴⁰Ar-³⁹Ar dating results suggest that the D₁ deformation occurred at ~79 Ma and may represent an extrusion-related structure formed under a back-arc compressional regime induced by the low-angle subduction of the Neo-Tethys Ocean plate. The D₂ deformation is marked by the folding of the pre-existing shear foliation (S₁), generating an axial planar cleavage (S₂). S₂ planes dip north or south with angles of 40–70° and fold hinges plunge westward or NWW. Based on regional tectonic evolution, it is inferred that the deformation may have resulted from sustained north–south compressional stress during the Late Cretaceous (79–70 Ma), which caused the overall upward extrusion of the southern Gangdese back-arc basin, leading to upper crustal shortening and thickening and subsequently initiating folding. The D₃ deformation is dominated by E-W-striking ductile shear zones. The regional shear foliation (S₃) exhibits a preferred orientation of 347°∠75°. Outcrop-scale ductile deformation indicators reveal a top-to-the-NW shear sense. Combined with regional tectonic evolution, the third-phase (D3) deformation is interpreted as a combined product of the transition from compression to lateral extension within the Lhasa terrane, associated with the activation of the Gangdese Central Thrust (GCT) and the uplift of the Gangdese batholith since ~25 Ma. Full article

Carbonate sedimentation was spread widely on the southern margin of the Neo-Tethys Ocean in the mid-Cretaceous. New information from four exploration wells sheds light on the peculiarities of the Sarvak Formation (late Albian–Cenomanian) at the narrow transition between the Dezful Embayment and Coastal Fars in the southern Zagros. The solution of this task was necessary to understand whether the fragmentation of the Zagros Basin into domains affected the carbonate platform development. The methods included the analyses of carbonate microfacies, paleoecological patterns of foraminifera, and depositional environments. The results of this study show the existence of ten carbonate microfacies. Prevailing wackestones and packstones with a muddy matrix and absent carbonate buildups imply the development of a large carbonate ramp. Paleoecological interpretations based chiefly on foraminifers prove this model. For instance, the presence of oligosteginids signifies shallower parts of the platform, and the cooccurrence of planktonic foraminifera and oligosteginids suggests a deeper environment. The stratigraphical distribution of the established microfacies in the wells indicates three cycles in the evolution of this platform. The third of these cycles marked an abrupt deepening episode because it includes microfacies suggesting the relatively deeper environments. Three maximum flooding surfaces established in the study area are common to the Arabian plate. The discussion of the results suggests that the influence of the Kazerun fault on the carbonate ramp in the Cenomanian is uncertain. Neither eustatic nor tectonic factors of the carbonate platform development can be excluded. Conclusively, it appears that the studied Cenomanian carbonate ramp was integral at the transition between the Dezful Embayment and Coastal Fars. Full article

Amphibole-rich cumulates provide crucial information pertaining to the petrogenetic history of suprasubduction zone ophiolites and are, therefore, helpful in constraining the evolution and closure of the Neo-Tethys during the late Cretaceous to the early Tertiary period. Following this, the present contribution examines the meta-hornblendite and meta-hornblende-gabbro lithologies in the Mayudia ophiolite complex (MdOC), NE Himalaya, based on their field and petrographic relations, constituent mineral compositions, whole rock major and trace element chemistry and bulk strontium (Sr)—neodymium (Nd) isotope systematics. MdOC cumulates potentially represent the fossilized record of an island arc root, where amphibole + titanite + magnetite was fractionally crystallized from a super hydrous magma (10.56–13.61 wt.% melt water content) prior to plagioclase in a stable physico-chemical condition (T: 865–940 °C, P: 0.8–1.4 GPa, logfO₂: −8.59–−11.19 unit) at lower crustal depths (30–38 km). Such extreme hydrous nature in the parental magma was generated by the flux melting of the sub-arc mantle wedge with aqueous inputs from the dehydrating slab. A super hydrous magmatic reservoir was, therefore, extant at sub-arc mantle depths in the eastern Neo-Tethys, which has likely modulated the composition of the oceanic crust during intraoceanic subduction. Full article

The İspir–Ahlatlı region in northeastern Türkiye, situated within the Eastern Pontides, hosts significant Miocene trachy-andesite volcanic rock exposures. This work seeks to elucidate their petrographic, geochemical, and isotopic compositions to enhance comprehension of their genesis and tectonic significance. Geochemistry reveals a transitional affinity, an enrichment in large-ion lithophile elements (LILEs), and a decrease in high-field-strength elements (HFSEs), suggesting a subduction-modified mantle source. Geochemical variations and fractional crystallisation trends indicate that the parental magma underwent significant differentiation, likely involving the fractionation of amphibole, clinopyroxene, and plagioclase. As supported by recent thermal modelling studies, the presence of intermediate volcanic rocks without associated bimodal suites in the study area may reflect elevated geothermal gradients and lithospheric delamination during post-collisional extension. The signatures indicated that the trachy-andesites originated in a post-collisional extensional environment after the closing of the Neo-Tethys Ocean and the ensuing tectonic reconfiguration of the Eastern Pontides. The reported geochemical traits correspond with post-collisional volcanic phases documented in various sectors of the Alpine–Himalayan orogenic system, such as the Eastern Pontides, the Iranian Plateau, and the Himalayan Belt, reinforcing the notion of a subduction-influenced mantle source. These findings increase the comprehension of magma formation in post-collisional settings and offer novel insights into the geodynamic context of the area. This research improves the understanding of post-collisional volcanic systems, their petrogenetic evolution, and their role in regional tectonic processes. Full article

The transition zone between a shallow-water delta and tidal flat is characterized by a high degree of mixed siliciclastic–carbonate sedimentation. There are frequent lateral and vertical variations in sandstone, dolostone, limestone, and mixed siliciclastic–carbonate rock (MSR); however, their influence on reservoir quality remains uncertain. Member B of the Asmari Formation (Asmari B) in Iraq’s C Oilfield was deposited in a remnant ocean basin formed by the closure of the Neo-Tethys Ocean. During the Oligocene–Miocene, frequent exposure of the Arabian Shield provided intermittent sediment sources to the study area. Under shallow water and relatively arid conditions, widespread mixed sedimentation of siliciclastic sand and dolomitic components occurred. Taking Asmari B as a case study, this research employs core and thin-section observations, trace element analyses, and quantitative mineralogical interpretations of logging data to investigate the characteristics of mixed sedimentation and to evaluate its impact on reservoir quality. Four key aspects were identified: (1) Four main types of mixed lithofacies developed in Member B of the Asmari Formation, namely sandstone-bearing dolomite, dolomitic sandstone, dolostone-bearing sand, and sandy dolostone. These lithofacies were deposited in the transition zone between distributary channels and intertidal zone with different water depths. As the terrigenous input decreased, the water depth for sand-bearing facies increased. In particular, sandy dolostone was predominantly formed in subtidal settings under the influence of storm events. (2) MSRs are categorized based on the proportion of the minor component into high and low mixing degrees. Based on mineral compositions interpreted from well logging data, the mixing degree of MSRs was characterized by the thickness ratio, using the thickness of high- and low-mixing-degree MSRs relative to the total thickness of the formation. The MSRs mainly developed in the B1, B2, B3-1, B3-2, and B4 sublayers, where moderate provenance supply facilitated the high mixing of terrigenous clastic and carbonate components. (3) The pore and throat patterns of MSR reservoirs change with the mixing degree index. When the dolomite content in sandstone exceeds 25%, the pore–throat structure changes significantly. A small amount of sand in dolostone has little effect on the pore and throat. Sandy dolostone exhibits the poorest reservoir quality. (4) Mixed sandstone reservoirs are distributed on both sides of the distributary channels and mouth bar. The dolostone-bearing sand reservoirs are distributed in the transition zone between the sandy flat and dolomite flat. Sandy dolostone is mainly thin and isolated due to the influence of storm events. This study provides guidance for understanding the development patterns of MSR reservoirs under similar geological settings, facilitating the next step of oil and gas exploration in these special reservoirs. Full article

The North Caspian Basin, known for its oil and gas potential, was formed because of the evolution of the ancient Tethys Ocean and is also a result of the collision of the East European, Kazakhstania, and Siberian paleocontinents. At the beginning of the Mesozoic Era, it was a part of the northern continental margin of the Neo-Tethys, which formed Eurasia. In the Late Triassic and Early Jurassic, a major restructuring of the North Caspian sedimentary basin occurred, characterized by angular unconformity and the erosion of underlying sediments in the coastal zones of the basin. The sedimentary succession of the depression accumulating in the Mesozoic Era consisted of alternating siliciclastic and carbonate rocks. It began to form due to the destruction of the uplifts formed north and west of the East European craton and Urals, which resulted in coastal clastic material in the Triassic and Jurassic, but by the end of the Jurassic and Cretaceous, when all uplifts existing in the north of Tethys were leveled, it was mostly marine environments that contributed to the accumulation of siliciclastic and carbonate strata. The appearance of a large amount of sedimentary material towards the center of the depression, causing stress, as well as the deflection of the basement, contributed to fault tectonics and the resumption and manifestation of salt tectonics. As a result of the continuous diapirism of salt bodies during the Late Mesozoic, mini basins were formed, in which different sedimentogenesis was manifested. These processes contributed to the redistribution of hydrocarbons from the underlying pre-salt formations to the intermediate depth interval post-salt succession with Permian–Triassic and also near-surface Jurassic–Cretaceous formations. Full article

The two-phase source rocks deposited during the Lower Cretaceous in the Persian Gulf Basin play a pivotal role in the regional hydrocarbon system. However, previous studies have lacked a macroscopic perspective constrained by the Tethyan Ocean context, which has limited a deeper understanding of their developmental patterns and hydrocarbon control mechanisms. To address this issue, this study aims to clarify the spatiotemporal evolution of the two-phase source rocks and their hydrocarbon control effects, with a particular emphasis on the critical impact of terrestrial input on the quality improvement of source rocks. Unlike previous studies that relied on a single research method, this study employed a comprehensive approach, including time series analysis, sequence stratigraphy, lithofacies, well logging, well correlation, seismic data, and geochemical analysis, to systematically compare and analyze the depositional periods, distribution, and characteristics of the two-phase source rocks under different sedimentary facies in the region. The goal was to reveal the intrinsic relationship between the Neo-Tethyan Ocean context and regional sedimentary responses. The results indicate the following: (1) the late Tithonian–Berriasian and Aptian–Albian source rocks in the Northern Persian Gulf were deposited during periods of extensive marine transgression, closely aligning with the global Weissert and OAE1d anoxic events, reflecting the profound impact of global environmental changes on regional sedimentary processes; (2) in the early stages of the Neo-Tethyan Ocean, controlled by residual topography, the Late Tithonian–Berriasian source rocks exhibited a shelf–intrashelf basin facies association, with the intrashelf basin showing higher TOC, lower HI, and higher Ro values compared to the deep shelf facies, indicating more favorable conditions for organic matter enrichment; (3) with the opening and deepening of the Neo-Tethyan Ocean, the Aptian–Albian source rocks at the end of the Lower Cretaceous transitioned to a shelf–basin facies association, with the basin facies showing superior organic matter characteristics compared to the shelf facies; (4) the organic matter content, type, and thermal maturity of the two-phase source rocks are primarily controlled by sedimentary facies and terrestrial input, with the Aptian–Albian source rocks in areas with terrestrial input showing significantly better quality than those without, confirming the decisive role of terrestrial input in improving source rock quality. In summary, this study not only reveals the differences in the depositional environments and hydrocarbon control mechanisms of the two-phase source rocks, but also highlights the core role of terrestrial input in enhancing source rock quality. The findings provide a basis for facies selection in deep natural gas exploration in the Zagros Belt and shale oil exploration in the western Rub’ al-Khali Basin, offering systematic theoretical guidance and practical insights for hydrocarbon exploration in the Persian Gulf and broader tectonic domains. Full article

The Yahşihan/Kırıkkale sedimentary basin, located in Central Anatolia within the İzmir-Ankara-Erzincan suture zone, mostly consists of Upper Cretaceous to Lower Pliocene sediments developed on the Ankara Melange, which is linked to the Northern Neo-Tethys Ocean. Although the stratigraphic, sedimentological, and tectono-stratigraphic characteristics of the basin have been investigated by many researchers, its mineralogical and geochemical characteristics have not been studied extensively. In this study, the provenance, paleoclimatological properties, and tectonic structure of the sedimentary rocks were interpreted using detailed mineralogical and geochemical analysis data. Formations such as the Karadağ (Cenomanian-Campanian), Çiçekdağ (Santonian-Campanian), Samanlık (Maastrichtian), Dizilitaşlar (Paleocene-Early Eocene), Çayraz (Middle Eocene), İncik (Upper Eocene-Lower Miocene), Central Anatolia Group (Middle Miocene-Pliocene), and Quaternary alluvium were deposited in the basin. X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM), and geochemical analyses were employed to determine the mineralogical and chemical composition of the units. Although highly oxic paleo-environmental conditions predominated in the basin, anoxic and suboxic conditions could also be present in the Dizilitaşlar and İncik formations. The units are primarily felsic with some mafic contributions, suggesting an oceanic island arc environment with varying paleoenvironmental conditions, reflecting seasonal changes between humid and arid periods. Full article

The India–Asia collision represents the most significant geological event in the formation of the Tibetan plateau. The subsidence of the Neo-Tethys oceanic slab and the closure of the ocean basin were precursors of the India–Asia collision. The Linzizong volcanic formations, which range in age from the late Cretaceous to early Cenozoic (70–40 Ma), are widely distributed across the Lhasa terrane and are considered products of the closure of the Neo-Tethys oceanic basin and the India–Asia collision. Here, we report a newly identified series of rhyolite porphyries, which share similar age and geochemical features with typical Linzizong volcanic formations. These porphyries are the northernmost extension of Linzizong volcanic formations discovered to date. Zircon U-Pb dating suggests that they formed between 58.8 and 56.1 Ma. These porphyries are characterized by high SiO₂ (75.04%–77.82%), total alkali (K₂O: 4.71%–5.03%), and Na₂O (2.54%–3.63%) values; relatively low Al₂O₃ (12.30%–13.62%) and MgO (0.13%–0.33%) values; and low Mg# values (15.8–25.7). They also exhibit strong enrichment in light rare earth elements ([La/Yb]_N = 3.76–11.08); negative Eu anomalies (Eu/Eu* = 0.10–0.32); Rb, Ba, Th, U, and Pb enrichments; as well as Nb and Ta depletions. The samples have relatively low εNd(t) values (−6.0 to −3.8) and variable zircon εHf(t) values (−6.3 to +3.6). These features suggest they originated from the remelting of the juvenile lower crust of the North Lhasa terrane under high-temperature and extensional conditions. We propose that the Mazin rhyolite porphyries resulted from mantle-derived magma diapirism, triggering juvenile lower crust remelting during Neo-Tethys oceanic slab rollback at the onset of the India–Asia collision. These findings provide new insights into the magmatic processes associated with early collisional tectonics. Full article

The Indo-Burma Range (IBR), as one of the youngest accreted units in the Eastern Neotethys, plays a crucial role in understanding the interactive relationships between the Gondwana supercontinent and its rifted microcontinents in SE Asia. However, its basement nature and tectonic evolution remain debated. Here, we conducted a comprehensive structural analysis across six sections within the IBR and correlated Late Triassic flysch units between the Western IBR (Pane Chaung Formation) and the Tethyan Himalaya. Within the Mindat section, the eastern segment of the Pane Chaung Formation unit displays top-to-east vergent overturned folds, indicating eastward backthrusting, in contrast to the prevailing top-to-west vergence structures in Kalemyo, Natchaung, Magwe and the western segment of the Mindat flysch unit. By reconstruction of this backthrust sheet, a megathrust separates the Pane Chaung Formation unit in the footwall to the west from schist units in the hanging wall to the east. The Pane Chaung Formation unit in the Western IBR and its counterparts in the Tethyan Himalaya share common characteristics, including herringbone cross-beddings, Carnian–Norian Halobia fossils, and dominant detrital zircons of 220–280, 500–620, 900–1000, and 1100–1140 Ma. Alongside the Paleozoic strata and Precambrian one-stage model ages of Mesozoic dikes, as evidenced by ɛ_Nd (t) (−13.4 to −0.1) and ɛ_Hf (t) (−24.2 to −0.1) in the Tethyan Himalaya, these facts suggest that the major tectonic units of the Western IBR–Tethyan Himalaya are the result of the amalgamation of a microcontinent with the West Burma Block. The transition from OIB to E-MORB and N-MORB, the rapid deepening of sedimentary waters, and the presence of the 155–152 Ma Indian ocean crust collectively indicate that the microcontinent rifted from the host East Gondwana as a fragment of the Argoland archipelago in the Late Jurassic. This identification sheds light on the orogenic processes of the doublet subduction zones in the Indo-Myanmar orogenic belt. Full article

Intermediate-acidic granites occur extensively in the Chazangcuo copper-lead-zinc mining area (hereinafter referred to as the Chazangcuo mining area) in Tibet, China. Exploring their rock types, sources, and tectonic settings is essential for understanding the genesis of granites in the region. This study investigated the petrology of the Chazangcuo granites, as well as the geochemical characteristics of their major elements, trace elements, and rare earth elements (REEs). Results indicate that the Chazangcuo granites are high-K calc-alkaline metaluminous rocks. These granites are enriched in large-ion lithophile elements (LILEs; e.g., Rb and Ba), depleted in high-field-strength elements (HFSEs; e.g., Nb, Ta, Zr, and Hf), with a relative enrichment in light rare earth elements (LREEs), and relatively depleted in heavy rare earth elements (HREEs), exhibiting a V-shaped distribution pattern and weak negative Eu anomalies. The granites are classified as typical I-type granites, displaying characteristics of crust-derived magmas with contributions from mantle sources and exhibiting significant fractional crystallization. The Chazangcuo granites were derived from the partial melting of mafic rocks, with protoliths formed in a moderate temperature environment. Influenced by the subduction of the Neotethys Ocean, the Chazangcuo granites were formed in an arc caused by the collision between the Indian and Eurasian plates (also referred to as the Indo–Eurasian collision) during the Late Triassic. Under the effect of geological activities such as upwelling of the asthenosphere and fluid intrusion and differentiation, metal mineralization was prompted to be distributed in the granite fissures, forming the Cu-Pb-Zn polymetallic deposits of Chazangcou in Tibet, suggesting that the granites are closely associated with mineralization. Full article

The Gangdese metallogenic belt in Tibet is an important polymetallic metallogenic belt formed during the subduction of the Neo-Tethys Ocean and subsequent India–Asia collision. Adakitic rocks are widely distributed in this belt and are considered to be closely related to porphyry–skarn Cu-Mo polymetallic mineralization. However, the petrogenesis and geodynamic setting of the Late Cretaceous adakites in the Gangdese belt remain controversial. In this study, we focus on the quartz diorite in the Nuri Cu-W-Mo deposit along the southern margin of the eastern Gangdese belt. LA-ICP-MS zircon U-Pb dating yields a Late Cretaceous age of 93.6 ± 0.4 Ma for the quartz diorite. Whole-rock geochemistry shows that the quartz diorite possesses typical adakitic signatures, with high SiO₂, Al₂O_3, and Sr contents, but low Y and Yb contents. The relatively low K₂O content and high MgO, Cr, and Ni contents, as well as the positive zircon εHf(t) values (+6.58 to +14.52), suggest that the adakites were derived from the partial melting of the subducted Neo-Tethys oceanic slab, with subsequent interaction with the overlying mantle wedge. The Late Cretaceous magmatic flare-up and coeval high-temperature granulite-facies metamorphism in the Gangdese belt were likely triggered by Neo-Tethys mid-ocean ridge subduction. The widespread occurrence of Late Cretaceous adakitic intrusions and associated Cu mineralization in the Nuri ore district indicate a strong tectono-magmatic-metallogenic event related to the Neo-Tethys subduction during this period. This study provides new insights into the petrogenesis and geodynamic setting of the Late Cretaceous adakites in the Gangdese belt, and has important implications for Cu polymetallic deposit exploration in this region. Full article

There is a wide variety of ore deposits in Albania, where 20% of the Cu resources belong to a deposit type of unknown genesis (sulphide-bearing quartz veins in gabbroic rocks). The focus of this paper is on two mineralisations of this type (Kçira and Thirra) in the Mirdita Zone, an ophiolite zone representing the Mesozoic Neotethys Ocean in the Dinarides. Our aim is to understand the ore-forming processes and the genesis of these deposits, which can be used in future exploration projects. According to the petrographical analysis, the host rock suffered propylitic alteration or subgreenschist facies metamorphism. Mineral chemistry of pyrite and epidote suggests a VMS related origin, more precisely, the deeper part of its stockwork feeder zone. The bulk rock geochemical analyses confirms that the mineralisations are classified as mafic-, Cyprus-type VMS deposits. Differences in the geochemical compositions and the corresponding mineralogical observations are attributed to the distinct original geotectonic positions: higher amount of compatible elements (Cr, Ni, V and Cu) occur in Kçira, which formed in a mid-oceanic ridge environment, while incompatible elements (Ag, As, Co and Zn) are more abundant in the Thirra deposit, which formed in a supra-subduction zone setting. Full article

The Bulfat Igneous Complex comprises the Bulfat and Walash groups and is situated in the Zagros Suture Zone, in the junction of Arabian and Eurasian plates. Zircon U-Pb data indicat an age of 63.7 ± 1.5 Ma for the trondhjemite rocks within the Bulfat group. Walash group is primarily composed of basalt to andesite rocks, interbedded with sedimentary rocks. Zircon U-Pb dating yields an age of 69.7 ± 2.7 Ma for the Walash group. Whole rocks chemistry shows that the Bulfat rocks have affinity to MORB and calc alkaline series but Walsh are mainly plot in the calc alkaline field. Whole rocks Sr-Nd isotope ratios show that the ¹⁴³Nd/¹⁴⁴Nd (i) changes from 0.51243 to 0.52189 and 87Sr/86Sr(i) ratios vary from 0.70345 to 0.7086. The calculated εNd(t) values, based on the CHUR, yield predominantly high positive values ranging from +6 to +8 for most samples. However, a few samples exhibit lower values (+2 to +3). Our data suggest that the interaction between lithospheric (depleted mantle, MORB-Like) and asthenospheric mantle (OIB-like) melts significantly controlled the magmatic evolution of the Bulfat group. The strong positive εNd(t) values (ranging from +6 to +8) align more consistently with a highly depleted lithospheric mantle source for the Walsh group. Therefore, the gradual transition from an arc signature at 70 Ma to a MORB signature around 63 Ma, occurred over a relatively short period of about 10 million years, and indicates the presence of an arc and back-arc system in the Neotethys ocean before the collision of the Arabian and Iran plates during the Cenozoic. Full article