Southern Neotethys Research Articles

Postcollisional transition from subduction- to intraplate-type magmatism in the eastern Sakarya zone, Turkey: Indicators of northern Neotethyan slab breakoff

AbstractPostcollisional magmatism in the eastern Sakarya zone was recorded by voluminous basic volcanism and repeated plutonism during the early Cenozoic. The temporal and geochemical evolution of these magmatic rocks is important for understanding the possible geodynamic history of the Sakarya zone. Here, we investigated three representative plutons lying between the towns of Çamlıhemşin (Rize) and İspir (Erzurum), Turkey. These are largely composed of medium-K gabbroic diorites (Marselavat Pluton), shoshonitic monzonites (Güllübağ Pluton), and high-K granites (Ayder Pluton). We present whole-rock geochemistry, 40Ar/39Ar geochronology, and Sr, Nd, and Pb isotope analyses from the plutons to constrain the timing of variations in magmatism and source characteristics, and we provide a new approach to the proposed geodynamic models, which are still heavily debated. The 40Ar/39Ar geochronology reveals a cooling sequence from ca. 45 Ma for the Marselavat Pluton through ca. 41 Ma for the Güllübağ Pluton to ca. 40 Ma for the Ayder Pluton. Whole-rock geochemistry and Sr, Nd, Pb isotopes suggest that crustal contamination was not an important factor affecting magma compositions. Although there was no arc-related tectonic setting in the region during the middle Eocene, the Marselavat Pluton shows some subduction affinities, such as moderately negative Nb and Ta anomalies, and slightly positive Pb anomalies. These signatures were possibly inherited from a depleted mantle source that was modified by hydrous fluids released from the oceanic slab during Late Cretaceous subduction. Geochemical traces of the earlier subduction become uncertain in the Güllübağ samples. They display ocean-island basalt–like multi-element profiles and Nb/Ta, Ce/Pb, and La/Ba ratios. All these point to a mantle source in which earlier subduction signatures were hybridized by the addition of asthenospheric melts. Melting of calc-alkaline crustal material, probably emplaced during the first phase of middle Eocene magmatism (Marselavat), led to the formation of granitic plutonism (Ayder Pluton). Our data in conjunction with early Eocene adakite-like rocks show that melt generation, as in the given sequence, was most probably triggered by breakoff of the northern Neotethyan oceanic slab, ∼13 m.y. after the early Maastrichtian collision between the Sakarya zone and Anatolide-Tauride block, and continued until the end of the middle Eocene. A shallow-marine transgression occurred contemporaneously with the middle Eocene magmatism throughout the Sakarya zone. An extension in this magnitude seems unlikely to be the result of orogenic collapse processes only. The main cause of this extension was most probably related to the northward subduction of the southern Neotethys Ocean beneath the Anatolide-Tauride block. The result is a volumetrically larger amount of middle Eocene magmatism than that expected in response to slab breakoff.

Adakite-like parental melt generation by partial fusion of juvenile lower crust, Sakarya Zone, NE Turkey: A far-field response to break-off of the southern Neotethyan oceanic lithosphere

The timing of major tectonic events and the driving mechanisms for magma generation during Late Cenozoic convergence and collision between Arabia and Eurasia still remain unknown. The Sakarya Zone (SZ) in northern Turkey is a critical member of this collisional assemblage. In the easternmost part of the SZ, we have recognized a Late Miocene volcanic suite termed the Çağirankaya volcanics which displays characteristic post-collisional geochemical features. Here, we report a new data set of zircon UPb ages, whole-rock major and trace element, as well as SrNd isotope analyses for dacite and andesite samples from the Çağirankaya volcanics. Zircon UPb ages for a selected dacitic lava sample average 5.16 ± 0.11 Ma (mean square of weighted deviates, MSWD = 0.45, n = 35), confirming a late Miocene age of this volcanic episode. The high-K calc-alkaline andesites and dacites exhibit an adakite-like geochemical signature, and are characterized by high Sr (424 to 552 ppm), Sr/Y ratios (31–43), and low Mg# (42 to 46) values, along with low Y (12–14 ppm) and heavy rare earth element (HREE) concentrations, that resemble those in adakites formed by partial melting of hot oceanic slab during subduction. Isotopic compositions are near bulk Earth (87Sr/86Sr(t) = 0.70482 to 0.70489, εNd(t) = +1.08 to +1.33), which rules out a solely asthenospheric origin. Elevated Nb/Ta (14 to 17) and K2O/Na2O (0.6–1.0) imply a juvenile mafic lower crustal source composed of ~20% garnet-bearing amphibolite. Geochemical modeling suggests that adakite-like parental melts were generated in the absence of subduction and without large-scale delamination of lower continental crust. Instead, our findings suggest that Late Miocene adakite-like volcanic rocks in the SZ formed in a post-collisional intra-continental setting, which experienced far-field extension after the subducted slab of the southern Neotethyan branch became detached in the collision zone. Asthenospheric upwelling and underplating of basaltic magma provided the heat for partial melting of lower crustal amphibolite, forming minor amounts of adakite-like melts in the SZ.

Temporal, spatial and geochemical evolution of late Cenozoic post-subduction magmatism in central and eastern Anatolia, Turkey

Indentation of the Arabian platform into the eastern domain of the Anatolide-Tauride Block (ATB) led to sub-horizontal rupture and break-off of the Arabian segment of the subducting southern Neotethyan oceanic slab beneath ATB in the late Cenozoic. Although this rupture has been well-defined by seismic tomography and numerical modeling, its relationship with concomitant magmatism in central and eastern Anatolia has not been firmly demonstrated. To address this issue, we compiled, integrated and interpreted an extensive database of previously-published age and geochemical data. Our analysis shows that late Cenozoic magmatism in both eastern and central Anatolia was nearly continuous over a distance of ~1000 km, and is herein named the Eastern Anatolian Magmatic Belt. Magmatism initiated at 23 Ma in response to rupturing of the north-dipping subducting oceanic slab below eastern Anatolia and upwelling of hot asthenospheric mantle. The onset of initial rupture-related magmatism is ~12 Ma older than previously proposed. The magmatic belt migrated westward from eastern Anatolia (23-15 Ma) to central Anatolia (12 Ma-present) and is a proxy for the westward progression of the slab rupture and related asthenospheric infiltration. Magmatism generated from the shallow melting of the previously-metasomatized Anatolian subcontinental lithospheric mantle and asthenosphere by decompression due to the impingement of the Arabian sub-slab asthenospheric mantle. In eastern Anatolia, slab-rupture magmatism was followed by a second phase of magmatism that formed in response to destabilization and convective removal of the thick Anatolian lithospheric root (13 Ma-present). This new magmatic model emphasizes that the geochemical signature of post-subduction magmatism, as recorded by primitive basalts that constantly evolved through time and space. Magmatic sources recorded the shifting of mantle melt source domains that were controlled by slab segmentation and induced mantle flow.

GEOCHEMISTRY AND TECTONIC SIGNIFICANCE OF THE OPHIOLITIC ROCKS OF THE YARPUZ-KAYPAK (AMANOSLAR, OSMANİYE) AREA

Amanoslar’da, Yarpuz-Kaypak (Osmaniye) yoresindeki ofiyolitik kayaclar harzburjitik tektonitler ve mafik kumulat kayaclarindan olusmaktadir. Tektonitler serpantinize harzburjitler ile temsil edilirken kumulat kayaclari gabronorit ve gabro ile temsil edilmektedir. Kumulat kayaclardaki minerallerin kristallenme sirasi klinopiroksen, ortopiroksen, plajiyoklaz ve amfibol seklindedir. Tektonit ve kumulatlarin ana element icerikleri yay ile iliskili tektonik ortamlar ile uyumludur. Bu kayaclar, iz element konsantrasyonlari bakimindan, buyuk iyon yaricapli elementlerce zenginlesme gostermektedir. Elde edilen jeokimyasal ve petrografik veriler, Yarpuz-Kaypak (Osmaniye) yoresindeki tektonit ve kumulat kayaclarin Guney Neotetis okyanusunun Gec Kretase’de kapanmasi sirasinda okyanus ici yitim zonu dalma-batma zonu uzerinde olusan ve Arap platformunun kuzey kenarina yerlesen okyanusal litosfer kalintilari olduguna isaret etmektedir.

Geochemistry and Provenance of Sandstone Unit in Tanjero Formation in Sulimania Area, NE-Iraq.

Sandstone rocks occurring in the Tanjero Formation in the Sulimania and Pera-Magron areas, which crops out within the Imbricated and High Folded Zones in Northeastern Iraq, are lithic arenites with high proportions of sedimentary rock fragments. The presence of quartz, chert, carbonates and igneous and metamorphic lithic grains and fossils in the Tanjero sandstone clastic rocks indicates that the southern Neotethys Ocean was a shallow seaway during their deposition. Geochemical classification of the an Upper Cretaceous Tanjero sandstone clastic rocks are lithic arenites to Fe-Sand and indicates that they were mainly derived from Albian-Cenomanian Gimo–Qandil sequence ophiolite-bearing terrane and Hemipelagic sediments (Parautochthonous Qulqula rocks)..

Frequent euxinia in southern Neo-Tethys Ocean prior to the end-Permian biocrisis: Evidence from the Spiti region, India

In this study, we reconstruct water-column oxygen availability during the deposition of Late Permian shales (Wuchiapingian to approximately early Changhsingian) using the geochemistry and morphology of sedimentary pyrite (FeS2). Deposition of the shales occurred prior to the end-Permian mass extinction within the southern Neo-Tethys Ocean (Spiti region, Himachal Pradesh, India). We found that the variability of pyritic sulfur to organic carbon (Spyr/Corg) and the pyritic sulfur isotopic composition (δ34Spyr) did not record changes in oxygen availability at Spiti sections. This was due to the removal of original pyritic sulfur by modern oxidative weathering and diagenetic pyrite formation which overwhelmed the original δ34Spyr values. However, pyrite framboid size distributions was a reliable recorder of paleoredox conditions. The degree of oxygen limitation varied with multiple transient euxinic events interrupting a predominantly oxic-dysoxic trend near the top of the Gungri Formation upper member (approximately late Wuchiapingian to early Changhsingian). These transient euxinic intervals provide important insight and regional evidence of environmental stress and instability in the southern Neo-Tethys well prior to the end-Permian mass extinction.

Palaeoenvironmental signature of the Late Campanian-Early Maastrichtian benthonic foraminiferal assemblages of Kurdistan, Northeast Iraq

The Late Campanian to Early Maastrichtian benthic foraminiferal assemblages in the Shiranish Formation of Kurdistan region (NE- Iraq) are placed into three temporally distinct assemblages that are interpreted to reflect environmental changes, principally involving factors associated with paleodepth. In stratigraphic succession the assemblages are: the Lenticulina macrodiscus-Lenticulina pseudosecans Assemblage (Late Campanian), occupying a succession of strata that are equivalent to the lower and upper parts of the Bolivinoides decoratus subzone within the Bolivinoides decoratus benthic foraminiferal biozone; the Gavelinella monterelensis-Gavelinella stephensoni Assemblage (Late to Latest Campanian), occupying a succession of strata that are equivalent to the uppermost part of the Bolivinoides decoratus and B. laevigatus subzones within the Bolivinoides decoratus benthic foraminiferal biozone; and the Coryphostoma incrassata gigantea-Praebulimina carseyae-Loxostomum eleyi Assemblage (Early Maastrichtian), occupying a succession of strata that are equivalent to the Bolivinoides miliaris and B. draco benthic foraminiferal biozones. The foraminiferal assemblages are interpreted as representing outer shelf to middle slope environments, between ca 200 m to at least 600 m water depth, with maximum water depths in the Late Campanian, followed by shallowing into the Early Maastrichtian. The most likely control mechanism for shallowing sea level was the beginning of southern Neo-Tethys Ocean closure at this time. Almost manifesting the turnover from pre-flysch facies to the overlying flysch facies within Kurdistan foreland basin. Such variation in the benthic foraminiferal assemblages controlled essentially by the interactions between the palaeobasin configuration and sea level changes from the Late Campanian to Early Maastrichtian.

Paleomagnetic results along the Bitlis-Zağros suture zone in SE Anatolia, Turkey: Implications for the activation of the Dead Sea Fault Zone

The tectonic evolution of SE Anatolia is associated with the collision between the Taurides and the Arabian Platform in the early Cenozoic, after the final closure of the southern branch of the Neotethys ocean during Late Cretaceous to Early Eocene times. The ongoing deformation was characterized by northward movement of Arabia, followed by westward extrusion of Anatolia, having been displaced along the northern and eastern Anatolian transform faults. The neotectonic deformation history between the Anatolian Plate and the Arabian platform since the closure of the southern Neotethyan oceanic basin from Late Cretaceous to present has not been studied in detail paleomagnetically. Therefore we carried out a paleomagnetic study of Mesozoic and Cenozoic rocks at 34 localities along the Bitlis-Zağros suture zone in SE Anatolia located in the boundary region between the Taurides and the Arabian platform and delimited by the Dead Sea Fault.Paleomagnetic results from the area show clockwise rotations of 35.6° ± 14.1° and 26.7° ± 8.0° with respect to the African plate from Upper Jurassic - Lower Cretaceous and Upper Cretaceous limestones, respectively. The paleomagnetic results indicate also an earlier deformation/opening due to the Dead Sea Fault Zone (DSFZ). Farther north on the Tauride Block, counterclockwise rotation of −34.5° ± 12.5° is recorded by Upper Cretaceous limestones. In the SE of the study area on the northern margin of Arabia, however, smaller counterclockwise rotations of -12.3° ± 8.3° and −2.5° ± 10.0° in Late Cretaceous and −12.7° ± 13.6° in middle Eocene rocks show relative tectonic stability. Middle Miocene rocks close to the suture zone show counterclockwise rotation by about −39.4° ± 10.9°, while farther away from the suture zone counterclockwise rotations of −21.9° ± 9.9° and −7.5° ± 5.8° are observed. Paleolatitudinal motion from south to north from the Late Jurassic to the Present is in concordance with the apparent polar wander path of Eurasia and Africa.

Tectono-stratigraphic evolution of the SE Mediterranean passive margin, offshore Egypt and Libya

Abstract The regional tectono-stratigraphic evolution of the offshore SE Mediterranean passive margin is evaluated using detailed 2D seismic interpretations. New models for the development of the margin are proposed in the context of the break-up of northern Gondwana and the subsequent evolution of the southern Neotethys Ocean. The SE Mediterranean margin is segmented into distinct rift and transform-dominated tectonic domains as a consequence of multiple phases of rifting and continental break-up during the Middle Triassic–Middle Jurassic ( c. 240–170 Ma) and the Late Jurassic–Mid-Cretaceous ( c. 145–93 Ma), controlled by reactivation of pre-existing Pan-African basement fabrics and shear zones in varying regional stress fields. The pre-existing basement-involved extensional fault systems were repeatedly reactivated during major phases of inversion in the late Santonian–Maastrichtian ( c. 84–65 Ma) and Middle–Late Eocene ( c. 49–37 Ma) and episodes of mild inversion during the Oligocene–Early Pleistocene, as a consequence of the convergence of the African–Arabian and Eurasian plates and closure of the Neotethys oceans. The inversion history was fundamentally controlled by the structure and along-strike segmentation of the margin inherited from Neotethyan rifting.

Petrogenesis of kyanite‐ and corundum‐bearing mafic granulite in a meta‐ophiolite, SE Turkey

AbstractAlthough ophiolitic rocks are abundant in Anatolia (Turkey), only in rare cases have they experienced high‐grade metamorphism. Even more uncommon, in Anatolia and elsewhere are high‐grade meta‐ophiolites that retain an oceanic lithosphere stratigraphy from upper crustal mafic volcanic rocks through lower crustal gabbro to mantle peridotite. The Berit meta‐ophiolite of SE Turkey exhibits both features: from structurally higher to lower levels, it consists of garnet amphibolite (metabasalt), granulite facies metagabbro (as lenses in amphibolite inferred to be retrogressed granulite) and metaperidotite (locally with metapyroxenite layers). Whole‐rock major and trace‐element data indicate a tholeiitic protolith that formed in a suprasubduction setting. This paper presents new results for the metamorphic P–T conditions and path of oceanic lower crustal rocks in the Berit meta‐ophiolite, and an evaluation of the tectonic processes that may drive granulite facies metamorphism of ophiolite gabbro. In the Doğanşehir (Malatya, Turkey) region, granulite facies gabbroic rocks contain garnet (Grt)+clinopyroxene (Cpx)+plagioclase (Pl)+corundum (Crn)±orthopyroxene (Opx)±kyanite (Ky)±sapphirine (Spr)±rutile. Some exhibit symplectites consisting of Crn+Cpx, Ky+Cpx and/or coronas of garnet (outer shell) around a polygonal aggregate of clinopyroxene that in some cases surrounds a polygonal aggregate of orthopyroxene. Coronitic and non‐coronitic textures occur in proximity in mm‐ to cm‐scale layers; corona structures typically occur in plagioclase‐rich layers. Their formation is therefore related primarily to protolith type (troctolite v. gabbro) rather than P–T path. Phase diagrams calculated for a kyanite‐rich granulite, a plagioclase‐rich non‐coronitic granulite, and a plagioclase‐rich coronitic granulite (taking into account changes in effective bulk composition during texture development) predict peak conditions of ~800°C, 1.1–1.5 GPa; these conditions do not require invoking an unusually high geothermal gradient. In the coronitic metagabbro, reaction textures formed along the prograde path: Crn–Cpx symplectites grew at the expense of garnet, sapphirine and plagioclase. Peak conditions were followed by isobaric cooling of ~150°C. Hornblende–plagioclase thermometry results for host amphibolite (Hbl+Pl±Crn±Grt±relict Cpx) indicate retrograde conditions of 620–675°C and 0.5–0.8 GPa accompanied by infiltration of H2O‐rich fluid. This anticlockwise P–T path differs from an isothermal decompression path previously proposed for these rocks based on the presence of symplectite. Metamorphism of the ophiolitic rocks was driven by closing of the southern Neotethys Ocean, as oceanic lithosphere was obducted (most SE Anatolian ophiolites) or underthrust (Berit meta‐ophiolite). This was followed by subduction of a continental margin, driving cooling of the Berit granulite after the thermal peak at depths of ~40 km.

Two plutonic complexes of the Sanandaj-Sirjan magmatic-metamorphic belt record Jurassic to Early Cretaceous subduction of an old Neotethys beneath the Iran microplate

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.

Textural records and geochemistry of the Kermanshah mantle peridotites (Iran): implications for the tectonic evolution of southern Neo-Tethys

Textural records and geochemistry of the Kermanshah mantle peridotites (Iran): implications for the tectonic evolution of southern Neo-Tethys

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.

A magnetite-rich Cyprus-type VMS deposit in Ortaklar: A unique VMS style in the Tethyan metallogenic belt, Gaziantep, Turkey

The Ortaklar VMS deposit is hosted in the Koçali Complex consisting of basalts and deep sea pelagic sediments, which formed by rifting and continental break-up of the southern Neotethyan in Late Triassic. The basalts are of NMORB-type without notable crustal contamination. From the surface to depth, the Ortaklar deposit consists of a gossan zone, a thick massive ore zone and a poorly developed stockwork zone. Primary mineralisation is characterised by distinctive facies including sulphide breccias (proximal), graded beds (distal), stockworks and chimney fragments. Ore mineral abundances decrease in the order of pyrite, magnetite, chalcopyrite, and sphalerite. Two distinct phases of mineralisation, massive magnetite and massive sulphide, are present in the Ortaklar deposit. Textural evidence (e.g., magnetite replacing sulphides) and the spatial relationships with the host rocks indicate that magnetite and sulphide minerals were generated in different stages. The transition from sulphide to magnetite mineralisation is interpreted to relate to variation in H2S content of ore fluids. The 1st stage massive sulphide ore might have formed by early hydrothermal fluids rich in Fe and H2S. The 2nd stage massive magnetite might have formed by later neutral hydrothermal fluids rich in Fe but poor in H2S, replacing the pre-existing sulphide ore.The alteration patterns, mineral paragenesis, lithological features (massive ore-stockwork ore-gossan) of the Ortaklar deposit together with its trace elements, Cu-Pb-Zn-Au-Ag and REE signatures are all consistent with a Cyprus-type VMS system. The δ34S values in pyrite and chalcopyrite samples range from 2.6 to 5.7‰, indicating that the hydrothermal fluids were associated with sub-seafloor igneous activity, typical of Cyprus-type VMS deposits. However, magnetite formed later than sulphide minerals in the Ortaklar deposit, contrasting with typical Cyprus-type VMS deposits where magnetite generally occurs in lower sections. Consequently, although the Ortaklar deposit generally conforms to Cyprus-type deposits, it is distinguished from them by its late stage and high magnetite concentration. Thus, the Ortaklar deposit is thought to be an exceptional and perhaps unique Cyprus-type VMS deposit.

Geochemistry of tholeiitic to alkaline lavas from the east of Lake Van (Turkey): Implications for a late Cretaceous mature supra-subduction zone environment

Arc-related rocks of the Yüksekova Complex extend from Kahramanmaraş to Hakkari throughout the Southeast Anatolia representing the remnants of the Southern Branch of Neotethys. The volcanic members of this zone from the eastern parts of Lake Van suggest three different types of rock chemistry; tholeiitic (type I), calc-alkaline (type II) and alkaline (type III). Tholeiitic and calc-alkaline members suggest a subduction-related environment with their HFS and LIL element distributions. RE and trace element systematics and modelings indicate that i) the intermediate and the felsic calc-alkaline rocks are the result of fractional crystallization from a basic endmember, ii) alkaline members have originated from enriched mantle source relative to the tholeiitic and calc-alkaline lavas. Overall data from Yüksekova Complex suggest a mature supra-subduction zone environment within the southern Neotethyan Ocean during Upper Cretaceous time. The existence of Lutetian OIB like asthenospheric lavas at the upper parts of the ophiolitic assemblage in the eastern parts of Lake Van proposes the end of the normal ophiolite formation and the possible continuation of the magmatism with OIB like lavas during Middle Eocene.

The tectonic history of the Niğde‐Kırşehir Massif and the Taurides since the Late Mesozoic: Paleomagnetic evidence for two‐phase orogenic curvature in Central Anatolia

AbstractThe Niğde‐Kırşehir Massif, known also as the Central Anatolian Block, is bordered by the sutures of the Neotethys Ocean. The massif suffered several deformation phases during and after the consumption of the surrounding oceans and the postcollisional events of the continental pieces of Anatolia in latest Cretaceous to Miocene. Previous paleomagnetic studies on the Niğde‐Kırşehir Massif and its surroundings displayed either insufficient data or have claimed large rotations and/or remagnetization. In order to understand the tectonic history of the Niğde‐Kırşehir Massif and its adjacent blocks we have sampled 147 different sites in the age range of Upper Jurassic to Miocene from the Niğde‐Kırşehir Massif throughout its W/SW and E/SE boundaries and the central‐southeastern Taurides. The results display that except the limestones in central Taurides, all rocks examined carry a primary magnetization. Among these an important finding is that rotations between the massif and the central‐eastern Taurides indicate an oroclinal bending with counterclockwise rotation of R = 41.1° ± 7.6° in the SE and clockwise rotation of R = 45.9° ± 9.3° in the central Taurides from Upper Cretaceous rocks with respect to the African reference direction. Paleomagnetic rotations in the SE Taurides are compatible with the vergent direction of the thrusts generated from consumption of the Intra‐Tauride Ocean prior to postcollisional convergence between Taurides and the massif. In the central Taurides it has been shown that the clockwise rotation of 45.9 ± 9.3 started in Middle Eocene, because of a remagnetization in Upper Cretaceous limestones. The deformation was linked to the final closure of the southern Neotethys and the collision between the African and Eurasian plates. In the Niğde‐Kırşehir Massif counterclockwise rotation up to 25.5° ± 7.3° is recognized during Middle Eocene and interpreted in terms of block rotation together with the Taurides. After the Miocene a counterclockwise rotation of 16.8° ± 3.9° along the Eastern Taurides shows that this area was mostly affected by the westward movement of Anatolia despite the Niğde‐Kırşehir Massif and its SW/W area—the central Taurides—which is recognized as stable with counterclockwise rotation less than 10°.

The temporal evolution of the active margin along the Southeast Anatolian Orogenic Belt (SE Turkey): Evidence from U–Pb, Ar–Ar and fission track chronology

The Southeast Anatolian Orogenic Belt (SAOB) resulted from the north-dipping subduction of the southern Neotethyan oceanic lithosphere in late Mesozoic and early Cenozoic. However, the timing and the rate of the continental collision are still under debate. Here, we present new U–Pb, Ar–Ar and Fission Track ages from the I-type calc-alkaline granitoids (Esence, Doğanşehir and Baskil) cutting the Göksun, İspendere and Kömürhan ophiolites and also the Malatya–Keban metamorphics representing the Tauride active continental margin along the SAOB. In this study, high- to low-temperature thermochronological methods, applied to the granitoids, are used to understand the temporal and geodynamic evolution of the Tauride active continental margin and continental collision between Tauride and Arabian platforms in the frame of the Neotethyan convergence during Cretaceous and Miocene. The U–Pb zircon ages range from 83 to 88Ma for the Baskil and from 81 to 83Ma for the Esence granitoids. The 39Ar–40Ar ages indicate that these late Cretaceous granitoids cooled below 300°C in 6–10Ma. The formation ages and the timing of the gradual cooling of the late Cretaceous granitoids are similar to metamorphism age and the timing of the exhumation of the HP/LT Bitlis metamorphics during this stage. The combined field, geochemistry and geo-thermochronological data suggest that the first continental collision event occurred between Bitlis–Pütürge micro-continents to the south and Tauride platform to the north in an oblique subduction zone between 84 and 74Ma. The granitoids continued uplifting during early-middle Eocene together with the exhumation of HP/UHT Berit metaophiolite in an extensional regime related to the opening of the Maden back-arc basin. This period also let the intrusion of the Doğanşehir arc magmatism, intruding the Pütürge and Malatya–Keban metamorphics, Berit metaophiolite, and Maden Complex. The Eocene Doğanşehir granitoid has similar U–Pb and 39Ar–40Ar ages, suggesting a fast cooling. The apatite fission track (AFT) ages for all granitoid bodies suggest that they were mainly cooled or uplifted in two episodes, where the first one is in the Eocene in an extensional setting. The AFT data marked the final continental collision between the Taurides and the Arabian platform first in Oligocene and the break-off of the subducted slab and the delamination process caused fast uplift of the Eastern Anatolia during middle to late Miocene.

Geochemistry of the Eocene magmatic rocks from the Lesser Caucasus area (Armenia): evidence of a subduction geodynamic environment

Abstract This paper is focused on petrological and geochemical data obtained on a series of Middle and Upper Eocene magmatic rocks from the Lesser Caucasus of Armenia in order to elucidate magma sources and geodynamic processes. Middle–Upper Eocene magmatism is present in two main zones: the Amasia–Sevan–Hakari suture zone (ASHSZ) and the so-called South Armenian Microplate (SAM). Volcanic rocks from both places range from basalt to rhyolite and mostly display a calc-alkaline character. Trace element patterns from the SAM and ASHSZ samples show mobile-elements enrichment (Rb, Ba, Th) together with strong negative high field strength elements (Nb, Ta, Hf, Zr) anomalies. The (La/Sm) N ratio yields very close values for both areas. Conversely, the (La/Yb) N ratio is, on average, significantly higher for SAM than for ASHSZ, suggesting the presence of residual garnet at the source of the SAM volcanic rocks. Nevertheless, trace elements suggest partial melting from phlogopite- and amphibole-bearing spinel lherzolitic mantle sources. Neodymium and strontium isotopes yield εNd (40Ma) and 87 Sr/ 86 Sr (40Ma) ratios ranging, respectively, from –0.3 to +6.6 and from 0.70314 to 0.70531 for SAM samples, and from +3.4 to +6.8 and from 0.70393 to 0.70433 for ASHSZ samples. Initial Pb/Pb isotopic ratios yield close values for both areas but with slightly higher and more homogeneous 207 Pb/ 204 Pb and 208 Pb/ 204 Pb ratios for SAM samples. Such features concur with a more pronounced slab-component contribution in the frontal part of the volcanic belt, that is, in the SAM domain. No significant crustal contamination has been detected in the studied Eocene magmatic rocks from both the ASHSZ and SAM. Considering geodynamic and geochemical constraints, we propose that this magmatism is connected with a north-dipping Southern Neotethys subduction, in an extensional (back-arc) environment of orogenic belts. The Arabia–Eurasia collision and the closure of the Neotethys Ocean may have occurred after this magmatic event.

Structural development of the central Kyrenia Range (north Cyprus) in its regional setting in the eastern Mediterranean region

A detailed structural analysis of the Mesozoic–Cenozoic geological development of the central segment of the Kyrenia Range in its regional tectonic context is given here. The structural evidence comes from five structural traverses, outcrop observations, small-scale structures and related regional evidence. The majority of the structures are fault planes, of which a subordinate number exhibit slickenlines (fault plane data, n = 2688; with kinematics, n = 537). Additional kinematic data were obtained from C–S fabrics and folds. Small-scale structures in each stratigraphic unit were ‘backstripped’ to reveal relative chronology. Synthesis of the structural information indicates three phases of convergence-related deformation: (1) Late Cretaceous, associated with greenschist facies metamorphism, followed by exhumation that was probably associated with WNW–ESE to ENE–WSW-trending high-angle faulting; (2) Mid-Eocene, associated with southward thrusting, coupled with ~N–S strike-slip (transfer faulting) and oblique faulting in an overall sinistral transpressive stress regime; (3) Late Miocene-earliest Pliocene, involving southward thrusting and folding, localised back-thrusting, extensive fault reactivation and large-scale segmentation of the range. Intense uplift of the Kyrenia Range took place during the Plio-Pleistocene, possibly related to the collision of the Eratosthenes Seamount with the Cyprus trench to the south of the island. The three main convergent phases relate to stages of northward subduction and diachronous continental collision affecting the northerly, active continental margin of the Southern Neotethys.

Neotethys seawater chemistry and temperature at the dawn of the end Permian mass extinction

The end of the Permian was a time of great death and massive upheaval in the biosphere, atmosphere and hydrosphere. Over the last decades, many causes have been suggested to be responsible for that catastrophe such as global warming, anoxia and acidification. The Gyanyima limestone block was an open ocean seamount in the southern Neotethys at subtropical latitude, and it affords us insight into open-ocean oceanographic changes during the end of the Permian. After careful screening using multiple tests, we reconstructed carbonate/seawater curves from the geochemical data stored in pristine brachiopod shell archives from the shallow water limestone of the Changhsingian Gyanyima Formation of Tibet. The reconstructed strontium isotope curve and data for the late Changhsingian are relatively invariant about 0.707013, but in the upper part of the succession the values become more radiogenic climaxing at about 0.707244. The 87Sr/86Sr curve and trend are similar to those observed for the Upper Permian succession in northern Italy, but dissimilar (less radiogenic) to whole rock results from Austria, Iran, China and Spitsbergen. The Ce/Ce* anomaly results ranging from 0.310 to 0.577 for the brachiopods and from 0.237 to 0.655 for the coeval whole rock before the event, and of 0.276 for whole rock during the extinction event, suggest normal redox conditions. These Ce* values are typical of normal open-ocean oxic water quality conditions observed in modern and other ancient counterparts. The biota and Ce* information clearly discounts global anoxia as a primary cause for the end-Permian biotic crisis. Carbon isotopes from brachiopod shells and whole rock are relatively invariant for most of the latest Permian interval, which is in stark contrast to the distinct negative carbon isotope excursion observed near and about the event. Estimates of seawater temperature at shallow depth fluctuated from 22.2 to 29.0°C up to unit 8–2, and then gradually rise from 29.7°C in unit 8–13 to values exceeding 35°C at a stratigraphic level about 120ky before the Permian–Triassic boundary, and just before the onset of the extinction interval. This dramatic increase in seawater temperature has been observed in global successions from tropical to mid latitude and from restricted to open ocean localities (e.g., northern Italy, Iran). The brachiopod archive and its geochemical proxies from Tibet support the paradigm that global warming must have been an important factor of the biotic crisis for the terrestrial and marine faunas and floras of the late Paleozoic world.