Tauride Block Research Articles

Significance of the Paleocene olistostrome–turbidite belt (Abant Formation) along the Intra-Pontide Suture, northern Turkey

A belt of Paleocene turbidites with olistostromes, the Abant Formation, crops out for 350 km along the Intra-Pontide Suture in northern Turkey. The suture constitutes the contact between two major Pontide tectonic units, the Istanbul and Sakarya zones, and the Abant Formation was used as evidence for the Paleocene–early Eocene closure of the Intra-Pontide ocean. We mapped and studied the Abant Formation along the Intra-Pontide Suture. The Abant Formation consists of deformed Paleocene siliciclastic turbidites with mass flows. The blocks in the olistostromes are mainly Late Cretaceous pelagic limestones; there are also Late Jurassic–Early Cretaceous, Late Cretaceous and Paleocene shallow-marine limestone blocks. Other rare block types include late Neoproterozoic and Permian granites, basalt, chert and serpentinite. The ophiolitic blocks make up less than 5% of the Abant Formation. Most of the blocks were derived from the south, from the Sakarya Zone; detrital zircon ages from the turbidite sandstones also indicate a predominantly southern source. The Abant Formation was deposited in a foreland basin, which was formed during the Paleocene collision between the Pontides and the Anatolide–Tauride Block. The basin was preferentially located on the Intra-Pontide Suture because the suture constituted an old crustal lineament.

Low-Temperature Thermochronology Records the Convergence between the Anatolide–Tauride Block and the Arabian Platform along the Southeast Anatolian Orogenic Belt

SE Anatolia is witnessing the final stage of the Wilson Cycle, where a continental collision between the Tauride–Anatolide block and Arabian platform occurred, and a 1.5 km Eastern Tauride mountain chain formed. We present new low-temperature thermochronology (LTT) ages, including eight apatite fission track (AFT) and seven apatite and zircon U-Th-Sm/He (AHe, ZHe) ages, for the metamorphic rocks from the Nappe Zone of the Southeast Anatolian Orogenic Belt. The ZHe ages vary from 51.2 ± 0.7 Ma to 30.4 ± 0.6 Ma, the AFT ages range from 33.1 ± 1.6 Ma to 18.1 ± 0.9 Ma, and the AHe ages range from 23.6 ± 2.5 Ma to 6 ± 1.9 Ma. The LTT data show a continuous slow uplift of the region. However, the thermal modeling results suggest an Eocene and middle–late Miocene fast uplift of the region. Similar to our results, the LTT studies along the SAOB show that the vertical movements initiated during the Eocene period have continued in a steady-state regime to recent times. The Eocene epoch is identified by arc–back-arc setting in the region, whereas the Miocene epoch is marked by the continental collision. Within this tectonic framework, vertical movements on the overriding plate are controlled by both extensional and compressional tectonics. The LTT data obtained along the SAOB show fingerprints of thrust propagation from north to south.

Frequency-dependent shear wave attenuation across the Central Anatolia region, Türkiye

Abstract. The Central Anatolian Plateau with its volcanic provinces represents a broad transition zone between the compressional deformation in the east and the extensional regime in the west. The Central Anatolian Fault Zone separates the Kırşehir Block in the north and the Anatolide–Tauride Block in the south within the plateau. A proper understanding of physical properties such as seismic attenuation in the crustal volume of this region can provide hints toward the possible source for the geodynamic events in the past and present that likely lead to the observed deformation. In order to model intrinsic and scattering attenuation separately, we perform a nonempirical coda-wave modeling approach in which a fitting process between observed and synthetic coda-wave envelopes is performed for each earthquake in multiple frequency bands. Here, the acoustic radiative transfer theory, assuming multiple isotropic scattering, was utilized for the forward modeling of the synthetic coda-wave envelopes of local earthquakes. Our findings generally highlight the prominent nature of intrinsic attenuation over scattering attenuation, implying the presence of thick volcanic rocks with relatively high attenuation values beneath Central Anatolia. Overall, the spatial distribution of the attenuation at varying frequencies marks the Kırşehir Massif distinctively with its considerable high-attenuating character. Our findings, combined with early seismological and geo-electrical models, suggest a possible partial melt beneath most of the Central Anatolian Volcanic Province, and the resultant zones of elevated fluid-rich content exhibit high and dominant intrinsic attenuation. To the southeast, a gradual decrease in the observed attenuation coincides with the Central Taurus Mountains where high altitude is considered to be evolved following the slab break-off and resulting mantle upwelling.

No sediment transport across the Tethys ocean during the latest Cretaceous: detrital zircon record from the Pontides and the Anatolide–Tauride Block

No sediment transport across the Tethys ocean during the latest Cretaceous: detrital zircon record from the Pontides and the Anatolide–Tauride Block

Growth of the imbrication zone along the southeast Anatolian orogenic belt: evidencefrom fission track thermochronology from Gölbaşı region (SE Turkey)

One of the major components of continental collision zones is their imbricated zones. Such a zone along the Southeast Anatolian Orogenic Belt (SAOB) is solely controlled by a still-active convergence and accretion system between the Anatolian Plate and Arabian platform since at least Late Cretaceous. The zone is characterized by NEE/SWW-trending, northward-dipping thrust slices that are squeezed between the Tauride Block to the north and the Arabian platform to the south. The units cropping out within the zone comprise Neo-Tethysrelated magmatic, ophiolitic, sedimentary and metamorphic rocks with Late Cretaceous to Miocene formation/metamorphism ages. The Karanlıkdere granitoid intrudes into Late Cretaceous Meydan ophiolite, Helete volcanics, and Malatya metamorphics. These units thrust over Cenozoic volcanic and sedimentary rocks. Although various scenarios have been proposed for the late Cretaceous to Neogene evolution of the complex region, quantitative data aiming to understand the growth mechanism of the imbrication zone in the region are limited. The zircon U-Pb and the apatite fission track (AFT) thermochronology were applied to the Karanlıkdere granitoid within the imbrication zone of the Southeast Anatolian Orogenic Belt (SAOB). The LA-ICP-MS zircon U-Pb age yields 79.67 ± 0.24 Ma with 0.23?0.65 Th/U ratios. This age is slightly younger than the previously published ages, indicating that the main body of the Karanlıkdere granitoid formed 3-4 Ma later than the small dikes intruded into other units. The AFT ages are directly controlled by altitude and range between 40.38 ± 3.4 Ma and 22.81 ± 0.63 Ma. The oldest AFT age has the highest altitude, whereas the youngest has the lowest height. The age-temperature models show a slow uplift rate between 40 Ma and 22 Ma. The results indicate that the growth of the imbrication zone in front of the Nappes of the SAOB continued in a steady-state mode with a slow uplift rate of 0.02 ± 0.005 mm/a, during middle-late Eocene to early Miocene and increasing uplift rate during early-middle Miocene, which might be explained by continental collision during early-middle Miocene.

Cadomian (ca. 550 Ma) magmatic and thermal imprint on the North Arabian-Nubian Shield (south and central Israel): New age and isotopic constraints

The Arabian-Nubian Shield (ANS) is a province of mostly juvenile Neoproterozoic continental crust in NE Africa and Arabia, forming the northern extension of the East-African orogen. Subsequent to widespread, mostly late- to post-orogenic early-Ediacaran calc-alkaline granitoid emplacement, the latest magmatic phase in the ANS saw the intrusion of alkaline shallow plutons alongside volcanic massifs and dikes of variable compositions. While some of these intrusions were dated to 550–530 Ma by Rb-Sr and Ar-Ar, U-Pb zircon data has mostly limited ANS magmatism to no younger than ca. 580 Ma. Here we report new age and isotopic data from latest Neoproterozoic intrusions along a N-S transect within the northern ANS and its periphery, substantiating the record of a ca. 550 Ma igneous-thermal event in the area. In the northern Negev of Israel, mafic igneous rocks intruded into the subsurface late Neoproterozoic clastic wedge of the Zenifim Formation produced apatite U-Pb isochron ages between 557 and 545 Ma. In the Amram alkaline massif, 150 km to the south, an alkali-granite was dated to 605 ± 2.5 Ma by zircon U-Pb, but apatite U-Pb ages from all rocks of the massif concentrate at ca. 550 Ma indicating thermal resetting. Apatites from the zircon dated 611 ± 5 Ma Roded quartz diorite in the Elat area, south of Amram, produced a 600 ± 4 Ma U-Pb age, demonstrating that southern segments were not thermally reset at ca. 550 Ma. Nd isotopes in apatite and whole rock show the ca. 550 Ma igneous rocks to be variable in their isotopic composition, ranging between εNd(t)=(-4) – (+2), far less juvenile than typical ANS magmas. The ca. 550 Ma intrusions resemble in their age and isotopic properties Cadomian granites and volcanic rocks that are known from southern Turkey, Iran and Europe. We interpret the ca. 550 Ma igneous overprint and thermal resetting documented in the northernmost ANS as related to the superposition of Cadomian orogeny on the ANS periphery. This can be related to the late Ediacaran subduction of proto-Tethys accompanying the accretion of the Cadomian basement of the Tauride block to NE Africa and Arabia, before the area was overstepped by Cambrian platform sedimentation.

The lower crust of the Northern broken edge of Gondwana: Evidence for sediment subduction and syn-Variscan anorogenic imprint from zircon U-Pb-Hf in granulite xenoliths

The continental basement in the Eastern Mediterranean area represents the northern edge of Gondwana, which has been the site of repeated crustal accretion and has subsequently been modified by consecutive rifting events. We investigated the geologic and thermal history of the North Gondwana lower crust by examining the U-Pb-Hf isotope systematics in zircons within 6 mafic granulite xenoliths from Pliocene lava cone in North Israel. The lava cone protrudes through the platform cover that seals the late Neoproterozoic junction between the Arabian-Nubian basement to the South and the Cadomian basement exposed in the Taurides to the North. The mafic granulite xenoliths are composed of plagioclase + orthopyroxene + clinopyroxene ± garnet ± spinel ± secondary amphibole. U-Pb zircon ages from the granulites vary among the different samples with distinct zircon age populations at 400–1200 Ma, 170–350 Ma, and 3.6–4.2 Ma, attesting the lower crust preserves a prolonged thermal and igneous history. While 400–550 Ma U-Pb ages are interpreted to be the result of Pb loss, the wide scatter of zircon grains aged between 550 and 1200 Ma, alongside their diverse εHf(t) values (−25–+10), is an extraordinary evidence for the accretion of Neoproterozoic sediments into the North Gondwana arc root lower crust. The U-Pb-Hf signature of these zircons resembles Cadomian sediments of the Tauride block to the north, indicating southward (present coordinates) subduction under North Gondwana and possible accretion of fore-arc sediments to the lower crust through relamination in the latest Neoproterozoic. One xenolith contained metamorphic-shaped zircons aged 170–350 Ma with positive εHf values and Hf-TDM of 0.85 Ga interpreted to reflect Paleozoic recycling of the Neoproterozoic juvenile Arabian basement, which we consider to form a major component of the lower crust in the region. An overwhelming cluster of Carboniferous zircons concentrating at 305 Ma with exclusively negative εHf values around −6, was retrieved from three xenoliths. Some of these zircons portrayed igneous textures and shape. While Carboniferous igneous activity is the hallmark of Western Europe's Variscan orogeny, the latter did not affect the southern rifted edge of Neo-Tethys where our xenoliths were retrieved. The Paleozoic age-Hf composition in our xenoliths is therefore interpreted to result from syn-Variscan recycling of Neoproterozoic sedimentary remains in the lower crust, and some degree of melting in a non-orogenic environment. Rather than with horizontal plate motions and orogeny, the Carboniferous zircon ages in the xenoliths appear to coalesce with significant vertical movements that created continental scale unconformities and a broad basin and swell architecture known to develop over the entire North Gondwana margin at that time. The Carboniferous aged zircons in northern Israel lower crustal xenoliths are therefore a unique gauge of the thermal perturbation that accompanied the large-scale mantle dynamics below the then passive North African margin of Gondwana, while Variscan orogenic accretion occurred on the Eurasian margin. These lower crustal granulite xenoliths therefore contain important information with respect to the nature of the lower crust under Israel, with implications on the geodynamic setting during the Cadomian and Variscan cycles.

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.

Lithostratigraphy and planktonic foraminifera of the uppermost Cretaceous-Upper Paleocene strata of the Tavas nappe of the Lycian nappes (SW Turkey)

The Lycian nappes lying on top of the para–autochthonous metamorphosed Menderes and unmetamorphosed Bey Daglari successions in SW Anatolia belong to the Tauride segment of the Anatolide–Tauride Block. The Tavas nappe is one of several nappe slices of the Lycian nappe sand forms structurally the lowermost tectono–stratigraphic unit. The upper part of the Tavas nappe succession is represented by planktonic foraminifera–bearing uppermost Cretaceous cherty micritic limestones and calciturbidites of the Babadag Formation and Lower Palaeogene micritic limestones and calciclastic rocks of the Faralya Formation in the study area. Lithostratigraphic characteristics and planktonic foraminiferal assemblages of the two formations in the Bozburun hill locality (S of Koycegiz) are documented for the first time in three stratigraphic sections in this study. The uppermost part of the Babadag Formation mainly comprises of alternating calciclastic and micritic limestones, which include diverse planktonic foraminiferal assemblages of mainly keeled morphotypes. The presence of Racemiguembelina fructicosa and Abathomphalus mayaroensis within the assemblages indicates a late Maastrichtian age for the uppermost part of the succession. Two sections of the overlying Faralya Formation comprise mainly planktonic foraminifera–bearing laminated micritic limestones, brecciated limestones and mudstones. Planktonic foraminiferal assemblages of the laminated micritic limestones are dominated by keeled Late Palaeocene morphotypes. The occurrence of Morozovella acuta and Globanomalina planoconica at the base of two sections suggests a Thanetian age for the deposits. The boundary between the Babadag and Faralya formations is characterized by a stratigraphic gap ranging from the latest Maastrichtian to the earliest Selandian. The gap was linked with the first of the three main events, when ophiolite obduction and incorporation of the Koycegiz Thrust Sheet into the Lycian allochthon occured. Cretaceous limestone clasts and foraminifers within the Thanetian calciclastic rocks of the Faralya Formation could be clues to that exposure anderosion.

Origin of the Eastern Mediterranean: Neotethys rifting along a cryptic Cadomian suture with Afro-Arabia

The Eastern Mediterranean is a land-locked basin, a remnant of the Neotethys Ocean. It was formed in the Permian−Triassic as a result of the drift of the Tauride block from the Afro-Arabian margin of Gondwana. Herein, we show that rather than being a genuine Afro-Arabia crustal fragment, the Tauride block is underlain by late Neoproterozoic Cadomian basement, which differs significantly from the Neoproterozoic “Pan-African” basement of NE Africa from which it was detached. Resembling other Cadomian terranes of western Europe, the Tauride basement is chiefly a graywacke succession deposited in a mid- to late Ediacaran back-arc basin formed on the periphery of Afro-Arabia, above the southward-subducting proto-Tethys Ocean. The back-arc region was deformed and metamorphosed to various degrees and intruded by latest Ediacaran−Cambrian granites and volcanics during the Cadomian orogeny. Unlike the protracted (∼300 m.y.) Neoproterozoic crustal evolution recorded in Afro-Arabia, the Cadomian basement of the Taurides evolved briefly, over ∼50 m.y. We show that the entire cycle of sedimentation, metamorphism, and magmatism in the Tauride basement took place in the late Ediacaran−Cambrian and lagged after Neoproterozoic Pan-African orogeny and igneous activity in Afro-Arabia. The Cadomian orogeny accreted the Taurides, and adjoining peri-Gondwana Cadomian terranes, with an already-consolidated Afro-Arabian continent. Permian−Triassic rifting of the Eastern Mediterranean occurred close to the transition between these two domains. Rifting was thus inherited from, and superimposed on, late Ediacaran structures formed in front of the current Afro-Arabia margin of Gondwana during Cadomian orogeny. The boundary between the Cadomian edifice and the Pan-African crust of Afro-Arabia appears to lie presently on the southern margin of the Mediterranean, extending from Morocco in the west to Arabia in the east. Hence, the continental margin of the Eastern Mediterranean, including in the Levant Basin, is probably underlain by a thinned Cadomian crust.

Cadomian basement and Paleozoic to Triassic siliciclastics of the Taurides (Karacahisar dome, south-central Turkey): Paleogeographic constraints from U–Pb–Hf in zircons

The Tauride block in Turkey is a peri-Gondwana, Cadomian-type terrane that rifted from the Afro-Arabian margin of Gondwana in the Permo-Triassic and re-accreted to Arabia in the Neogene. In the Karacahisar dome in the southern-central Taurides, Neoproterozoic basement metasediments and intrusive rocks are overlain by Cambro-Ordovician, Carboniferous and Triassic sediments. We studied U–Pb–Hf in zircons from major rock units exposed in Karacahisar in order to constrain the Cadomian crustal evolution of the Taurides, to evaluate the provenance of the Neoproterozoic and overlying sediments, to constrain the paleogeography of the Taurides, and to assess their linkage to Gondwana.The Neoproterozoic metasediments are low-grade metamorphic wacke-type turbidites that evolved in a broad back-arc basin peripheral to Afro-Arabia. Their detrital zircon U–Pb signal comprises a preponderance (40–68%) of Neoproterozoic-aged zircons (peak ages defined at 635 and 830Ma), indicating that the sedimentary pile was built mainly from the erosion of Pan-African terranes from Afro-Arabia. The εHf values of the younger population (635Ma) are mostly positive, indicating derivation from a juvenile arc, whereas Cryogenian–Tonian detrital zircons spread vertically (−25<εHf<15), indicating a different provenance where mixing of juvenile magmas with Paleoproterozoic to Neoarchean crust was widespread.An unusually high proportion of pre-Neoproterozoic zircons is found in all Cadomian metasediments, including up to 31% Grenvillian-aged (ca. 1.0Ga) and up to 35% of ca. 2.5Ga zircons; about a third of the latter possess positive εHf values. Because only minor exposures of 1.0 and 2.5Ga crustal vestiges are currently known in North Africa and Arabia, we infer that pre-Neoproterozoic terranes were dispersed within the Cadomian realm itself.The youngest detrital zircons in all Cadomian metasediments concentrate at 0.58Ga, indicating that the proto-Cadomian back-arc basin was formed towards the Late Ediacaran. The termination of Neoproterozoic sedimentation is marked by the intrusion of dyke swarms yielding a U–Pb zircon age of 544±4Ma, coeval with magmatism in other Cadomian basement units in the Taurides (e.g., Sandıklı and Menderes massif). Shortly afterwards the Tauride basement was overstepped by the Cambro-Ordovician platform.From the Cambrian to the Triassic, the U–Pb–Hf detrital zircon signal of the cover sediments in the Taurides in Karacahisar portrays remarkable resemblance to that of typical North Gondwana Cambro-Ordovician cover sediments, and shows that the Taurides accreted to Afro-Arabia by the onset of the Cambrian. The short time interval between Cadomian basin fill and deposition of the Cambrian platform implies that the Taurides evolved within a short distance from their present position relative to the Afro-Arabian margin of Gondwana. The Gondwana provenance of the Tauride sedimentary cover is maintained through the Upper Triassic, indicating that Neo-Tethys rifting was incipient at that time, allowing Afro-Arabian detritals to reach the Taurides.

Late Neoproterozoic gabbro emplacement followed by early Cambrian eclogite-facies metamorphism in the Menderes Massif (W. Turkey): Implications on the final assembly of Gondwana

Numerous (meta-)gabbroic dikes or stocks occur within the latest Neoproterozoic–early Cambrian series of the Menderes Massif (Anatolide–Tauride Block, western Turkey). These well-preserved rocks were locally converted into eclogitic metagabbros and garnet amphibolites along the contacts or shear zones. Both bulk-rock composition and compositions of igneous clinopyroxenes suggest continental tholeiitic affinity. U–Pb dating of igneous zircons from gabbroic rocks yielded a mean age of 563±1Ma (2σ), indicating emplacement during the latest Neoproterozoic (Ediacaran). On the other hand, rims of zircons from eclogitic metagabbro gave 535±3Ma (2σ) (early Cambrian), in addition to 558±3Ma (2σ) obtained from the igneous core of zircons. These ages are interpreted as the time of high-P metamorphism and crystallization age of gabbroic protolith, respectively. Given the estimated paleogeographic position of the Anatolide–Tauride Block during the late Neoproterozoic and early Cambrian, this orogenic event can be spatially and temporally related to the northward continuity of 600–500Ma orogenic event (Malagasy/Kuunga orogeny) extending from western margin of India, Madagascar, via Arabia up to northern margin of Gondwana beneath thick Phanerozoic cover series in Arabian Peninsula. Therefore, the high-P evolution of the basement of the Menderes Massif and associated basic intrusions can be interpreted to mark the latest stages of consumption of the basin/oceanic branches and final amalgamation of the Gondwana during the late Neoproterozoic–early Cambrian around the Arabian region.

P–T–t evolution of eclogite/blueschist facies metamorphism in Alanya Massif: time and space relations with HP event in Bitlis Massif, Turkey

The Alanya Massif, which is located to the south of central Taurides in Turkey, presents a typical nappe pile consisting of thrust sheets with contrasting metamorphic histories. In two thrust sheets, Sugozu and Gundogmus nappes, HP metamorphism under eclogite (550–567 °C/14–18 kbar) and blueschist facies (435–480 °C/11–13 kbar) conditions have been recognized, respectively. Whereas the rest of the Massif underwent MP metamorphism under greenschist to amphibolite facies (525–555 °C/6.5–7.5 kbar) conditions. Eclogite facies metamorphism in Sugozu nappe, which consists of homogeneous garnet–glaucophane–phengite schists with eclogite lenses is dated at 84.8 ± 0.8, 84.7 ± 1.5 and 82 ± 3 Ma (Santonian–Campanian) by 40Ar/39Ar phengite, U/Pb zircon and rutile dating methods, respectively. Similarly, phengites in Gundogmus nappe representing an accretionary complex yield 82–80 Ma (Campanian) ages for blueschist facies metamorphism. During the exhumation, the retrograde overprint of the HP units under greenschist–amphibolite facies conditions and tectonic juxtaposition with the Barrovian units occurred during Campanian (75–78 Ma). Petrological and geochronological data clearly indicate a similar Late Cretaceous tectonometamorphic evolution for both Alanya (84–75 Ma) and Bitlis (84–72 Ma) Massifs. They form part of a single continental sliver (Alanya–Bitlis microcontinent), which was rifted from the southern part of the Anatolide–Tauride platform. The P–T–t coherence between two Massifs suggests that both Massifs have been derived from the closure of the same ocean (Alanya–Bitlis Ocean) located to the south of the Anatolide–Tauride block by a northward subduction. The boundary separating the autochthonous Tauride platform to the north from both the Alanya and Bitlis Massifs to the south represents a suture zone, the Pamphylian–Alanya–Bitlis suture.

Timing Aegean extension: Evidence from in situ U–Pb geochronology and cathodoluminescence imaging of granitoids from NW Turkey

The Biga Peninsula of NW Turkey hosts granitoid plutons that record the timing of extension in the Aegean region. Here we focus on three plutons, the Kozak, Eybek, and Kestanbol and apply new methods to obtain a detailed tectonic history of their generation and exhumation. In situ (in thin section) ion microprobe zircon geochronology and color cathodoluminescence (CL) imaging of zircon grains and whole thin sections show these granites experienced magma mixing, brittle deformation, and significant fluid-rock interactions. Zircon ages range from the Late Eocene to Late Miocene with two ages from a single grain that are Permian. The Late Eocene–Early Oligocene ages record the end stages of subduction during the closure of a branch of the Neo-Tethyan Ocean, whereas Late Oligocene–Late Miocene ages record the plutons' extension and exhumation. We present a model in which Kozak, Eybek, and Kestanbol magmas were initially generated by fluid-flux melting from dehydration of the subducting Anatolide–Tauride block, as evidenced by the Late Eocene to Early Oligocene ages. Late Oligocene ages document the initiation of extension in the Biga Peninsula region and correlate to ages timing exhumation of the Kazdağ Massif. Early Miocene ages indicate continued Aegean extension in the southern Biga Peninsula region at this time.

Geodynamics of the Tavşanlı zone, western Turkey: Insights into subduction/obduction processes

Abstract The tectono-metamorphic evolution of the high-pressure low-temperature (HP–LT) Tavsanli zone (Western Anatolia, Izmir–Ankara suture zone) is herein reappraised to highlight processes occurring along a fossil subduction interface, from initial obduction stages to continental subduction. Structural and petrological data allow in particular to constrain the nature, internal structure and PT conditions of the oceanic accretionary complex sandwiched between the subducted continental margin of the Anatolide–Tauride Block (Orhaneli unit) and the non-metamorphic obducted ophiolite on top. Two distinct oceanic units (termed complexes 1 and 2) are recognised on top of one another, with metamorphic conditions ranging from incipient HP-LT imprint (complex 1) to blueschist facies conditions (complex 2). Based on the first occurrence of Fe–Mg carpholite and on pseudosection calculations, PT estimates of 250–350 °C and 11–13 kbar are inferred for complex 2. The internal structure of the accretionary complex points to the underplating of kilometre-scale units at different depths along the plate interface and to contrasting dynamics with respect to both the underlying continental unit and the ophiolite. Inter-plate mechanical coupling within the Tavsanli zone is compared to the Oman case-study. The variable HP–LT overprint of the metamorphic sole places further constraints on regional scale tectonics, the accretionary dynamics and on the rapid thermal reequilibration of the subduction interface.

An olistostrome–mélange belt formed along a suture: Bornova Flysch zone, western Turkey

The Bornova Flysch Zone (BFZ) in western Turkey is a regional olistostrome–mélange belt located between the İzmir–Ankara Tethyan suture in northwest and the Menderes Massif in the southeast. The BFZ consists mostly of tectonized gravity mass flows. The blocks are Mesozoic limestone and ophiolite, which are enclosed in Cretaceous–Paleocene sheared sandstone and shale. The limestone blocks are of two types. The first type consists of Late Triassic to Cretaceous shallow marine carbonates. The second type has an Upper Triassic shallow marine section overlain by Jurassic to Cretaceous pelagic limestones. A semi-intact part of the platform occurs in the Karaburun peninsula and on the island of Chios. The ophiolitic blocks in the BFZ include ultramafic rock, gabbro, basalt and radiolarian chert of Middle Triassic to Cretaceous in age. The formation of the BFZ overlaps with the Cretaceous subduction and HP/LT metamorphism of the northern passive continental margin of the Anatolide–Tauride Block. This subduction zone was bounded in the west by a strike–slip tear fault. The BFZ formed in a narrow basin between this tear fault and the Tethyan ocean. The mass flows came from the southeast from the overriding ophiolite and accretionary complex, and from the northwest from the uplifted segments of the platform margin. This model provides an explanation as why the BFZ is unmetamorphosed, whereas the equivalent strata in the Menderes Massif were metamorphosed at depths of over 20km. It also explains the prominence of gravity flows and the southward younging in the BFZ, and for the apparently anomalous observation that, although the Tethyan ocean lay to the northwest, the ophiolitic blocks are more common on the southeastern part of the BFZ. Regions away from the tear fault, such as the Karaburun peninsula, were least affected by subsidence and deformation during the Cretaceous and Paleocene.

TWO SPECIES OF PROFUSULINELLA ( P. ALJUTOVICA AND P. OVATA ), EARLY MOSCOVIAN (PENNSYLVANIAN) FUSULINES FROM SOUTHERN TURKEY AND SUBDIVISION OF PRIMITIVE GROUPS OF THE FAMILY FUSULINIDAE

Early Moscovian (Pennsylvanian) fusulines, Profusulinella aljutovica and Profusulinella ovata , from the Hadim area, southern Turkey are described systematically. They are contained in the bedded limestone (algal fusuline grainstone) of the Yaricak Formation of the Aladag Unit in the Tauride Block. Morphologic analysis of these and similar species suggests: (1) Aljutovella should be synonymous with Profusulinella ; (2) Ovatella, Depratina , Staffellaeformes , Aljutovella ( Elongatella ), Tikhonovichiella , Skelnevatella , and Priscoidella proposed in 1980’s and 1990’s are also synonymous with Profusulinella ; and (3) the families Profusulinellidae and Aljutovellidae are not necessary and Profusulinella is included in the subfamily Fusulinellinae placed under the family Fusulinidae.

Post-collisional adakite-like magmatism in the Ağvanis Massif and implications for the evolution of the Eocene magmatism in the Eastern Pontides (NE Turkey)

In the Anatolia, the Caucasus and northwest Iran, the Eocene epoch is characterized by widespread basic to acidic magmatism, whose temporal and spatial evolutions and origin are poorly understood. In this paper, we provide geochronological and geochemical data on a suite of Early Eocene intrusions from northeast Turkey and discuss their origin within a regional tectonic framework. Post to late-collisional, moderate to small bodies of quartz diorite and leucogranodiorite as well as later dacite porphyries intrude Permo-Triassic low-grade metamorphic rocks in the southern part of the Eastern Pontides very close to the Neo-Tethyan İzmir–Ankara–Erzincan suture. In places, the intrusives display well-developed subsolidus foliations, indicating on-going penetrative deformation during and shortly after emplacement. Different emplacement depths were inferred based on the contact metamorphic mineral assemblages, Al-in-hornblende barometry and igneous textures (quartz diorite ~14–16km vs dacitic porphyries ≤7km). Biotite and hornblende Ar–Ar and zircon U–Pb data indicate that the compositionally and texturally different intrusives were emplaced at ~51Ma (Ypresian). Three lines of evidence indicate that the Early Eocene represents a tectonically active time with high exhumation rates (≥0.6cma−1): (i) the quartz diorite and dacitic porphyries were emplaced at different crustal depths, (ii) the emplacement ages of these texturally distinct intrusive rocks are geochronologically undistinguishable, and (iii) intrusive rocks locally show a well-developed foliation. The intrusive rocks display high abundances of Al2O3, Sr, Ba, LREEs and low abundances of Y, Sc and HREEs, and are similar to high-silica adakites from supra-subduction zone settings. The geochemical features imply a residual and/or fractionating assemblage rich in hornblende, garnet, pyroxene, and poor in plagioclase. All rock types display similar Sr–Nd isotopic characteristics with initial εNd and 87Sr/86Sr values ranging from 1.0 to −1.1 and from 0.70421 to 0.70494, respectively. These three coeval rock groups (quartz diorite, leucogranodiorite and dacite porphyries) were generated from a similar source by variable degrees of partial melting and fractionation. These data together with those from the literature clearly reveal that the adakitic signature is common in Paleocene to Early Eocene igneous rocks in northern Turkey on both sides of the İzmir–Ankara–Erzincan suture, but disappears towards the Middle Eocene. Regional geological constraints indicate that the continental collision between the Pontides and the Anatolide–Tauride block occurred in the Paleocene and that the Middle Eocene represents a period of major extension, characterized by a marine transgression. We therefore suggest that the Early Eocene adakitic magmatism in northern Turkey resulted from the presence of a thickened continental crust following the continental collision along the Neo-Tethyan İzmir–Ankara–Erzincan suture whereas the voluminous Middle Eocene magmatism was related to extensional collapse of a thickened orogen.

Reconciling the geological history of western Turkey with plate circuits and mantle tomography

We place the geological history since Cretaceous times in western Turkey in a context of convergence, subduction, collision and slab break-off. To this end, we compare the west Anatolian geological history with amounts of Africa–Europe convergence calculated from the Atlantic plate circuit, and the seismic tomography images of the west Anatolian mantle structure. Western Turkish geology reflects the convergence between the Sakarya continent (here treated as Eurasia) in the north and Africa in the south, with the Anatolide–Tauride Block (ATB) between two strands of the Neotethyan ocean. Convergence between the Sakarya and the ATB started at least ~ 95–90 Myr ago, marked by ages of metamorphic soles of ophiolites that form the highest structural unit below Sakarya. These are underlain by high-pressure, low-temperature metamorphic rocks of the Tavşanlı and Afyon zones, and the Ören Unit, which in turn are underlain by the Menderes Massif derived from the ATB. Underthrusting of the ATB below Sakarya was since ~ 50 Ma, associated with high-temperature metamorphism and widespread granitic magmatism. Thrusting in the Menderes Massif continued until 35 Ma, after which there is no record of accretion in western Turkey. Plate circuits show that since 90 Ma, ~ 1400 km of Africa–Europe convergence occurred, of which ~ 700 km since 50 Ma and ~ 450 km since 35 Ma. Seismic tomography shows that the African slab under western Turkey is decoupled from the African Plate. This detached slab is a single, coherent body, representing the lithosphere consumed since 90 Ma. There was no subduction re-initiation after slab break-off. ATB collision with Europe therefore did not immediately lead to slab break-off but instead to delamination of subducting lithospheric mantle from accreting ATB crust, while staying attached to the African Plate. This led to asthenospheric inflow below the ATB crust, high-temperature metamorphism and felsic magmatism. Slab break-off in western Turkey probably occurred ~ 15 Myr ago, after which overriding plate compression and rotation accommodated ongoing Africa–Europe convergence. Slab break-off was accommodated along a vertical NE trending subduction transform edge propagator (STEP) fault zone, accelerating southwestward slab retreat of the Aegean slab. The SE Aegean slab edge may have existed already since early Miocene times or before, but started to rapidly roll back along the southeastern Aegean STEP in middle Miocene times, penetrating the Aegean region in the Pliocene.

Structure and geochemistry of the adakitic Horoz granitoid, Bolkar Mountains, south-central Turkey, and its tectonomagmatic evolution

High-Al granitic and granodioritic rocks of the 55 Ma Horoz pluton in the Bolkar Mountains of southern Turkey provide important new constraints on the early Cenozoic evolution of the eastern Mediterranean region. The ENE–WSW-trending, sill-like pluton is intrusive into late Palaeozoic–early Mesozoic metamorphic rocks of the Central Tauride block, and is unconformably overlain by Plio-Pleistocene alluvial deposits. The metaluminous to peraluminous granitoids have high-K calc-alkaline to high-K shoshonitic compositions, and show enrichment in large ion lithophile and depletion in high-field strength elements relative to ocean ridge granite. Their high Al2O3 contents (15.9–20.06 wt%) and low SiO2, MgO, and Mg numbers are consistent with adakitic compositions. These geochemical features, coupled with low Sr/Y and La/Yb ratios and trace-element patterns, suggest that the Horoz magmas were produced in part by partial melting of a subduction-metasomatized mantle. The high-Al adakitic and calc-alkaline compositions are consistent with partial melting of a hydrated lithospheric mantle and an amphibolitic–eclogitic mafic lower crust that was triggered by delamination-induced asthenospheric upwelling. We propose that, following Palaeocene continental collision between the Tauride and Central Anatolian Crystalline Complex, the inferred lithospheric delamination was a result of foundering of the overthickened orogenic root. Asthenospheric upwelling beneath the young orogenic belt thermally weakened the crust, and caused uplift and tectonic extension leading to core complex formation (Nigde massif), development of an extensional volcanic province (Cappadocia), and tectonic collapse of the Central Tauride block (Bolkar Mountains). The shallow-level Horoz pluton was unroofed by ∼23 Ma as a combined result of crustal uplift and erosion throughout the Palaeogene.