Relative contributions of crust and mantle to generation of Campanian high-K calc-alkaline I-type granitoids in a subduction setting, with special reference to the Harsit Pluton, Eastern Turkey

We present elemental and Sr-Nd-Pb isotopic data for the magmatic suite (similar to 79 Ma) of the Harsit pluton, from the Eastern Pontides (NE Turkey), with the aim of determining its magma source and geodynamic evolution. The pluton comprises granite, granodiorite, tonalite and minor diorite (SiO(2) = 59.43-76.95 wt%), with only minor gabbroic diorite mafic microgranular enclaves in composition (SiO(2) = 54.95-56.32 wt%), and exhibits low Mg# (<46). All samples show a high-K calc-alkaline differentiation trend and I-type features. The chondrite-normalized REE patterns are fractionated [(La/Yb)(n) = 2.40-12.44] and display weak Eu anomalies (Eu/Eu* = 0.30-0.76). The rocks are characterized by enrichment of LILE and depletion of HFSE. The Harsit host rocks have weak concave-upward REE patterns, suggesting that amphibole and garnet played a significant role in their generation during magma segregation. The host rocks and their enclaves are isotopically indistinguishable. Sr-Nd isotopic data for all of the samples display I(Sr) = 0.70676-0.70708, epsilon(Nd)(79 Ma) = -4.4 to -3.3, with T(DM) = 1.09-1.36 Ga. The lead isotopic ratios are ((206)Pb/(204)pb) = 18.79-18.87, ((207)Pb/(204)Pb) = 15.59-15.61 and ((208)Pb/(204)Pb) = 38.71-38.83. These geochemical data rule out pure crustal-derived magma genesis in a post-collision extensional stage and suggest mixed-origin magma generation in a subduction setting. The melting that generated these high-K granitoidic rocks may have resulted from the upper Cretaceous subduction of the Izmir-Ankara-Erzincan oceanic slab beneath the Eurasian block in the region. The back-arc extensional events would have caused melting of the enriched subcontinental lithospheric mantle and formed mafic magma. The underplating of the lower crust by mafic magmas would have played a significant role in the generation of high-K magma. Thus, a thermal anomaly induced by underplated basic magma into a hot crust would have caused partial melting in the lower part of the crust. In this scenario, the lithospheric mantle-derived basaltic melt first mixed with granitic magma of crustal origin at depth. Then, the melts, which subsequently underwent a fractional crystallization and crustal assimilation processes, could ascend to shallower crustal levels to generate a variety of rock types ranging from diorite to granite. Sr-Nd isotope modeling shows that the generation of these magmas involved similar to 65-75% of the lower crustal-derived melt and similar to 25-35% of subcontinental lithospheric mantle. Further, geochemical data and the Ar-Ar plateau age on hornblende, combined with regional studies, imply that the Harsit pluton formed in a subduction setting and that the back-arc extensional period started by least similar to 79 Ma in the Eastern Pontides.Geochemistry & GeophysicsMineralogySCI(E)33ARTICLE4467-48716

Northern Dobrogea and the Crimean Mountains: The Key Areas in the Tectonic Evolution of the Black Sea Basin

International audienceThe work poses the question about the impact of inherited structures in the Black Sea back-arc basin (BAB) tectonic evolution. The new structural analysis of the Northern Dobrogea (ND) and the Crimean Mountains (CM) shows that the origins of structural patterns of both regions are in close relationship with deep faults/or fault zones. The comparative analyses of structures, of tectonic stages and their duration allow us to better understand the connections in time and space between the ND and the CM, against the back-ground of the long-living subduction. In particular during: (1) the Cimmerian orogeny; (2) the opening of the BS and (3) the inversion of the BS during the Cenozoic shortening

Uppermost Triassic limestone in the Karakaya Complex - Stratigraphic and tectonic significance

Two important tectonostratigraphic units of the Karakaya Complex in northwest Turkey are: a lower metamorphic sequence of metabasite, phyllite and marble, called the Nilufer Unit; and an upper clastic sequence with Permian and Carboniferous limestone olistoliths called the Hodul Unit. In northwestern Turkey, the Hodul Unit consists of arkosic sandstones, which pass upward into greywacke and siltstone with Permian and Carboniferous limestone blocks. A scarce macrofauna in the sandstones indicates a Norian age for the Hodul Unit. We report for the first time Norian-Rhaetian limestones, here named the Kasal Limestone Member, from the Hodul Unit to the southwest of Balikesir. The Kasal Limestone Member forms similar to80-m-thick, several-hundred-metres large blocks in a sheared siltstone, sandstone, and shale matrix of Norian age. The clastic matrix also includes neritic Permian limestone blocks. The Kasal Limestone Member is a variegated, medium-bedded, nodular limestone with abundant coral, brachiopod, lamellibranch, crinoid, gastropod, algae, bryzoa, sponge spicules and foraminifera. A varied microfauna in the limestone indicates a Norian-Rhaetian age. The age similarity between the matrix and the Kasal Limestone, and transition to a muddy facies observed in one of the blocks indicate that, unlike the exotic Permian limestones, the Kasal Limestone Member represents in situ carbonate deposition in the Hodul basin. The subsequent shearing of the limestone contacts occurred during the deformation associated with the arrival of the olistostromes. The deformation leading to the closure of the Hodul basin is constrained to Rhaetian-Hettangian; that is, between 210 to 202 Ma, from the age of the Hodul Unit and that of the overlying Bayirkoy Formation. This age is similar to the isotopic age of regional metamorphism in the Nilufer Unit (215 to 205 Ma), and suggests that Cimmeride deformation in northwestern Turkey occurred over a short interval in the latest Triassic-earliest Jurassic

The Karakaya Complex: A review of data and concepts

The Karakaya Complex in the Pontides consists of highly deformed and partly metamorphosed clastic and volcanic series of Permian and Triassic age. It is generally subdivided into two parts: The structurally lower part, called the Lower Karakaya Complex, consists of a mafic lava-mafic pyroclastite-shale-limestone succession metamorphosed in the greenschist and blueschist facies during the Late Palaeozoic or Triassic. The structurally upper part is made up of highly deformed Permian and Triassic clastic, volcaniclastic and volcanic rocks with exotic limestone blocks. There are currently two different models for the depositional setting and tectonic evolution of the Karakaya Complex. The rift model assumes that the Karakaya Complex was formed in a Late Permian rift, which developed into a marginal oceanic basin and closed by the latest Triassic. The subduction-accretion model regards the Karakaya Complex as subduction-accretion units of the Palaeo-Tethys

Apatite fission-track data for the Miocene Arabia-Eurasia collision

The collision between the Eurasian and Arabian plates along the 2400-km-long Bitlis-Zagros thrust zone isolated the Mediterranean from the Indian Ocean and has been linked to extension of the Aegean, rifting of the Red Sea, and the formation of the North and East Anatolian fault systems. However, the timing of the collision is poorly constrained, and estimates range from Late Cretaceous to late Miocene. Here, we report the fi rst apatite fissiontrack (AFT) ages from the Bitlis-Zagros thrust zone. The AFT samples are distributed over the 450 km length of the Bitlis thrust zone in southeast Turkey and include metamorphic rocks and Eocene sandstones. Despite the disparate lithology and large distance, the AFT ages point consistently to exhumation between 18 and 13 Ma. The AFT ages, along with a critical appraisal of regional stratigraphy, indicate that the last oceanic lithosphere between the Arabian and Eurasian plates was consumed by the early Miocene (ca. 20 Ma). The results imply that Aegean extension predated the Arabia-Eurasia collision

Obduction, subduction and collision as reflected in the Upper Cretaceous-Lower Eocene sedimentary record of western Turkey

Late Cretaceous-Early Eocene Tethyan evolution of western Turkey is characterized by ophiolite obduction, high-pressure/low-temperature metamorphism, subduction, are magmatism and continent-continent collision. The imprints of these events in the Upper Cretaceous-Lower Eocene sedimentary record of western Anatolia are studied in thirty-eight well-described stratigraphic sections. During the Late Cretaceous period, western Turkey consisted of two continents, the Pontides in the north and the Anatolide-Taurides in the south. These continental masses were separated by the Imir-Ankara Neo-Tethyan ocean. During the convergence the Pontides formed the upper plate, the Anatolide-Taurides the lower plate. The are magmatism in the Pontides along the Black Sea coast is biostratigraphically tightly constrained in time between the late Turonian and latest Campanian. Ophiolite obduction over the passive margin of the Anatolide-Tauride Block started in the Santonian soon after the inception of subduction in the Turonian. As a result, large areas of the Anatolide-Tauride Block subsided and became a region of pelagic carbonate sedimentation during the Campanian. The leading margin of the Anatolide-Tauride Block was buried deeply and was deformed and metamorphosed to blueschist facies during Campanian times. The Campanian are volcanic rocks in the Pontides are conformably overlain by shaley limestone of Maastrichtian-Palaeocene age. However, Maastrichtian sedimentary sequences north of the Tethyan suture an of fore-are type suggesting that although are magmatism ceased by the end of the Campanian age, continent-continent collision was delayed until Palaeocene time, when there was a change from marine to continental sedimentation in the fore-are basins. The interval between the end of the are magmatism and continent-continent collision may have been related to a northward jump of the subduction zone at the end of Campanian time, or to continued obduction during the Maastrichtian

Lutetian arc-type magmatism along the southern Eurasian margin: New U-Pb LA-ICPMS and whole-rock geochemical data from Marmara Island, NW Turkey

The rocks of Turkey, Greece and Syria preserve evidence for the destruction of Tethys, the construction of much of the continental crust of the region and the formation of the Tauride orogenic belt. These events occurred between the Late Cretaceous and Miocene, but the detailed evolution of the southern Eurasian margin during this period of progressive continental accretion is largely unknown. Marmara Island is a basement high lying at a key location in the Cenozoic Turkish tectonic collage, with a Palaeogene suture zone to the south and a deep Eocene sedimentary basin to the north. North-dipping metamorphic thrust sheets make up the island and are interlayered with a major metagranitoid intrusion. We have dated the intrusion by Laser Ablation ICP-MS analysis of U and Pb isotopes on zircon separates to 47.6 ± 2 Ma. We also performed major- and trace-elemental geochemical analysis of 16 samples of the intrusion that revealed that the intrusion is a calc-alkaline, metaluminous granitoid, marked by Nb depletion relative to LREE and LIL-element enrichment when compared to ocean ridge granite (ORG). We interpret the metagranitoid sill as a member of a mid-Eocene magmatic arc, forming a 30 km wide and more than 200 km long arcuate belt in NW Turkey that post-dates suturing along the İzmir-Ankara-Erzincan Suture zone. The arc magmatism was emplaced at the early stages of mountain building, related to collision of Eurasia with the Menderes-Taurus Platform in early Eocene times. Orogenesis and magmatism loaded the crust to the north creating coeval upward-deepening marine basins partially filled by volcanoclastic sediments.P. Ayda Ustaömer, Timur Ustaömer, Alan S. Collins and Jörg Reischpeitsc