Kerim Koçak

The petrology of the Ortakoy district and its ophiolite at the western edge of the Middle anatolian Massif, Turkey

Abstract The geological history of a regionally metamorphosed sequence of Silurian on early Devonian sediments, now calcite marbles, quartzites, semipelitic, psammitic and migmatitic gneisses containing K-feldspar, sillimanite, and garnet with later andalusite and cordierite, is outlined with chemical analyses of the rocks and minerals, the latter suggesting peak metamorphic conditions about 600 to 700° C at 4kb. Deposition was in part at an active continental margin and in part probably at a passive margin and was followed by basic intrusions, now amphibolites. Later gabbroic rocks are shown for the first time by their geochemistry, especially REE, to be probably part of a major ophiolite sheet, tectonically emplaced and containing late magmatic or metamorphic hornblende. Later intrusive hornblende diorite, with appinitic (diorite dykes with voluminous euhedral hornblende) and calc-alkaline lamprophyric affinites, immediately preceded the intrusion of voluminous granitoids (granite, tonalite, quartz monzonite) of probably late Cretaceous to Palaeocene age, whose geochemistry indicates a continental volcanic arc setting. Neogene formations completed the rock sequence.

Geochemical characteristics of the lava domes in Yatagan village and Sağlik town, from Erenlerdagi (Konya, Central Turkey) volcanites

Extensive Late Miocene to Pliocene Erenlerdagi volcanism produced lava domes, nuee ardentes and ignimbrite deposits in west and southwest of the Konya. The domes may contain various enclaves, which range in size from a few cm to a few meters, and in shape cornered to spherical. The volcanic rocks are made up of plagioclase (15-45%), brown amphibole (3-15%), brown biotite (5-10 %), quartz (0-5%), sanidine (0-5%), clinopyroxene (0-5 %), epidote (0-8%), opaque iron ore (3-20%), and accessory acicular apatite and zircon in a holocrystalline porphyric texture. Geochemical data shows that all samples are high-K calc-alkaline, mostly metaluminous, and rhyodacite to andesite in composition. They are characterized by an enrichment in Large Ion lithophile Elements (e.g. Cs, K), and a depletion in High Field Strength Elements (e.g. Ti, Y). In Harker variation diagrams, SiO2 increases with increasing K2O, Na2O, Rb, Th, U, Nb, Zr contents; and decreasing TiO2, FeOt, MgO, CaO contents, suggesting fractional crystallisation of hornblende (± pyroxene, olivine) and titanite. The REE pattern of the samples shows an enrichment in Light Rare Earth Elements, and a depletion in Heavy Rare Earth Elements, resultant with high ((La/Lu)N= 8.2-18.0) ratios. Existence of slight Eu anomaly (Eu/Eu*: 0.66-0.80 ) may suggest plagioclase fractionation in the samples. Based on field, mineralogical and geochemical data, it has been suggested that the Erenlerdagi volcanics could have formed by chemical mixing of felsic and mafic magmas possibly coupled with fractional crystallisation of hornblende (± pyroxene, olivine), plagioclase and titanite, in relation with the subduction of the African plate underneath the Anatolian plate during Miocene.

Petrogenesis of the Üçkapılı Granitoid and its Mafic Enclaves in Elmalı Area (Niğde, Central Anatolia, Turkey)

The Late Cretaceous Uckapili Granitoid including mafic microgranular enclaves intruded into metapelitic and metabasic rocks, and overlain unconformably by Neogene ignimbrites in the Nigde area of Turkey. It is mostly granite and minor granodiorite in composition, whereas its enclaves are dominantly gabbro with a few diorites in composition. The Uckapili Granitoid is composed mainly of quartz, K-feldspar, plagioclase, biotite, muscovite and minor amphibole while its enclaves contain mostly plagioclase, amphibole, minor pyroxene and biotite. The Uckapili Granitoid has calcalkaline and peraluminous (A/CNK= 1.0-1.3) geochemical characteristics. It is characterized by high LILE/HFSE and LREE/HREE ratios ((La/Lu)N= 3-33), and has negative Ba, Ta, Nb and Eu anomalies, resembling those of collision granitoids. The Uckapili Granitoid has relatively high 87 Sr/ 86 Sr(i) ratios (0.711189-0.716061) and low eNd(t) values (-5.13 to -7.13), confirming crustal melting. In contrast, the enclaves are tholeiitic and metaluminous, and slightly enriched in LILEs (K, Rb) and Th, and have negative Ta, Nb and Ti anomalies; propose that they were derived from a subduction-modified mantle source. Based on mineral and whole rock chemistry data, the Uckapili granitoid is H-(hybrid) type, post-collision granitoid developed by mixing/mingling processes between crustal melts and mantle-derived mafic magmas.

Some Geological Features of Limestone Aggregates Produced From Central Anatolian Carbonate Formations

For the last fifteen years, there has been extensive motorway and railway constructions in Turkey. This requires enormous amount of road-fillers and aggregates, and the construction companies open many open-pit limestone quarries to fulfill their aggregate needs. The partly double (four lines), partly one-way (double line) motorway of KonyaHüyük have recently been enlarged and partly re-constructed. During this construction, a total of five limestone quarry were opened to produce limestone aggregate. The Bozlutepe Limestone member of Asmalıtepe Formation near the town of Selki (HüyükKonya, central Anatolia) were used for this demand, and it has been operated for the last 6 years. The limestone member is approximately 200 m thick at most and mostly made of three type of minerals and these are dolomitic limestone, crystalline limestone and quartz-bearing crystallized limestones. All the minerals are crystallized and the minerals locally dominate at the quarry. The produced aggregates have relatively f lat granulometry curve indicating most of the grains are of thin and have clay-silt sized particles. Our studies revealed that Bozlutepe Limestones are formed in carbonate facies in shallow marine environments during Permian-Carboniferous times. The member most likely have low-grade metamorphism during Paleozoic and Mesozoic eras.

The Bauxite deposits of Seydişehir region (Mortaş and Doğankuzu deposits); Their geological, mineralogical and geochemical characteristics

Turkey hosts essential bauxite deposits, typically of the karstic-type. The most economically important bauxite deposits of Turkey form in the Seydisehir-Akseki region of the central Taurides Mountains. The Mortas and Dogankuzu deposits are the most important deposits in that region. The bauxite beds contain boehmite, hematite, rutile, smectite, quartz, diaspore, calcite, pyrite, marcasite and goethite. Brown to red-colored bauxite minerals are massive, oolitic – pisolitic textured. The Seydisehir schists could be possible parent rocks of bauxites, and have unearthed acidic source (mostly granite) with hornblende and plagioclase minerals. The schists were compositionally mature with minimal alkali feldspar sediments. The Mortas deposit is 400 m long and up to 40 m thick; it averages 10 m thick. It has about 5 million tons of ore reserves, with ~50 percent Al2O3. The Dogankuzu bauxite deposit is situated 2 km southwest of the Mortas deposit, with 14.9 million metric tons of ore at 61 percent Al2O3. The Dogankuzu ore was deposited on a fault-controlled karst surface of Cenomanian limestone succession, which was overlain by 5- to 10-cm-thick Santonian limestones. The bauxite has been mined by the Seydisehir aluminum factory, which was founded in 1973, and privatized in 2005. The plant is capable to produce 65.000 ton liquid aluminum per year, around 15% of Turkey’s Aluminum demand.

Stratigraphic Characteristics of the Derinkuyu Area, Nevsehir, Turkey

The study area is located in the Derinkuyu area, central Anatolia. The oldest formation in the area is Cretaceous Karatepe hornblende gabbro, which is overlain by upper Miocene Melendizdagi tuffs, Melendizdagi andesites, Gostuk tuff and ignimbrite, and the Karakaya Formation. These units are followed by lower Pliocene Selime tuff, Kizilkaya ignimbrite, and the Agilli Formation, above which lie various Pleistocene ashes, namely, the Hasandagi ash, the Kumtepe ash, and the Golludag ash flow tuffs. Above these are the Pleistocene Kizildag basalts and Holocene basaltic cinder cones. Talus is the youngest unit in the area. The young volcanics and volcaniclastics in the area may have originated from the volcanism of Mts Erciyes, Melendiz, and Hasan.

Stratigraphic Features of the Yesilova Ophiolite, Burdur, South-Western Turkey

The Yesilova ophiolite is located in the Alpine zone as a major part of the Lycian nappes of western Taurus. It was formed at the southern branch of Neo-Tethys, and was abducted over the southern edge of the Menderes Massif during the Cenonian during Laramian orogenesis. The ophiolite in the study area starts with tectonite, consisting mainly of harzburgites (37.02 % MgO, 38.77 % SiO2, and 0.42 % Cr2O3) and smaller amounts of dunite and chromite pods. The sequence continues with cumulates, including (from bottom to top) dunite, wehrlite, clinopyroxenite, layered and nonlayered gabbro (45.53 % SiO2, 11.92 % Al2O3, and 13.11 % MgO), and plagiogranite (77.41 % SiO2, 0.25 % K2O). The tectonite and cumulates have been cut by isolated gabbro and diabase dikes. The altered volcanites are found at the top of ophiolitic sequence, and were abducted by the Upper Cretaceous Kizilcadag Melange, with limestone, chert–radiolarite blocks, and ophiolitic rock fragments. The upper Eocene Varsakyayla Formation rests over the melange; it contains abundant nummulites and is composed of conglomerate sandstone, limestone, and conglomerate towards the top. The stratigraphic sequence continues with the Pliocene–Quaternary Niyazlar Formation, consisting of terrigenous conglomerate intercalated with sandstone, and ends with rock talus and alluvium.

Constraints on the Age of Metasediments from the Western Part (Ortaköy, Aksaray) of the Central Anatolian Crystalline Complex, Turkey

The Central Anatolian Crystalline Complex (CACC) is the largest metamorphic domain, a ~300 × 200 km triangular region, exposed in Turkey. The basement is composed mainly of migmatites, paragneisses, alternations of marble and paragneiss, and a thick metacarbonate sequence. The sequence in the area starts with graphite-bearing paragneiss with interlayers of marble, and metabasics (Tamadag Formation), and continues with marble containing paragneiss, and rare metabasics (Bozcaldag Formation). The basement is overlain by Cretaceous ophiolites, which are cut by voluminous Late Cretaceous–Palaeocene granitoids. Neogene formations complete the rock sequence in the area. The first certain macrofossil, Heliolitinae (Heliolitidae fam.) Paeckelmannophora sp., has been discovered in the marble of the Tamadag Formation. Also found are Acritarchs Leiosphaeridia sp. and Lophosphaeriduim sp. together with possible graptolite fragments (questionably of Retiolites sp.) in the marble residue obtained by treatment with acetic acid. Paeckelmannophora sp. and fragments of Retiolites sp. have been found, pointing to a Silurian–Devonian age. The Bozdag Formation, overlying conformably the Tamadag Formation, could hence be late Palaeozoic in age. Based on the age of the metasediments and the geochemistry of the amphibolites in the Nigde Massif, it has been suggested that the CACC could have undergone Hercynian metamorphism, whose effects may have been destroyed by intensive polyphase Alpine metamorphism. The Tamadag Formation may be correlated with the Silurian–lower Carboniferous Bozdag Formation of the Konya Complex (Afyon–Bolkardag Zone), 200 km WSW of the study area.