1,721,005 research outputs found
Petrography, Geochemistry, Geochronology and Petrogenesis of the Campanian Volcanic Rocks in the South of Akçaabat (Trabzon) and Surrounding Area
No full textDoğu Pontid Orojenik Kuşağında Akçaabat (Trabzon) güneyi ve çevresinde yüzeyleme veren Kampaniyen yaşlı volkanik kayaçlar; bazalt, bazaltik andezit ve andezit bileşiminde olup, petrografik olarak klinopiroksen , plajiyoklas (An80-84), olivin ve opak minerallerden oluşurlar. Tüm kayaç hamurunda uygulanan 40Ar-39Ar yaşlandırma metoduyla volkanitlerin yaşları 82.61±0.34 My (Üst Kretase, Kampaniyen) olarak belirlenmiştir. Volkanitler kalk-alkalen karaktere sahiptirler. İlksel manto (İM)'ya normalize edilmiş iz element değişim diyagramlarında büyük iyon yarıçaplı litofil element (BİLE; Sr, K2O, Rb, Ba), Th ve Ce bakımından zenginleşme, Zr, Y, Nb, Ta ve TiO bakımından fakirleşme ile karakterize edilen yitim imzasına sahiptirler. Ayrıca, kondrite normalize edilmiş nadir toprak element (NTE) dağılımları, kayaçların düşük-orta derecede zenginleştirklerini göstermiştir (LaN/LuN=2-3.4). Volkanitlerin ana magmasının gelişiminde fraksiyonel kristallenmenin rolü magma karışımı ve asimilasyonfraksiyonel kristalleşmeye (AFC) göre daha etkindir. Tüm bu veriler ışığında Kampaniyen yaşlı volkanitlerin ana magmasının yitim etkisiyle, daha çok akışkanlar tarafından metazomatizmaya uğratılmış spinel lerzolitik bileşimdeki zenginleşmiş bir kaynaktan türediği ve daha sonra kabuk içerisinde özellikle fraksiyonel kristallenme ve daha az oranda da magma karışımı gibi magmatik olayların etkisiyle geliştiği düşünülmektedirThe Campanian volcanic rocks cropped out in the south of Akçaabat (Trabzon) region and surrounding area in the Eastern Pontides Orogenic Belt are basalt, basaltic andesite and andesite in composition and petrographycally consist of clinopyroxene , plagioclase (An80–84), olivine and opaque minerals. 40Ar-39Ar step-heating dating method carried out on groundmass of volcanic rocks yielded 82.61±0.34 Ma (Upper Cretaceous, Campanian). The volcanic rocks have calc-alkaline affinity and primitive mantle (PM) normalized trace element patterns imply subduction fingerprints with enrichment in large ion lithophile elements (LILEs; Sr, K2O, Rb, Ba), Th and Ce, and depletion in Zr, Y, Nb, Ta and TiO2. Additionally, the chondritenormalized rare earth element (REE) patterns show low to medium degree of enrichment (LaN/LuN=2-3.4). The role of fractional crystallization involved in parental magma generation of the volcanics is more effective than magma mixing and assimilation-fractional crystallization (AFC) processes. In the light of all data, the parental magma(s) of the Campanian volcanics were derived from a enriched lithospheric mantle source in spinel lerzolitic composition, previously enriched by subduction related fluids and it reached the final composition with the effect of fractional crystallization and minor amount of magma mixin
40Ar-(39) Ar dating, whole-rock and Sr-Nd isotope geochemistry of the Middle Eocene calc-alkaline volcanic rocks in the Bayburt area, Eastern Pontides (NE Turkey): Implications for magma evolution in an extension-related setting
No full textDiscussions continue about whether Middle Eocene magmatism in the Eastern Pontides is associated with collision or subduction. This paper presents new whole-rock geochemistry, Sr-Nd isotopic and Ar-40-Ar-39 age data for Middle Eocene volcanic rocks from the Bayburt area of the Eastern Pontides (NE Turkey) to investigate their sources and evolutionary history. The new Ar-40-Ar-39 ages reveal that these volcanic rocks erupted between 44.6 +/- 0.1 Ma and 43.5 +/- 0.1 Ma, within the Lutetian (Middle Eocene). The studied volcanic rocks are composed of basalt, andesite, basaltic andesite and minor dacite lava and pyroclastic rocks. These rocks consist of plagioclase, amphibole, pyroxene, olivine, biotite, sanidine and minor quartz phenocrysts with Fe-Ti oxides. They have microlithic, hyalo-microlithic, porphyritic and rarely glomeroporphyritic textures. The volcanic rocks have low to high-K calc-alkaline affinities. They display enrichment in large-ion lithophile elements and depletion in high-field strength elements with high Th/Yb ratios, which indicate that the magmas forming the volcanic rocks were derived from lithospheric mantle sources enriched by mostly slab-derived fluids in the spinel stability field. Sr-87/Sr-86((i)) values vary between 0.70485 and 0.70551 and Nd-143/Nd-144((i)) values vary between 0.51255 and 0.51267. These data correspond to the mantle array on the isotope ratio diagram. The main solidification processes consist of fractional crystallization with minor assimilation. In light of the data obtained in this study together with data from previous studies, petrogenetic character of the Middle Eocene magmas from the southern parts of the Eastern Pontides may be explained by melting of an enriched lithospheric mantle source initially metasomatized by subduction fluids in a post-collisional extensional-related tectonic setting.Gumushane University Grant number 17 Gümüşhane Üniversitesi Araştırma Fonu F5114.01.03WOS:00082894700000
Mineral chemistry, crystallization conditions and petrography of Cenozoic volcanic rocks in the Bahçecik (Torul/Gümüşhane) area, Eastern Pontides (NE Turkey).
No full textMineralogical, petrographical and mineral chemistry properties are presented for the Cenozoic aged Bahcecik volcanics in the Eastern Pontides (NE Turkey). The studied volcanic rocks are composed of basaltic andesitic, andesitic, dacitic and trachydacitic lavas and pyroclastics. Petrographic and mineral chemistry studies reveal some disequilibrium textures reflecting magma mixing process. These rocks contain labradorite (An67-50), andesine (An46-34), oligoclase (An29-15), and albite (An1-01), magnesio-hastingsite (Mg# = 0.73-0.9), pargasite (Mg# = 0.76-0.78) and edenite (Mg# = 0.76-0.85), augite (Wo43-45), diopside (Wo46) and clinoenstatite (En68-69), K-feldispar, biotite, quartz and Fe-Ti oxide minerals. Crystallization temperatures calculated from amphibole and clinopyroxene minerals are 834 °C to 1149 °C, pressure values are 1.4 to 6.5 kbar, oxygen fugacity (log10 ƒO2) are -11 to -9.6. Estimation of water content calculated by using amphiboles is between 6.6 and 8.5%. Based on the obtained data, it is suggested that the magmas had undergone hydrous and anhydrous crystallizations in the shallow to mid-crustal magma chambers
Highly siderophile element and Os isotope systematics of the Cenozoic volcanic rocks from the Eastern Pontides, NE Turkey: Constraints on the origin and evolution of subcontinental mantle-derived magmas
No full textThe Cenozoic subalkaline to alkaline volcanic rocks from the Eastern Pontides Orogenic Belt (EPOB) in NE Turkey exhibit wide range of highly siderophile element (HSE) contents and Os isotope compositions that can be related to their mantle sources and parental melt evolution. Although some Eocene rocks show signs of late-stage modification, most of the studied volcanic rocks possess primary HSE and Os systematics. The Eocene volcanic rocks have largely variable PdN/IrN (~0.25–751), PdN/PtN (~0.25–87) and (187Os/188Os)i ratios (~0.113 to 0.51). The Miocene volcanic rocks have high PdN/IrN (~2.6–441), low PdN/PtN (~0.11–1.7) and radiogenic (187Os/188Os)i ratios ranging from ~0.166 to 0.52 while the Mio-Pliocene volcanic rocks show high PdN/IrN of ~7.2–29, low PdN/PtN (~1.2–2.7), and only mildly radiogenic (187Os/188Os)i values between ~0.132 and 0.177. Finally, the Quaternary volcanic rocks have low PdN/IrN (~2.3–3.6), PdN/PtN (~0.9–1.6) and radiogenic (187Os/188Os)i values ranging from ~0.133 to 0.194. Overall, the primitive mantle-normalized HSE patterns of the studied volcanic rocks are characterized by PPGE (Pt, Pd) and Re enrichment with respect to IPGE (Os, Ir, Ru). The variations in HSE and radiogenic Os isotope compositions of the relatively differentiated volcanic rocks indicate that crustal assimilation played active role in their parental melt evolution, especially in the Eocene and Miocene period. Besides, the obtained HSE data also suggest that the parental magmas of all the studied volcanic rocks were generated mainly in the S-saturated conditions. The temporal and spatial HSE and Os isotope variations observed in the studied Cenozoic volcanic rocks reflect the heterogeneity of the mantle source beneath the EPOB, which could be attributed to variations in response of different fluid/melt metasomatism of the underlying SCLM. © 2021WOS:00076236270000
U-Pb geochronology, bulk-rock geochemistry and petrology of Late Cretaceous syenitic plutons in the Gölköy (Ordu) area (NE Turkey): Implications for magma generation in a continental arc extension triggered by slab roll-back
No full textLate Cretaceous felsic plutons in the Eastern Pontides orogenic belt of Turkey are found in varying ages, sizes and compositions. The Late Cretaceous syenitic bodies, namely Direkli and Yeniköy Tepe plutons in the Ordu area, intruded into the Late Cretaceous volcanics and volcanoclastics, and compositionally consist of syenite and minor quartz-syenite with mainly granular and rarely porphyric, poikilitic and perthitic textures. The studied plutons contain K-feldspar, plagioclase, quartz, clinopyroxene, biotite and minor hornblende, and Fe-Ti oxide, apatite, and zircon. Mineral thermobarometer estimations imply that the syenitic plutons were crystallized in P-T conditions representing mid to shallow crustal levels. Petrochemically, these syenitic plutons show I-type, metaluminous-peraluminous transitional (A/CNK = 0.85–1.04) and shoshonitic features. LA-ICP-MS U-Pb zircon dating on the syenitic plutons yielded weighted mean ages of 78.5–72 Ma. Primitive mantle-normalized trace element patterns of the studied plutons are characterized by negative anomalies of Ba, Sr, Nb, Ta and Ti, and enrichment in Rb, Th, K, Ce and La. The chondrite-normalized rare earth element (REE) plots of the studied plutons show moderately enriched concave-shaped patterns (LaN/LuN = 10.3–10.7 for the Direkli pluton; LaN/LuN = 6.8–11.7 for the Yeniköy Tepe pluton) with negative Eu anomalies. The plutons have 87Sr/86Sr ratios (0.705368–0.706954), 143Nd/144Nd ratios (0.512600–0.512672), 206Pb/204Pb ratios (19.29–19.52) and 207Pb/204Pb ratios (15.65–15.67). The geochemical data, as well as regional geology, suggest that the Late Cretaceous syenitic plutons have formed in an extensional continental arc setting triggered by slab roll-back. The parental magma of syenitic plutons was derived from melts of lower crustal materials (metabasalt/metaandesite) and lithospheric mantle component
Tersiyer Yaşlı Altınpınar Hornblendli Andezitlerinin (Torul-Gümüşhane) Petrografisi, Mineral Kimyası ve P-T Kristalleşme Koşulları
No full textDoğu Pontid orojenik kuşağında (KD Türkiye) farklı magma türleri altında oluşmuş farklı volkanik kayaçlar yüzeyleme vermektedir. Tersiyer volkanizması, Gümüşhane ve çevresinde asidik, nötr ve bazik volkanik ve piroklastik kayaçlardan meydana gelmektedir. Bu volkanizma doğu Pontidler’in evriminde ise önemli bir rol oynamaktadır. Bu çalışma kapsamında Altınpınar (Torul/Gümüşhane) civarında yüzeyleme veren Tersiyer yaşlı hornblendli andezitik kayaçların petrografisi, mineral kimyası ve sıcaklık-basınç koşulları irdelenmiştir. Andezitler başlıca hornblend (amfibol), plajiyoklas (An40-61Ab38-57Or1-5), klinopiroksen (Wo44-45En43-44Fs12) ve opak (genellikle magnetit ve pirit) mineralleri, ikincil kil, serizit, kalsit ve klorit mineralleri içerir ve mikrolitik-porfirik ve vitrofirik porfirik dokular sergiler. Bazı hornblend mineralleri iri kristalli gelişmiş olup, plajiyoklas ve opak mineral kapanımları içermektedir. Tüm hornblendler CaB ? 1.5, (Na+K)A <0.5 ve CaA <0.5 parametrelerine sahip kalsik tip olup, magnezyohornblend bileşimi sunmakta, Mg# (Mg/Mg+Fe2+) ise 0.72-0.91 arasında değişmektedir. Andezitlerde kalsik amfibol jeotermobarometri denklemlerini kullanarak hesaplanan tahmini jeotermometre (T), jeobarometre (P) ve oksijen fugasitesi (ƒO2 /??NNO) değerleri sırasıyla 765 – 867 °C (ort= 790±20 °C); 2.5 – 4 kbar ve –14.4 ile –11.1 olarak hesaplanmıştır. Elde edilen bu değerler hornblendlerin kıtasal kabukta 9 – 15 km derinliklerde kristallendiğini işaret etmektedir. Minerallerin kimyasal özellikleri inceleme alanındaki andezitlerin kalk-alkali bir ana magmadan itibaren kristallenmiş olduğunu göstermektedir
Petrogenesis of Late Cretaceous A-type plutonic rocks from the Eastern Pontides Orogenic Belt (NE Turkey): constraints from zircon U-Pb geochronology, zircon Lu-Hf and whole-rock Sr-Nd-Pb-Hf isotopes
No full textThe Late Cretaceous magmatic history of the Eastern Pontides Orogenic Belt (NE Turkey) was generally characterized by common I-type and lesser A-type plutons in varying size and composition. Of these, A-type plutons from the Şebinkarahisar (Giresun) area yield SHRIMP zircon U-Pb age of 77.36 ± 0.96 Ma. The rocks of these plutons display a wide range of SiO2 contents (53.63 to 70.96 wt.%) and Mg-numbers (6.2–32.19) with A-type affinities characterized by enrichment in K2O and Na2O, Ga, Zr, and strong negative Eu anomalies. They also show arc-type petrochemical features including enrichment of large-ion lithophile elements (e.g. Cs, K, Rb) and light rare earth elements (LaN/LuN = 6.27–15.61), but depletion in high strength field elements (e.g. Nb, Ta, Ti, and P). The (87Sr/86Sr)i ratios and ɛNd(i) values of the studied rocks are in the range of 0.705129 to 0.0705347 and −3.64 to −3.12, respectively, while bulk rock ɛHf(i) values are between 1.86 and 4.36. They are characterized by positive zircon ɛHf(i) (1.74 to 10.88) plotting between the chondrite and depleted mantle evolutionary line values. Our data combined with the previous studies suggest that the magmas, that formed the Late Cretaceous plutons, were generated in an extensional tectonic environment due to slap roll-back and trench ward migration of the subduction zone to the south. The generation of hybrid magmas forming the studied plutons is in response to the melts derived from a metasomatized lithospheric mantle source, a relatively deeper mantle source, and the juvenile crust along with the heat transfer and decompression. Multi-sourced magmas rise through the continental crust and reach the final composition by predominantly fractional crystallization processes. © 2023 Informa UK Limited, trading as Taylor & Francis Group
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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