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ÖgeOrigin, age and deformation history of the Çataldağ metamorphic core complex(Lisansüstü Eğitim Enstitüsü, 2021) Kamacı, Ömer ; Altunkaynak, Şafak ; 693613 ; Jeoloji MühendisliğiIn this thesis, a new metamorphic core complex was identified in NW Anatolia, located between Balıkesir and Bursa cities, and named as Çataldağ Metamorphic Core Complex (ÇMCC) based on thorough field observations, meso-microstructural features, geochronology and geochemistry data. The ÇMCC is divided into three parts with different structural characteristics: (1) footwall rocks; (2) the hanging wall rocks and (3) a mylonitic shear zone separating the footwall rocks from the hanging wall rocks. The footwall rocks are made up of a granite-gneiss-migmatite complex (GGMC) in which migmatitic rocks experienced HT/LP metamorphism in amphibolite (upper amphibolite?) facies; and a synkinematic granitic intrusion (Çataldağ syn-kinematic pluton: ÇSP). The hanging wall rocks are composed of basement rocks of the Sakarya continent, supra-detachment sediments and Neogene lacustrine sediments. The mylonitic shear zone, on the other hand, consists of footwall rocks that underwent continuous ductile to brittle deformation below the Çataldağ detachment fault zone (ÇDFZ), which separates the footwall and hanging wall rocks. U-Pb zircon and monazite ages of anatectic leucogranites range from 33.8 ±0.14 Ma. to 30.1 ±0.23 Ma (Late Eocene-Early Oligocene). 40Ar/39Ar ages obtained from biotite, muscovite, and feldspar minerals of the footwall rocks and the mylonitic rocks vary from 20.7±0.1 Ma to 21.3±0.3 Ma (Early Miocene). The 40Ar/39Ar biotite ages of the ÇSP range from 20.8±0.1 Ma to 21.1±0.02 Ma. These age data clearly indicate that GGMC and ÇSP were formed in different periods (Eo-Oligocene and Early Miocene, respectively), but they uplifted together during the Early Miocene (21.3–20.7 Ma). Microstructural studies on quartz, feldspar and mica minerals show that GGMC and ÇSP underwent continuous deformation from ductile to brittle conditions during their cooling and exhumation with top‑to‑north and top‑to‑northeast sense of shear. Two main deformation zones were determined within the ÇMCC, based on the temperature and the intensity of the strain: The ductile deformation zone at the central parts of GGMC and ÇSP; and the mylonitic zone at the peripheral zones of the GGMC and ÇSP, through the ÇDFZ. Within the ductile zone, microcline twinning, myrmekite development along the K-feldspar megacrysts, flame-shaped perthite, chessboard extinction, grain boundary migration and sub-grain rotation recrystallization of quartz are observed. These microstructures indicate that dynamic recrystallization processes at high temperatures (>600oC–450oC) were dominant in the ductile zone. In the mylonitic zone, mylonitic gneiss and schists show distinct foliation which is accompanied by C-S structures in K-feldspar and micas, and ribbon structures in quartz. In addition, feldspars show bulging recrystallization, feldspar-fishes and domino-type microfractures. These microstructures indicate that the dynamic deformation within the mylonitic zone was continuous from the mid-temperature (500oC–<250oC) to brittle conditions. Two-feldspar thermometer calculations estimated that the deformation temperatures for the ductile and mylonitic zone were 501–588°C (avg. 544°C for ÇSP and avg. 517°C for GGMC) and 430–557°C (avg. 484°C for ÇSP and avg.436°C for GGMC), respectively. Microstructures, two-feldspar geothermometry and thermochronology data show that the GGMC cooled slowly (<50 °C/my) during the Eo-Oligocene and then rapidly (> 500 °C/my) during the Early Miocene (21 Ma) along the ÇDFZ. The ÇSP, on the other hand, was gradually deformed from sub-magmatic to brittle conditions and cooled rapidly (> 500 °C/my) in the Early Miocene (21 Ma). ). The Early Miocene granodioritic intrusion was considered as a "synkinematic" pluton (Çataldağ Syn-kinematic pluton: ÇSP) which was emplaced at shallow depths along the ÇDFZ due to its progressive sub-solidus deformation, C-S fabrics, and spatiotemporal link with the ÇDFZ, The Eo-Oligocene granites within the GGMC are represented by peraluminous garnet-bearing leucogranite and two-mica leucogranite. Garnet-bearing leucogranites consist of quartz (30-35%) + plagioclase (25-30%) + K-Feldspar (25-30%) + muscovite (5%) + garnet (2%) ± biotite, while two-mica leucogranites is formed from quartz (30-35%) + plagioclase (25-30%) + K-Feldspar (20-22%) + biotite (5-8%) + muscovite (3%) ± garnet. Both leucogranite types are enriched in LREE (Rb, U, K, Pb) and depleted in HFSE (Nb, Ta, Zr, Ti). Their 87Sr/86Sr, 206Pb/204Pb and 207Pb/204Pb initial isotope values range from 0.7094 to 0.7113, 18.79 to 18.91, and 15.71 to 15.73, respectively, and εNd(33) values vary between -5.13 and -7.79. On the other hand, gabbroic syn-plutonic dykes show similar isotopic characteristics (87Sr/86Sr(33) = 0.7055, εNd(33) = -1.8 and 206Pb/204Pb = 18.8) to enriched mantle melts. Trace element and isotope models show that the leucogranites have a dominant crustal melt component (85-70%) and a minor mantle component (<30%). Partial melting modeling (via PhasePlot/MELTS) and Ti-in-zircon thermometer calculations indicate that the leucogranitic melt was formed by water-absent muscovite dehydration melting of a mica-schist source (a melt fraction of max. 35%) at ≥ 7–10 kb and 739–840 °C. The inherited zircon core ages of the leucogranites change between Precambrian and Cambrian. TDM model ages of the leucogranites are relatively high (> 1.2 Ga). Whole-rock geochemistry, isotopic features, TDM ages, and inherited zircon chronology combined with the geology of the region indicate that leucogranitic melts were formed by the partial melting of the Anatolide-Tauride continental crust which was underthrusted below the Sakarya Continent along the İzmir-Ankara Suture Zone. The source of the syn-plutonic mafic (gabbro-diorite) dykes within the core of the ÇMCC, on the other hand, is inferred to be derived from the enriched mantle (EMII) beneath western Anatolia. It is inferred that the migmatization and melt generation which produced leucogranites were most likely caused by thermal weakening and partial removal of the western Anatolian young orogenic lithosphere during the transitional phase between the latest phase of collision and the earliest phase of extension, in the Eo-Oligocene. The exhumation of GGMC and ÇSP as a domal-shaped core complex at the footwall of the Çataldag detachment fault was developed under the back-arc extension driven by slab rollback beneath the Hellenic arc during the Early Miocene.
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ÖgeUnconventional gas system characteristics and depositional environment modeling of silurian mudstones: Central Taurides and western Pontides, Turkey(Graduate School, 2021-03-16) Döner, Zeynep ; Kumral, Mustafa ; 505132309 ; Geological Engineering ; Jeoloji MühendisliğiThe increasing global demand for energy has made it imperative to explore and exploit unconventional oil and gas resources. An investigation of new resources has become mandatory for countries like Turkey with very limited supplies of conventional oil and natural gas. Silurian (generated 9% of the world's reserves) is one of the six anoxic stratigraphic intervals that more than 90 % of the original recoverable oil and gas reserves in the world have been generated from source rocks. In this context, Silurian mudstones from central Taurides and western Pontides can be evaluated one of the alternative unconventional gas resources. This study focus on evaluating the unconventional gas/oil system characteristics of Silurian mudstones in central Taurides and western Pontides, in a comparative way with each other and making a comparison with world shale basins, in terms of the mineralogical constituents & lithofacies, geochemical modeling of depositional environment, organic geochemical characteristics, reconstruction of original hydrocarbon generative potential, and petrophysical properties to evaluate reservoir quality, covering the theoretical understanding of assessment for shale plays evaluation and the discussing of the content of each property. In this study, it is adopted that the terms of both "shale" and "mudstone" in lithologic description and in the general discussion of the play type according to shale gas reservoir description of various researchers. This work uses outcrop samples which can be considered as a hybrid system where organic-rich and organic-lean intervals were juxtaposed, that could be grouped into three rock types: siliceous, carbonate-dominated, and mixed mudstones. The central Taurides and western Pontides mudstones were located in passive margin of tectonic setting. Geochemical data of major and trace elements obtained for a total 39 of central Taurides and 19 of western Pontides' outcrop samples were interpreted to determine the depositional model, water column productivity, and preservation conditions. Several redox indicators, such as V systematics (V/Sc, V/Ni) as well as ratios of Ni/Co, Th/U and Mo/Mn, showed that the organic-rich mixed mudstones were deposited in suboxic to anoxic environments, as opposed to oxic-dysoxic conditions for organic-lean ones in central Taurides. In western Pontides, organic-rich mixed mudstones were deposited oxic-dysoxic conditions, and organic-lean mudstones were deposited in an oxidizing conditions. However, organic matter enrichment is not restrained by water column productivity, as indicated by a lack of correlation between total organic carbon (TOC) and productivity indexes (P/Ti and Ba/Al), but rather probably controlled by dysoxic-anoxic water column environment. In addition, a detrital material input cannot be ignored for its influence on organic matter enrichment in the mudstone deposition for both areas. The increase in the clastic fluxes probably resulted from the deposition in the extended shelf with coastal upwelling. A lack of correlation between K2O, Al2O3, SiO2 and TOC contents among these mudstones imply that clay minerals may not influence organic matter preservation. According to w(La)N/w(Yb)N and ΣREE values, a high sedimentation rate is determined during the central Taurides and western Pontides mudstone deposition, which would result in a dilution of organic matter. Furthermore, slight marine influences with sulphur limitation and low salinity, semi-arid/warm to humid-warm climatic conditions are widespread, according to total sulphur (TS), Sr/Ba, Sr/Cu, chemical index of alteration (CIA), C-value and related discrimination diagrams. In the end, a depositional models of the central Taurides and western Pontides' mudstones are established to display an excellent preservation condition as the major controlling factor for organic matter enrichment in the Silurian mudstones. In addition, this study used a range of integrated and complementary experiments to examine pore-structure, fluid-shale wetting characteristics, sample size-dependent porosity towards different fluids, and imbibition behavior, as well as the relationships between these properties of Silurian mudstones in the central Taurides and western Pontides. Working with different sample-sizes, the experiments consisted of helium pycnometry (HP), low-pressure nitrogen physisorption (LNP) isotherm, mercury intrusion porosimetry (MIP), fluid immersion porosimetry (FIP), liquid displacement (LD), fluid droplet wettability and contact angle measurements, and spontaneous imbibition of fluids; four fluids with different hydrophilicity [deionized (DI) water, API brine (8% NaCl and 2% CaCl2 by weight), 2DT (n-decane:toluene, v/v of 2:1), THF (tetrahydrofuran, (CH2)4O)] were used to assess the characteristics of fluid-shale interaction and its influence on pore-structure. Siliceous and mixed mudstones for both areas have higher porosities, pore-throat diameters, and surface areas than the carbonate-dominated mudstones, regardless of sample sizes and fluids used. Central Taurides' siliceous and mixed mudstones have H3 type slit- or plate-like pores for central Taurides, while all type of mudstones for western Pontides have H4 type slit-like pores. Furthermore, the tortuosities of siliceous and mixed mudstone samples for both areas are higher than carbonate-dominated mudstones, which suggests that migration pathways for fluids within the former samples will be more complex. With low permeabilities and medium pore-throat sizes for the siliceous and mixed mudstones, the wettability and imbibition results show that central Taurides and western Pontides' mudstones are both oil-wet and moderately-to-high water-wet. In contrast, the carbonate-dominated mudstones exhibit moderately-to-highly oil-wet characteristics. These results indicate that studied siliceous and mixed mudstones in the central Taurides and western Pontides seem to have appropriate petrophysical properties in the context of reservoir quality. The central Taurides and western Pontides' Silurian mixed mudstones can be considered as targeted zone for shale gas. These mixed mudstones in both areas were originally a Type II oil/gas prone marine mudstone. The present-day total organic carbon (TOCpd) contents range from 0.56 to 4.06 wt.% for central Taurides and from 0.68 to 1.57 wt. % for western Pontides, suggesting that moderate shale gas storage potential. The central Taurides and western Pontides mudstones have lost 97% and 95% for their original hydrocarbon potentials, seems to be a spent hydrocarbon source rock, indicating good risk for gas. The original TOCo content of studied mudstones range from 0.88 to 6.34 wt.% (average of 2.35 wt.%) and 1.06-2.45 wt.% (average of 1.70 wt.%), respectively. In addition, these targeted zones for both areas are in the overly mature stage / dry gas window, based on graptolite, chitinozoan reflectences and equivalent vitrinite reflectances, S2/S3 ratios, illite/chlorite crystallinity indices and sharpness ratios. It should be specified that Tmax was affected by low S2 values for both areas, resulting in unreliable Tmax estimates. In the gas window, TOC reduced approximately 36%, but the remaining potential and hydrogen index are reduced by over 90%, indicative of a high degree of conversion of organic matter to hydrocarbons and a carbonaceous residue. The ratio of organic porosity to total porosity in organic matter were determined as 26.5% for central Taurides and 26.7% for western Pontides, indicating that mudstones with high quartz and carbonate contents appear to be more resistant to the collapse of organic pores related to burial compaction, hydrocarbon generation, and expulsion than those with high content of clay mineral, as in central Taurides and western Pontides mudstones. However, these mudstones originally may have good to very good source rock potential, according to calculated original potential yields (S1o+S2o values ranging from 7.89 to 55.1 mg HC/g TOC and from 9.44-21.3 mg HC/g TOC, respectively). The amounts of hydrocarbons will be produced by the system in potential areas were calculated as 2.90 ×1013 kg HC for central Taurides and 5.64 ×1012 kg HC for western Pontides. Moreover, the targeted zone for both areas have a significant silica content (average of 44% for central Taurides and 37% for western Pontides) with calcite minerals, are generally >30%. Clay minerals are mainly illite and chlorite, which are non-swelling clays, and have <30% contents. The permeabilities of studied mudstones in both areas are low and the porosities are moderate to high which are <15%. The fractal dimensions and brittleness values of studied mudstones indicate that these mudstones have a suitable interval for hydraulic stimulation and the hydro-fracturing would be needed for viable hydrocarbon production for both areas and will escalate the flow of hydrocarbon more efficiently. Although the characteristics of central Taurides and western Pontides' mudstones seems to be nearly compatible with data of Ordovician Utica Shale in North America that can be commercially exploited in terms of the hydrocarbon generative potential (based on the GOC, TOCpd and S2o values), but it is possible that the source rock is very deep and deformed from the past to the present day, considering the paleogeographical location and geological evolution of the study areas. The measurements conducted and results achieved in this research thus could contribute to the understanding on these mudstone formations in north and south Turkey and greatly add to what is known from other published data. Nevertheless, more detailed investigations are necessary.
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ÖgeZayıf jeolojik ortamlarda (İstanbul metrosu) sığ ve çoklu yeraltı açıklıklarının neden olduğu yüzey deformasyonlarının kestirilmesi(Lisansüstü Eğitim Enstitüsü, 2021-08-06) Topal, Candaş ; Mahmutoğlu, Yılmaz ; 505152304 ; Jeoloji MühendisliğiArtan kent nüfuslarının, kentlerdeki ulaşım problemleri üzerinde büyük etkisi olduğu açıktır. Bu durumu çözebilmek için pek çok gelişmiş kentte toplu ulaşım çözümleri yeraltına taşınmaktadır. Bu sayede daha fazla kişi uzak mesafelere hızlı ve ekonomik olarak kent trafiğini zorlamadan taşınırken ulaşım konforu da beraberinde arttırılmaktadır. Ancak, metro hatlarının inşaatı sırasında birbirine yakın çoklu kazıların yapılması kaçınılmaz hale gelmektedir Özellikle sığ derinliklerde zayıf ortam koşullarında açılan kentiçi yeraltı kazıları, kent altyapısında ve yüzeydeki yapılarda hasarla sonuçlanan sorunlara neden olabilmektedir. Bu sorunlar, proje maliyeti ve çevre sağlığı ve güvenliği açılarından ciddi yükleri de beraberinde getirmektedir. Bu riskleri en aza indirmek amacıyla, son yıllarda modern teknolojik imkanlar kullanılarak, kazı aynasında ve kazı çeperindeki örtü yükünü dengeleyen makinalı (EPB-TBM) kazılar yapılmakta, kazıların yüzeye yansıyabilecek etkileri önceden belirlenen noktalarda yapılan periyodik ölçümlerle denetlenmektedir. Kazı bağımlı oluşan düşey deformasyonların, tekil kazılar ile olan ilişkisi değişik jeolojik ortamlar için literatürde geniş olarak ele alınmıştır ve konuyla ilgili ampirik ve analitik çözümler önerilmiştir. Ancak uygulamada kent içi ulaşımına yönelik çift hatlı, birbirine paralel (özellikle metro tünelleri) ve yakın mesafelerde açılmakta olan tüneller için, bilinen yaklaşımların geçerli olmayabileceği sıkça yaşanan vakalardan anlaşılmaktadır. Tünellerin açımı sırasında çoğu zaman teorik açıdan benzer ikiz tünel kazılardan biri önden diğeri arkadan yürütülmektedir. Proje karakteristikleri nedeniyle kazılar arası yatay mesafe olabildiğince sınırlı tutulmaktadır. Dolayısıyla bu tür çoklu kazılar birbiri ile gecikmeli de olsa etkileşmektedir. Yapılan çalışmalar, önde yürütülen kazının zayıf ortamlarda örselenmeye neden olduğunu, dolayısıyla arkadan gelen tünelin açıldığı ortam aynı olsa bile, teorik olarak önden ilerletilen kazı nedeniyle örselendiği, bu nedenle de ortamın jeomekanik parametrelerinde negatif yönde bir değişimin olduğunu göstermektedir. Arkadan gelen tünelin önde yürütülen tünelin etki alanı içerisinde kalması durumunda daha zayıf bir ortamdan geçmesi söz konusu olacaktır. Bu durum tünel kazılarına bağlı gelişen yüzey oturma formları üzerinde de etkiye sahiptir. Genel şekliyle birinci tünelin kazısı sonrası yüzeyde oluşan form Gauss eğrisi ile yakın benzerlik göstermektedir. İkinci tünelin kazısından sonra bu form,eğrinin birinci tünele yakın olan tarafı ile ikinci tünele yakın olan tarafı üzerinde farklılaşarak asimetrik bir görünüme kavuşmaktadır. Bu sonuç, tünellerin yüzeyde oluşturdukları etki alanlarının birinci ve ikinci tüneller için farklı bölgeleri etkilediğini göstermektedir. Tez çalışmasında, İstanbul ilinin Avrupa yakasında açılmış ve açılmakta olan Kirazlı-Olimpiyat-Başakşehir ve Ataköy-İkitelli Metro Hatları üzerindeki 6 farklı lokasyon incelenmiştir. Bu lokasyonların araştırma için seçilmelerindeki temel neden, bölgelerde zayıf zemin şartlarının geçerli olması ve sığ tünel kazılarının neden olacağı yüzey deformasyonlarının kentsel alanda hasar riski oluşturmasıdır. İnceleme çalışmasında, EPB makinaları (Earth Pressure Balanced Machine) kullanılarak, aynı hat üzerinde birbirine yakın ve sıralı olarak açılan ikiz tünel kazılarının yüzeyde neden olduğu deformasyonların zaman ve kazı aşamasıyla ilişkisi değerlendirilmiştir. Çalışmada bu hatlarda, yapılar açısından hasar riski yüksek, sığ yeraltı kazılarının yüzeyde neden olduğu oturmaların güvenilir düzeyde kestirimi için uygun yöntemin belirlenmesi ve yüzey oturma teknesi formunun ikincil tünel kazılarından sonra nasıl değiştiğinin ortaya çıkarılması amaçlanmıştır. Bu bağlamda, izleme verileri (projelerden elde edilen yüzey deformasyon verileri) ile iki ve üç boyutlu (2D, 3D) sayısal analiz yönteminden elde edilen sonuçlar birlikte değerlendirilmiştir. Tez çalışması kapsamında gerçekleştirilen tüm analizler birlikte değerlendirilmiş ve karşılaştırılmıştır. Sonuç olarak, birbirine yakın, sığ ve zayıf jeolojik ortamlarda aynı kotta açılan çoklu kazıların etkilediği alanların kısmen de olsa çakıştığı sonucuna varılmıştır. Birinci tünellerin ortamda yarattığı örselenmeden dolayı, ikinci tünellerin yüzeyde oluşturduğu deformasyon etki alanının büyüdüğü ve bu etki alanının oturma teknesi formunda değişikliğe neden olduğu anlaşılmıştır. Erişilen bu durum yeraltı kazılarının yüzeyde neden olabileceği yerdeğiştirmeleri izleme amacıyla oluşturulacak izleme projesi için teknik ve önemli bir temeldir. Ortaya çıkan bu negatif etkinin azaltılabilmesi için, özellikle kentiçi zayıf zemin koşullarının hakim olduğu bölgelerde gerçekleştirilen çoklu yeraltı kazılarında, proje güzergahının jeolojik/jeoteknik parametrelerinin dizayn aşamasından önce detaylıca incelenmesi ve belirlenmesi, tünelcilik yönteminin bu parametreler nazarında seçilmesi ve şekillendirilmesi, yeraltı kazılarına bağlı yüzeyde gelişebilecek olan etkileşim bölgesinin izlenmesi adına oluşturulacak olan sistemlerin detaylıca tasarlanması ve yeraltı kazılarının teknik parametreler dahilinde dikkalice takip edilip kayıt altına alınması gerekmektedir.