LEE- Jeoloji Mühendisliği Lisansüstü Programı

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Konu "Structural geology" ile LEE- Jeoloji Mühendisliği Lisansüstü Programı'a göz atma
  • Öge
    Origin, age and deformation history of the Çataldağ metamorphic core complex
    (Lisansüstü Eğitim Enstitüsü, 2021) Kamacı, Ömer ; Altunkaynak, Şafak ; 693613 ; Jeoloji Mühendisliği
    In 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.