Tepeldağ Granitoyidi'nin jeolojisi, petrografisi ve yerleşim koşulları
Geology, petrography and emplacement conditions of Tepeldağ granitoid
Yazar: GÜN AKINCI
Danışman: PROF. DR. ŞAFAK ALTUNKAYNAK
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Jeoloji Mühendisliği Ana Bilim Dalı / Jeoloji Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2019
Konu: Jeoloji Mühendisliği = Geological Engineering
Dizin: Optik mineraloji dersi = Optical mineralogy course ; Yapısal jeoloji = Structural geology

Özet:
Bu tez çalışması kapsamında KB Anadolu'da Bursa ilinin kuzeydoğusunda mostra veren Orta Eosen yaşlı Tepeldağ Granitoyidi'nin ve çevre kayaçların jeolojisi, petrografisi ve granitoyidin yerleşim koşulları incelenmiştir. Çalışma alanı yaklaşık 115 km2'lik bir alan kapsamaktadır. İnceleme alanında temel kayaları (Kocasu Formasyonu), Tepeldağ Granitoyidi, çökel kayalar (İnegöl Formasyonu) ve alüvyon olmak üzere 4 farklı birim bulunmaktadır. Temel kayaları, Tavşanlı Zonu'na ait Kocasu Formasyonu'na dahil amfibolit fasiyesinde metamorfizmaya uğramış metapelit, metabazit ve mermerlerden oluşmaktadır. Tepeldağ Granitoyidi temel kayaları içine intrüzif olarak yerleşmiş, D-B uzanımlı plütonik bir gövde ile temsil edilir. Granitoyid, temel kayalarını kesmesine rağmen çevresinde bir kontak metamorfizma geliştirmemiştir. Tepeldağ Granitoyidi inceleme alanında üç farklı plütonik üye ile temsil edilmektedir; granodiyorit, mafik mikrogranüler anklavlar ve aplit daykları. Granodiyorit, Tepeldağ Granitoyidi'nin ana kütlesini oluşturmaktadır ve holokristalen granüler ve nadiren porfirik doku gösterir. Mafik magmatik anklavlar, holokristalen mikrogranüler dokuludur ve diyorit/kuvars diyorit bileşimi sergilerler. Granodiyorit inceleme alanında birçok alanda magmatik foliasyon-lineasyon gösterir. Mafik mikrogranüler anklavlar da bu foliasyon-lineasyona paralel uzama gösterirler. Gerek Tepeldağ Granitoyidi gerekse temel kayaları aplit daykları tarafından kesilir.
Petrografik incelemelere göre Tepeldağ Granitoyidi'nin ana kütlesi granodiyorit bileşimindedir (%40-50 Plajiyoklaz, %35-50 Kuvars, %13-20 K-feldspat, %5-10 Biyotit, %4-9 Hornblend). Ana granodiyorit kütlesinde bulunan amfibol ve plajiyoklaz mineralleri üzerinde yapılan mineral kimyası analizlerine göre, plajiyoklazlar andezin bileşimi ile temsil edilirler ve zonlu plajiyoklazlarda genellikle merkezden sınırlara doğru kalsiyum oranlarının azaldığı gözlenmiştir. Amfiboller ise magnezyohornblend ve çermakit bileşimleri sergilerler.
Tepeldağ Granitoyidi birçok alanda hem sünek hem de kırılgan deformasyon etkisi altında kalmıştır. Deformasyonun şiddeti, granitoyidin kuzey dokanağına gidildikçe artmaktadır. Mezo ve mikro ölçekli incelemelere göre, Tepeldağ Granitoyidi 500oC'den başlayarak 250oC'nin altına inen sıcaklıklara kadar sünekten kırılgana değişen sürekli deformasyona maruz kalmıştır. Bu deformasyon, plütonu kuzeyde sınırlayan sağ yanal oblik bir fay ile ilişkili olarak gelişmiştir.
Yapılan saha, petrografi ve jeotermobarometre çalışmaları ile elde edilen veriler Tepeldağ Granitoyidi'nin kabukta nispeten derine yerleşmiş bir magmatik gövde olduğunu göstermiştir. Aynı kaya içindeki amfibol ve plajiyoklazların kimyası kullanılarak yapılan jeotermobarometre hesaplamalarına göre Tepeldağ Granitoyidi 3,7 kbar basınç ve 700oC sıcaklık koşullarında oluşmuş ve 11-12 km derinliğe yerleşmiştir.

Abstract:
In this thesis, the geology, petrography and emplacement conditions of the Middle Eocene Tepeldağ Granitoid and surrounding rocks in the northeastern part of Bursa (NW Anatolia) were investigated. Tepeldağ Granitoid has exhumed in the Izmir Ankara Erzincan Suture Zone (IAESZ) and the magmatic activity which also caused plutonism in Eocene is related to collapse of the western Anatolian orogenic belt, which formed during the collision of the Sakarya and Tauride–Anatolide continental blocks in the late Paleocene. The study area covers an area of approximately 115 km2. The area is circumscribed by Fevziye Village at the North, Bogazköy at the South, Barakli Village at the West and Lutfiye Village at the east.
In the study area, there are 4 different rock units: basement rocks (Kocasu Formation), Tepeldağ Granitoid, sedimentary rocks (İnegöl Formation) and alluvium. According to field studies and petrographic investigations, the basement rocks in the study area are metamorphic rocks which have gone through metamorphism in amphibolite facies conditions; metapelites, metabasites and marbles of the Kocasu Formation of Tavşanlı Zone. Primary rocks of metapelites are conglomerates, sandstone, shale, claystone and mudstone. Metabasites are represented by metalavas and metatuffs and the formation includes calcschists and marble lenses where the calcic-carbonated composition increases gradually.
Both the basement rocks and Tepeldağ granitoid are overlain by sedimentary rocks which are named as Inegol Formation. This formation consists of clastic sediments and also consists of boulders and lithic clasts of Tepeldağ granitoid and basement rocks. The age of the unit has called İnegöl formation by Genc (1986) is determined as Upper Miocene according to the vertebrate fossil it contains.
Tepeldağ granitoid is represented by a plutonic body of approximately 55 km2 with an E-W extension, emplaced intrusively within the basement rocks (Kocasu Formation). The granitoid cuts the metamorphics of basement rocks, however, there is no evidence of contact metamorphism. Due to it has not developed contact metamorphism at the contacts between magmatic body and ground rocks Okay and Satir (2006) refers that indicates that the schists were already hot and deforming prior to the intrusion; the temperature was probably increased by the advection of heat into the upper crust by magmas. Intimate mixing of the contact and regional effects of the intrusions are also reported from several other regions. They also state that there is no difference between the P-T conditions of contact metamorphism and that of low-pressure regional metamorphism and the two may only be separated by the absence or presence of an accompanying progressive ductile deformation.
Tepeldağ granitoid is represented by three different plutonic members; granodiorite, mafic microgranular enclaves and aplite dykes. Mafic microgranular enclaves are recognized by their magmatic microgranular textures and melanocratic colors in the field. They are determined to be coeval with Tepeldag granitoid because of their magmatic texture and mineral paragenesis.
Granodiorite is the main body of the Tepeldag granitoid and has holocrystalline granular and rarely porphyritic texture. Mafic microgranular enclaves display magmatic texture and exhibit diorite / quartz diorite composition. Granodiorite shows magmatic foliation-lineation throughout the study area. Mafic microgranular enclaves elongate parallel to this foliation-lineation. Both the Tepeldağ Granitoid and the basement rocks are cut by aplite dykes, which are distinguished from other rocks by their aplitic textures and felsic minerals.
According to the petrographic studies, the main body of Tepeldağ granitoid has 40- 50% Plagioclase, 35-50% Quartz, 13-20% K-feldspar, 5-10% Biotite, 4-9% Hornblende mineral composition. This composition shows that the main body is in granodiorite composition in accordance with the field observations. According to the mineral chemistry analysis on the amphibole and plagioclase minerals found in the main body with granodiorite composition, plagioclases are represented by the andesine composition, and calcium compositions increase from the cores to the rims of the zoned plagioclases. Amphiboles exhibit magnesiohornblende and tschermakite compositions.
For determining the age of Tepeldag granitoid, many researchers have used different dating methods. Tepeldağ granitoid has been dated previously at 44.99 ± 0.23 and 44.7 ± 0.4 Ma using zircon U–Pb and Rb–Sr on biotite, respectively (Okay and Satır, 2006). And other analyze results show; zircon SHRIMP age 45.41 ± 0.34 Ma, Ar-Ar biotite age 45.2 ± 0.1 Ma, Ar-Ar hornblende age 44.9 ± 0.2 Ma (Altunkaynak et al., 2012a). With these data obtained from previous studies; the age of the Tepeldağ Granitoid is Middle Eocene.
The mafic microgranular enclaves are diorite to quartz-diorite in composition. They can be easily identified as melanocratic minerals in the field. Also according to the petrographic studies, mafic microgranular enclaves within the Tepeldağ granitoid has 60-65% Plagioclase, 22-25% Hornblende, 15-20% Biotite, 8-10% Quartz mineral composition.
According to meso and micro scale structural geology studies, Tepeldağ Granitoid has been subjected to both ductile and brittle deformation in many areas. The intensity of the deformation increases in the northern contact of the granitoid. According to meso and micro scale studies, Tepeldağ granitoid underwent a deformation starting from 500oC to below 250oC and this deformation is proved to be continuous. It is understood that the deformation developed in relation to a right lateral oblique fault bounding the pluton to the north. Deformed granitoid exhibits many deformation patterns in microscale according to thin section studies made from samples taken from Tepeldağ Granitoid. Chessboard texture is a kind of wavy extinction that is seen in recrystallized quartz crystals. Chessboard structures indicate that the deformation has reached around 500-550 ° C (Passchier and Trouw, 1996). Another deformation structure observed in the Tepeldağ Granitoids is grain boundary migration (GBM). The grain boundary migration structure takes its name from the indented protruding borders indicated by quartz crystals. This structure is formed as a result of deformations developed at temperatures of 450-550oC (Passchier and Trouw, 1996). Subgrain rotation recrystallization (SGR) is also observed in the quartz in the Tepeldağ granitoid. This structure is defined by the separation of a part of the quartz grain by the pressure generated by shear forming sub-grains and the displacement of this sub-grains. Grain rotation recrystallization (SGR) occurs as a result of deformation at a temperature of 300-400 oC (Passchier and Trouw, 1996). Another sign of the deformation developing at 300-400 oC is the ribbon structures seen in quartz. Ribbon structures are defined as indicative of directional deformation. Accordingly, it is possible to say that Tepeldağ Granitoid is exposed to shear in the W-E direction. Another indicator of the deformation that develops in micas (mica fish) is accepted as lens shear indicators (Grotenhuis, 2000). The direction of thrust seen in mica fish was generally towards W.
The results obtained by field, petrography and geothermobarometer studies imply that Tepeldağ granitoid is a magmatic body which intruded comparatively deep locations in the continental crust. According to the geothermobarometer calculations made in the chemistry of amphibole and plagioclase on the same rock, Tepeldağ granitoid was formed under 3.7 kbar pressure and 700oC temperature conditions and intruded at a depth of 11-12 km.