Manyas-Susurluk-Kepsut (Balıkesir) civarının jeolojisi
The Geology Susurluk-Kepsut-Area (Balıkesir)
Yazar: H. SERDAR AKYÜZ
Danışman: PROF.DR. ARAL İ. OKAY
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü
Derece: Doktora, 1995
Konu: Jeoloji Mühendisliği = Geological Engineering
Dizin: Balıkesir-Kepsut = Balıkesir-Kepsut ; Balıkesir-Manyas = Balıkesir-Manyas ; Balıkesir-Susurluk = Balıkesir-Susurluk ; Jeomorfoloji = Geomorphology

Özet:
ÖZET Kuzeybatı Anadolu'da, Balıkesir'e bağlı Manyas-Susurluk-Kepsut ilçelerini kapsayan inceleme alanında, farklı dönemlerde gelişmiş okyanuslann kapanmalarını temsil eden birimler ve tektonizma sonrasında gelişmiş magmatik ve çökel kayalar yer alır. Bu birimler dört ana başlık altında incelenmiştir 1) Sakarya Zonu (Karakaya Kompleksi) 2) Anatolid Grubu (Orhaneli Birimi) 3) İzmir-Ankara kenet zonu 4) Tektonizma sonrası birimler Sakarya Zonu'nun temelini oluşturan Karakaya Kompleksi, inceleme alanında, Nilüfer Birimi, Hodul Birimi ve Orhanlar Grovağı ile temsil edilir. Nilüfer Birimi, yeşilşist fasiyesinin yüksek koşullannda metamorfizma geçirmiş volkano- sedimentlerden (Kiraz Metamorfiti) ve bunları birincil olarak uyumsuz örten mermerlerden (Çataltepe Mermeri) oluşur. Okyanus içi yay-önünde çökelmiş olan Nilüfer Birimi Permo-Triyas'ta oluşmuş, Geç Triyas'ta metamorfizmaya uğramıştır. Hodul Birimi arkozik kumtaşı ve şeylden oluşur. Kireçtaşı ve az oranda spilit bloklan içeren Hodul Birimi üst kesimlerinde kireçtaşı bloklannın boylannın ve miktarının artmasıyla olistostromal bir karakter kazanır. Üst seviyeleri Üst Triyas'a kadar çıkan Hodul Birimi, ön-ülke havzasında gelişmiş olmalıdır. Orhanlar Grovağı, şiddetli makaslanmış kırıntılı bir matriksten ve yaygın Permiyen kireçtaşı ve az spilit ve çört bloklanndan oluşmuş olistostromal bir istiftir. Permo-Triyas yaşlı Oranlar Grovağı hendek çökellerini temsil eder. Anatolid Grubu birimler, mavişist fasiyesinde metamorfizma geçirmiş pasif kıta kenan çökellerinden oluşan Orhaneli Birimi ile temsil edilir. Orhaneli Birimi, en altta metakırıntılılardan oluşan Kocaçay Metamorfiti, bunun üstünde uyumlu duran İnönü Mermeri ve inceleme alanınında allokton olarak yer alan ve metabazitlerden oluşan Yayla Metamorfiti'nden ibarettir. Çökelme yaşı Geç Paleozoyik-Erken Mesozoyik olarak kabul edilen Orhaneli Birimi, Geç Kretase'de Neo-Tetis okyanus kabuğunun kuzeye dalması esnasında mavişist metamorfizmasına uğramıştır. Sakarya Zonu ile Anatolidler arasında yer alan Neo-Tetis okyanusunun kapanması esnasında farklı kaya gruplan gelişmiştir. İzmir-Ankara kenet zonu birimleri olarak değerlendirilen bu birimler ofiyolitli melanj özelliğindeki Ovacık Melanjı ve bir wildflis karakterindeki Bornova Flişi'dir. Ovacık Melanjı, Neo-tetis okyanus kabuğunun yığışım kamasında traşlanmasıyla oluşmuştur. Bornova Flişi, Neo-Tetis okyanusunun kapanması döneminde gelişen transform faylann kontrolünde gelişmiş bir kaya grubudur. Kınntılı, şiddetli makaslanmış bir matriks içinde kireçtaşı ve az oranda spilit, çört, mavişist bloklanndan oluşan Bornova Flişi'nin yaşı Üst Kretase-Paleosen'dir. Tektonizma sonrası birimler, Neo-Tetis okyanusunun kapanmasını izleyen kabuk kalınlaşmasına bağlı magmatik kayalar (Çataldağ ve Ilıca-Şamlı Granodiyoritleri ve Ezine Volkanitleri) ve akarsu ve göl çökellerinden oluşan Soma Formasyonu'dur. XV

Abstract:
THE GEOLOGY OF THE MANYAS - SUSURLUK - KEPSUT AREA (BALIKESİR) SUMMARY The study area is located on two orogenic belts and straddles a major Tethyan suture. There are four tectonic units in the study area, that show different stratigraphic, structural, metamorphic and magmatic evolution. These are: 1) Sakarya Zone (Karakaya Komplex) 2) Anatolides (Orhaneli Unit) 3) Izmir-Ankara Suture Zone 4) Post-tectonic units Sakarya Zone consists of Permo-Triassic basement rocks and overlying trangressive sedimentary and volcano-sedimentary rocks ranging from Liassic to Eocene with major unconformities. The basement rocks, named as Karakaya Complex, contain different units which reflect different tectonic environments. Nilüfer Unit is formed in an intra-oceanic fore-arc basin and underwent high degree greenschist metamorphism. It consists of a volcano-clastic sequence (Kiraz Metamorphite) at the bottom and an unconformably overlying marble sequence at the top (Çataltepe Marble). Kiraz Metamorphite is made up of amphiboleschist, micaschist, quartzschist, calcschist and marble lenses. The mineralogical compositions of the schists are as follows; amphiboleschist: amphibole (actinolite/hornblende) + plagioclase + epidote + chlorite ± quartz micaschist: muscovite + biotite + quartz + chlorite + plagioclase + epidote ± garnet quartzschist: quartz + muscovite ± biotite ± epidote calcschist: calcite + muscovite Metamorphic conditions in the Nilüfer Unit have been estimated petrographically as 425-500 °C and 4-6 kbar. Çataltepe Marble is a thick, homogenous succession which shows middle to thick primary bedding in places. Hodul Unit consists of arkosic sandstone intercalated with shale and passes up to olistostromes with Permian limestone and rare spilite blocks in a clastic matrix. It shows intense deformation but no metamorphism. The XV!limestone blocks in the olistostromes range from a couple of centimeters to 600 meters in size. Spilite blocks are rare and change between a couple of centimeters to 80 meters. Hodul Unit probably was deposited in a fore-land basin. Orhanlar Greywacke consists of intensely sheared greywacke and intercalated shale with abundant Permian limestone and rare splite and chert blocks. The primary bedding planes are destroyed due to shearing. Nilüfer Unit, Hodul Unit and Orhanlar Greywacke do not show stratigraphic contacts in the studied region. Hodul Unit is in contact with Nilüfer Unit along a major strike-slip fault to the northwest of the study area. Orhanlar Greywacke is thrust over Nilüfer Unit with an east-west trending low-angle thrust. Anatolides in the area studied is represented by Orhaneli Unit which has undergone blueschist fades metamorphism. Orhaneli Unit consits of three different formations. Kocaçay Metamorphite at the bottom consists of micaschist, phyllite and rare calcschist. It is overlain by a thick carbonate sequence named as İnönü Marble. The Yayla Metamorphite, dominantly made up of metabasites, constitutes the upper part of the Orhaneli Unit. Although Yayla Metamorphite is allocthonous in the study area, it is known that it is underlain by İnönü Marble in the Tavşanlı Zone to the further east of the study area. Yayla Metamorphite has index minerals for the blueschist fades metamorphism such as glaucophane, jadeitic pyroxene and lawsonite. The metamorphic conditions of the Orhaneli Unit which are determined from the index minerals in the Yayla Metamorphite are 280-400 °C and 8-1 1 kbar. The Orhaneli Unit represents passive northern margin of Anatolide-Tauride block. During Late Cretaceous, the continental margin deposits of the Anatolide-Tauride block were subducted under Neo-Tethyan oceanic crust to the north. The İzmir-Ankara Suture Zone units are divided into two different rock groups. Ovacık Melange has ophiolitic melange character while Bornova Flysch is a wildflysch. Ovacık Melange consists of serpantinite, spilite, peridotite, chert, limestone and blueschist tectonic blocks. It does not contain any matrix. Spilites rarely have some index minerals representing incipient blueschist metamorphism conditions such as glaucophane, jadeitic pyroxene and lawsonite. The metamorphic conditions were 150-200 °C and 5-8 kbar. The Ovacık Melange represents an accretionary prism formed above the north-subducting Neo-Tethyan oceanic crust. The western boundary of the Ovacık Melange is a strike-slip fault which seperates it from the Bornova Flysch. Bornova Flysch is made up of an intensely sheared detritic matrix and limestone, chert, spilite, serpantinite and blueschist exotic blocks. North of the strike-slip fault, which constitutes part of its boundary with the Ovacık Melange, the two units grade into each other. The transition from the Ovacık Melange to the Bornova Flysch is characterised by the appearance of the detritic matrix and by gradual decrease of the basic volcanic blocks. The western contact of Bornova Flysch is not clear due to young volcanic and sedimentary cover although Karakaya Complex units are seen to the west of Bornova Flysch. XVIIÇataldağ Granodiorite and Ilıca-Şamlı Granodiorite were formed during Oligo-Miocene after the closing of the Neo-Tethyan ocean. Çataldağ Granodiorite shows foliation, porphyritic and cataclastic texture on its outer zone while it has a homogenous character and granuler texture in core. Its mineralogical composition is quartz + K-feldspar + plagioclase + biotite + muscovite + hornblende ± garnet ± sphene. Çataldağ Granodiorite has cut the Nilüfer Unit with the formation of a contact aerole of 100 m-2 km in width. The contact metamorphism is characterised by development of andalusite, garnet, idocrase and wollastonite. It shows honblende-homfels facies contact metamorphic conditions. The temperature and pressure conditions of the contact metamorphism are determined by mineralogic compositions and it is estimated that the temperature is 550-650 °C, pressure is less than 3.5 kbar. Ilıca-Şamlı Granodiorite is very similar to the Çataldağ Granodiorite except it shows no foliation and does not contain muscovite. Ilıca-Şamlı Granodiorite always cuts the marbles of the Nilüfer Unit. It is made up of quartz + K-feldspar + plagioclase + biotite + hornblende + garnet + sphene and accessory minerals such as epidote, apatite, turmaline. The marbles in the aeurole have undergone hornblende-homfels facies contact metamorphism similar to those around the Çataldağ Granodiorite. The geochemical characters of the both granodiorites are also similar. Çataldağ and Ilıca-Şamlı granodiorites have probably formed due to crustal thickening during the period after the closure of the Neo-Tethyan ocean and resultant collision of Pontides and Anatolides. Ezine Volcanites consist of lavas, tuffs, agglomerates and massif volcanites of dacitic-andesitic compositions. They cover or cut the older units. Massif volcanites, lavas, tuffs and agglomerates are intercalated with each other and with rare volcanogenetic shale. Ezine Volcanites have probably the same origin as that of Çataldağ and Ilıca-Şamlı Granodiorites. This is supported by the very similar chemical compositions and ages of the Ezine Volcanites and the granodiorites. Both give latest Oligocene to Middle Miocene ages. Soma Formation is composed of conglomerate, sandstone, mudstone, marl and limestone. It covers Ezine Volcanites and older units uncomformably. The elastics represent alluvial and lacustrine sediments. Detritic sediments contain blocks and pebbles derived from granodiorites, volcanites and older units. The lower parts of the Soma Formation have some important mammalian species which are dated to the northern part of the study area. The age of Soma Formation is middle Miocene to Pliocene. The structures of the study area belong to at least three different stages. However, in many cases it is impossible to determine the age of these structures due to superimposion of structures with diffrent ages and lack of general age markers. Therefore, the structures in the area studied have been separated age-indepedently as "folds", "normal faults", "reversed faults and thrusts" and "strike-slip faults". The largest fold is located to the east of Susurluk which Çataldağ Granodiorite is intruded to the axial dome. Most of the other folds are common especially to the south of Manyas. Their XVIIIaxes directions are mostly WNW-ESE. Normal Faults are the youngest structures in the study area because they cut always the Miocene units. The biggest normal fault is the Kepsut Fault lying in an east-west direction to the south of Kepsut. It has 18 km of length in the study area. The other normal faults have concentrated to the west of Susurluk. Most of the normal faults have a small oblique component. The reversed faults and thrusts are concentrated to the southeast and east of the study area. Some of thrusts are located only between Karakaya Complex units. They may be related to the closure of Paleo-Tethys ocean. But there are also younger reversed faults and thrusts in the same area. That is why it is difficult to know whether they have been affected by younger tectonics. The most important structure of the study area is the Bükdere Fault which probably represents the Izmir-Ankara suture. It has 50 km of length in the study area and juxtaposes Karakaya Complex units with Izmir-Ankara Zone units (The Bornova Flysch and The Ovacık Melange). The strike-slip faults can be seen throughout the study area. They mostly cut the Miocene units. The biggest and most important strike slip fault is the Tal Fault which constitutes a boundary between the Ovacık Melange and the Bornova Flysch. It has probably formed during the closure of the Neo-Tehys ocean and controlled the formation of the Bornova Flysch. The study area is located on one of the tectonically critical places in northwest Anatolia. The northern part of the study area is represented by the Karakaya Complex units. The Hodul Unit is seen only on the westernmost part of the area which constitutes the north end of NNE-SSW trending zone of the Hodul Unit in the northwestern Anatolia. The Orhanlar Greywacke is located only on the eastern part of the area except some small outcrops. It is seen in tectonic relation with the Nilüfer Unit and Bornova Flysch as an east-west trending allochtonous body. Bornova Flysch is an important formation in the western Anatolia. Its relation with the Karakaya Complex is represented by a steeply dipping reverse fault named as Bükdere Fault. The relation between Bornova Flysch and Ovacık Melange is seen in the field as a strike-slip fault named as Tal Fault which is probably continuation of an important transform fault in the northwestern Anatolia reported by Okay and Siyako (1993). The Ovacık Melange and blueschists of the Tavşanlı Zone (Orhaneli Unit) outcrop extensively to the further east of the study area. They terminate on the study area. Orhaneli Unit is overlain by Ovacık Melange to the southeast of the study area. Orhaneli Unit is suprisingly seen on the Karakaya Units lying tectonically to the south of Manyas. The reason of this may be continuing post-tectonic compression. The crustal thickening of the northwest Anatolia after the closure of the Neo-Tethyan ocean probably led to extensive calc-alkaline magmatism during Oligo-Miocene. The firs products of the magmatism in the study area are Çataldağ and Ilıca-Şamlı Granodiorites. The last products are Lower to Middle Miocene-aged Ezine Volcanites. During Middle Miocene to Pliocene Soma Formation was deposited. It consists mainly of alluvial and rarely lacustral deposits. It forms probably the continuation of the Gönen- XIXM.Kemalpaşa pull-apart basin to the north of the study area. Moreover, the neo-tectonic events which are characterised by strike-slip faulting mostly to the northern part of northwest Anatolia and by graben system to the Western Anatolia has affected the study area. XX