Kemalpaşa-dağkızılca (izmir) Bölgesinin Jeolojisi

Abstract

Batı Anadolu'da izmir ilinin GGD yönünde yeralan yaklaşık 4002 km. bir alanı kapsayan bu çalışma iki temel konunun aydınlatılmasına yönelik olarak gerçekleştirilmiştir. Bunlardan biri, bölgede yüzeylenmiş tektonik ünite olan Bornova Fliş Zonu'nun oluşum koşullarını belirleyerek ve diğer tektonik ünite olan Menderes Masifi ile olan dokanak ilişkisini araştırmak, diğeri ise bu iki birlik arasında yeralan ve Torbalı Grabeni (Dağkızılca Havzası) olarak bilinen KKD-GGB gidişli havzanın evrimini araştırmaktır. Bu amaçlara yönelik olarak yapılan arazi çalışmalarında veri toplama ve 1/25.000 ölçekli topoğrafik haritalar üzerine jeolojik harita alımı şeklinde yapılan çalışmalardan sonra hava fotoğrafları yardımıyla arazide belirlenen unsurlar denetlenmek suretiyle kontrol çalışmaları yapılmıştır. Yapılan araştırmalar sonrasında Bornova Karmaşığının fliş tipi kırıntılı bir matriks içerisinde yüzen değişik boyutlarda kireçtaşı, bazik volkanik kayaç, spilit, çört ve ultramafit kaya bloklarından oluştuğu belirlenmiştir. Bornova Karmaşığının diğer tektonik ünite olan Menderes Masifi ile olan dokanağını ise muhtemelen bir transform fay sistemi oluşturmakdaydı. Bu fay sistemi, bir zayıflık zonu olarak Neotektonik dönemin başlangıcındaki K-G gerilme döneminde etkin rol oynamıştır. Bu gerilme döneminde, D-B uzan imli olarak gelişen ana grabenlere 30^40°açı yaparak açılan Dağkızılca Havzası bu zayıflık zonunda gelişen faylarla sınırlanmıştır. Havzanın evriminde önemli rol oynayan bu iki fay belirlenerek Başpınar ve Kurcaoluk fayları olarak isimlendirilmiştir. Muhtemelen Kuzey Anadolu Fayı'nın harekete geçmesi sonrasında bu faylardan Başpınar fayı yanal atım özelliği kazanarak havzanın kontrolüne devam etmiştir.

The extencion of Anatolian tectonic units to the Western Anatolia is situated between the Pontides in the north and Torid-Anatolid belt in the south. Along the margins of these two tectonic belts in the Izmir-Ankara Zone lies (BRINKMANN, 1966). This zone symbolises the seperation between the Laurasians and Gondwana continents by Neo-Tethys.This sea way which existed during Mesozoyik has subducted to the north and created the Izmir-Ankara Zone in its extinction. The research area covers the Bornova Flisch, a sub zone of above and a part of Menderes Massif which is an important entity of Tourid- Anatolid Belt. The co-existance of these two elements is a particularly important subject. The southern part of the Neo-Tethys has closed in early- Miocene as aresult of the collision of Arabian Peninsula with Eurasia. After this collision the Neo-Tectonic era has started in Turkey. The effects of this era in western Anatolia is still on debate in Turkisch Geology. An important issue of this debate is the structural changes after the initiation of North Anatolian Fault. The research area is nearly 400 km2. It is situated to the E-SE of Izmir in Western Anatolia where the elements of the concerned debate critically exposed. To the NW of mapping area Upper Maastrihtian-Paleocene aged sediments are exposed. These formation is a part of Bornova Melange. The sediment are mainly in the form of various blocks in a severaly deformed and sheared flisch type matrix. The blocks are mainly (90%) limestone blocks of Triassic-Jurassic age ranging in size from metres to kilometres. The remaining 10 % of the blocs are mainly volcanics of basic composition, spilits, radiolariancherts and ultramafics. The lithologies of the matrix of Bornova Melange are granular. These are mainly lithic wacke type of sandstone and turbiditic type of conglomerates. The matrix exhibits a chaotic texture as a result of strong VII deformation and shearing. The lateral tracing of these rocks is often impossible even for a few meters despite occasional bedding does exist The rare red and green silty limestone levels of matrix is dated Upper Maastricthian by the pelagic foraminifera fossils. Considering Upper Paleocene age as upper limit from earlier studies (AKDENİZ, et al., 1986), the entire unit can be dated as Upper Maastrihtian-Paleocene The limestone blocs in the mapping area vary in size from metres to kilometres. The Kurudağ and Nif blocks form the highhest altitudes in the area with their sizes near 20 kms each. These limestones were primarly blocs in the matriks but they have moved after their emplecement. The oblique and reverse faults to the west of Manastır Tepe in Kurudağ Block, to the NW of Palamutdağı and to the east of Nifkarlığıtepe in Nif Block provides good evidence for this type of movements. The non-limestone blocs of the Bornova Melange are only observed to the west of mapping area. These are exposed along the NE-SW fault zone and probably bordered by these offsets. The fossils of these limestones give a Liassic-?Lower Cretaceous age. The researcher have determinated Triassic-Upper Cretaceous fossils in the limestone blocks of Bornova Flische Zone. Authors studying about Bornova Melange in Western Anatolia have sugessted similar descriptions mentioned above. It is noteworth that there are not any ophiolitic nappes and HP/LT regional metamorphic rocks in Bornova Melange which is located to just south of Izmir-Ankara suture. Although it is expected in the suture belts that passiv continental margin deposits must have been preserved as allocthonous units, there are not any passive continental margin rocks in Bornova Melange which represent a Neo-Tethyan suture zone that is an open ocean during Triassic to Cretaceous. Menderes Massif units are located to the southwest of study area. They consist of mcaschist, quartzschist, calcschist and slate-phillite of Paleeozoic age called Yeşilköy Formation.They are overlain conformably by recrystallise limestone-marble of Mesozoic age called Akkaya Marbles. The contact of these two units are covered by Neogene sediments, which made up of alluvial fan and alluvium sediments. Kesmedağı Formation of Middle Miocene consist of conglomerate, sandstone and lacustral limestone and reflect alluvial fan, river and lacustrine sediments. It passes up gradually to Vişneli Formation which has similar lithologies but VIII Upper Miocene age. They are overlain uncomformably by alluvial fan sediments of Pliocene. Neogene filled basin named as Dağkızılca Basin is bounded dexral Başpınar Fault to the north and by dextral-oblique Kurcaoluk Fault to the south. Considering these NE-SW directed faults are the ghost structures, they have must been activ in Paleotectonic term. These faults wish were active in Paleotectonic term, thus, have been probably belonged a transform fault zone. This approach is compatible with the suggestion of a transform fault between Pontides and Anatolides for western Anatolia of OKAY and SİYAKO(1993) and OKAY et al., (in press) Alluvium sediments of Quetemary which constitutes the northern boundary of study area are seperated from the other sediments by Kemalpaşa Fault to the east. There is not evidence about the age of these faults. Considering from the map that Kemalpaşa Fault cuts Miocene sediments and controls recent sedimentation it is considered that Kemalpaşa Fault is the youngest one of the study area It maybe suggested here that Kemalpaşa Fault as probably been an active fault since early Miocene as recently suggested by SEYİTO?LU and SCOTT (1991), (1992) and Barka et al., (1994) that the fault bounding E-W trending basins in Western Anatolia has started their activity in early Miocene. This boundry is seen partly discordance and partly tectonic on the map. It probably reflects first neotectonic structure in the study area and fits N-S extension period of western Anatolia (ŞENGÖR, 1980). In the weakness zone forming a boundary between Izmir- Ankara Zone and Menderes Massif in middle Miocene a new seconder basin formed that zone. This aproach is compatible ŞENGÖR' s suggestion (1987) with the differences angles amounts. The seconder basin has not formed perpendicular to E-W grabens because the potential fault zone makes an angle of 30° 40° to main system. The first deposits of this periot of middle Miocene is Kesmedağı Formation. Vişneli Formation has formed during the middle Miocene to upper Miocene. In this period Dağkızılca Basin is probably bounded steep normal-oblique faults. The faults forming Dağkızılca Basin since Mio-Pliocene turnback their first character namely dominantly strike-slip faults and start to control the basin form. This alternation of Başpınar and Kurcaoluk Fault is contemporaneus with the start of North Anatolian Fault. Due to this IX alternation dextral deformation has started to be dominant and the basin has started to be broken up by E-W trending normal faults. NE-SW trendings folds have formed in Vişneli Formation by nearly E-W compression together with extention. With the geometrical calculation it is estimated that the a shrink of 9% has formed due to dextral shear strain. On the other hand E-W trending listric faults in Dağkızılca Basin have caused the formation of alluvial fan deposits of Pliocene age. This mechanism in which lateral-slip is dominant and this lateral slip tectonic dominated mechanism which has continued up to recent has probably effected and has gave lateral slip component to Kemalpaşa Fault leading offsets seen especially around Savanda Creek. As a result, that the area that covers Pınarbaşı, Kavaklıdere, Kemalpaşa, Dereköy, Cumalı ve Dağkızılca villages on the scale of 1/25 000, it is defined the relation between the Bornova Flisch Zone and the Menderes Massive is represented by a transform fault. Başpınar Fault that constitutes the northern boundary of both Bornova Complex and the Dağkızılca basin is a dextral strike-slipe faultand still active today. Moreover the other boundary of he basin is controlled by a dextral oblique fault. Kurcaoluk and Başpınar Faults are determined and firstly named in this study. Although these faults had been showed different character during an episodes at the beginning of the Neotectonic Period, they are " Ghost Structures" playing an important role in the forming of Dağkızılca Basin. Kemalpaşa Fault is described and named firstly, which forms the northern boundary of Bornova Complex with Quaternary sediments. This fault was also a normal fault at the beginning of the Neotectonic period and then it has an oblique character during Late Miocene- Pliocene. The Formation mechanism and conditions of the Neogene deposits that locate between two tectonic units (Borbova Complex and Menderes Massive) has been determined. These basin named as Dağkızılca Basin has opened as a graben at the beginning of the Neotectonic period, but later it is effected by strike-slip faults after the end of Miocene that is why it is not a graben basin today. The faults that controll the secondary forming basin in the study area had a lateral! ofsett after late Miocene and this event has resulted the narrowing of the basin in the rate of 9 %. This model may be applied to the similar basen in western Anatolia. The offset amount of the faults maybe determined by flattening of the large scaled folds. In addition apart from the conclusions mentioned above that the movementof North Anatolian Fault has resulted the changing character of most x structures in the study area, and has considerably controlled thhe evolution of the area. The kind of basins which cut the E-W trending basins in west Anatolia has probably formed by lateral slip tectonics. Thus, the faults controlling the E-W trending basins may be changed their character by lateral-slip tectonics.