Eskiçine Ve Kafaca Arasında Menderes Masifi'nin Jeokronolojisi, Jeokimyası, Yapısal Jeolojisi Ve Evrimi

Abstract

Menderes Masifi' nin güney kesiminde, Kafaca-Eskiçine köyleri arasında yer alan inceleme alanında başlıca 3 petro-tektonik topluluk yer almaktadır. Bunlar güneyden, kuzeye doğru, güney topluluk, makaslama zonu ve kuzey topluluktur. Bu topluluklar kuzeye verjanslı bu yapısal düzenlenim içinde güneyden kuzeye üst üste durmaktadırlar. Kuzey topluluk olarak nitelendirilen grup, gnays ve lökogranitlerden oluşmaktadır. Gnayslar inceleme alanının oldukça büyük bir kesimini kaplamaktadır ve inceleme alanında temeli oluşturur. Çoğunlukla gözlü olmak üzere yer yer porfiroblastik ve granitik gnays karakterindedir. Lökogranitler makaslama zonu ile gnayslar arasında yer alır ve yaklaşık KD-GB doğrultulu olarak gnays ve metasedimentlerin dokanağına paralel devam ederler. Makaslamaya bağlı olarak gelişen lökogranitler içice sokulmuş bir kompleks görünümde olup hem makaslama zonunu hem de gnaysları keser. Güney topluluk ise, alttan üste doğru makaslama zonu ve metasedimentlerden oluşmaktadır. Metasedimentler çoğunlukla kuvarsit, mikaşist ve mermer ardalanmasından oluşmaktadır ve yapısal olarak makaslama zonunun üzerinde yer alır. Makaslama zonu ise yapısal olarak metasedimentlerin altoda yer alır ve genel olarak metasedimentler ile gnaysların yapmış olduğu dokanağa paralel devam eder. Çoğunlukla gametçe zengin metasedimentlerden oluşur. Gnayslar, mineralojik ve jeokimyasal verilere göre granitik bir kayanın amfibolit üst fasiyesinde metamorfizmaya uğramış halini temsil eder. Lökogranitler ise, makaslamaya bağlı olarak gelişmiştir ve post-tektonik karakterlidir. Metasedimentlerin mineralojik bileşimleri, kayanın yeşil şist alt fasiyesinde metamorfizmaya uğradığım gösterir. Metasedimentlerde, makaslama zonundaki deformasyona bağlı olarak gelişmiş yaygın basit makaslama yapılan vardır. Makaslama zonu içinde bulunan kayalardaki genel mineral bileşimine göre sözkonusu kayalar, amfibolit alt fasiyesinde metamorfizmaya uğramışlardır. Makaslama zonunda gözlenen deformasyon oranı, makaslama zonundan yapısal olarak hem üst, hem de alt kesimlere gidildikçe düşüş gösterir. Yukarıda belirtilen saha ve petrolojik verilere göre, bölge bir gerilme sistemi içinde evrim geçirmiştir. Buna bağlı olarak sünek bir makaslama zonu gelişmiştir. Bu makaslama zonu ile derinde olan gnayslar yüzeye çıkmıştır. Bu özellikler Menderes Masifi'nin en azından güney kesiminin bir çekirdek kompleks olarak ortaya çıktığını gösterir.

The high grade metamorphics of the Menderes Massif have an roughly elliptical outcrop which exhumed due to continental extension, across 40 000 km in western Anatolia. To the south these metamorphics dip below the Lycian Nappes, to the north-northwest and northeast they are tectonically overlain by the Izmir-Ankara Neo-Tethyan suture zone and the Afyon Zone respectively. To the southwest the massif connects with the Attic-Cycladic Massif in the central Aegean. In the southern sector, the Menderes Massif between Eskicine (Çine-Aydm) and Kafaca (Yatağan-Muğla) has three main lithological units, a basal gneisses, schists which covers the gneisses and the Irmadan shear zone. Between gneisses and schists, there is a ductile shear zone which can be recognized as a highly deformed, mylonitic amphibolit facies metasediments and young leucogranites which is intruded into the adjacent hangingwall shear zone, during the mylonitization. This boundary was interpreted as a major unconformity, the "Supra-Pan-African unconformity"(Şengör et. al., 1984). The origin of the gneisses has been subjected of debatable for years. Some of the previous researchers have believed the origin of the gneisses is sedimentary (Schuiling 1962, Başarır 1970 and 1975, Dürr 1975, Çağlayan et. al. 1980, Öztürk & Koçyiğit 1983, Şengör et al. 1984 and Satır & Friedrichsen 1986), however granitic origin for the gneisses has also been suggested (Graciansky 1965, Konak 1985, Konak et al. 1987, Erdoğan 1992 andBozkurt etal. 1993). The metasedimentary rocks are composed of alternating sequence of various metasediments such as mica schists, quartzites and marbles showing relatively low grade metamorphism. xiv The basal gneisses, shear zone and schist "mantle" exhibit a moderately dipping foliation and NNE-SSW trending mineral lineation. The kinematic indicators show pervasive non-coaxial deformation, top-to-the NNE-NE, up-dip sense of shear. Gneisses are located widely in the studied area, north of Irmadan. The gneisses have a granitoid composition and it has porphyroblastic texture. In the same way based on the field relations and geochemical data, the protoliths of the gneisses are more likely to represent syn-collision granites. Moreover all zircons which collected from the augen gneisses analysed were euhedral and their morphology suggests an also igneous origin. It shows a crude and indistinct mylonitic foliation defined by flattened quartz agregates and planar minerals, such as micas and well developed NNE-SSW- to NNW-SSE- trending stretching mineral lineation defined by the subparallel alignment of micas, stringer of quartz and the longest dimension of feldspars augen. They are characterized by large megacrysts (augen) of K-feldspar ranging from 2 or 4 cm along their longest axes. These megacrysts are wrapped with a more ductile fine- to medium grained matrix contain quartz + muscovite + biotite + K-feldspar. They also contain tourmaline, garnet, apatite, zircon, rutile. In some places augen structures and garnets become larger as much as 5 cm and 1.5 cm respectively. The gneisses contain numerous enclaves of metasediment both peripherally and internally. These enclave sizes variable from centimeters to meters and some of them are large enough to represent mappable units on shear zone klip in the north of study area. The biggest one is on the topographically higher elevations and it could be a part of the Irmadan shear zone as a klippe on the gneisses. It consists of various schists and quartzites which are very similar with the schists. In some places, especially smaller enclaves are biotite-rich concentrations. The gneisses are cut by quartz veins, coarse-grained, tourmaline bearing pegmatite dykes and aplitic dykes. Some of these veins and dykes are relatively undeformed but some of them highly deformed and has assymetric boudin form particularly quartz veins. These assymetric boudinages are also show top- to the NNE-NE shear sense as a kinematic indicator. Some of the boudinages are cut by shear plane. Moreover, quartz veins has prygmatic and assymetric fold form and their fold axes are trending approximately E-SE and S-SW. xv The gneisses show different kinemetic indicators such as assymetric feldspar porphyroclasts, S-C fabrics and extensional crenulation cleavages. Both increase in degree of the mylonitization towards to the schist and kinematic indicators suggest that there is a shear zone between gneisses and schist mantle. The schists overlies shear zone structurally and composed of alternating sequence of various schists, quartzites and marbles showing lower greenschist facies metamorphism. According to the our field relations, the relationship between the shear zone and the schists is tectonic. Although both the shear zone and the schists seem conformable. The schist unit conspicuously foliated and main deformational fabric is a well-defined by moderately dipping foliation defined by the preferred orientation of muscovite and biotite, pervasive NNE-NE- trending mineral elongation lineation, extensional crenulation cleavage and boudinage such as quartz and leucogranite boudin. Some of the quartz boudins have assymetric boudin forms that show top-to- the NNE-NE shear sense as a kinematic indicator. The thicknesses of the Palaeozoic Schists have been measured by Eşder and Sanfakıoğlu (1994) up to Mesozoic-lower Tertiary dolomitic-recrystallized limestones as being 1890 m between Irmadan and south of Kafaca village. Numerous part of Irmadan shear zone are settle on the topographically higher elevations of the gneisses as a possible klippe. These klippes are sequence of mainly garnetiferous mica schists alternating with gametiferous chlorite schists, chlorite schists. The thicknesses of the klippe were measured as being 100 m. There are abundant leucogranite boudin forms along the zone between the gneisses and the klippe. These longest axes of leucogranite boudins are parallel with the contact that indicate shear. In the schists deformation degrees decreases away from the shear zone. The upper levels of the schists (Palaeozoic metasediments) have been dated as late Permian (Bozkurt et al., 1993 and references therein: Onay, 1949, Çağlayan et. al., 1980). XVI The leucogranite is located between the gneissses and the shear zone. It shows indistinct mylonitic foliation defined by rare augen forms, flattened quartz agregates and preferred oriantation of micas. Mineral-elongation lineations in the leucogranite are approximately same with surrounding rocks and defined by alignment micas and stringers of quartzs. In most areas of lower strain their original euhedral habit is retained. This leucogranite contact is intrusive with the gneisses to the north and the shear zone to the south. The contact of the leucogranite between the gneisses is generally obscured because of the similar composition to gneisses, however in the south the leucogranite contact with the shear zone is sharp. This leucogranite is texturally and compositionally heterogeneous with more biotite-rich granite alternating with more felsic granite. It essentially consists of quartz, feldspar (plagioclase, orthoclase), muscovite and some biotite. As minor constituents it contain tourmaline, apatite, zircon, rutile and opaque minerals. Radial clusters of tourmaline and quartz veins are abundant in a zone along the margin of the shear zone. The lack of the contact metamorphic aureole both at the margins of the leucogranite and surrounding rocks and very limited alteration in adjacent wall rock indicate that the leucogranite could have been emplaced while the country rocks were still at a high temperature. According to the numerous schist enclaves in the leucogranite and leucogranitic veins, dykes and sills both in the shear zone and the gneisses the leucogranite was emplaced in the footwall of the shear zone during mylonitization. The shear zone overlies the leucogranite and underlyies the schists structurally. It consists of mylonitic amphibolite facies metasediments which is intruded locally by some sheeted younger leucocratic granite sill complex and cut by pegmatite and quartz veins. Pegmatite and quartz veins largely show boudin forms and some of them are cut by shear zone perpendicular to the boudin axes. The shear zone is conspicuously foliated and main deformational fabric is well-defined by moderately dipping foliation defined by the preferred orientation of planar minerals such as muscovite and biotite. The well-developed NNE-SSW to NNW-SSE trending stretching mineral lineation is defined by micas and stringers of quartz. xvu This shear zone has a pervasive non-coaxial deformation as a kinematic indicators which indicates an apparent thrust zone motion of the hangingwall up-dip towards to the NNE. However, the observation that lower grade metamorphics form the hangingwall of this is a deformed (tilted) extensional shear zone. At the shear zone, footwall and hangingwall high-strain zones show abundant top- to- the NNE- NE shear sense indicators.