Türkiye Jeoloji Bülteni

Abstract: The Ophiolites, which includes green and blueschists cover large areas in the Middle Sakarya Region. Theformation of the ophiolites, the age of the green-blueschists and their age of emplacement were established with somecertainity. These findings have vontributed to the understanding of the general geology of the area in the following ways:Extensive spilitic volcanism occured between Late Permian-Triassic times. Within this time period the area waseffected by tensional forces. Limestones which had been deposited on the shallower parts of the area were faulted andgenerated different size of blocks. These limestone blocks were mixed with the products of the spilitic volcanism.Serpantinized ultrabasic rocks; gabbros which were out by diabases; red pelagic ciaystones, radiolarites which wereformed in an already existed ocean basin during Triassic time were later emplaced over continental crust during Pre -Jurassic / in early Jurassic times.Clastics and volcano-clastics which had been metamorphosed to blueschist were also deposited in the Triassic sea thenthay were thrusted over continental crust during Late Triassic / very Early Liassic times.The area which had the stable shelf character particularly during Late Triassic time were again effected by thetensional system towards the Early Cretaceous time and thick clastic rocks were deposited in the outcomingdepressions.

Abstract: The present research area lies in the eastern part of the Menderes Massif, near Alaşehir-Manisa. In thisregion, three metamorphic rock groups are recognised on the basis of their lithologies and structural positions, namely,the Gneiss Complex, the Schist Complex and the Marbles.Petrographic, mineralogical and structural data indicate that the Schist Complex have undergone at least threephases of metamorphism. The first phase has been partially obliterated by the second phase which is in the amphibolitefacies. The Gneiss Complex comprises porphyroblastic, augen, massive granitic and banded gneises, and some migmatites. Geological, petrographical and chemical evidence shows that the Gneiss Complex suffered partial anatexis.For example mafic inclusions in certain gneisses of the Gneiss Complex represent restites. The Schist Complexcontains quartzo-feldspathic gneiss, garnet- mica schist, quartzite and augen gneiss.During the second phase of regional metamorphism, temperatures reached 600°C with accompanying pressures of5 kb in the Schist Complex, while 660°C with pressures of 5-6 kb in the Gneiss Complex.

Abstract: Quaternary volcanic rocks widespread in Ceyhan, Osmaniye,Yumurtalık and Haruniyeregions are investigated petrologically to interpret the type of crust from which they originated. The rocks are composed mainly of plagioclase, augite andolivine phenoerysts and ground massof similar bult chemistry. They are plateau basalts of tholeiiticcharacter with a weak alkaline affinity. The area lies in a critical region from the point of view of plate tectonics.Thus, detailed petrochemical work: has been carried  out; as a result of attachment of great importance of geochemistryof volcanic rocks to lead to plate tectonic interpretations.  Sedimentary rocks of Cenozoic age are also briefly described.

Abstract: The studied area lies between Tokat and Sivas (Yıldızeli, Karaçayır). The rocks taking place at thenorthern part of the area are mainly made of greenish shists and crystallized limestone blocks which some of themPermian aged. Metamorphic rocks outcrops at the south and they are made of two layers; calcschist interbedded withgreenish schist and marble is overlain by quartzite.Ophiolitic melange of east-west trend takes place between the units described above. Ophiolitik melange is madeof a matrix is formed of tuff, agglomerate and mainly serpantinite and having lots of shear fracture; marble, phyllite,cyristaliized limestone, radiolarite, sedimentary rocks of Upper Jurassic-Lower Cretaceous age interval, pelajik limestone of Cenomanian age, peridotite (generally werlite), gabbro, diabase blocks with in the matrix.Upper Cenonian limestone unit including olisthostromes belonging to the ophiolitic melange overlies on the ophioliticmelange unconformably at the north. According to these data, it could be concluded that the ophiolitic melangeemplaced between Cenomanien and Ltower Cenonian.Metamorphits at the south around Karaçayır and ophiolitic melange are cut by granodiorite.Eocene aged conglomerate, sandstone and argillastone alternation overlies the ophiolitic melange with an unconformity at the north. Conglomerate, limestone, sandstone and arglEastone layers generally containing Upper Cretaceousaged blocks are underlain by metamorphites unconformably around Karaçayır.Neogene units are continental and they overlies all other units unconformably.

Abstract: Four tectonic units have been differentiated in the Gevaş (Van) region. These are; (a) ophiolite association, (b)metamorphic rocks of the outer envelope of the Bitlis masif, (c) a zone of transition between theophiolite and the metamorphic rocks and, (d) the overlying sedimentary cover. Within the present sequence, theophiolite is at the bottom. The ophiolite may well be regarded as an ordered type of ophiolite. Although its membersare locally displaced / missing, the tectonic readjustment nowhere appears to have gone to form a caotic assemblage.The ophiolite is overlain by the merbles through a zone of tectonic transition. The Eocene sediments rest on the earlier rocks on a surface of angular unconformity. Following the deposition of the Eocene the primary position of the unitshave been largely disturbed and the underlying units were locally pushed over the young sedimentary rocks in a northerly direction. The thrustings have modified the original of "the zone of transition". Analyses of the structural features have enabled to reconstract the primary position of the sequence prior to the development of the thrusting.Initially the ophiolite obducted on the carbonates of the Bitlis masif. During the obduction, 500 to 1000 m thickmetamorphic aureole were formed. Metamorphic rocks of the aureole range from amphibolite at the immediate contactdownwards in greenschists which inturn grade to unmetamorphased volcanic rocks and associated sedimentaryrocks (mainly the cherts). Later the zone of transition were intensely deformed. Still it can be traced continously as abelt over the whole region at the same structural level, and contains inclusions of the high grade amphibolites.This feature as well as the evidence derived from the followings indicate that the aureole rocks were shearedto the end stage of the obduction, forming a zone of tectonic transition. At the immediate contact the aureole mineralsshow semi-plastic rotation. Going away from the contact apparent increase in deformation of cataclastic nature, displaying structural features of the same sense of deformation are observed.During Eocene, shallow water marine detritics were deposited on the preexisting rocks including the zone oftransition. Later, northward thrustings occured. This displaced the primary position of the tectonic units in the sequence. The zone of transition were folded and in some places slices of the Eocene sediments were incorporated in thezone.As a result the present position of the units, where the ophiolite at the base while the marbles on the top wereformed.

Abstract: In the upper levels of Aşıgediği Formation which constitutes the youngest unit of the Niğde Massif, viridine gneisscrops out within the marbles, together with a complex consisting of amphibolite, greenschist, meta-gabbro, serpentinite andpyroxenite. The rock, containing Mn silicates such as piedmontite and allurgite as well as viridine which is a very rare form ofandalusite, is fine-grained, banded textured, and occurs as discontinous bands and lenses.Its banded texture, high manganese content and association with the above rocks show that the protolith of viri-dinegeneiss is comparable to that of the sedimentary rocks developed around the fracture zones of modern oceans. Thus, the viridinegneiss and the equivalent rocks do not belong to the environment in which the Aşıgediği Formation has been deposited, and theyshould have been added to the sequence later.

Abstract: Investigation of the nature of stress, strain and displacement distributions in the North Anatolian Fault(NAF) zone, has been attempted on an analytical model of tha plates adjacent to the fault, utilizing the finite elementtechniques. Concentrtion of tensile stresses occurs around the eastern end of the fault zone, as a consequence of northwardmovement of the Arabian plate. Initial faulting occurs at this end, in the form, of a tensile fracture, opens and propagatesdiagonally in NE - SW direction along the East Anatolian Fault (EAF). Movements along the EAF, releases the tensilestresses originally developed at the eastern end of the NAF; and thus causes a redistribution of stresses and strains in theNAF zone. This redistribution is responsible for the subsequent ruptures, predominantly in ‘slip’ mode; and associated witha frictional strength criterion. These shear fractures initiate at the eastern end of the NAF and propagate towards west,are described as ‘progressive faulting’. Before these progressive ruptures could reach to the central portion of the fault zone;a third mode of faulting begins, again as shear fractures, at the western end of the NAF and propagates backward along thefault, towards east. This third mode of faulting is described as ‘retrogressive’. So, the proposed faulting mechanism forthe NAF, is a `progressive and retrogressive strike-slip` mechanism.The elastic strain energy accumulated in the fault zone, is largely released by these progressive and retrogressivefaultings in the eastern and western sections; and no important ruptures occur in the central section of the fault to causelarge earth-quakes. Therefore, this central section of the NAF zone, specifically between the longitudes of 33` E and 35 E,may be considered as a ‘seismic gap’. However, there are evidences of continuous creep events in the central section ofthe fault zone indicating a continuous strain energy occumulation in this area. Therefore, the possibility of a largeearthquake to occur in the future in this seismic gap area, should be seriously considered.

Abstract: Three different units which have different characteristics were identified within the Aladağ ophioliticmelange. The lowest one is called "uniform basal sequence", the middle one "olistostrome sequence" and the top unit"chaotic sequence".Gravitational mass-flow and slide mechanism were effective during the formation of the first two sections. Thechaotic section, however, was formed by block accumulationdue to tectonic activity.The Aladağ ophiolitic melange acquired its lithostratigraphic features within the Senonian basin which was formed over the Upper Triassic-Liower Cretaceous platform carbonate basement.The contact between the ophiolitic melange and the carbonates which constitute the basement of the melange isdepositional. Aladağ ophiolitic melange should be considered as an autochthonous litostratigraphic unit which acquiredits properties in the site of formation.

Abstract: A succession of marine and continental rocks which ranges in age from. Lower Eocene to Pliocene has beenwell preserved in the Sungurlu (Çorum) region of central Turkey. The Sungurlu Group consists of two marine formations.The Cevherli Formation is a turbidite sequence which has been deposited by southward prograding submarine fan.There are also olistoliths and olistostromes which are closely associated with turbidites. The Kepir Tepe Formation iscomposed of limestone, marl and lenses of conglomerate and sandstone. This formation has been deposited in a shallowwater environment.Since Late Middle Eocene time, continental sediments have been deposited in the area. The Büyükpolatlı Formation (UpperEocene-Miocene) consists of red coloured conglomerate, sandstone and mudstone. These sediments have been deposited in afluvial environment dominated by meandering rivers. The direction of sediment transportation was from northeast to southwest.The Terzili Formation is composed of alternations of gypsum, mudstone and fine-grained sandstone which have been deposited inan interior playa (continental sabkha) environment. The Büyükşeyhefendi Tepe Formation (Pontian) is composed of poorlybedded, poorly sorted conglomerate, sandstone and mudstone which appear to have been originated in an alluvial fanenvironment on the foot of the high mountain range.

Abstract: Varied aged rock units of distinct fades and different position have been defined, as a result of investigations caried out in the research area. The oldest of these rocks are the schists covering the Menderes Massif of sedimentary origin. The metamorphics are composed of various schists with metamorphic grades not exeed the green-schistfaeies, and their age is probably Sillurian. The cover schists are folloved upward by the marbles which outcrop inwider areas. It is thought that the age marbles, which appear to be conformamle with, underlying schists althoughthere is probable a stratigraphic gap between them, is Devonian.Rhyolites constitute the origin of Kocayayla metamorphics which is an autochthonous mass like the MenderesMassif. No direct connection with the Menderes Massif is not certain yet, but it may possibly be correlated with thecover-schists of the Menderes Massif. The formations starting from Liassic and continuing up to the end of Lutetian have autochthonous positions. Liassic agedDerealanı formation which commences with basal conglomerates and developes in pelitic facies, Dogger aged Akdağ formation,Upper Jurassic aged Çamoluk formation consisting of siliceous pelagic limestones from the Jurassic system. The rocks belonging toCretaceous system display normal transition with Jurassic units. Akçay for mation of Lower Cretaceous age is developed in pelagicandneritic limestone fades. These limestones are conformably overlain by the pelagic limestones of Paleocene age. Theautochthonous units terminate with red clayey limestones of Lutetian age. Resting on these are overthrustedallochthonous units ofvarious age and lithology. Emplacement age of the allochthonous units is Upper Eocene.Çağlayan formation is regressive series which is represented by lacustrine deposits. limestones exist at the base, red clays withconglomerate and sandstone interca lations comprise the Upper levels, and the bedded conglomerates derived from nearbysources are present at the top.Lithologic charecter of the rocks exposed in the research area and their distribution indicate that different sedimantary environments were existent within short intervals, and generally these environments were deepening fromeast to west.

Abstract: Peridotite, ophiolite, blueschist and marble are the major rock types northeast of Tavşanlı, In the areastudied a large peridotite massif tectonically overlies an ophiolite melange. This ophiolite melange consists of volcanic and sedimentary rocks (spilite, pyroclastie, chert, shale, pelagic limestone etc.), and lenses of serpentinite. Althoughrocks of the ophiolite melange appear unmetamorphosed in the field, a detailed petrographic study has revealed that allhave undergone an incipient high pressure/low temerature metamorphism. Bluschists sensu stricto are produced by theprogressive metamorphism of this ophiolite sequence. Two stages of blueschist metamorphism have been recognised inthe field and by petrography. In the first stage the typical paragenisis of lawsonite-sodic pyroxene-ehlorite is produced inthe metabasites. Sodic amphibole develops in the second stage through a reaction between sodic pyroxene and chlorite. Thesubsequently produced glaucophane lawsonite blueschists are the most extensive lithology in the studied area. They lieconformably on a thich marble sequence, which has undergone the same high pressure/low temperature metamorphism anddef ormation as the surrounding blueschists.