Gediz Graben Research Articles

The importance of heritage roads on the development of Western Anatolia and Izmir

Topographic corridor passing the heritage roads is one of the main factors of the social and economic development in Western part of Turkey. The grabens forming a lowlands named Buyukmenderes, Kucukmenderes and Gediz grabens provide the transportation easily east-west direction between coastal belt of the Aegean Sea and the inland part of the Anatolia. For example the Sardes State owes the existence of the Gediz graben naturally way extending between Gulf of Izmir and the inland part of the Anatolia. The gold obtained from the Menderes masse supported the richness of this state. In historical process Royal Road or King Road played an important role in this richness.Indeed during the historical times the roads named Royal Road (King Road), Silk and Spices (baharat) roads passed along the mentioned grabens. The trade items had been transported via the caravans along the grabens. On the other hand, the depressed areas of the Aegean Sea also fit the natural harbors such as Izmir (Smyrna), Ephesus, Phokaia, Klozomenai and Cesme. These harbors are shelters areas protecting from the severe winds. The suitable situation of the grabens caused the railway construction between Izmir harbor and Aydın. The agricultural products obtained from the fertile agricultural lands in the grabens exported from the Izmir harbor. These trade activities have contributed the fast economic development of the Izmir Gulf and its hinterland. The Royal Road, Silk Road, Spice Road and railways connecting inland part of the Anatolia and the harbors along the Aegean Sea have contributed not only the trade developments but also the agricultural heritage of humanbeing in Izmir and in the Western Anatolia region. In this study, it is discussed these ways in terms of the development of the West Anatolia and Izmir. And it is emphasized that these roads should be evaluated as a tourism product in terms of heritage tourism.

Structural evolution of the Gediz Graben, SW Turkey: temporal and spatial variation of the graben basin

ABSTRACTThe structural evolution of the Miocene to Recent Gediz Graben is intimately related to the evolution of its southern margin. This margin is shaped by a time‐transgressive, composite structure that possesses flat‐ramp geometry with three separate dip domains: a low‐angle shallow segment; a steeper middle segment; and a low‐angle deeper segment. This geometry was probably produced by one of two mechanisms, which operated perpendicular to the general trend of the graben, resulting in gradual back‐rotation followed by abandonment of the shallow segment as it was dissected by the high‐angle normal fault(s). The geometry of the southern margin structure is not simple along‐strike. It includes broad undulations and discrete fault segments, developed by large‐scale fault growth processes through segment linkage. The along‐strike growth of the southern margin‐bounding structure is responsible for the composite character of the Gediz Graben and controls the observed stratigraphic variability. Two sub‐basins aligned with the major segments of the southern graben margin structure have been investigated. The Salihli and Alaşehir sub‐basins comprising 3000 m sedimentary thickness are separated by an intervening basement high, that is covered by a thin veneer of post‐Miocene sediments. The two sub‐basins, which evolved as isolated basins during most of the graben history, amalgamated during post‐Miocene time to form the composite configuration of the graben. There is a general east to west trend of growth for the Gediz Graben.

Geology of Neogene basins of Buldan-Sarıcaova region and their importance in Western Anatolia neotectonics

The Buyuk Menderes and Gediz (Alasehir) grabens are two significant segments of the Western Anatolian extensional province. They merge around Buldan-Saricaova in the east. Outcropping Neogene sedimentary units in this area display a rather complex structure. This paper summarizes the importance and meaning of the data obtained during a detailed investigation of the Neogene units and aims to improve our understanding of the neotectonic evolution of Western Anatolia. The Buldan-Saricaova Neogene sequence is composed of three different sedimentary units: (1) the Lower Unit, (2) the Middle Unit, and (3) the Upper Unit. The Lower Unit crops out on the Buldan horst which is located between the Buyuk Menderes and Alasehir grabens. The sequence starts as a coarse conglomerate and sandstone (Isalar Formation) and continues as lagoonal-lacustrine mudstone, interbedded with coal seams and shales (Bostanyeri Formation) and also with lacustrine limestones. The age of this succession is Lower-Middle Miocene. The development of the basin is structurally controlled by NNW-trending normal faults. The Middle Unit begins with a conglomerate–mudstone sequence (Kizilburun Formation), followed by a sandstone–mudstone–marl sequence (Saraykoy Formation). A lacustrine limestone–marl unit occurs at the top (Aktepe Formation). Some thin gypsum lenses and layers are observed in the Saraykoy Formation. The unit contains some brackish-water fossils. The rocks of the Middle Unit crop out mostly at the low altitudes of the Buldan horst, i.e. the southeast piedmont, around the junction of the Buyuk Menderes and the Gediz grabens. The Middle Unit was deposited in fluvial and lacustrine environments during the Late Miocene–Pliocene period. These rocks were formed in response to the uplift of the Buldan horst. The Upper Unit, which is composed of conglomerates, was deposited within the Buyuk Menderes Graben–Gediz Graben depressions as alluvial fill.

Evolution of the Miocene sedimentary fill of the Gediz Graben, SW Turkey

The Gediz Graben is a continental extensional basin filled with Miocene to Recent sediments. The evolution of the graben can be expressed in terms of two phases: (i) Miocene half graben phase; and (ii) post-Miocene graben phase. The Miocene half graben phase was governed by the southern margin structure evolution of which significantly controlled the stratigraphic variability in the basin. Alluvial, fluvial and lacustrine systems developed in the graben as a function of distance to the southern margin. Thus, alluvial deposits with coarse-grained facies dominate the southern margin and grade into finer fractions of fluvial and/or lacustrine deposits to the north. This depositional architecture repeated three times during the Miocene and deposited Alaşehir, Çaltılık and Gediz formations. These formations depict distinct thickness and grain size decrease from south to north to emphasize the half-graben configuration for the favour of the southern margin. The post-Miocene graben phase started with the faulting of the northern margin. This resulted in relatively balanced partitioning of the subsidence between the two margins although the preceding asymmetry was inherited by the graben. Sediment influx became bipolar and alluvial fan systems developed along the both margins.

Pattern of normal faulting in the Gediz Graben, SW Turkey

Hanging-wall deformation of the fault systems controlling the southern margin of the Gediz Graben were investigated separately within the Plio-Quaternary and Neogene (predominantly Miocene) deposits of the graben fill. Fault styles observed in both packages share many similarities in terms of geometry and comprise conjugate fault sets that show clustering of strike orientations predominantly around WNW–ESE but also SW–NE and NW–SE directions. The main difference between the two units is observable in terms of fault dips and rake of the slickenside lineations measured on the exposed fault planes. Both measurements show a uni-modal distribution for the Plio-Quaternary deposits but a tri-modal distribution for the Neogene deposits. This variation is probably related to the geometrical modification of the older faults by the process of domino style back-rotation in the hanging wall of higher order faults. Similarities among the two units are not limited to geometrical aspects of the fault systems but also counts for the orientation of the principal stress axes that controlled the deformation during the deposition of each sedimentary package. Inversion of the fault-slip data showed that approximately N–S-oriented extension, which varies in the range of NNW–SSE and NNE–SSW, controlled the faulting during the accumulation of the entire graben fill, with almost no evidence of change in the state of stress during the graben evolution. However, some heterogeneity, in terms of stress field, is observable among the fault systems formed within the same time frame. This heterogeneity is probably related to poorly defined direction of extension in the graben. Indeed, low ϕ-ratio in the order of 0.25 suggests that ( σ 2) and ( σ 3) are close in magnitudes and the direction of extension is not well-constraint with a potential of ( σ 2)/( σ 3) axes permutations. Local stress field anomalies related to fault segment interaction could also contribute to the observed heterogeneity.

Folding of the Gediz Graben Fill, SW Turkey: Extensional and/or Contractional Origin?

Folds constitute a significant part within the dominantly extension-related deformation pattern of the Gediz Graben and their origin either extensional or contractional has been the subject of debate. Field and subsurface data presented in this paper suggest that folds of contractional and extensional origin coexist in the graben-fill sediments. Contractional folds are predominantly observed within the Alasehir formation. A north vergent, plunging, asymmetrical to overturned geometry characterizes these folds and they are commonly observed in association with south dipping both thrust and reverse faults; the presence of thrust/reverse faults in the Gediz Graben is documented for the first time here. Fault data suggest an approximately N–S direction of compression that has governed the contractional deformation. Yet the limited distribution of these structures prevents to relate them with confidence to a regional deformation phase. Extensional folds occur in association with normal faults either as structures longitudinal or transverse with respect to the general graben trend. Transverse folds are a very common within the buried graben block, owing to the lateral displacement gradients (lateral difference in offset) on the individual fault segments along the southern margin of the graben. Synclines and anticlines have formed at displacement maxima and minima, respectively. Thickness of strata increases at synclines and decreases at anticlines, thus indicating the syn-depositional origin of the folding.

Origin of petroliferous bitumen from the Büyük Menderes–Gediz geothermal graben system, Denizli – Sarayköy, western Turkey

The KB-5 well is located at the intersection of the geothermally active Menderes and Gediz graben systems in western Turkey. Significant volumes of “petroleum-like material” (PLM) with its associated thermal water (120 °C) erupted onto the surface during drilling from a depth of 120–132 m (i.e., from the claystone and marl-rich Early to Middle Pliocene Kolonkoya formation). The purpose of this paper is: (1) to characterize this PLM, (2) to assess the source characteristics from which the PLM was likely generated, and (3) to recognize the generation mechanism considering the geothermal-gradual versus the hydrothermal-rapid processes. Analytical organic geochemistry using thin layer chromatographic separation followed by gas chromatography–mass spectrometry (GC–MS) was carried out. The PLM is composed primarily of polar NSO compounds + asphaltenes (77%). This feature is similar to hydrothermal petroleums (e.g., Calcite Springs, Yellowstone National Park, Wyoming). The PLM shows n-alkanes ranging from n-C 19 to n-C 38 (i.e., with a maximum at n-C 30) but n-alkanes are depleted in < n-C 19. An absence of acyclic isoprenoids (pristane and phytane) and considerably large UCM (unresolved complex mixture) indicate that the PLM has been subjected to a moderate degree of alteration possibly by the accompanying hot geothermal waters. The source specific biomarkers [i.e., low C 29NH/C 30H ratio; presence of gammacerane and 18α( H)-oleanane; high C 35/C 34 homohopane ratio and ββ-C 29 sterane concentration; n-C 28 < n-C 27 < n-C 29; C 28 < C 27 < C 29ααα R steranes; %C 29ααα R > %C 27ααα R] suggest that the PLM is a petroleum and was most likely generated from a Tertiary source rock with a carbonate-clay-rich lithology. The source organic matter was predominantly terrestrial and bacterial detritus deposited in relatively saline – anoxic environmental conditions. Maturity sensitive biomarker parameters (i.e., T m > T s; C 29 sterane 20 S/(20 S + 20 R) = 0.35; C 32 hopane 22 S/(22 S + 22 R) = 0.57; low diasterane/regular sterane ratio) correspond to a maturity level of approximately 0.50–0.60% R o. This level of maturation could not be reached by such a young (Upper Miocene–Lower Pliocene) and shallow sedimentary column (max. 600 m) in the absence of “instantaneous” hydrothermal activity. PAHs are not detectable, but series of alkylbenzenes, alkyltoluenes, alk-1-enes and triaromatic steranes are present. The lack of organic richness and maturity in the drilled section of the KB-5 well indicates that the petroleum was generated in the deeper sections of the formation. The temperature profile of the well and composition of the hydrocarbons in the petroleum suggest that the temperature of the hydrothermal activity during hydrocarbon generation was <180 °C.

Evolution of the Large-scale Active Manisa Fault, Southwest Turkey: Implications on Fault Development and Regional Tectonics

This paper aims to illustrate and discuss mechanism(s) responsible for the growth and evolution of large-scale corrugated normal faults in southwest Turkey. We report spectacular exposures of normal fault surfaces as parts of the Manisa Fault - a ?50-km-long northeast-ward arched active fault that defines the northwestern edge of the Manisa graben, which is subsidiary to the Gediz Graben. The fault is a single through-going corrugated fault system with distinct along-strike bends. It follows NW direction for 15 km in the south, then bends into an approximately E-W direction in the northwest. The fault trace occurs at the base of topographic scarps and separates the Quaternary limestone scree and alluvium from the highly strained, massive bed-rock carbonates. The fault is exposed on continuous pristine slip surfaces, up to 60 m high. The observed surfaces are polished and ornamented by well-preserved various brittle structural features, such as slip-parallel striations, gutters and tool tracks, and numerous closely spaced extension fractures with straight or crescentic traces. The rocks both in the footwall and hanging-wall of the fault possess a well-developed fault rock stratigraphy made up, from structurally lowest to the top, of massive undeformed recrystallized limestone, a zone of cemented breccia sheets, corrugated polished slip planes, and first brecciated, then unbrecciated scree. The observed slip surfaces of the Manisa Fault contain two sets of striations that suggest an early phase of sinistral strike-slip and a subsequent normal-slip movements. The first phase is attributed to: (i) approximately E-W-directed compression that commenced during either (?) Early-Middle Pliocene time or (ii) the current extensional tectonics and consequent modern graben formation in southwest Turkey that initiated during the Plio-Quaternary. During this period, the Manisa Fault was reactivated and it became a major segment. Stress inversion of fault slip data suggests that southwest Turkey has been experiencing multidirectional crustal extension, with components of approximately N-S, E-W, NE-SW and NW-SE extension. Following the reactivation, the inherited fault segments were connected to each other through interaction, linkage and amalgamation of previously discontinuous and overlapping smaller stepping adjacent faults. Linkage was via the formation of new connecting (breaching) fault(s) or by curved propagation of fault-tips. The result is a single through-going corrugated fault trace with distinct along-strike bends. The final geometry of the Manisa Fault is thus the combined result of reactivation and continuing interaction between previously discontinuous segmented fault traces.

INV2P5DSB—A code for gravity inversion of 2.5-D sedimentary basins using depth dependent density

A program, INV2P5DSB, has been developed to simultaneously estimate the depth of a 2.5-D sedimentary basin and regional background from observed gravity anomalies. The density contrast is assumed to be varying parabolically with depth above the basement interface. The main program is supported with two subroutines GRAV2P5D and SIMEQ and a function GPRM. The analysis of gravity anomalies due to a synthetic model of a 2.5-D sedimentary basin with and without regional background illustrates that the code is insensitive to regional background. Interpretation of gravity anomalies over the Gediz graben, Western Anatolia with parabolic density function yields geologically plausible model.

Seismotectonics of western Turkey from high resolution earthquake relocations and moment tensor determinations

We have relocated 364 earthquakes in western Turkey between 2002 and 2003 using more than 45,000 accurate P and S differential travel‐times. We also have determined moment tensors for 71 of these earthquakes using their broadband regional waveforms. After relocation the events are highly concentrated in three clusters and delineate two nearly vertical faults. Their strikes agree with the strike of one of the fault planes of the averaged fault‐plane solution of the cluster, which allowed us to pick the true fault plane and the slip direction. We identified a NNW‐striking left‐lateral strike‐slip fault near Buldan that connects the Gediz graben in the north and the eastern end of the Buyuk Menderes graben in the south. The other right‐lateral strike‐slip fault near Izmir strikes ENE–WSW direction. Our results indicate that part of the N–S extension occurring in western Turkey is accommodated by strike‐slip faults and is accompanied by E–W shortening.

Plio-Quaternary evolution of the Küçük Menderes Graben Southwestern Anatolia, Turkey

The Küçük Menderes Graben (KMG) is part of the horst-graben system of southwestern Anatolia (Turkey), bounded by the Bozdağ horst in the north and the Aydın horst in the south. The Plio-Quaternary evolution of the KMG has been evaluated using the nature of the Miocene-Quaternary fill sediments and palaeostress analysis of slip data measured in different parts of the graben. The graben is composed of five subbasins—the Kiraz, Ödemiş, Bayındır, Dağkızılca-Torbalı and Selçuk—that are connected to each other through narrow Quaternary troughs. The Dağkızılca, Kiraz and Selçuk basins bear Miocene and younger sequences whereas the other subbasins are largely filled by Quaternary sediments. The maximum thickness of the Quaternary fill reaches about 270 m in the Ödemiş and Bayındır subbasins. The calculated slip results indicate multidirectional extension, three successive deformational periods, and possible counterclockwise rotation in the KMG during the post-Miocene period. The first phase was a strike-slip regime under N-S compression, followed by a second phase of deformation which resulted in ENE-WSW extension with strike-slip components. The final phase of deformation was NE-SW extension which constituted the final evolution of the KMG. The graben gained its present morphological configuration via the onset of E-W-trending, high-angle normal faulting imposed on the regionwide synformal structure during the Plio-Quaternary. The KMG evolved as a result of rifting during the Plio-Quaternary which followed Late Miocene unroofing of the Menderes Massif and the evolution of the Büyük Menderes and Gediz grabens.

Pleistocene mammals from travertine deposits of the Denizli basin (SW Turkey)

The Denizli basin, which is famous by its modern travertine accumulations such as that of Pamukkale is located at the eastern junction of Büyük Menderes and Gediz grabens in the western Anatolian extensional province. This basin contains large travertine formations, the origin and age of which are still debated. This study briefly recalls the tectonic and stratigraphic context of travertine occurrences and describes some vertebrate remains, which have recently been recorded in travertines. The material mainly consists of jaw fragments referred to Equus aff. suessenbornensis Wüst, 1901, lower teeth and antlers of Dama sp. and some lower teeth of Bos sp. The presence of E. aff. suessenbornensis, indicates a Middle Pleistocene age in agreement with thermoluminescense dating of the travertines.

Sediment thicknesses of the western Anatolia graben structures determined by 2D and 3D analysis using gravity data

Western Turkey is tectonically one of the most active and rapidly deforming regions of continental crust in the world. The most pronounced structural and morphological features of this region are defined by normal faulting in an E–W direction, which creates the boundaries of the Büyük Menderes, Küçük Menderes and Gediz grabens. The graben systems may have become active between 11–7 Ma and are now deeper than the surrounding topography. The Gediz and Büyük Menderes grabens exhibit negative Bouguer gravity anomalies. The Bouguer gravity anomalies increase towards the center of the Aegean Sea in a regional sense. The grabens are filled with recent sediments giving rise to relative negative gravity anomalies. These anomalies were interpreted using 2D and 3D gravity inversion techniques in order to determine the depth to the metamorphic basement. Inversion of geophysical anomalies implies fitting the observed data to theoretical anomalies possibly produced by subsurface bodies. Inversion of gravity anomalies is a non-linear problem in the sense that body parameters are not linearly related to the anomalies. Gravity anomalies caused by structures are mostly determined by a 2D model, which has an n-sided polygonal cross-section. For non-linear problems, theoretically it is more suitable to determine the parameters of the structure by a series of juxtaposing prisms or vertical dykes extending to infinity, rather than using a single n-side polygonal model. The depths to the top surfaces of a rectangular prisms with infinite depth represent the relief of the basement. The basement relief can be computed on the basis of density contrast if the reference depth is assessed. As a result of 3D analysis of the Bouguer gravity map, the maximum thickness of sedimentary cover appears to be more than 2.0 and 1.5 km for the Gediz and Büyük Menderes grabens, respectively. Towards the Sarayköy-Kızıldere area, the sedimentary thickness cover thickens to more than 2.0 km. 2D analysis of the Bouguer gravity profiles indicate that the maximum thickness of the sedimentary cover is between 2.5 and 3.5 km in the Büyük Menderes graben, and between 0.5 and 2.0 km in the Gediz Graben.

Rare earth elements, yttrium and Pb isotope ratios in thermal spring and well waters of West Anatolia, Turkey: a hydrochemical study of their origin

Rare earth elements (REE), yttrium, major elements and Pb isotope ratios were determined in thermal well and spring waters, and rocks of the Büyük Menderes and Gediz grabens, Turkey, which includes the geothermal fields of Kizildere, Salavatli, Germencik, Kula and Salihli. Together with the results of short- and long-time leaching of local rocks, REE and Y and Pb isotope ratios indicate that the Palaeozoic mica schists dominantly control the REE and Y signatures of the deep-seated Na–HCO 3 waters. Marbles may also be involved, but their low REE contribution is overridden by the much higher REE and Y abundances in the mica schists. Palaeozoic gneisses can be excluded as source rocks by both Pb isotope ratios and REE leaching behaviour. The deep-seated waters either ascend rapidly in production wells and precipitate carbonate-silica scales at temperatures of about 200 °C or these waters ascend slowly to springs, become enriched in Ca 2+, Cl − and SO 4 2−, and discharge with temperatures up to 100 °C as fumaroles or hot springs. Some of these spring waters precipitate large amounts of travertine upon exsolution of CO 2. In contrast, the thermal Ca–HCO 3-type of water from Pamukkale has its source in the regional Pliocene limestones.

Analysis of Tunnel Stability: Comparison Between Continuous and Discontinuous Approaches

The Neogene Alasehir supradetachment basin in western Turkey occurs in the footwall of the modern Alaşehir–Gediz graben and is a major component of the Aegean extensional province in Anatolia that developed during the late Cenozoic exhumation of the Menderes core complex. The size, geometry, accommodation space and internal structure–stratigraphy of this basin were strongly controlled by the kinematics and interplay of four different fault generations throughout its early Miocene-Pleistocene evolution. The ~ E − W-striking, NNE-dipping (10°–30°) Alaşehir detachment fault separates the high-grade crystalline rocks of the core complex below from the Neogene deposits of the basin in the hanging wall above. The basin-parallel, synthetic and antithetic high-angle normal faults represent a block-faulting stage of the continued horizontal extension that terminated the northerly slip along the detachment surface and produced horst-graben structures in and across the basin. These faults were also responsible for the back-tilting of the basinal strata into steeper dips and the rotation of the previously formed faults into gently dipping planes. The mutually crosscutting relationships between the intra-basinal low-angle and basement-involved high-angle and normal faults indicate their contemporaneous development and operation. The NNE-striking, basin-perpendicular oblique–slip hinge faults are reminiscent of transfer (cross) faults in both continental and oceanic extension, and divide the supradetachment basin into a series of fault blocks with their own internal structure and stratigraphy. Differential uplift and exhumation of the core complex rocks along these hinge faults and the varied displacement and slip along and across them within the basinal strata caused differential extension and block-uplift, leading to the formation of local unconformities in the supradetachment basin. Significant changes in the dip directions and strike orientations of the sedimentary beds and the observed deviations from the inferred direction of maximum extension in the adjacent fault blocks resulted from rotational deformation due to hinge faulting. Fault segmentation of the Alaşehir basin as a result of extension-parallel hinge-faulting is a characteristic feature of its supradetachment basin evolution.

Discussion on the extensional folding in the Alașehir (Gediz) Graben, western Turkey

Erdin Bozkurt writes: Seyitoglu et al. (2000) described their interpretation of the broad folds exposed in the Miocene sediments—exhumed on the southern margin of the Gediz graben (western Turkey)—as products of extensional tectonics. They also concluded that present-day north–south extensional tectonics and consequent east–west graben formation in western Turkey commenced by Early Miocene and continued since then. Previously, Kocyigit et al. (1999a) provided the first ever field evidence for the presence of east–west folds in the Gediz graben and interpreted these structures as suggesting a shortlived north–south compressional deformation during the late Serravalian–late Early Pliocene times. As much of the evidence presented by Seyitoglu et al. (2000) contradicts the available literature on the origin of extensional folding, in particular rollover anticlines; and as other detailed publications on the age and origin of extensional tectonics in western Turkey and that of the east–west folds in the Gediz graben present evidence for a contradictory model(s), I would like this opportunity to describe diffculties that arise over the published evidence and interpretation of Seyitoglu et al. (2000). Tectonic significance of Sart Formation. The map pattern of various lithologies and the relationships between the structures in Figures 2 and 3 of Seyitoglu et al. (2000) are useful to drive a relative chronology of faulting. The Pliocene Sart Formation lies unconformably above the Miocene Kursunlu Formation in the hanging wall of the fault II, indicating synchronous faulting and sedimentation, i.e. the movement along FII commenced by the Pliocene. As the Sart Formation is exhumed in the footwall of fault III and FII antithetic is cut by FIII, FIII faulting must postdate Pliocene. Since the folds in extensional terrains form at the same time or just prior to the faulting, the folds in the Miocene Kursunlu Formation cannot be attributed to …

Conductivity Structure along the Gediz Graben, West Anatolia, Turkey: Tectonic Implications

Groups of grabens in west Anatolia have contrasting E-W and NE-SW orientations and are the subject of debate as to their relative ages and relationships. We investigated the E-W-trending Gediz graben and its neighboring NE-SW-trending Gördes, Demirci, and Selendi grabens, which form an important graben system representative of the region. We studied gravity data from one profile and magnetotelluric (MT) data from two profiles, 73 km and 93 km long. The data supports the hypothesis that the Gediz graben was superimposed onto the (older) NE-SW grabens. 2D gravity and MT modelling revealed an undulating graben floor, varying in depth between 500 and 3000-4000 m (gravity-MT); within the graben two apparent basins 3–4 and 1.5-2.5 km deep (gravity-MT) are separated by a subsurface horst. The residual gravity map appears to indicate the continuation of NE-SW grabens from north of Gediz graben to beyond its southern border. The MT model revealed three main zones of varying thickness within the crust. The britde upper crust comprises two zones: sedimentary fill (apparent resistivity 15-50 ohm.m) and Menderes massif basement (200 ohm.m). The third zone is highly conductive lower crust (10 ohm.m), identified by our MT modeling at an average depth of 10 km. This conductive layer was considered in conjunction with two other regional features, high heat flow values and shallow earthquake focal depths. A heat flow map shows a very high average value of 108 mWm−2 for west Anatolia and 120-300 mWm−2 for the Gediz graben area specifically, compared with the world average of 80 mWm−2. Seismological records showing shallow earthquake focal depths together with the high conductivity zone were taken to indicate a partially melted, viscoelastic lower crust.

Late Alpine evolution of the central Menderes Massif, western Turkey

The central Menderes Massif (western Turkey) is characterized by an overall dome-shaped Alpine foliation pattern and a N–NNE-trending stretching lineation. A section through the southern flank of the central submassif along the northern margin of Buyuk Menderes graben has been studied. There, asymmetric non-coaxial fabrics indicate that the submassif has experienced two distinct phases of Alpine deformation: a top-to-the N–NNE contractional phase and a top-to-the S–SSW extensional event. The former fabrics are coeval with a regional prograde Barrovian-type metamorphism at greenschist to upper-amphibolite facies conditions. This event, known as the main Menderes metamorphism, is thought to be the result of internal imbrication of the Menderes Massif rocks along south-verging thrust sheets during the collision of the Sakarya continent in the north and the Anatolide–Tauride platform in the south across the Izmir–Ankara suture during the (?)Palaeocene–Eocene. Top-to-the S–SSW fabrics, represented by a well-developed ductile shear band foliation associated with inclined and/or curved foliation, asymmetric boudins, and cataclasites, were clearly superimposed on earlier contractional fabrics. These fabrics are interpreted to be related to a low-grade (greenschist?) retrogressive metamorphism and a continuum of deformation from ductile to brittle in the footwall rocks of a south-dipping, presently low-angle normal fault that accompanied Early Miocene orogenic collapse and continental extension in western Turkey. A similar tectono-metamorphic history has been documented for the northern flank of the dome along the southern margin of the Gediz graben with top-to-the N–NNE extensional fabrics. The exhumation of the central Menderes Massif can therefore be attributed to a model of symmetric gravity collapse of the previously thickened crust in the submassif area. The central submassif is thus interpreted as a piece of ductile lower-middle crust that was exhumed along two normal-sense shear zones with opposing vergence and may be regarded as a typical symmetrical metamorphic core complex. These relationships are consistent with previous models that the Miocene exhumation of the Menderes Massif and Cycladic Massif in the Aegean Sea was a result of bivergent extension.

Tertiary evolution of the central Menderes Massif based on structural investigations of metamorphics and sedimentary cover rocks between Salihli and Kiraz (western Turkey)

Augen gneisses, mica schists, and marbles of the Menderes Massif and its sedimentary cover rocks are exposed south of the Gediz graben. The augen gneisses form the structurally lowest part of the studied lithological sequence, and are overlain by a schist complex. The structurally highest part is formed by a series of marbles. The ages of this lithological sequence range from Precambrian to Early Paleocene. Furthermore, this sequence records the tectonic evolution since the Precambrian. The sedimentary cover of the Menderes Massif consists of two groups of sediments from Early Miocene to Quaternary. The lower group, the Alasehir group, consists of Early- to mid-Miocene-aged fluvial and limnic sediments which form the lower and the upper parts, respectively. The Alasehir group is overlain by mainly fluvial sediments of the Gediz group. Both the Alasehir and the Gediz groups are separated by an angular unconformity. Six deformational phases could be distinguished within the metamorphic rocks of the Menderes Massif and its Tertiary cover. The structures which were interpreted to belong to deformational events predating the Paleocene are summarized as deformational phase D1. D1 structures were nearly completely overprinted by the subsequent deformation events. The second deformational phase D2 occurred between Early Eocene and Early Oligocene. D2 occurred contemporaneously with a Barrovian-type regional metamorphism. The third deformational phase D3 is characterized by folding of the axial planes which formed at the end of Early Oligocene. The deformational event D4 occurred during the Late Oligocene and is related to an extensional period. The deposition of the sedimentary rocks which belong to the Tertiary cover of the Menderes Massif that started in the Early Miocene was interrupted by a compressional phase (D5) during the Late Miocene. Sediments which were deposited since the Early Pliocene record structures which were related to a young extensional phase (D6). This extensional phase has continued to the Present.

The Plio-Pleistocene age of B�y�k Menderes and Gediz grabens and their tectonic significance on N-S extensional tectonics in West Anatolia: mammalian evidence from the continental deposits

The Büyük Menderes and Gediz grabens form the two main E–W trending structures in the western Anatolian extensional province. This paper concerns the dating of continental deposits within these grabens based on their small mammal content, and its implications for the stratigraphy and tectonics of the region. Four new small mammal localities yielded an Arvicolidae fauna including Mimomys cf. ostramosensis and Kalymnomys major, indicating a late Pliocene–early Pleistocene age for the deposits, related to the graben systems. The Plio-Pleistocene deposits in these localities have a discordant relationship with the older depositional systems revealing a regional disconformity in the Pliocene–Pleistocene boundary interval. The age of accessible sedimentary infills and their localization along the grabens suggest that the N–S extension produced significant effects in the Pliocene–Pleistocene boundary interval. The E–W normal faults chopped up and uplifted the late Pliocene–early Pleistocene deposits. This indicates that these grabens formed mainly during the Quaternary. Copyright © 2000 John Wiley & Sons, Ltd.