Northern Menderes Massif Research Articles

Tracing the protoliths of the garnet amphibolitic and retrogressed eclogitic slices and a conceptual tectonic model for their emplacement onto the Central Menderes Massif, Turkey: New geochemical data and laser ablation-inductively coupled plasma-mass spectrometry U-Pb zircon and rutile ages

The age, emplacement, and metamorphic history of the garnet amphibolitic and retrogressed eclogitic slices in the Menderes Massif (Eastern Aegean) have been a matter of debate since the 1990’s. Late Cretaceous garnet amphibolitic and retrogressed eclogitic slices in the Bozdağ and Çine nappes show low-angle tectonic contacts with the surrounding Early Cambrian meta-siliciclastics in the Alaşehir-Yahyaalcı and late Neoproterozoic basement rocks in the Birgi and Tire-Çamlıca Klippe in the northern Menderes Massif. Lower and upper intercept ages on the discordia diagrams of the garnet amphibolitic slices are 82 ± 230 Ma and 554 ± 14 Ma, respectively, in the Yahyaalcı-Alaşehir area of the Bozdağ Nappe; and 96 ± 260 Ma and 550 ± 13 Ma, respectively, in the Camlica-Tire Klippe area of the Çine Nappe. Retrogressed eclogitic slices give dates of 81 ± 13 Ma lower intercept and 546 ± 13 Ma upper intercept discordant ages in the Yenişehir-Kiraz area of the Çine Nappe. Lower intercept age of 81 ± 13 Ma is supported by two spots dated on metamorphic zircons showing positive Eu patterns yielding 86.0 ± 1.3 Ma concordant age. Zircon U-Pb dating on the oscillatory zoning spots are dated as 537.5 ± 1.6 Ma (mean square weighted deviation [MSWD] = 1.5, n = 41) for the garnet amphibolic slices in the Yahyaalcı-Alaşehir area (Bozdağ Nappe), 539.0 ± 1.1 Ma (MSWD = 1.4, n = 56) for the garnet amphibolite slices in the Camlica-Tire Klippe area (Çine Nappe), and 536.6 ± 2.3 Ma (MSWD = 1.7, n = 32) for the retrogressed eclogitic slices (Çine Nappe). These ages combined with Eu negative anomalies on the dated spots are evaluated as representing their magmatic crystallization ages of the protoliths. Garnet isopleth intersections and pseudosections gave pressure-temperature conditions of 14 kbar and ∼680 °C for the retrogressed eclogites, whereas garnet amphibolites display disequilibrium in whole rock scale. We propose that the age of their protoliths likely correlate with the Cadomian rift-related Early Cambrian meta-mafic dykes that were subducted beneath the İzmir-Ankara-Erzincan Neotethyan lithosphere during the Late Cretaceous. The new rutile U-Pb age of 30.1 ± 2.0 Ma supports that the tectonic slices of the İzmir-Ankara oceanic lithosphere and metamorphosed Tauride-Anatolide continental margin were emplaced onto the Menderes Massif to generate the “main Menderes metamorphic terrane” during the latest Paleocene and early Eocene.

Documenting Exhumation in the Central and Northern Menderes Massif (Western Turkey): New Insights from Garnet-Based P-T Estimates and K-Feldspar 40Ar/39Ar Geochronology

AbstractThe Menderes Massif (Turkey) is a metamorphic core complex that records Alpine crustal shortening and extension. Here, nine garnet-bearing schist samples in the Central Menderes Massif (CMM) from below the Alaşehir detachment (AD) were studied to reconstruct their growth history. P-T estimates made using a chemical zoning approach, and petrological observations, indicate garnet grew between ~6 kbar and 550°C and 7.5-9 kbar and 625-650°C. Two P-T path shapes from two samples emerged (isobaric and burial), suggesting that either separate garnet-growth events occurred, or different garnet generations from the same metamorphic event were sampled. Despite observable diffusional modification in most garnets, thermobarometric estimates for crystal-rim growth yield P-T estimates similar to those reported elsewhere in the region. Ion microprobe monazite ages, paired with textural observations, from three of the samples time early retrograde metamorphism (~36-28 Ma). To better understand Neogene extension/exhumation, K-feldspar 40Ar/39Ar ages were obtained from two synextensional granites (Salihli and Turgutlu) exposed along the AD and two from the northern Simav detachment (Koyunoba and Eğrigöz). This data suggests the Simav detachment footwall rapidly exhumed at ~20 Ma, whereas the AD experienced two periods of exhumation/cooling (~14 Ma and~5 Ma). AD ages support a pulsed exhumation model for the massif.

Crustal fluid flow in hot continental extension: tectonic framework of geothermal areas and mineral deposits in western Anatolia

Abstract Lithospheric thinning and crustal extension have shaped the Alpine orogen in western Anatolia since the late Oligocene, resulting in the denudation of one of Earth's largest metamorphic core complexes, the Menderes Massif. We review locations and characteristics of geothermal fields and of Miocene mineral deposits in the context of crustal structure and geodynamic processes. Thermal spring locations show a close spatial association with active fault zones; the largest geothermal areas are located in the widest graben and at fault intersections, but show little relation to volcanic activity. During the first stage of tectonic denudation in the Miocene, epithermal, porphyry-type gold and structurally controlled base-metal deposits formed synchronously with K-rich volcanic and plutonic complexes in the northern Menderes Massif. Depositional environments favoured the formation of lignite, sedimentary uranium and borate deposits. Throughout this phase of extension in a hot continental setting, secondary porosity caused by brittle faulting of metamorphic basement rocks provided the key pathways for fluids and magmas. Although the Menderes Massif has remained in a similar position relative to active plate boundaries from the Miocene to the present, three significant changes in subcontinental mantle dynamics affected the nature of hydrothermal flow. First, the partial removal of lithospheric mantle changed the primary source component of magmatic rocks and metals from metasomatized lithosphere mantle to asthenospheric mantle. Secondly, surface uplift and progressive crustal extension led to segmentation of the Miocene land surface along NNE–SSW- and east–west-orientated fault zones, which changed the overall structural control on crustal permeability. Finally, hydrothermal flow changed from locally magmatic driven, to focused flow of topographically and thermally driven fluids in the crust, with high background heat flow caused by regional upwelling of the asthenosphere. The Menderes Massif is a continental tectonic domain that has experienced rapid thinning of lithospheric mantle and crustal extension in an overall convergent plate tectonic setting. The tectonic and geodynamic framework for evolving hydrothermal activity in western Anatolia may be applicable to other ore-forming systems in hot, extending continental crust in Earth's history.

An extensional and transtensional origin of elongated magmatic domes and localised transfer faults in the northern Menderes metamorphic core complex, western Turkey

The northern Menderes metamorphic core complex has complex exhumation history and is one of the key localities to investigate the spatial and temporal relationships of extensional and compressional structures. Detachment faults and syn-extensional plutons are linked to a series of antiforms and synforms and the denudation of the northern Menderes Massif occurred in three stages. The first stage is related to the development of detachment faults under the consistent NE–SW-directed extension. The second stage is represented by a series of elongated magmatic domes that were oriented parallel, oblique and perpendicular to the regional extension direction. Emplacement of these asymmetrical magmatic domes appears to have been controlled by heterogeneous extension and post-dates the extensional Simav detachment fault. On the third stage, progressive heterogeneous extension that led to updoming of plutons has been finally accommodated by a localised and short-lived transfer zone, which was described as the Gerni shear zone for the first time in this study. The transfer zone is formed by a NE-striking, dextral ductile/brittle shear zone that accommodated the propagation of folds, conjugated strike-slip faults and normal- and oblique-slip faults. Mylonites associated with the transfer zone are related to the localisation of strain along the thermally weakened strike-slip fault systems by short-lived intrusions rather than to the development of regional-scale detachment faults. These structures are consistent with a transtensional simple shear model, which properly explains the evolution of extensional and compressional structures exposed in the northern Menderes core complex. Structural setting of the Eğrigöz region is somewhat similar to that of the NE-trending gneiss domes in the northern Menderes Massif and updoming of magma during late stages of detachment faulting appears to have played an important role in the exhumation of lower and upper plate rocks.

Crustal structure of the northern Menderes Massif, western Turkey, imaged by joint gravity and magnetic inversion

In western Anatolia, the Anatolide domain of the Tethyan orogen is exposed in one of the Earth’s largest metamorphic core complexes, the Menderes Massif. The Menderes Massif experienced a two-stage exhumation: tectonic denudation in the footwall of a north-directed Miocene extensional detachment, followed by fragmentation by E–W and NW–SE-trending graben systems. Along the northern boundary of the core complex, the tectonic units of the Vardar–Izmir–Ankara suture zone overly the stage one footwall of the core complex, the northern Menderes Massif. In this study, we explore the structure of the upper crust in the northern Menderes Massif with cross-gradient joint inversion of gravity and aeromagnetic data along a series of 10-km-deep profiles. Our inversions, which are based on gravity and aeromagnetic measurements and require no geological and petrophysical constraints, reveal the salient features of the Earth’s upper crust. We image the northern Menderes Massif as a relatively homogenous domain of low magnetization and medium to high density, with local anomalies related to the effect of interspersed igneous bodies and shallow basins. In contrast, both the northern and western boundaries of the northern Menderes Massif stand out as domains where dense mafic, metasedimentary and ultramafic domains with a weak magnetic signature alternate with low-density igneous complexes with high magnetization. With our technique, we are able to delineate Miocene basins and igneous complexes, and map the boundary between intermediate to mafic-dominated subduction–accretion units of the suture zone and the underlying felsic crust of the Menderes Massif. We demonstrate that joint gravity and magnetic inversion are not only capable of imaging local and regional changes in crustal composition, but can also be used to map discontinuities of geodynamic significance such as the Vardar–Izmir–Ankara suture and the West Anatolia Transfer Zone.

Complete Alpine reworking of the northern Menderes Massif, western Turkey

This study focuses on the petrology, geochronology and thermochronology of metamorphic rocks within the northern Menderes Massif in western Turkey. Metasediments belonging to the cover series of the Massif record pervasive amphibolite-facies metamorphism culminating at ca. 625–670 °C and 7–9 kbars. U–Th–Pb in situ ages on monazite and allanite from these metapelites record crustal thickening and nappe stacking associated with the internal imbrication of the Anatolide–Taurides platform during the Eocene. In addition, new 39Ar/40Ar single muscovite grain analyses on deformed rocks were performed in three localities within the northern Menderes Massif and ages range from 19.8 to 25.5 Ma. These mylonites may be related to both well-known detachments, Simav to the north and Alasehir to the south, which accommodate Oligo–Miocene exhumation of the Menderes core complex. U–Th–Pb data on monazite grains (22.2 ± 0.2 Ma) from migmatites emplaced within the Simav detachment confirm these ages.

Spatiotemporal evolution of brittle normal faulting and fluid infiltration in detachment fault systems: A case study from the Menderes Massif, western Turkey

K‐Ar dating of fault rocks coupled with hydrogen isotope analysis allows constraining the timing of brittle faulting and the influx of meteoric fluids into such fault systems. Here we apply this approach to resolve the spatiotemporal activity of three detachment‐fault systems in western Turkey and to evaluate how deep meteoric fluids infiltrated these fault systems. K‐Ar ages of cataclasites and gouges from two detachment fault systems that accomplished the bivergent extension of the central Menderes Massif suggest diachronous brittle deformation. The Büyük Menderes detachment in the south was already active at ~22 Ma, whereas the earliest brittle deformation recorded at the Gediz fault system in the north occurred at ~9 Ma. K‐Ar ages of secondary and splay faults indicate that both fault systems continued to be active until 4–3 Ma—consistent with rapid Pliocene cooling inferred from published thermochronological data. In the northern Menderes Massif, the boundary fault of the Simav graben became active at 17–16 Ma, after the end of faulting on the Simav detachment. Hydrogen isotope (δD) values of −109‰ to −87‰ for fault gouges, cataclasites, and mylonites document that meteoric fluids infiltrated the upper crustal normal faults and penetrated into the detachments and the uppermost levels of their mylonitic footwalls. This explains the ubiquitous retrogression of biotite to chlorite in extensional shear zones and the growth of chlorite in detachment‐related cataclasites. Our results document that brittle normal faults were active over ~20 Ma of the extensional history and provided effective pathways for meteoric fluids.

Episodic two-stage extensional evolutionary model for southwestern Anatolian graben–horst system: New field data from the Erdoğmuş-Yenigediz graben (Kütahya)

The study area is the Erdoğmuş-Yenigediz graben, located along the western section of the Akşehir-Simav normal fault system in western Turkey. The Erdoğmuş-Yenigediz graben development commenced on the erosional surface of the northern Menderes Massif, under the control of several normal fault zones such as the Simav, Şaphane and Yelşilova fault zones during the late Early Miocene (Burdigalian). Later it gained its present-day configuration under the control of both older and younger normal faults. Three graben fills accumulated in the Erdoğmuş-Yenigediz graben. These are, from oldest to youngest, the Arıca formation of Burdigalian age; the Akdere formation of Late Miocene–Early Pliocene age; and the Erdoğmuş formation of Plio-Quaternary age. The first two fills are termed pre-modern graben fills, while the third one is named a modern (neotectonic) graben fill. The pre-modern graben fills are deformed (folded and reverse to strike-slip faulted) and overlain with an angular unconformity by the nearly flat-lying (non-deformed) modern graben fill. The Erdoğmuş-Yenigediz graben experienced three phases of deformation. These are, in turn, the first phase of extension (D1), the first phase of contraction (D2), and the second phase of extension or neotectonic extension (D3). D1 corresponds to the extensional exhumation mode of the Menderes Massif while D3 represents the rifting mode of the Southwest Anatolian graben–horst system (SWAGHS). These phases of deformation are evidenced by a series of reactivated older faults, folds, overturned contacts, reverse to strike-slip faults, angular unconformities, the young (neotectonic) normal faults (e.g., the Muratdağı, Dörtdeğirmen, Gümüşlü, and Yenigediz faults) and more than one overprinted sets of slip-lines recorded on both the boundary faults and in the graben fills. Analyses of slip-plane data and the folds reveal that the D1 and D2 deformation phases occurred in an approximately NW–SE direction, while the D3 deformation phase occurred in the NE–SW extension direction, confirmed by the fault plane solution diagram of the March 28, 1970 Gediz earthquake of Ms=7.2. These three phases of deformation strongly support the episodic two-stage extensional evolutionary history but precludes the uniform and continuous evolutionary model for the SWAGHS.

Long-term exhumation of an Aegean metamorphic core complex granitoids in the Northern Menderes Massif, western Turkey

The Egrigoz, Koyunoba, and Alacam plutons are located in the northern portion of the Menderes Massif, a region characterized today by large-scale extension. To gain a better understanding of their exhumation history, we acquired zircon ages, geochemical analyses, and cathodoluminescence (CL) images to search for evidence of micro- to macro-scales of deformation. The combination is a powerful means to decipher their tectonomagmatic history. In situ ion microprobe 238U/206Pb zircon ages of the granitoids range from 30.0 ± 3.9 Ma to 14.7 ± 2.6 Ma (±1σ) and indicate the plutons crystallized over ∼15 m.y. The dated zircons show CL zoning consistent with igneous crystallization and are only located adjacent to or as inclusions in biotite grains. The youngest ages are dominated by a blue color in CL, whereas a majority of older zircons are yellow. Higher Th/U contents are typically shown by zircons with black or dark green colors in CL. Most of the samples of these granitoids indicate they are magnesian, calc-alkalic and peraluminous granite to granodiorites, but variations exist, likely reflecting heterogeneity caused by magma mixing, partial melting, crustal contamination, and post-emplacement fluid interactions as evidenced by the CL images. CL images show that all samples experienced magma mixing, multiple episodes of brittle deformation, and fluid-mediated alteration. Sources for the generation of Northern Menderes Massif granitoids include simple slab induced upwelling from the subduction of the African plate along the Hellenic arc, adiabatic decompression as the northern edge of Turkey9s Anatolide-Tauride block delaminates, and upwelling asthenosphere as the continental lithosphere thins during extension. We present a model in which western Turkey is an amalgamation of stacked subduction zones that transition from north to south over time. Northern Menderes Massif granitoids document their complex geologic history in their ages, chemistry, and textures.

Surprisingly young Rb/Sr ages from the Simav extensional detachment fault zone, northern Menderes Massif, Turkey

The present paper demonstrates that exposed semi-brittle–brittle detachment fault zones, in addition to footwall mylonites and syn-extensional granitoids, can be used to date the timing of faulting and constrain the history and evolution of metamorphic core complexes. We employed Rb–Sr geochronology on micas, sampled directly from a part of the Simav detachment fault (SDF) zone in the northern Menderes Massif (western Turkey). The exposed part of the fault zone is marked by ∼3-m thick zone of low-grade mylonites/foliated cataclasites, in which mylonitic fabrics in orthogneisses are overprinted by fabrics of semi-brittle deformation. The low-grade mylonites/foliated cataclasites are characterized by coexistence of brown and green biotites. Rb–Sr ages on muscovite and brown and green biotite from the low-grade mylonites/foliated cataclasites are ca. 30 Ma, 17–13 Ma and 12–10 Ma, respectively; green biotite ages are interpreted as dating fluid-assisted deformation-induced dynamic recrystallization and suggest that a part of the SDF was active during a 12–10 Ma interval. The ca. 30 Ma muscovite ages date dynamic crystallization and probably beginning of extensional exhumation of the northern Menderes Massif. The coexistence of brown and green biotites in the same sample indicates retrogressive processes associated within a detachment faulting during which green biotites have recrystallized from primary brown biotites with an age of 19 ± 2 Ma in this area. This further means that the isotopic system became opened during faulting and that the green biotite ages therefore record the activity of the SDF. We have also dated an orthogneiss sample exposed well away from the detachment fault zone (devoid of any retrogressive processes); muscovites and biotites from this sample yield Rb–Sr ages of 45.7 ± 0.6 and 18.17 ± 0.18 Ma, respectively. The biotite age is in accord with regional biotite ages (19 ± 2 Ma) and record cooling of the footwall rocks of the detachment fault. We argue that the ca. 46 Ma muscovite age record synkinematic recrystallization during, and lend credibility to interpretation of, the prograde Barrovian-type regional Main Menderes Metamorphism as an Eocene event and that, prior to the onset of extensional detachment formation, the northern Menderes Massif (or at least the rocks we measured) experienced Eocene temperatures in excess of 500 °C to get this age. New brown biotite and secondary green biotite ages together with previously published age data argues that the footwall rocks reached to biotite cooling temperature conditions by ca. 18 Ma and stayed at similar conditions for a longer period until ca. 12 Ma. The ca. 18–12 Ma time interval corresponds to a period of tectonic quiescence during the Neogene and is attributed to the locking of SDF activity by the intrusion and rapid cooling of I-type syn-extensional granites. Secondary green biotite Rb–Sr ages indicate that the fault then become active during 12–10 Ma. Published low-temperature apatite–zircon fission track and apatite (U–Th)/He ages further suggest that displacement along the entire fault zone has continued until 8.0 ± 0.5 Ma. Combined with previous radiometric and low-temperature thermochronologic ages, the new ages argue for episodic core-complex formation and the Simav detachment fault activity between ca. 30 and 8 Ma. The data therefore argues for a complex history of core-complex formation in the northern Menderes Massif; it occurs in pulses and involves periods of alternating rapid and slow cooling/denudation rates.

Stratigraphy of the Afyon Zone around Emet (Kütahya, NW Anatolia) and geochemical characteristics of the Triassic volcanism along the northern Menderes Massif

Stratigraphy of the Afyon Zone around Emet (Kütahya, NW Anatolia) and geochemical characteristics of the Triassic volcanism along the northern Menderes Massif

Early Miocene granite formation by detachment tectonics or not? A case study from the northern Menderes Massif (Western Turkey)

The northern border of the Menderes Massif is dominated by gneiss–schist–marble association and metagranites. The high-grade units of the massif are tectonically overlain by a meta-platform sequence of the Afyon Zone and the Cretaceous-early Tertiary HP/LT Tavşanlı Zone. The Simav Magmatic Complex, comprising the shallow-seated, I-type, calc-alkaline, post-collisional Eğrigöz and Koyunoba granites, and associated subvolcanic-volcanic sequences crosscuts the Menderes Massif, Afyon Zone and tectonic contact between them. In this paper, the age relation between gneisses, metagranites of the Menderes Massif and the Eğrigöz and Koyunoba granites was evaluated by isotope dating. 207 Pb/ 206 Pb evaporation ages between 607 and 501 Ma and U–Pb zircon ages of 543 ± 10 and 30.04 ± 0.56 Ma were obtained for two gneiss samples and a metagranite in the Menderes Massif, respectively. U–Pb zircon analyses yield crystallization ages of 21.7 ± 1.0 Ma for the Koyunoba granite and 19.4 ± 4.4 Ma for the Eğrigöz granite. A cooling age of 18.77 ± 0.19 Ma for the Eğrigöz granite was obtained by Rb–Sr (whole rock, biotite) analyses. Field occurrences, geochemical characteristics and geochronological data obtained from the Eğrigöz and Koyunoba granites show close similarities with other Oligo-Miocene granitoids in northwestern Anatolia indicating that they emplaced along an E-W trending regional magmatic belt and are not individual bodies related to local, north-dipping, low-angle detachment faults as suggested in previous papers.

Tectono-stratigraphic evolution of the NE–SW-trending superimposed Selendi basin: Implications for late Cenozoic crustal extension in Western Anatolia, Turkey

Selendi basin is located in the eastern part of Western Anatolia that is the easternmost part of the Aegean extensional province. In Western Anatolia, crustal extension resulted in exhumation of the mid-crustal units (the Menderes Massif) synchronously with volcano-sedimentary basin formation. The stratigraphic and tectonic features of the volcano-sedimentary succession reflect the exhumation processes and the modes of extension. We present new stratigraphical, sedimentological, structural and 40Ar/ 39Ar age data from the Neogene volcano-sedimentary fill of the NE–SW-trending Selendi basin. The data show that crustal extension in the region occurred in four distinct episodes and accommodated the exhumation of the Menderes Massif and the basin formation throughout the late Cenozoic. Late Oligocene to early Miocene detachment faulting (the Simav detachment fault, SDF) is attributed to the first episode. Clastic sedimentation and bimodal volcanism of ∼ 20.0–17.5 Ma (the Hacıbekir group) age was formed in the hanging wall of the SDF during the exhumation of northern Menderes Massif in the footwall. During second episode, the Menderes collapse occurred and was manifest by formation of the Gediz detachment fault (GDF) during the middle Miocene. Activity on the GDF has resulted in the exhumation of the central Menderes Massif in the Bozdağ area. During this period, the hanging wall of the GDF was dissected by NE–SW-trending high-angle oblique-slip cross-faults and accommodated clastic to lacustrine carbonate deposition and syn-sedimentary bimodal volcanism of 16–15 Ma (the İnay group). The third episode is represented by formation of NW–SE-trending sinistral and NE–SW-trending dextral strike- to oblique-slip faults and associated dip- to oblique-slip normal faults during the late Miocene, indicating that the area was deformed under a strike-slip tectonic regime. The faults localized alluvial sedimentation (the Kocakuz formation) and basaltic volcanism of 7–8 Ma (the Kabaklar basalt) in the Selendi basin. The last episode commenced by the start of the Plio-Quaternary. This period is represented by the currently active N–S extensional tectonic regime that resulted in the formation of E–W-trending high-angle normal faults that controls the present-day E–W-trending graben-type basin formation (e.g., Gediz and Simav grabens) and the Quaternary (1200–60 ka) basaltic volcanism.

Cenozoic extensional tectonics of the Western Anatolia Extended Terrane, Turkey

The Western Anatolia Extended Terrane in Turkey is located on the eastern side of the Aegean Extended Terrane and contains one of the largest metamorphic core complexes in the world, the Menderes massif. It has experienced a series of continental collisions from the Late Cretaceous to the Eocene during the formation of the Izmir-Ankara-Erzincan suture zone. Based our field work and monazite ages, we suggest that the north-directed postcollisional Cenozoic extension in the region is the product of three consecutive stages, triggered by three different mechanisms. The first stage was initiated about 30 Ma ago, in the Oligocene by the Orogenic Collapse the thermally weakened continental crust along the north-dipping Southwest Anatolian shear zone. The shear zone was formed as an extensional simple-shear zone with listric geometry at depth and exhibits predominantly normal-slip along its southwestern end. But, it becomes a high-angle oblique-slip shear zone along its northeastern termination. Evidence for the presence of the shear zone includes (1) the dominant top to the north-northeast shear sense indicators throughout the Menderes massif, such as stretching lineations trending N10E to N30E; and (2) a series of Oligocene extensional basins located adjacent to the shear zone that contain only carbonate and ophiolitic rock fragments, but no high grade metamorphic rock fragments. During this stage, erosion and extensional unroofing brought high-grade metamorphic rocks of the Central Menderes massif to the surface by the early Miocene. The second stage of the extension was triggered by subduction roll-back and associated back-arc extension in the early Miocene and produced the north-dipping Alaşehir and the south-dipping Büyük Menderes detachments of the central Menderes massif and the north-dipping Simav detachment of the northern Menderes massif. The detachments control the Miocene sedimentation in the Alaşehir, Büyük Menderes, and Simav grabens, containing high-grade metamorphic rock fragments. The third stage of the extension was triggered by the lateral extrusion (tectonic escape) of the Anatolian plate when the North Anatolian fault was initiated at about 5 Ma. This extensional phase produced the high-angle faults in the Alaşehir, Büyük Menderes and Simav grabens and the high-angle faults controlling the Küçük Menderes graben.

Late orogenic crustal extension in the northern Menderes massif (western Turkey): evidence for metamorphic core complex formation

The Simav metamorphic core complex of the northern Menderes massif, western Turkey, consists of a plutonic (Tertiary) and metamorphic (Precambrian) core (footwall) separated from an allochthonous cover sequence (hanging wall) by a low-angle, ductile-to-brittle, extensional fault zone (i.e. detachment fault). The core rocks below the detachment fault are converted into mylonites with a thickness of a few hundred metres. Two main deformation events have affected the core rocks. The first deformational event (D1) was developed within the Precambrian metamorphic rocks. The second event (D2), associated with the Tertiary crustal extension, includes two distinct stages. Stage one is the formation of a variably developed ductile (mylonitic) deformation (D2d) in metamorphic and granitic core rocks under greenschist facies conditions. The majority of the mylonites in the study area have foliations that strike NNW to NNE and dip SW to SE. Stretched quartz and feldspar grains define the mineral lineation trending SW-NE direction and plunging gently to SW. The kinematic indicators indicate a top-to-NE sense of shear. Stage two formation of brittle deformation (D2b) that affected all core and cover rocks. D2b involves the development of cataclasites and high-angle normal faults. An overall top towards the north sense of shear for the ductile (mylonitic) fabrics in the core rocks is consistent with the N-S regional extension in western Turkey.

The origin and evolution of the Menderes Massif, W-Turkey: A rubidium/strontium and oxygen isotope study

The Menderes Massif, located in the Alpine orogen of Western Turkey, has three litho-structural units, a basal »gneiss core«, a »schist mantle« covering the gneiss core, and an overlying »marble mantle«. This study reports isotopic data from samples of metasediments and migmatites from the southern (Type A) and of tonalitic to granitic metaigneous rocks from the northern Menderes Massif (Type B). Type A rocks define a Rb/Sr whole rock isochron age of 502±10 Ma and an initial87Sr/86Sr ratio of 0.71174±73. This is interpreted as the age of migmatization. Type B rocks give a Rb/Sr whole rock isochron age of 471±9 Ma with an initial87Sr/86Sr ratio of 0.70684±25, which we interpret as the intrusion age. K-White micas from rock type A give an average Rb/Sr mineral age of 56±1 Ma, which can be interpreted as the formation age of the Alpine mineral paragenesis. K-white micas from rock type B give Rb/Sr mixed ages of 120–230 Ma between Alpine and Pan-African orogenies. Biotites from both rock types yield an average Rb/Sr age of 37±1 Ma, which is interpreted as an Alpine cooling age. The oxygen isotope ratios of type A rocks range from 10.4 to 14.6‰, and of type B from 8.9 to 11.8‰. The oxygen and strontium isotopic compositions together clearly distinguish rocks of types A and B. Compositions of type A rocks suggest a crustal origin: type B rocks have compositions transitional between those of crustal and mantle-derived materials.