Intra-Pontide Suture Zone Research Articles

Paleo-exhumation histories of the Sakarya and the Istanbul Zones of the Western Pontides, the Almacık Block and its surroundings, NW Turkey

ABSTRACT The Almacık Block is a tectonic sliver formed during the activity of the North Anatolian Fault Zone (NAFZ). It includes two important tectonic zones of the Western Pontides (NW Anatolia): the İstanbul and the Sakarya Zones meet along a suture zone called the Intra-Pontide Suture Zone (IPSZ). The units within the İstanbul Zone are exposed in the eastern part of the Almacık Block, whereas the rocks of the Sakarya Zone are exposed in the west. In the presented study, some of the magmatic rocks have been analysed using the zircon U-Pb method: these rocks have previously been either incorrectly or not dated. The U-Pb results have shown that some of the granitic rocks in the İstanbul Zone, which intruded into the amphibolites of the Intra-Pontide Suture Zone, have a crystallization age of 559–556 Ma. A granitoid block in the Upper Cretaceous wild flysch formed over the units of the İstanbul Zone had an age of ~566 Ma. Two distinct granitoid bodies in the Sakarya Zone were dated at 404.5 ± 3.9 Ma (Early Devonian) and 161.8 ± 0.82 Ma (Late Jurassic) ages. The palaeo-exhumation evolutions of the zones were obtained using the zircon (U-Th)/He technique (ZrHe) to understand the differences in the geological evolution of the individual zones. ZrHe ages of the samples obtained from the İstanbul Zone indicate a pronounced Early Cretaceous palaeo-exhumation period. The Middle-Upper Jurassic Mudurnu Formation in the Sakarya Zone gave ZrHe ages close to its sedimentation age, which indicates that the major part of the unit was not buried too deep to open the ZrHe closure system. Unlike those the İstanbul Zone, the main ZrHe age peaks of the Sakarya Zone are ~202, 160, 98, 74, and 52 Ma. Finally, a sample of the metamorphic rocks that were assigned to the IPSZ yielded a peak age of ~63 Ma, which indicates that the final closure of the Intra-Pontide Ocean (IPO) took place during the Early Tertiary.

Evaluation of Pb isotope systematics and metal sources of the Biga Pb–Zn Province (NW Turkey) and comparison with the Pb isotope systematics of the Rhodope Massif

This study presents the Pb isotope values of the galenas and the wall rocks related to the Pb–Zn mineralizations in the Biga Peninsula which include two different continental crusts; Sakarya Zone and Rhodope Massif. Pb–Zn mineralizations in the Sakarya fragment in Biga Peninsula have higher 207Pb/204Pb (15.677–15.710, avg: 15.688) and 208Pb/204Pb (38.895–39.000, avg: 38.935) ratios compared to the Rhodope fragment in Biga Peninsula ratios (15.650–15.709, avg: 15.668 for 207Pb/204Pb, 38.771–38.947, avg: 38.814 for 208Pb/204Pb), though the 206Pb/204Pb ratios of both crusts (Sakarya fragment in Biga Peninsula: 18.749–18.782, avg: 18.763; Rhodope fragment in Biga Peninsula: 18.750–18.839, avg: 18.802) are similar. Also, both crusts have radiogenic 207Pb/204Pb ratios indicating an orogenic source of lead. The Pb isotope ratios of the wall rocks related to the mineralizations in the Sakarya fragment were plotted in close, though different areas on uranogenic and thorogenic diagrams. Only the areas of Oligo-Miocene plutonics and Miocene volcanics, considered to be the main sources of mineralization, coincide with each other. The Pb isotope ratios of galena samples from the Sakarya fragment overlap the Permo-Triassic metamorphic rock (Karakaya Complex) area and seem to be related to the Cenozoic magmatism, both in proximity and trend, in uranogenic-thorogenic diagrams. The intense calc-alkaline magmatism occurrence that followed the closure of the Neo-Tethys Ocean appears to have played an essential role in forming the Pb–Zn mineralizations of the Sakarya fragment by leaching lead from the wall rocks. This study has utilized the Pb isotope ratios of the wall rocks related to mineralizations in the Rhodope fragment from a previous study (one sample for each reservoir). With this data, the magmatic effect on the Pb–Zn mineralizations in the Rhodope fragment is shown to be more dominant compared to those of the Sakarya fragment. In addition, through this study, it was determined that the Pb isotope ratios of two different continental crusts (Sakarya and Rhodope fragments) which came together with the Intra-Pontide suture zone followed two different trends.The Pb isotope compositions of Pb–Zn deposits in Rhodope Massif (both in the fragments of the Balkans and Biga Peninsula) were also compared in this study. According to the Pb isotope ratios, crustal thickness, and amount of the acidic rocks, the crustal materials are dominant in the western part of the massif. These findings also indicate that the western part of the massif is typical for Pb–Zn deposits whereas the eastern part of the massif is typical for the Cu–Au deposits.

Geological, Structural and Mineralogical Approach to Investigate the Evolution of Low- and very Low-Grade Metamorphic Units from the Intra-Pontide Suture Zone, Central Pontides, Turkey

Geological, Structural and Mineralogical Approach to Investigate the Evolution of Low- and very Low-Grade Metamorphic Units from the Intra-Pontide Suture Zone, Central Pontides, Turkey

First evidence for the subduction initiation and boninitic magmatism from the Armutlu Peninsula (NW Turkey): geodynamic significance for the Cadomian magmatic arc system of the Gondwanan margin

ABSTRACT The Cadomian Orogeny was active along the northern margin of Gondwanaland during the Late Neoproterozoic–Early Cambrian period. Remains of this orogenic activity are traced from Western Europe to the Himalayas, including some metamorphic basement rocks of Turkey. In this study, we provide new whole-rock and mineral chemistry, and zircon U–Pb age data for the metagabbro and metagranites in the Armutlu Peninsula, north of the Intra Pontide suture zone (IPSZ), which are the equivalent of the Cadomian basement of the İstanbul Zone (İZ). Geochemically, the metagabbros show an extreme depletion in Nb, Zr, Th, and Hf; low TiO2 contents; and high Mg# values exhibiting boninitic affinity, which are commonly associated with fore-arc settings. The metagranites are calc-alkaline and high-K calc-alkaline in character. They are slightly enriched in LREE and have similar features to shear-type plagiogranites. The yielded zircon U-Pb crystallization ages are 564 ± 4.4 Ma for metagabbros and 561 ± 9.5 Ma (Late Ediacaran) for metagranites. In this study, we provide additional information for the Cadomian basement of the İZ and the geodynamic evolution of Cadomian magmatism by discussing the tectonic setting for two geochemically contrast but almost coeval magmatic products.

Application of particle swarm optimization to 3D Euler deconvolution and 3D modeling of gravity data—a case study from Biga and Çan towns, NW Turkey

The subsurface density distribution in the NW Turkey, between Biga and Can towns, is interpreted using 3D Euler deconvolution and 3D modeling methods. Particle swarm optimization is used for the both methods to show its ability to solve a wide range of geophysical gravity problems with minor changes. During 3D modeling, the desired level of smoothness is forced using a smoothing filter, and a penalty is added to the cost function to prevent artifacts. Using these measures, the method is found to be able to recover models from gravity data successfully. 3D Euler solutions revealed possible branches of the known faults. 3D modeling suggests densities up to ρ =2.9 g/cm3 for the basement rocks and ≤2.6 g/cm3 for the sedimentary cover. According to the recovered model, 3D Euler solutions for structural index value of 0 has a better fit to the sedimentary thicknesses. The study area is placed in the Intra-Pontide suture zone, formed by the collision of the Sakarya continent with the Istanbul Zone, and the recovered model indicates that the Can-Biga Fault Zone may correspond to the Intra-Pontide suture in the region. The model also shows that the earthquakes in the region are mostly occurring near the boundaries of the low- and high-density areas. Even though the previous studies have shown this relation using conductivity models, the results indicate that the same relation can also be inferred from gravity data.

Metamorphic imprint of ridge subduction on the Neo-Tethyan ophiolites from the Saka Unit (Central Pontides, northern Turkey)

The Intra-Pontide suture zone is the northernmost ophiolite suture zone exposed in the Anatolian peninsula. It consists of several variably deformed and metamorphosed tectonic units derived from the Neo-Tethyan Intra-Pontide oceanic (IPO) basin, and its continental margins that are currently represented by the Istanbul-Zonguldak and the Sakarya terranes. Recent data suggests that the IPO was a wide supra-subduction oceanic basin whose closure began in the uppermost Early Jurassic by a north dipping intra-oceanic subduction that divided the IPO into two different oceanic areas, namely IPO1 and IPO2. The Saka Unit is a small tectonic unit exposed in the eastern portion of the Intra-Pontide suture zone in the Central Pontides, which is interpreted as a tectonic mélange produced during the intra-oceanic subduction that led to the closure of IPO1. The unit was affected by polyphase deformation and epidote–amphibolite facies metamorphism peak conditions experienced during the uppermost Middle Jurassic. Metamorphic studies and thermodynamic investigations constrain the peak pressure conditions to T ≈ 650–700 °C and P ≈ 0.9–1.3 GPa. These conditions reveal a ‘hot’ and anomalous geothermal gradient (15–22 °C/km) with respect to those of the other ophiolite-bearing units of the Intra-Pontide suture zone involved in the subduction. This anomalous gradient was herein attributed to the thermal pulse produced by the subduction of the IPO1 mid-oceanic ridge. The final re-equilibration occurred under greenschist facies conditions during the Early Cretaceous exhumation, when the oceanic lithosphere of the IPO was completely consumed and the continental collision between the Istanbul-Zonguldak and Sakarya terranes occurred.

The Intra-Pontide ophiolites in Northern Turkey revisited: From birth to death of a Neotethyan oceanic domain

The Anatolian peninsula is a key location to study the central portion of the Neotethys Ocean(s) and to understand how its western and eastern branches were connected. One of the lesser known branches of the Mesozoic ocean(s) is preserved in the northern ophiolite suture zone exposed in Turkey, namely, the Intra-Pontide suture zone. It is located between the Sakarya terrane and the Eurasian margin (i.e., Istanbul-Zonguldak terrane) and consists of several metamorphic and non-metamorphic units containing ophiolites produced in supra-subduction settings from the Late Triassic to the Early Cretaceous. Ophiolites preserved in the metamorphic units recorded pervasive deformations and peak metamorphic conditions ranging from blueschist to eclogite facies. In the non-metamorphic units, the complete oceanic crust sequence is preserved in tectonic units or as olistoliths in sedimentary mélanges. Geochemical, structural, metamorphic and geochronological investigations performed on ophiolite-bearing units allowed the formulation of a new geodynamic model of the entire “life” of the Intra-Pontide oceanic basin(s). The reconstruction starts with the opening of the Intra-Pontide oceanic basins during the Late Triassic between the Sakarya and Istanbul-Zonguldak continental microplates and ends with its closure caused by two different subductions events that occurred during the upper Early Jurassic and Middle Jurassic. The continental collision between the Sakarya continental microplate and the Eurasian margin developed from the upper Early Cretaceous to the Palaeocene. The presented reconstruction is an alternative model to explain the complex and articulate geodynamic evolution that characterizes the southern margin of Eurasia during the Mesozoic era.

U-Pb zircon geochronology of intrusive rocks from an exotic block in the Late Cretaceous – Paleocene Taraklı Flysch (northern Turkey): Constraints on the tectonics of the Intrapontide suture zone

In the Boyalı area (northern Anatolia), a thick succession of the Early Maastrichtian - Middle Paleocene Taraklı Flysch crops out. The Taraklı Flysch represents a foredeep sediment deposited during the final stage of collision between the Sakarya and Istanbul-Zonguldak continental margins, that developed as a consequence of the closure of the Intrapontide oceanic basin.The top of the Taraklı Flysch is characterized by a level of slide-block in shaly-matrix lithofacies that can be considered as the result of several fast catastrophic events predating the closure of the basin and its deformation. This level consists of slide-blocks surrounded by monomict pebbly-mudstones and pebbly-sandstones. Among the slide-blocks, the biggest one consists of quartz-monzonites and leucocratic granodiorites of Late Permian age (260.8 ± 2.2 Ma) dated by zircon LA-ICP-MS method. By comparison with the regional data, the source area of these granitoids can be identified in the Istanbul-Zonguldak terrane. This evidence suggests a new picture for the paleogeographic setting of the ultimate stage of the continental collision between the Istanbul-Zonguldak and the Sakarya continental margins. In this scenario the coarse-grained deposits of the Taraklı Flysch are supplied by an orogenic wedge, consisting of oceanic units topped by the Istanbul-Zonguldak terrane. This orogenic wedge represented the north side of the foredeep, while the southern one was represented by the still undeformed Sakarya continental margin.

Burial and exhumation history of the Daday Unit (Central Pontides, Turkey): implications for the closure of the Intra-Pontide oceanic basin

AbstractIn northern Turkey, the Intra-Pontide suture zone represents one of the first-order tectonic structures located between the Istanbul–Zonguldak and the Sakarya continental terranes. It consists of an E–W-trending assemblage of deformed and variably metamorphosed tectonic units, including sedimentary rocks and ophiolites derived from a Neo-Tethyan oceanic basin, known as the Intra-Pontide oceanic basin. One of these units is represented by the Daday Unit that consists of a block-in-matrix assemblage derived from supra-subduction oceanic crust and related deep-sea sedimentary cover of Middle Jurassic age. This setting was acquired during Late Jurassic time by tectonic underplating at a depth of 35–42 km associated with blueschist-facies metamorphism (D1 phase). The following D2, D3 and D4 phases produced the exhumation of the Daday Unit up to shallower structural levels in a time span running from the Albian to late Paleocene. The high geothermal gradient detected during the D2 phase indicates that the Daday Unit was exhumed during a continent–arc collisional setting. The tectonic structures of the Intra-Pontide suture zone, resulting from the previously described tectonic history, are unconformably sealed by the upper Paleocene – Eocene deposits. This tectonic setting was intensely reworked by the activity of the North Anatolian Fault Zone, producing the present-day geometrical relationships of the Intra-Pontide suture zone of the Central Pontides.

The Intra-Pontide suture zone in the Tosya-Kastamonu area, Northern Turkey

ABSTRACTWe present the first detailed geological map of the tectonic units documented in the easternmost branch of the Intra-Pontide suture (IPS) zone in the Tosya-Kastamonu area (Northern Turkey). The Main Map is at 1:50,000 scale and covers an area of about 350 km2. It derived from 1:25,000 scale classic field mapping and represents a detailed overview of the complexities documented in the IPS zone, a tectonic nappe stack originating from the closure of the Intra-Pontide Oceanic basin and the subsequent collision between the Istanbul-Zonguldak terrane and the Sakarya composite terrane. The map shows the orientations of superposed foliations, fold axes and mineral lineations on the basis of geometric cross-cutting relationships documented within the five tectonic units of the IPS zone and provides information on its present-day architecture resulting from activity of the North Anatolian Fault.

Erratum to: Geological setting and geochemical signatures of the mafic rocks from the Intra-Pontide Suture Zone: implications for the geodynamic reconstruction of the Mesozoic Neotethys

Erratum to: Geological setting and geochemical signatures of the mafic rocks from the Intra-Pontide Suture Zone: implications for the geodynamic reconstruction of the Mesozoic Neotethys

Geological setting and geochemical signatures of the mafic rocks from the Intra-Pontide Suture Zone: implications for the geodynamic reconstruction of the Mesozoic Neotethys

A number of suture zones exist in Turkey, which is believed to represent the closure of Paleo and NeoTethyan oceanic basins. Regarding the development of the latter oceanic entity, namely Neotethys, the geodynamic evolution of the Intra-Pontide branch, the northernmost one of a number of oceanic basins remains enigmatic. The Intra-Pontide Suture Zone in Northwest Turkey includes several tectonic units most of which are characterized by the occurrence of mafic rocks with distinct geochemical signatures. In this paper, the mafic rocks collected from four of these units (the Domuz Dag Unit, the Saka Unit, the Daday Unit and the Arkot Dag Melange) have been studied in detail along two selected transects. The Domuz Dag Unit is characterized by amphibolites, micaschists and marbles, which have been overprinted by low-grade metamorphism.The Saka Unit is in turn represented by an assemblage of slices of amphibolites, marbles and micaschists metamorphosed under upper amphibolite facies metamorphic conditions in the Late Jurassic time. In these units, the amphibolites and their retrograded counterparts display E-MORB-, OIB- BABB- and IAT-type signatures. The Daday Unit is characterized by metasedimentary and metamafic rocks metamorphosed under blueschist to sub-greenschist facies conditions. The metamafic rocks comprise actinolite-bearing schists and Na-amphibole-bearing varieties possibly derived from basaltic and gabbroic protoliths. They have a wide range of chemical compositions, displaying N-MORB-, E-MORB-, OIB- BABB- and IAT-type signatures. The Arkot Dag Melange consists of a Late Santonian assemblage of slide-blocks mainly represented by basaltic lithologies showing affinities ranging from N-MORB- and IAT- to BABB-type magmas. The geochemical signature of the studied mafic rocks indicates that the tectonic units documented along the two studied transects of the Intra-Pontide Suture Zone have been derived from a supra-subduction zone. This hypothesis corroborates the available data collected from the Ayli Dag Ophiolite Unit cropping out in the westernmost studied transect. This finding can provide new insights for the reconstruction of the geodynamic history of the Intra-Pontide domain.

Late Jurassic amphibolite-facies metamorphism in the Intra-Pontide Suture Zone (Turkey): an eastward extension of the Vardar Ocean from the Balkans into Anatolia?

The palaeogeography of Neotethys during its closure is still a matter of debate. This study provides new insights into the Neotethys closure by the discovery in the Intra-Pontide Suture Zone (Turkey) of an accretionary complex that recorded a Late Jurassic ( c . 163 Ma) amphibolite-facies metamorphism. Results are discussed in the framework of the accretionary events that occurred at the southern margin of Laurasia. The resulting picture supports a new model in which the Vardar suture zone, in the Balkans, and the Intra-Pontide Suture Zone, in Anatolia, represent remnants of the same elongate oceanic basin. Supplementary material: Analytical procedures, representative mineral compositions, geothermobarometric estimates, step-heating and in situ 40 Ar− 39 Ar data and backscattered-electron photomicrographs showing the distribution of laser spot ages on rock chips are available at www.geolsoc.org.uk/SUP18759 .

The Arkot Dağ Mélange in Araç area, central Turkey: Evidence of its origin within the geodynamic evolution of the Intra-Pontide suture zone

In northern Turkey, the Intra-Pontide suture zone is represented by an east–west trending belt of deformed and/or metamorphic units located at the boundary between the Istanbul–Zonguldak terrane to the north and the Sakarya terrane to the south. These units can be regarded as issued from the Intra-Pontide domain, whose geodynamic history is still a matter of debate. Along the Akpinar–Araç–Bayramoren geotraverse, located in central Turkey, an ophiolite-bearing mélange known as the Arkot Dağ Mélange, is well-exposed along the Intra-Pontide suture zone. The Arkot Dağ Mélange plays a key role in the interpretation of the geodynamic history of the Intra-Pontide domain and can be described as a Late Santonian chaotic sedimentary deposit consisting of an up to 1000-m-thick succession of slide-blocks of different sizes and lithologies enclosed in a sedimentary matrix consisting of shales, coarse-grained arenites, pebbly mudstones and pebbly sandstones. The slide-blocks, from a few meters to hectometers in size, are represented by metamorphic rocks (mainly micaschists and gneisses), by ophiolites (peridotites, gabbros, IAT and BABB basalts and cherts) and by sedimentary rocks (cherts, neritic and pelagic limestone, marly limestone and ophiolite-bearing turbidites). The youngest age among the slide-blocks has been provided by the ophiolite-bearing turbidites where a late Coniacian nannofossil assemblage has been found. The cherts have provided a wide range of ages from the Middle Triassic to Late Cretaceous, whereas the fossils found in the limestone indicate Late Jurassic to Early Cretaceous ages. The matrix of the Arkot Dağ Mélange, even if unaffected by metamorphism, shows deformations represented by multiple meters-thick cataclastic shear zones at the boundaries of the mélange slices or inside of them. According to its features, the source area of the Arkot Dağ Mélange was most likely a continental and oceanic thrust sheet emplaced in the Late Cretaceous onto a continental margin. The data collected from the different slide-blocks suggest that the Intra-Pontide domain was characterised by an oceanic basin opened at the latest in the Early Jurassic. The opening of the Intra-Pontide oceanic basin was followed by the development of a subduction zone with a subsequent opening of suprasubduction oceanic basin in the Middle Jurassic–Early Cretaceous. The convergence in this suprasubduction oceanic basin started at the Early/Late Cretaceous boundary by an obduction process, whereas its final closure can be regarded as Late Paleocene in age.

The Taraklı Flysch in the Boyali area (Sakarya Terrane, northern Turkey): Implications for the tectonic history of the IntraPontide suture zone

In the Boyalı area, northern Turkey, the tectonic units of the İstanbul–Zonguldak Terrane and the IntraPontide suture zone are thrust over the deposits at the top of the Sakarya Terrane, known as Taraklı Flysch. It consists of Early Maastrichtian–Middle Paleocene turbidite and mass-gravity deposits, whose source mainly corresponds to the İstanbul–Zonguldak Terrane, and, with a lesser extent, to the IntraPontide suture zone. These deposits were sedimented in a foredeep basin developed during the convergence between Sakarya and Eurasian continental microplates. In the Late Paleocene–Early Eocene time span, the Taraklı Flysch was deformed (D1 phase) during the closure of the foredeep basin. In the Miocene time, the strike-slip tectonics (D2 phase) related to the North-Anatolian fault produced further deformations of the Taraklı Flysch.

Middle-Late Triassic radiolarian cherts from the Arkotdağ mélange in northern Turkey: implications for the life span of the northern Neotethyan branch

Moderately to well-preserved, relatively diverse Middle and Late Triassic radiolarian assemblages have been obtained from the chert slide-blocks within the Late Cretaceous mélange of the IntraPontide Suture Zone at the Pelitören village to the NE of Kastamonu- Araç in northern Central Anatolia. In this locality, chert slide-blocks are tectonically overlain by metamorphic sole of the serpentinized peridotites belonging to the IntraPontide ophiolites. The oldest radiolarian assemblages, with the middle Late Anisian and late Early Ladinian ages, were found in green cherts in a pebbly mudstone. They are underlain by a larger slide-block composed of an alternation of radiolarian cherts and mudstones with late Early and early Late Carnian radiolarians. Another slide-block with cherts and mudstones between the sub-ophiolitic amphibolite and the Carnian cherts includes the late Early to early Middle Norian radiolarian assemblages. These new data reveal that the IntraPontide basin was already open during the Middle to Late Triassic time and deep enough for radiolarian cherts to deposit. Moreover, it suggests that the IntraPontide Ocean is contemporaneous with a number of inferred Paleo- and Neotethyan oceanic basins in SE Europe and NW Anatolia, which were proposed in copious tectonic models.

Early Cretaceous closure of the Intra-Pontide Ocean in western Pontides (northwestern Turkey)

The Intra-Pontide suture is the boundary between the İstanbul and Sakarya terranes in northwest Turkey. We provide new isotopic and stratigraphical data from the Intra-Pontide suture zone, which indicate Early Cretaceous collision between the Sakarya and İstanbul terranes. These two terranes along with the Strandja Massif make up the Pontides. Metamorphic units of the Intra-Pontide suture zone are best exposed in the Armutlu Peninsula. In the eastern part of the Armutlu Peninsula, three metamorphic units crop out forming an eastward dipping thrust stack. At the base of the thrust stack there is a metaclastic-marble sequence, which is tectonically overlain by a Cretaceous subduction-accretion complex, farther up in the thrust stack there is a high-grade metamorphic unit, which represents the Proterozoic basement of the İstanbul Zone. New clastic zircon ages from the metaclastic-marble sequence indicate that deposition of the sandstones must be later than Permian (∼264Ma) possibly during Triassic. Similar Triassic metasediments are also reported in Strandja Massif. We interpret that these metasediments were deposited during Triassic along the rift flanks leading to the opening of the Intra-Pontide Ocean, which suggest a possible Early Triassic opening for the Intra-Pontide Ocean. Our new Rb–Sr mica and Sm–Nd garnet ages dates the regional metamorphism between Late Jurassic–Early Cretaceous (158–111Ma) along the Intra-Pontide suture zone, similar ages are also reported in the Strandja Massif. The metamorphic rocks of the Intra-Pontide suture are unconformably overlain by Campanian–Ypresian clastics. The collision between the İstanbul and Sakarya–Strandja terranes has occurred during Early Cretaceous and the Proterozoic basement of İstanbul terrane was reheated during this collision.

The Armutlu Network: an investigation into the seismotectonic setting of Armutlu–Yalova–Gemlik and the surrounding regions

Armutlu Peninsula is in the Marmara Region of Turkey, located at the western end of the 1999 Kocaeli rupture. Armutlu peninsula is believed to be adjacent to the Intra-Pontide Suture Zone, or even to be a part of it. This zone has a key role for the understanding of the neo-tectonic features of this region and the interactions between high seismicity with high thermal activity and neo-tectonic faults that have originated through the ongoing movement of the two branches north and south of Armutlu. A horst and graben structure appears in this region, whereby the Armutlu Peninsula represents a horst between two branches of the North Anatolian Fault System, which results in a complex dextral zone. To understand the relationships among the micro-earthquake activity, the hydrothermal activity, and the tectonic structure of the region, the Armutlu Network (ARNET) was installed. ARNET aims to monitor the chronological evolution of the seismicity, and to investigate the deformation of the Armutlu Peninsula, and possible interactions between seismic waves and pore-pressure variations in the geothermal systems. The Armutlu–Yalova–Gemlik region has a very complicated tectonic structure, and it has scattered micro-earthquake activity. The upper part of the crust includes a low-velocity zone that conforms to present tectonic activity and the brittle deformed metamorphic rocks. Recent seismic activity has been confined to Gemlik Bay, and the Yalova–Termal region. Therefore, special attention is needed to monitor the seismic activity in these regions, to understand the likely and forthcoming larger event(s) in the Marmara Region. We believe that this region will have an important role in our understanding of the formation of the next larger earthquake at the western extension of the North Anatolian Fault system.

Reply to discussion contribution by A. Elmas and E. Yiğitbaş on “Tectonic evolution of the Intra-Pontide suture zone in the Armutlu Peninsula, NW Turkey” by A.H.F. Robertson and T. Ustaömer [Tectonophysics 381 (2004) 175–209

Reply to discussion contribution by A. Elmas and E. Yiğitbaş on “Tectonic evolution of the Intra-Pontide suture zone in the Armutlu Peninsula, NW Turkey” by A.H.F. Robertson and T. Ustaömer [Tectonophysics 381 (2004) 175–209

Comment on ‘‘Tectonic evolution of the Intra-Pontide suture zone in the Armutlu Peninsula, NW Turkey’’ by Robertson and Ustaömer

Comment on ‘‘Tectonic evolution of the Intra-Pontide suture zone in the Armutlu Peninsula, NW Turkey’’ by Robertson and Ustaömer