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(A) Geologic map of the Niğde area, showing major features including the Niğde Massif; the Niğde Mafic Complex and other outcrops of mafic and ultramafic rocks; and the Ulukışla and Ecemiş basins. Sample locations are shown for the three main sample populations: outcropping rocks of the Niğde Mafic Complex and associated rocks, clasts in Çukurbağ conglomerate, and cobbles on alluvial terraces. (B) Representative cross sections through the Niğde Mafic Complex (NMC): NW-SE (section A–A′) and NE-SW (section B–B′). Locations of detailed geologic maps (Figs. 6A–6D) and clast count map (Fig. 9) are indicated.
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Ophiolitic rocks derived from Tethyan seaways are abundant in Anatolia; many are in arrays that mark sutures between Eurasia, Gondwana, and continental ribbons and island arcs. Ophiolitic fragments also occur dispersed between sutures, indicating tectonic transport of possibly hundreds of kilometers. Scattered fragments of the Central Anatolian Oph...
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... There, the headwaters occupy an area were rivers of the outer slope (such as the Çakıt River; Fig. 13A) have penetrated 25-35 km into the plateau interior and dissected the northern limb of the Taurus Mountains arch. This evolution is confirmed by provenance analysis of Miocene-Pliocene fluvial sedimentary rocks (Radwany et al., 2017). The coincidence of deep incision, divide breaching, and substantial incision of the formerly closed regions makes a case for drainage integration by capture along the outer slope. ...
Continental sedimentation was widespread across the Central Anatolian Plateau in Miocene–Pliocene time, during the early stages of plateau uplift. Today, however, most sediment produced on the plateau is dispersed by a well-integrated drainage and released into surrounding marine depocenters. Residual long-term (106–107 yr) sediment storage on the plateau is now restricted to a few closed catchments. Lacustrine sedimentation was widespread in the Miocene–Pliocene depocenters. Today, it is also restricted to the residual closed catchments. The present-day association of closed catchments, long-term sediment storage, and lacustrine sedimentation suggests that the Miocene–Pliocene sedimentation also occurred in closed catchments. The termination of sedimentation across the plateau would therefore mark the opening of these closed catchments, their integration, and the formation of the present-day drainage. By combining newly dated volcanic markers with previously dated sedimentary sequences, we show that this drainage integration occurred remarkably rapidly, within 1.5 m.y., at the turn of the Pliocene.
The evolution of stream incision documented by these markers and newly obtained 10Be erosion rates allow us to discriminate the respective contributions of three potential processes to drainage integration, namely, the capture of closed catchments by rivers draining the outer slopes of the plateau, the overflow of closed lakes, and the avulsion of closed catchments. Along the southern plateau margin, rivers draining the southern slope of the Central Anatolian Plateau expanded into the plateau interior; however, only a small amount of drainage integration was achieved by this process. Instead, avulsion and/or overflow between closed catchments achieved most of the integration, and these top-down processes left a distinctive sedimentary signal in the form of terminal lacustrine limestone sequences.
In the absence of substantial regional climate wetting during the early Pliocene, we propose that two major tectonic events triggered drainage integration, separately or in tandem: the uplift of the Central Anatolian Plateau and the tectonic completion of the Anatolian microplate. Higher surface uplift of the eastern Central Anatolian Plateau relative to the western Central Anatolian Plateau promoted more positive water balances in the eastern catchments, higher water discharge, and larger sediment fluxes. Overflow/avulsion in some of the eastern catchments triggered a chain of avulsions and/or overflows, sparking sweeping integration across the plateau. Around 5 Ma, the inception of the full escape of the Anatolian microplate led to the disruption of the plateau surface by normal and strike-slip faults. Fault scarps partitioned large catchments fed by widely averaged sediment and water influxes into smaller catchments with more contrasted water balances and sediment fluxes.
The evolution of the Central Anatolian Plateau shows that top-down processes of integration can outcompete erosion of outer plateau slopes to reintegrate plateau interior drainages, and this is overlooked in current models, in which drainage evolution is dominated by bottom-up integration. Top-down integration has the advantage that it can be driven by more subtle changes in climatic and tectonic boundary conditions than bottom-up integration.
... There, the headwaters occupy an area were rivers of the outer slope (such as the Çakıt River; Fig. 13A) have penetrated 25-35 km into the plateau interior and dissected the northern limb of the Taurus Mountains arch. This evolution is confirmed by provenance analysis of Miocene-Pliocene fluvial sedimentary rocks (Radwany et al., 2017). The coincidence of deep incision, divide breaching, and substantial incision of the formerly closed regions makes a case for drainage integration by capture along the outer slope. ...
Continental sediment was widespread across the Central Anatolian Plateau in Miocene–Pliocene time, during the early stages of plateau uplift. Today, however, most sediment produced on the plateau is dispersed by a well-integrated drainage and released into surrounding marine depocenters. Residual long-term (106–107 yr) sediment storage on the plateau is now restricted to a few closed catchments. Lacustrine sedimentation was widespread in the Miocene–Pliocene depocenters. Today, it is also restricted to the residual closed catchments. The present-day association among closed catchments, long-term sediment storage, and lacustrine sedimentation suggests that the Miocene–Pliocene sedimentation also occurred in closed catchments. The termination of sedimentation across the plateau would therefore mark the opening of these closed catchments, their integration, and the formation of the present-day drainage. By combining newly dated volcanic markers with previously dated sedimentary sequences, we show that this drainage integration occurred remarkably rapidly, within 1.5 m.y., at the turn of the Pliocene.
The evolution of stream incision documented by these markers and newly obtained 10Be erosion rates allow us to discriminate the respective contributions of three potential processes of drainage integration, namely, the capture of the closed catchments by rivers draining the outer slopes of the plateau, the overflow of closed lakes, and the avulsion of closed catchments. Along the southern plateau margin, rivers draining the southern slope of the Central Anatolian Plateau expanded into the plateau interior; however, only a small amount of drainage integration was achieved by this process. Instead, avulsion and/or overflow between closed catchments achieved most of the integration, and these top-down processes left a distinctive sedimentary signal in the form of terminal lacustrine limestone sequences.
In the absence of substantial regional climate wetting during the early Pliocene, we propose that two major tectonic events triggered drainage integration, separately or in tandem: the uplift of the Central Anatolian Plateau and the tectonic completion of the Anatolian microplate. Higher surface uplift of the eastern Central Anatolian Plateau relative to the western Central Anatolian Plateau promoted more positive water balances in the eastern catchments, higher water discharge, and larger sediment fluxes. Overflow/avulsion in some of the eastern catchments triggered a chain of avulsions and/or overflows, sparking sweeping integration across the plateau. Around 5 Ma, the inception of the full escape of the Anatolian microplate led to the disruption of the plateau surface by normal and strike-slip faults. Fault scarps partitioned large catchments fed by widely averaged sediment and water influxes into smaller catchments with more contrasted water balances and sediment fluxes.
The evolution of the Central Anatolian Plateau shows that top-down processes of integration can outcompete the erosion of outer plateau slopes to reintegrate plateau interior drainages, and this may be overlooked in the currently dominant models of bottom-up integration. Top-down integration can also be driven by more subtle changes in climatic and tectonic boundary conditions.
... (1) the Central Anatolian fault zone (Koçyiğit and Beyhan, 1998), including the southern (Ecemiş) segment that is discussed in this paper (e.g., Jaffey and Robertson, 2001;Umhoefer et al., 2007;Higgins et al., 2015;Yıldırım et al., 2016); (2) the central segment of the Tauride Mountains (uplifted since the Miocene; Cosentino et al., 2012;Schildgen et al., 2012aSchildgen et al., , 2012bMeijers et al., 2018); this segment is part of the Anatolide-Tauride belt; (3) a series of metamorphic and plutonic massifs that represent the Late Cretaceous orogenic crust of the CACC (Akıman et al., 1993), including the Niğde Massif, which is part of the focus of this study (Göncüoğlu, 1982;Whitney et al., , 2003; (4) fragments of Late Cretaceous ophiolites that lie on the CACC and the Anatolide-Tauride belt (e.g., Yalınız et al., 1996;Vergili and Parlak, 2005;van Hinsbergen et al., 2016;Radwany et al., 2017Radwany et al., , 2020; (5) large sedimentary basins formed from the Late Cretaceous through the Cenozoic (e.g., from east to west the Sivas, Ulukışla, and Tuz Gölü basins) (Cater et al., 1991;Clark and Robertson, 2002;Gürer et al., 2016Gürer et al., , 2018Darin et al., 2018), across the time period of debate on the timing of collision of Arabia; and (6) the Cappadocian volcanic province (Miocene to present) (e.g., Le Pennec et al., 1994;Aydar et al., 1995;Dhont et al., 1998;Temel et al., 1998;Reid et al., 2017). The entire Central Anatolian fault zone is >700 km long and extends from the Mediterranean Sea to the eastern end of the North Anatolian fault, with a prominent bend or step in central Anatolia at the Erciyes volcano (Fig. 2). ...
... Locally the gabbro clasts are common. Based on geochemical analysis of 17 gabbro clasts, Radwany et al. (2017) suggested that the Çukurbağ conglomerates were partly derived from the Tauride ophiolites and from an unmetamorphosed or low-grade part of the central Anatolian ophiolite, which may have covered much of the Niğde Massif in Oligoceneearly Miocene time. Paleocurrent data (Jaffey and Robertson, 2005) and the facies patterns suggest that the subbasins of the Çukurbağ Formation were elongate and inward-draining along the Ecemiş corridor with the Bademdere subbasin, the largest depocenter in the study area. ...
... At the top of the Ulukıșla Basin, the Cihanbeyli Formation unconformably overlies Paleogene and Miocene rocks south of the Niğde Massif and is composed of late Miocene lacustrine sediments interbedded with volcanic tuff and fluvial conglomerate (MTA map, 2002); this unit records major drainage changes in the late Miocene to Quaternary (Radwany et al., 2017); these changes postdate the events discussed in the present study. The Cihanbeyli Formation is dated as late Miocene from 6 to 7 Ma tuffs (Meijers et al., 2018). ...
The effects of Arabia-Eurasia collision are recorded in faults, basins, and exhumed metamorphic massifs across eastern and central Anatolia. These faults and basins also preserve evidence of major changes in deformation and associated sedimentary processes along major suture zones including the Inner Tauride suture where it lies along the southern (Ecemiş) segment of the Central Anatolian fault zone. Stratigraphic and structural data from the Ecemiş fault zone, adjacent NE Ulukışla basin, and metamorphic dome (Niğde Massif) record two fundamentally different stages in the Cenozoic tectonic evolution of this part of central Anatolia. The Paleogene sedimentary and volcanic strata of the NE Ulukışla basin (Ecemiş corridor) were deposited in marginal marine to marine environments on the exhuming Niğde Massif and east of it. A late Eocene–Oligocene transpressional stage of deformation involved oblique northward thrusting of older Paleogene strata onto the eastern Niğde Massif and of the eastern massif onto the rest of the massif, reburying the entire massif to >10 km depth and accompanied by left-lateral motion on the Ecemiş fault zone. A profound change in the tectonic setting at the end of the Oligocene produced widespread transtensional deformation across the area west of the Ecemiş fault zone in the Miocene. In this stage, the Ecemiş fault zone had at least 25 km of left-lateral offset. Before and during this faulting episode, the central Tauride Mountains to the east became a source of sediments that were deposited in small Miocene transtensional basins formed on the Eocene–Oligocene thrust belt between the Ecemiş fault zone and the Niğde Massif. Normal faults compatible with SW-directed extension cut across the Niğde Massif and are associated with a second (Miocene) re-exhumation of the Massif. Geochronology and thermochronology indicate that the transtensional stage started at ca. 23–22 Ma, coeval with large and diverse geological and tectonic changes across Anatolia.
... (1) the Central Anatolian fault zone (Koçyiğit and Beyhan, 1998), including the southern (Ecemiş) segment that is discussed in this paper (e.g., Jaffey and Robertson, 2001;Umhoefer et al., 2007;Higgins et al., 2015;Yıldırım et al., 2016); (2) the central segment of the Tauride Mountains (uplifted since the Miocene; Cosentino et al., 2012;Schildgen et al., 2012aSchildgen et al., , 2012bMeijers et al., 2018); this segment is part of the Anatolide-Tauride belt; (3) a series of metamorphic and plutonic massifs that represent the Late Cretaceous orogenic crust of the CACC (Akıman et al., 1993), including the Niğde Massif, which is part of the focus of this study (Göncüoğlu, 1982;Whitney et al., , 2003; (4) fragments of Late Cretaceous ophiolites that lie on the CACC and the Anatolide-Tauride belt (e.g., Yalınız et al., 1996;Vergili and Parlak, 2005;van Hinsbergen et al., 2016;Radwany et al., 2017Radwany et al., , 2020; (5) large sedimentary basins formed from the Late Cretaceous through the Cenozoic (e.g., from east to west the Sivas, Ulukışla, and Tuz Gölü basins) (Cater et al., 1991;Clark and Robertson, 2002;Gürer et al., 2016Gürer et al., , 2018Darin et al., 2018), across the time period of debate on the timing of collision of Arabia; and (6) the Cappadocian volcanic province (Miocene to present) (e.g., Le Pennec et al., 1994;Aydar et al., 1995;Dhont et al., 1998;Temel et al., 1998;Reid et al., 2017). The entire Central Anatolian fault zone is >700 km long and extends from the Mediterranean Sea to the eastern end of the North Anatolian fault, with a prominent bend or step in central Anatolia at the Erciyes volcano (Fig. 2). ...
... Locally the gabbro clasts are common. Based on geochemical analysis of 17 gabbro clasts, Radwany et al. (2017) suggested that the Çukurbağ conglomerates were partly derived from the Tauride ophiolites and from an unmetamorphosed or low-grade part of the central Anatolian ophiolite, which may have covered much of the Niğde Massif in Oligoceneearly Miocene time. Paleocurrent data (Jaffey and Robertson, 2005) and the facies patterns suggest that the subbasins of the Çukurbağ Formation were elongate and inward-draining along the Ecemiş corridor with the Bademdere subbasin, the largest depocenter in the study area. ...
... At the top of the Ulukıșla Basin, the Cihanbeyli Formation unconformably overlies Paleogene and Miocene rocks south of the Niğde Massif and is composed of late Miocene lacustrine sediments interbedded with volcanic tuff and fluvial conglomerate (MTA map, 2002); this unit records major drainage changes in the late Miocene to Quaternary (Radwany et al., 2017); these changes postdate the events discussed in the present study. The Cihanbeyli Formation is dated as late Miocene from 6 to 7 Ma tuffs (Meijers et al., 2018). ...
The effects of Arabia-Eurasia collision are recorded in faults, basins, and exhumed metamorphic massifs across eastern and central Anatolia. These faults and basins also preserve evidence of major changes in deformation and associated sedimentary processes along major suture zones including the Inner Tauride suture where it lies
along the southern (Ecemiş) segment of the Central Anatolian fault zone. Stratigraphic and structural data from the Ecemiş fault zone, adjacent NE Ulukışla basin, and metamorphic dome (Niğde Massif) record two fundamentally different stages in the Cenozoic tectonic evolution of this part of central Anatolia. The Paleogene sedimentary and volcanic strata of the NE Ulukışla basin (Ecemiş corridor) were deposited in marginal marine to marine environments on the exhuming Niğde Massif and east of it. A late Eocene–Oligocene transpressional stage of deformation involved oblique northward
thrusting of older Paleogene strata onto the eastern Niğde Massif and of the eastern massif onto the rest of the massif, reburying the entire massif to >10 km depth and accompanied by left-lateral motion on the Ecemiş fault zone. A profound change in the tectonic setting at the end of the Oligocene produced widespread transtensional deformation across the area west of the Ecemiş fault zone in the Miocene.
In this stage, the Ecemiş fault zone had at least 25 km of left-lateral offset. Before and during this faulting episode, the central Tauride Mountains to the east became a source of sediments that were deposited in small Miocene transtensional basins formed on the Eocene–Oligocene thrust belt between the Ecemiş fault zone and the Niğde Massif. Normal faults compatible with SW-directed extension cut across the Niğde Massif and are associated with a second (Miocene) re-exhumation of the Massif. Geochronology and thermochronology indicate that the transtensional stage started at ca. 23–22 Ma, coeval with large and diverse geological and tectonic changes across Anatolia.
... A significant exception is a metamorphosed and ductilely deformed mafic complex (Niğde Mafic Complex, NMC) that structurally overlies the Niğde Massif, a metamorphic core complex largely comprising high-grade metasedimentary rocks at the southern tip of the Central Anatolian Crystalline Complex (Figs. 1, 2). Despite its higher metamorphic grade, the NMC has been interpreted as part of the Central Anatolian Ophiolite (CAO) based on the geochemical and lithologic similarity of the NMC metagabbro to gabbroic fragments of the CAO elsewhere in Central Anatolia (Floyd et al. 2000;Radwany et al. 2017). ...
... The NMC records mid-to upper-amphibolite facies metamorphism and ductile deformation, similar to conditions experienced by structurally underlying metasedimentary rocks of the Niğde Massif (Radwany et al. 2017). Because obduction of the CAO has been proposed . ...
... BZSZ Bitlis-Zagros Suture Zone, IAESZ İzmır-Ankara-Erzıncan Suture Zone, ITSZ Inner Tauride Suture Zone. Map is modified from Radwany et al. (2017) as a mechanism for metamorphism of the underlying metasedimentary rocks, it is important to determine the pressure-temperature (P-T) conditions and timing of metamorphism and deformation of the Niğde Mafic Complex and to compare these with published data from the underlying Niğde Massif metamorphic rocks. In this paper, we present new petrologic, structural, and geochronologic data to elucidate the petro-tectonic events that juxtaposed the NMC and underlying metamorphic-plutonic complex and discuss these results in the context of the regional Fig. 5a is indicated. ...
Ophiolitic fragments scattered over a wide area of Central Anatolia exhibit varying degrees of metamorphism, from unmetamorphosed to upper amphibolite facies, although geochemical similarities suggest they are all part of the Central Anatolian Ophiolite (CAO). Magmatic crystallization of oceanic crust in the CAO at ~ 91 Ma coincided with high-grade metamorphism of rocks that underlie the southern, highest grade part of the CAO, raising questions about the tectonic relationship of the ophiolite to underlying metasedimentary and plutonic rocks. New geochronology results show that the 40Ar/39Ar hornblende age of amphibolite-facies metagabbro in the high-grade metamorphic part of the CAO is ~ 87 Ma, similar to hornblende ages from amphibolite in the underlying Niğde metamorphic/plutonic massif. Biotite in a deformed quartzofeldspathic rock associated with high-grade meta-ophiolitic rocks yielded an 40Ar–39Ar age of ~ 78 Ma, similar to biotite ages from the Niğde Massif. Hornblende in gabbro from unmetamorphosed CAO yielded an older 40Ar/39Ar age of ~ 90 Ma, similar to the previously determined crystallization age of the ophiolite. These data indicate that the southern part of the ophiolite was incorporated into and therefore metamorphosed and deformed with the orogenic mid-crust now exposed in the Niğde metamorphic–plutonic complex, whereas the northern, unmetamorphosed part of the ophiolite was obducted onto the continent. This distinct difference in different parts of the ophiolite may indicate oblique collision or irregularities in the continental margin, resulting in part of the ophiolite being incorporated into the orogenic crust and subsequently exhumed and cooled with it, and another part being obducted.
ABSTRACT
The Neogene-Quaternary volcanism in central Anatolia is characterized by ignimbrite sequences, and associated
calderas have been partly dismantled and buried as a result of tectonic, volcanic, erosional and depositional
processes, hindering the identification of these structures from surface expressions. To search the location of a
concealed caldera complex, one of the probable ignimbrite source vents, magnetotelluric data acquired at 60
stations in the period range from 0.001 s to 1000 s were used to derive an upper crustal three-dimensional
electrical resistivity model in the Cappadocian Volcanic Province, central Anatolia, Türkiye. The electrical resistivity
model provides constraints on the location, geometry and boundaries of a hidden caldera complex
situated in the Çiftlik basin, north of Mt. Melendiz accurately, as well as its morphology at depth, which is
characterized by a large depression with low resistivity values beneath the high resistivity layer consisting of
pyroclastic flow deposits. This area spatially coinciding with Neogene collapse structures is interpreted as a
buried caldera complex with a maximum diameter of ~12 km and depth of
3 km (below sea level) that is
formed by partially overlapped nested caldera structures of subsequent volcanic eruptions and attributed to the
probable source area for the Miocene-Pliocene ignimbrite emplacements. The collapse and burying process of the
caldera complex have been linked with the transtensional tectonics of the Cappadocia region. Besides, the
structural margins are inactive and probably bounded by faults buried under younger volcanic products within
the Cappadocian Volcanic Province. The results present major implications for a better understanding of the deep
three-dimensional structure of hidden caldera complexes, of which little is known, and also for describing the
relationship between hidden calderas and regional tectonics.
Continued Africa-Eurasia convergence resulted in post-11 Ma surface uplift of the Central Anatolian Plateau (CAP) and the westward escape of the Anatolian microplate. Contemporaneously, a central Anatolian fluvio-lacustrine system developed that covered extensive parts of the rising CAP. Today, the semi-arid CAP interior − except for the Konya closed catchment (KCC) − drains towards the Black Sea, the Mediterranean Sea, and the Persian Gulf. Lake connectivity and drainage patterns of the fluvio-lacustrine system in the evolving plateau region are, however, largely unknown.
Here, we present sedimentological and stable isotopic (δ13C and δ18O) data (N= 665) from thirteen well-dated lake sections covering the former fluvio-lacustrine depocenters of the southern CAP. Persistently (>1 Myr) stable paleoenvironmental and hydrological conditions suggest that a low-relief environment characterized the southern CAP during plateau uplift. Throughout the late Miocene, various open and closed lakes of the southern CAP drained into closed, terminal lakes within the plateau interior. Sedimentation east of the Tuz Gölü Fault ceased during the early Pliocene (~5.3-3.6 Ma), when the eastern CAP became connected to marine base level as a result of river incision shortly after the switch from regional compression to extension. A final phase of lacustrine carbonate sedimentation characterizes most sampled basins, yet occurred asynchronously over the extent of the CAP. Therefore, the final episode of lacustrine sedimentation is unlikely to be the result of a climatic event, consistent with the absence of a clear aridification trend in the lacustrine δ18O data. Rather, capping carbonates reflect the interplay of surface uplift and transition from inward to outward drained plateau regions and concomitant lake reorganization during the formation of the CAP and its margins.
The basins and orogens of the Mediterranean region ultimately result from the opening of oceans during the early break-up of Pangea since the Triassic, and their subsequent destruction by subduction accommodating convergence between the African and Eurasian Plates since the Jurassic. The region has been the cradle for the development of geodynamic concepts that link crustal evolution to continental break-up, oceanic and continental subduction, and mantle dynamics in general. The development of such concepts requires a first-order understanding of the kinematic evolution of the region for which a multitude of reconstructions have previously been proposed. In this paper, we use advances made in kinematic restoration software in the last decade with a systematic reconstruction protocol for developing a more quantitative restoration of the Mediterranean region for the last 240 million years. This restoration is constructed for the first time with the GPlates plate reconstruction software and uses a systematic reconstruction protocol that limits input data to marine magnetic anomaly reconstructions of ocean basins, structural geological constraints quantifying timing, direction, and magnitude of tectonic motion, and tests and iterations against paleomagnetic data. This approach leads to a reconstruction that is reproducible, and updatable with future constraints. We first review constraints on the opening history of the Atlantic (and Red Sea) oceans and the Bay of Biscay. We then provide a comprehensive overview of the architecture of the Mediterranean orogens, from the Pyrenees and Betic-Rif orogen in the west to the Caucasus in the east and identify structural geological constraints on tectonic motions. We subsequently analyze a newly constructed database of some 2300 published paleomagnetic sites from the Mediterranean region and test the reconstruction against these constraints. We provide the reconstruction in the form of 12 maps being snapshots from 240 to 0 Ma, outline the main features in each time-slice, and identify differences from previous reconstructions, which are discussed in the final section.
Although ophiolitic rocks are abundant in Anatolia (Turkey), only in rare cases have they experienced high‐grade metamorphism. Even more uncommon, in Anatolia and elsewhere, are high‐grade meta‐ophiolites that retain an oceanic lithosphere stratigraphy from upper crustal mafic volcanic rocks through lower crustal gabbro to mantle peridotite. The Berit meta‐ophiolite of SE Turkey exhibits both features: from structurally higher to lower levels, it consists of garnet amphibolite (metabasalt), granulite facies metagabbro (as lenses in amphibolite inferred to be retrogressed granulite), and metaperidotite (locally with metapyroxenite layers). Whole‐rock major and trace element data indicate a tholeiitic protolith that formed in a suprasubduction setting. This paper presents new results for the metamorphic pressure‐temperature conditions and path of oceanic lower crustal rocks in the Berit meta‐ophiolite, and an evaluation of the tectonic processes that may drive granulite‐facies metamorphism of ophiolite gabbro.
In the Doğanşehir (Malatya, Turkey) region, granulite facies gabbroic rocks contain garnet (Grt)+clinopyroxene (Cpx)+plagioclase (Pl)+corundum (Crn)±orthopyroxene (Opx)±kyanite (Ky)±sapphirine (Spr)±rutile. Some exhibit symplectites consisting of Crn+Cpx, Ky+Cpx and/or coronas of garnet (outer shell) around a polygonal aggregate of clinopyroxene that in some cases surrounds a polygonal aggregate of orthopyroxene. Coronitic and non‐coronitic textures occur in proximity in mm‐ to cm‐scale layers; corona structures typically occur in plagioclase‐rich layers. Their formation is therefore related primarily to protolith type (troctolite vs. gabbro) rather than P‐T path. Phase diagrams calculated for a kyanite‐rich granulite, a plagioclase‐rich non‐coronitic granulite, and a plagioclase‐rich coronitic granulite (taking into account changes in effective bulk composition during texture development) predict peak conditions of ~800°C, 1.1‐1.5 GPa; these conditions do not require invoking an unusually high geothermal gradient. In the coronitic metagabbro, reaction textures formed along the prograde path: Crn‐Cpx symplectites grew at the expense of garnet, sapphirine and plagioclase. Peak conditions were followed by isobaric cooling of ~150°C. Hornblende‐plagioclase thermometry results for host amphibolite (Hbl+Pl±Crn±Grt ± relict Cpx) indicate retrograde conditions of 620‐675 °C and 0.5‐0.8 GPa accompanied by infiltration of H2O‐rich fluid. This anticlockwise P‐T path differs from an isothermal decompression path previously proposed for these rocks based on the presence of symplectite. Metamorphism of the ophiolitic rocks was driven by closing of the southern Neotethys Ocean, as oceanic lithosphere was obducted (most SE Anatolian ophiolites) or underthrust (Berit meta‐ophiolite). This was followed by subduction of a continental margin, driving cooling of the Berit granulite after the thermal peak at depths of ~40 km.
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