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• Thermal water transport is influenced by the depth and geometry of intruded magmas and crustal faults. • Stress accumulation zones are directly associated with thermal water circulation. • We present a suite of models that simulate heat transfer through the crust and surface. • Varto caldera and Özenç volcanoes are the main heat source for thermal water in the Varto region. The Karlıova triple junction (KTJ) in eastern Turkey has been subjected to incremental deformation resulting in complex kinematic and mechanical interactions throughout the upper crust. These interactions have generated tectonic inversions and uplift, extensive seismicity and volcanism. The regional tectonics generate local stresses, some of which are favorable to magma transport and thermal water circulation throughout the lithosphere. Here we evalauate hydrogeochemical, geological and numerical results relating to the mechanism of thermal fluid circulation around the KTJ. Hydrogeochemistry of the samples indicates that the thermal water springs are probably heated by steam. Volcanic rocks at the site appear to be the host rock owing to the enrichment of Na+ and Cl− ions in water and the abundance of these elements in minerals of the volcanic rocks. In addition, it is clear that the thermal fluids are sourced from depth and migrate through permeable networks of faults. The effects of crustal heterogeneities, in particular the geometry and mechanical properties of many faults and layers, on thermal fluid circulation in relation to active magma chambers were investigated under a variety of different mechanical conditions. The numerical results indicate very close relationships between the stress field causing faulting and thermal fluid movement in the KTJ. The effect of thermal transfer was modeled with depth throughout the crust and along the the crustal surface. The models show that some faults encourage thermal fluid circulation below the Varto and Özenç volcanoes. Hydrogeochemical, geological and numerical results suggest that magmas residing beneath both the Varto caldera and the Özenç volcano are the main heat source for thermal fluid in the Varto region. Fluid-solid interactions and fluid circulation models show that the permeable faults are important factors affecting heat transport and fluid circulation. In a series of thermal fluid flow models we probe the mechanism for fluid and gas transport from the 900 °C 'hot' zone around the deep magma chambers and investigate how heat is lost throughout the crust on the way to the surface and so eventually creates water channels of temperatures between 50 to 60 °C. [ABSTRACT FROM AUTHOR]

We report the results of a study on early Miocene to Pleistocene volcanic rocks cropping out west of the Karlıova Triple Junction in Eastern Anatolia (Elazığ, Tunceli, and Bingöl provinces). Here the Eurasia-Arabia convergence resulted in collision, marked by the Bitlis-Zagros suture (~13 Ma), followed by activation of the dextral transform North Anatolian Fault (NAF). At ~6 Ma the formation of the sinistral transform East Anatolian Fault (EAF) marked the separation of the Anatolian block, which became a kinematically independent plate. On the basis of petrographic, geochemical and Sr-Nd-Pb isotopic characteristics, as well as new 40Ar-39Ar age determinations, we distinguish three phases of activity: (1) early-middle Miocene (16·3-15·5 Ma) production of calc-alkaline basaltic trachyandesite to dacites in the Pertek and Mazgirt districts; (2) emplacement of late Miocene (11·4-11·0 Ma) transitional basalts in the Tunceli area; (3) emplacement of Plio-Pleistocene Na-alkali basalts in Karakoçan (4·1 Ma) and Elazığ (1·7 Ma). The oldest samples are characterized by large ion lithophile element (LILE) enrichment (e.g. Ba/Nb = 32-76) with high 87Sr/86Sr (0·7052-0·7065) and low 143Nd/144Nd isotopic ratios (0·51246-0·51262). The late Miocene basalts display variable geochemical characteristics, including large variations in 87Sr/86Sr (0·7039-0·7068) and LILE/HFSE (high field strength element) ratios (e.g. Ba/Nb = 13-36). The Plio-Pleistocene alkali basalts have higher LILE and HFSE contents and lower LILE/HFSE ratios (Ba/Nb = 8-21) compared with the two previous groups, low 87Sr/86Sr (0·7033-0·7038) and high 143Nd/144Nd (0·51270-0·51290), with compositions similar to those of oceanic intraplate magmas. Pb isotopes vary slightly: 206Pb/204Pb ranges from 18·66 to 19·11, 207Pb/204Pb from 15·64 to 15·72 and 208Pb/204Pb from 38·67 to 39·24, with the calc-alkaline early-middle Miocene rocks characterized by higher 207Pb/204Pb and 208Pb/204Pb at a given 206Pb/204Pb. The evolution of volcanic activity is strictly linked to the geodynamic scenario. The early-middle Miocene magmas, emplaced in a convergent setting, indicate derivation from mantle sources modified by subduction components, whereas the late Miocene Tunceli transitional basalts mark the change from compressional to strike-slip tectonics. During the development of the NAF and EAF, passive upwelling of the sub-slab mantle, favoured by the formation of small pull-apart basins, led to the onset of Na-alkali basaltic activity. [ABSTRACT FROM AUTHOR]

Volcanic rocks in western Turkey show age progressive magmatism migrating from northeast to southwest that reflects a southward shift of the Aegean subduction zone during the Miocene. Slab segmentation during this period of trench-roll back is thought to have imposed source region heterogeneity trending northwest to southeast. In this study, we present new Sr, Nd, Pb and O isotopic analyses from the Miocene volcanic rocks of the Uşak–Güre basin and compare these to previously published data. The data demonstrate a change from subduction-related sources around the Menderes Core Complex to more asthenospheric sources in the Afyon region. Isotopic compositions (Sr–Nd–Pb) of volcanic rocks from the Demirci and Selendi basins to the west and the Afyon volcanic area to the east indicate minimal upper crustal contamination. The most primitive lavas also reveal increasing K contents from west (the NE–SW-trending basins) to east (Afyon region). It is suggested that the composition of the western Anatolian volcanic rocks change from orogenic (with lithospheric mantle sources) associated to denudation of the Menderes Massif Core Complex (MMCC) to anorogenic (with asthenospheric mantle sources) in the vicinity of the Kırka–Afyon–Isparta (KAI) volcanic province with time, from Early Miocene to Quaternary. There is no asthenospheric contribution during the late Miocene onwards in the eastern margin of the MMCC, while the asthenospheric upwelling occurred only in a small area beneath the exhuming core complex. We interpret the Uşak–Güre basin to reflect a structural boundary showing a transition from a subduction-influenced metasomatized mantle source to asthenospheric mantle source volcanism driven by slab-tearing between the Hellenic and Cyprus slab segments. The Uşak–Muğla Transfer Zone (UMTZ) most likely corresponds to slab-tear related westernmost faults that were induced by initiation of slab segmentation processes following the late Miocene (circa 11Ma), and possibly since the Early Miocene. [ABSTRACT FROM AUTHOR]

Abstract: Early to Mid-Miocene extension in western Anatolia, related to plate tectonic motions, resulted in the development of a number of normal fault-bounded sedimentary basins as well as different styles and compositions of volcanic activity. The Uşak and Güre basins accumulated a thick fluvio-lacustrine fill in which three distinct volcanic edifices (Elmadağ, İtecektepe and Beydağı) and their deposits can overlap with each other and with the sediments produced by the background sedimentation. In addition, complete facies architectures of small-volume (monogenetic) volcanoes have been recognised in association with the three large complex (polygenetic) volcanoes providing a complex mixed siliciclastic and volcaniclastic basin infill in the respective basins where volcanism took place. All three volcanic centres display a complex succession of effusive and explosive volcanisms and their reworked deposits, with abundant evidences of magma–water interaction such as peperites for non-explosive magma-water interaction with the lacustrine water-saturated sediment and standing water body in a large alkaline lake. During the constructive phase, proximal successions of pyroclastic flows, pyroclastic falls, and rarely surge deposits are associated with distally-emplaced debris flow deposits, sometimes of mixed volcanogenic and terrestrial origins, and are interbedded with lacustrine sediments of the Inay Group. All three volcanic centres then experienced a phase of volcano growth and degradation between 17 and 15Ma ago, most likely related to a combination of tectonic movements on NE–SW-trending basement faults, which triggered multiple flank collapses and volcanic debris avalanches (Elmadağ), and voluminous ignimbrite eruptions that triggered caldera formation (İtecektepe and Beydağı volcanic centres). Lacustrine conditions persisted during the destruction and post-destruction stages of the volcano''s evolution, as evidenced by indications of magma–water interactions within the central collapse structures, which also contain uplifted basement metamorphic rocks now exhumed in their eroded cores. [Copyright &y& Elsevier]

Abstract: In spite of much research over the past 30years, the dynamic evolution, origin of the volcanism and geometrical–stratigraphical relations of the NE–SW-trending basins in western Anatolia are poorly understood. The Uşak-Güre basin is one of the prominent NE–SW-trending basins developed on the northern part of the Menderes Massif core complex. Three distinct volcanic successions are found in the Uşak-Güre basin: (1) the Beydağı volcanic unit composed of shoshonite, latites and rhyolitic lavas followed by dacitic and andesitic pyroclastic deposits; (2) the Payamtepe volcanic unit composed of potassic intermediate composition lavas (latites and trachytes); and (3) the Karaağaç dikes composed of andesite and latite. The Beydağı volcanic unit occurs in three different NE–SW-trending volcanic centers—Beydağı, İtecektepe and Elmadağ calderas from southwest to northeast, respectively. The oldest radiometric ages for the Beydağı volcanic unit are from the Elmadağ volcanic center in the north and range from 17 to 16Ma. The data indicate that volcanism was active during the latest early Miocene. The youngest radiometric age for the Beydağı volcanic unit is obtained from the Beydağı caldera located (12Ma) in the south. The data indicate that Beydağı volcanism was active in the late middle Miocene and migrated from north to south with time. 40Ar/39Ar ages of the Payamtepe volcanic unit are restricted to a short period between 16.0 and 15.9Ma. Volcanic rocks of the Uşak-Güre basin are characterized by strong enrichment in LILE and LREE and depletions of Nb-Ta and Ti on MORB-normalized multi-element diagrams. Geochemical features of the volcanic rocks suggest that they experienced mixing processes between mafic and felsic end-members and also fractional crystallization of dominantly plagioclase and pyroxenes from mixed magma compositions. Crustal contributions to the magma sources may also have occurred during magmatic evolution. These processes have resulted in scattered major and trace element variations with respect to increasing silica contents. Geochemical features of the most mafic samples agree with the results of previous studies from other volcanic areas in western Anatolia, suggesting that the volcanic rocks in the region were derived from a mainly lithospheric mantle source that had been heterogeneously metasomatized by previous subduction events during convergence between the African and Eurasia plates. The volcanic activity in the region, which developed synchronously with the formation of the Menderes Massif core complex, is best explained by delamination of lithospheric mantle slices that were heterogeneously enriched by previous subduction-related processes. [Copyright &y& Elsevier]

A ~ 400 m thick Middle-Late Triassic volcano-sedimentary succession crops out in a relatively narrow corridor ~75 km long and ~ 25 km wide close to Antalya Gulf, SW Turkey. The volcanic and subvolcanic rocks represent the majority of the succession and are associated with epiclastic breccia, turbiditic sediments as well as chert and limestone layers. The igneous rocks are alkali basalts, with incompatible element content matching the classical HiMU-OIB types. These are considered as the precursors of a rift system that would have later evolved into a mature Neotethyan oceanic system, with emplacement of massive tholeiitic basalt sequences, not recorded in the investigated area. Clinopyroxene-melt thermobarometric constraints indicate the presence of two main magma chambers, one equilibrated at ~7–10 km depth and ~ 1070 °C and the other at ~15–21 km depth and ~ 1300 °C. Based on these estimates, a 3-D finite element modelling has been applied, simulating the presence of ellipsoidal magma chambers at different depths and with variable sizes, applying different boundary loading conditions. The scenario that best fits the distribution of the volcanic rocks assumes the contemporaneous presence of two magma reservoirs. One is shallow, with a size of ~17 × 1.5 × 1.5 km, and the second is deeper, with a size of ~37 × 3 × 3 km. Numerical simulations show maximum 6 m opening and dilation through horizontal plane at the surface during the Permian/Triassic intracontinental rift phases. Morphological constraints of this rift zone, with the presence of massive lava eruptions also as pillow facies, have been simulated with the existence of a slowly opening rift system. In order to produce the voluminous magma batches in the Antalya region, pure extensional tectonic regimes seem insufficient, and the presence of a transtensional regime must have accompanied the tectonic forces during the Triassic intracontinental rifting stage. • Thermobarometric shows the presence of two magma chambers at ~15–21 km and at ~7–10 km depth. • We suggest that in this OIB system two magma chambers, ~17 × 1.5 × 1.5 km- and ~37 × 3 × 3 km sizes, feed the volcanism • Numerical simulations indicate dilation, reaching 6 m, above the central magma chamber compartment. • The models show similarities with a slow-opening of the intracontinental rifting during the Triassic. [ABSTRACT FROM AUTHOR]

Abstract: The Nemrut stratovolcano, with its well defined summit caldera, is the most recent volcanic eruption center (1441 A.D.) in the East Anatolian High Plateau, one of the best examples of an active colllision zone. Widespread volcanism has been active in this region for the last ∼10 Ma, producing large volumes of lavas and pyroclastics covering a broad belt, across the Bitlis Suture Zone, from the Anatolian plate in the north to the Arabian plate in the south. Three major evolutionary stages have been identified in the evolution of the Nemrut stratovolcano: pre-caldera, post-caldera and late stages. The pre-caldera stage is further differentiated into effusive, extrusive and explosive phases, the latter being responsible for the caldera formation. The products of this stage cover a broad compositional range from basalts to rhyolites, and consist of lava flows, domes, large volumes of ignimbrites and associated pyroclastics. The post-caldera stage consists of three phases comprising phreatomagmatic eruptions, vitrophyric rhyolitic lava flows and dykes. The late stage consists of the explosive and the following effusive phases with vitrophyric rhyolitic and basaltic lava flows, respectively. The post-caldera and late stages show a compositional gap between the (younger) mafic and the (older) felsic members. The products of all three stages are silica-saturated and display a gradual transition in nature from sodic in the mafic to potassic in the felsic members. The overlaps in the compositional spectra and the geochemical trends on bivariate plots suggest the derivation of the products of all three stages from a single parental magma (or similar parental magmas), yet the stratigraphic position of the mafic and felsic members points to a periodically replenished magma chamber. The major and trace element systematics, along with petrographic evidences, suggest clinopyroxene + plagioclase ± olivine ± amphibole as the major fractionating phases governing the liquid evolutionary paths, with a progressive increase in the proportions of plagioclase and amphibole (joined by K-feldspar, biotite and apatite) in the fractionating assemblages during the course of magmatic differentiation. The volcanics of all three stages exhibit enrichment in light rare earth elements (LREE) over heavy rare earth elements (HREE), and large ion lithophile elements (LILE) over high field strength elements (HFSE). The multi-element patterns and low Th/Y and Nb/Y ratios imply a within-plate type mantle asthenospheric source for this volcanics. Trace element modelling suggests derivation of parental magma(s) from 10% to 30% partial melting of a spinel–lherzolite source. Assimilation-fractional crystallization (AFC) modelling reveals significant but variable degrees of crustal contamination in the evolution of the volcanics with a range of r values (assimilation rate/crystallization rate) from 0.2 to 0.8. These interpretations are in conformity with the recent findings from seismic studies showing that lithospheric mantle is absent in eastern Anatolia. The crust in the region is about 45 km thick and directly underlain by the asthenosphere, possibly due to slab breakoff following the collision of the Arabian and the Anatolian plates along the Bitlis Suture Zone. [Copyright &y& Elsevier]

A diffuse and voluminous (>1400 km3) Miocene-Quaternary volcanic activity developed around the Karlıova Triple Junction in East Anatolia as a consequence of collisional tectonics among Anatolia, Arabia and Eurasia continental plates. The volcanic rocks of this region are grouped into three phases of activity: 1) Early Phase (Solhan volcanism; ~7.3–4.4 Ma), with emplacement of alkali basalt to trachyte lava flows and pyroclastic successions; 2) Middle Phase (Turnadağ and Varto volcanism; ~3.6–2.6 Ma), mostly with products with the same compositional range plus minor dacites and rhyolites, and 3) Late Phase (Özenç volcanism; ~2.6–0.5 Ma), with emplacement of alkali basaltic, hawaiitic and mugearitic lavas and dykes. Primitive Mantle-normalized patterns of the three rock groups share an enriched LILE and depleted HFSE contents, with overall positive spikes of Pb and mildly fractionated LREE/HREE trends showing more similar affinity to global subducting sediments rather than to magmas emplaced in mid-plate settings (i.e., OIB). Initial Sr isotopic ratios of the least evolved compositions range from values lower than BSE (87Sr/86Sr i = 0.7041) to radiogenic compositions (87Sr/86Sr i = 0.7050). They reflect either FC-like processes, with 87Sr/86Sr i up to 0.7064, or closed system fractional crystallization, with 87Sr/86Sr i = 0.7046–0.7049. Initial Nd are higher than ChUR estimate for the most and the least evolved compositions (143Nd/144Nd i = 0.51267–0.51280), indicating provenance from isotopically depleted sources. Lead isotopic ratios are characterized by a remarkable homogeneous 206Pb/204Pb (18.95–19.04), with 207Pb/204Pb (15.65–15.72) and 208Pb/204Pb (38.87–39.21) slightly above the Northern Hemisphere Reference Line, pointing towards the EMII end-member. Geochemical modelling for the least evolved volcanic units indicate the likely generation from an amphibole-bearing spinel-lherzolitic source. P-T calculations for partial melting calculations gave lithospheric pressures for initial magma generation (0.8–1.3 GPa). Possible cause of melting might be related to passive upwelling of asthenosphere as a response to the local extension linked to the development of North Anatolian and East Anatolian Fault Zones. Anyhow, volcanic units from the KTJ display only limited geochemical signatures of garnet-bearing sources, or any HIMU-OIB like characteristics, as instead observed in the other portions of the Eastern Anatolia. The long-lasting complex tectonic evolution of the Eastern Anatolia is responsible for the large geochemical variability of the magmatic products. However, the general characteristics of KTJ volcanic rocks are mainly dominated by subduction-related signatures, with most of the primary magma characteristics having been heavily masked by fractionation and crustal assimilation processes. • Volcanic rocks in Karlıova-Varto region have been grouped in three phases. • Lead isotopic ratios are characterized by quite homogeneous pointing towards the EMII end-member. • Geochemical modelling indicate an amphibole-bearing spinel-lherzolitic source. • Melting might be related to passive upwelling of asthenosphere as a response to the local extension. [ABSTRACT FROM AUTHOR]

Abstract: The Miocene volcanic rocks along the İzmir-Balıkesir Transfer Zone along the western margin of the Menderes Core Complex (MCC) in western Anatolian Volcanic Province (WAVP), where strike–slip deformation is dominant, comprise: (Group 1) early-middle Miocene high-K to shoshonitic rocks with high-Mg# and relatively low SiO2, (Group 2) middle Miocene phonolitic rocks with low-Mg# and intermediate SiO2, (Group 3) early-middle Miocene medium- to high-K series from andesites to rhyolites, (Group 4) middle Miocene rhyolites with distinct trace element compositions; and (Group 5) late Miocene high-MgO basalts, K-trachybasalts and (Group 6) late Miocene high-MgO basaltic andesites. The geochemical features of these rocks are comparable with the other Oligocene to Miocene volcanic rocks, but differ from the Eocene volcanic rocks in WAVP. The geochemical features of the most primitive early-middle Miocene Group 1 rocks indicate that they were derived from an anomalously metasomatized lithospheric mantle. The mineralogical and geochemical properties of garnet–amphibole peridotite from the Ulten Zone (UZP), Eastern Alps, which is thought to represent a fossil metasomatic mantle wedge contaminated by continental subduction, is similar to the model mantle composition previously proposed for the genesis of the mafic rocks. Together with the presence of Eocene to early Miocene continental subduction beneath the Aegean-west Anatolia region, this strongly suggests that continental subduction was an important factor in the genesis of the high-MgO shoshonitic to ultrapotassic volcanism in this post-collisional area. The origin of the Group 3 andesitic to rhyolitic rocks includes; (1) lower crustal melting, (2) mixing between lower crustally-derived and mantle-derived melts, and (3) FC-AFC processes. The late Miocene Group 5 and 6 rocks, however, derived from a more depleted mantle source, indicating that the mantle became depleted over time. The rhyolites of Group 4 are most probably crustally-derived. OIB-type Quaternary Kula volcanics (QKV) were emplaced near the centre of the MCC. Among the late Miocene basalts in the region, only the basalts located close to the QKV show transitional geochemistry between the Miocene volcanic rocks and QKV, indicating that asthenospheric contribution to lavas in the region occurred only near the centre of the MCC. [Copyright &y& Elsevier]