Galatean Volcanic Province Research Articles

New bulk rock and age data on the changes in magma evolution during the Miocene, Galatean volcanic area, central Anatolia, Turkey: A review

The Galatean Volcanic Province (GVP) lies within the Sakarya tectonic belt in the northwest of central Anatolia, Turkey, south of the North Anatolian Fault, cropping out over 12,000 km2. It consists of Early Miocene intermediate to acid lavas, pyroclastic rocks, volcaniclastic deposits, and Late Miocene OIB-like basalts. Our study is based on new bulk geochemistry, SrNd isotopes, and 40Ar/39Ar dating of the volcanic rocks from the south-western part of GVP, but integrates all the available previous data to understand how magmas evolved in the post-collisional geodynamic condition in the GVP. The initial eruptions were rhyolitic, as domes or pyroclastic deposits (Group 1) and basaltic lavas (Group 2) during the Early Miocene. Group 2 is also represented by large volumes of basaltic-andesitic, trachyandesite-dacite/trachydacite lava flows, small intrusions, and pyroclastic deposits as generated between 21 and 14 Ma. Relatively low 87Sr/86Sr ratios (0.705–0.706) of the early rhyolites (Group 1), similar to all the rocks from Group (2), suggest the generation of hybrid melts with variable contributions of mantle-derived and crustal material. The volcanic activity ends with OIB-like basalts (11–7 Ma) showing the lowest 87Sr/86Sr (∼0.703) suggesting an asthenospheric origin.The geodynamic model, based on post-Cyprian slab rollback, results in long-term (22–13 Ma) post-collisional delamination/drip processes that support magmatism. This magmatism is generated in the lithospheric mantle, with the formation of basaltic melts and acid hybrid melts showing variable contributions of mantle-derived and crustal materials in a complex trans-crustal magma plumbing system. Complex mixing of various intra-crustal magmas and fractional crystallization processes generated a huge volume of volcanic rocks. The Late Miocene small-volume OIB basalts were asthenospheric melts that during the late stage recorded localized decompression melting processes.

K–Ar age constraints on the sources of K minerals in bentonites of the Ankara-Çankırı Basin, Central Anatolia, Turkey

Many of the bentonite deposits of the Ankara-Cankiri Basin, Central Anatolia, Turkey were found within the Miocene Hancili Formation, which comprises lacustrine sedimentary and volcaniclastic rocks that interfinger with Uludere pyroclastic rocks of the Miocene Galatean volcanic province. In the present study, the conventional K–Ar geochronological method was used to evaluate the contribution of volcanic materials to the K-bearing components of the bentonite clay fractions. Four dacite samples from near the southern end of the basin were indistinguishable in K–Ar age (average 18.4 Ma, standard deviation 0.3 Ma). K–Ar measurements of feldspar-enriched rock fragments and hydrobiotite separated from andesitic tuff from near the northern end of the basin indicated an age of 17 ± 1 Ma. The K–Ar age values of clay fractions of bentonites, which ranged from 77 ± 5 Ma to 162 ± 5 Ma, indicate that most of the K in the bentonite clay fractions occurs in minerals derived from the Mesozoic basement rocks adjacent to the Miocene basin. The K–Ar age values support field observations indicating that these bentonites are secondary bentonites formed by alteration of volcanic components during or after deposition of volcaniclastic phases. The K-bearing mineral components of these clay fractions consisted mostly of unaltered illitic material of detrital origin whereas the smectitic components were formed by alteration of Miocene pyroclastic materials.

The First Glyptostroboxylon and Taxodioxylon Descriptions from the Late Miocene of Turkey and Palaeoclimatological Evaluation

Taxodioxylon Hartig, (emended by Gothan 1905) was widely described from the late Oligocene of the European part of Turkey (Thrace) and the early Miocene of greater Turkey, Anatolia.,C,. was also described from the early Miocene of central Anatolia. The purpose of this paper is to present a more detailed extended history of these two genera up to the late Miocene (Tortonian) with new descriptions from the Galatean Volcanic Province in central Turkey. The wood identification showed the presence of two fossil species;,D,et B,and,(G,.) G,. In conclusion, the swamp and lowland warm-temperate forest composition including,and,in the Galatean Volcanic Province, continued from the early Miocene (Burdigalian) to the late Miocene (Tortonian).

An approach to compare the environmental conditions of Acer in the Miocene and in the modern flora of Turkey, based on wood anatomy

AbstractIn this study, xeromorphy ratios were calculated for Acer L. (maple) fossil woods in order to infer the precipitation conditions in the Miocene at the sites of the fossils, based on a comparison with the xeromorphy ratios of selected extant Acer species. The four studied petrified wood samples came from three localities of the Galatean Volcanic Province in Turkey: Kozyaka village (Bolu Province, Seben District), İnözü Valley (Ankara Province, Beypazarı District), and Kıraluç precinct between Nuhhoca and Dağşeyhler villages (Ankara Province, Beypazarı District). The calculated xeromorphy ratios ranged from 3 to 18 for the present-day wood and from 13 to 19 for the early Miocene wood. Values over 10 (11–18) represent xeric conditions; the lower values (3–7) indicate mesic conditions in modern Acer woods. The xeromorphy ratios of the Miocene wood indicate xeric conditions; we conclude that the sites of the fossil Acer woods were xeric, very similar to the modern Acer woodlands of central and southern Anatolia.

A conceptual model for groundwater flow and geochemical evolution of thermal fluids at the Kızılcahamam geothermal area, Galatian volcanic Province

Kızılcahamam geothermal area is one of the most important geothermal fields in the Galatean Volcanic Province northern Central Anatolia of Turkey. Kızılcahamam geothermal field is liquid-dominated system that have been developed in the rugged terrain, and usually consists of a geothermal systems that occur commonly associated with terrestrial volcanism. This field is characterized by thermal and mineralized springs, travertine, with wide alteration zones. Thermal waters are issue through the faults and fracture zones of the volcanics. The temperatures of the wells in the Kızılcahamam town center varies between 42 and 81°C, whereas the temperature of thermal and mineralized water springs in the area of Acısu Stream and Seyhamam varies between 23 and 43°C. Electrical conductivity values for thermal waters are between 1029 and 3700μS/cm. Thermal waters in Kızılcahamam area are mainly Na-HCO3-Cl and Na-Ca-HCO3 type, with high salinity, while cold groundwater is mostly of Ca (Na, Mg)-HCO3 type, with lower salinity. Both waters of Kızılcahamam town center and Acısu Stream appear to be derived from a deeper reservoir fluid, whereas Seyhamam thermal waters are compatible with shallow cold waters heated by steam absorbing high temperatures. High contents of some minor elements in thermal waters, such as F, B, Li, Rb, Sr and Cs probably derive from enhanced water–rock interaction.The isotopic values of thermal water (δ18O, δ2H, δ3H) indicates their deep-circulating meteoric origin and allow estimation of infilitration altitude ranging between 1350 and 1750m.a.s.l.This datum, supported by structural data, suggests the Işıkdağ and Aluçdağ Mountains as the recharge area of the system. As frequently observed in many geothermal systems positive I8O shifts of Kızılcahamam thermal waters relative to the local meteoric line were considered to be primarily due to interaction with host rocks at elevated temperature (T >150°C) and from CO2 exsolution of thermal and mineral springs. In this system, geothermal waters are heating by an intrusive-cupola and geothermal gradient, followed by the waters rising to the surface along faults and fractures that act as hydrothermal conduits. A conceptual hydrogeochemical model was developed for a hydrogeological flow system in the Kızılcahamam Region.

Silicified woods from two previously undescribed early Miocene forest sites near Seben, northwest Turkey

This paper introduces two new Miocene fossil forest sites in northwest Turkey. Both sites lie at an altitude of ~900m close to the town of Seben in the province of Bolu. One locality is near the village of Hoçaş; the second lies 17km to the northwest of the village of Kozyaka. The silicified wood represents lower parts of trunks that were felled by an eruption associated with volcanic activity in the Galatean Volcanic Province. The Hoçaş site yielded a total of 64 samples (51 in situ and 13 ex situ). Eight in situ trunks have been identified as Salix L./Populus L., Palmae, Juniperus L., Liquidambar L. and Quercus L. (evergreen); ex situ Cedrus Trew., Picea Mill. and Acer L. were found lying on the surface of the soil. The Kozyaka site yielded a total of 26 samples (six in situ, 20 ex situ) including Cedrus, Pinus L., Acer, Salix/Populus, evergreen Quercus and Ulmus L. Today in Turkey these genera grow in coastal locations across a narrow altitudinal range. Collating data found herein with evidence from previous studies suggests that during the early Miocene subtropical to warm temperate conditions prevailed that supported a lakeside vegetation at the Hoçaş site and a more typical upland or mountainous zone assemblage around the Kozyaka site.

Petrogenesis of the Neogene bimodal magmatism of the Galatean Volcanic Province, Central Anatolia, Turkey

A series of geochemical analyses and radiometric age determinations are undertaken on rock samples collected from the Çamlıdere region in the Galatean Volcanic Province of NW Turkey, to better understand the characteristics of the bimodal Early–Middle Miocene volcanism developed near the Late Cretaceous Tethyan Suture Zone. Çamlıdere volcanic rocks consist of large volumes of older (>20Ma) calc-alkaline andesites, dacites and rhyolites and pyroclastites, and small volumes of slightly younger (~19Ma) alkaline trachybasalts and basaltic trachyandesites, cropping out as dykes or small lava flows. The older rocks exhibit elevated LILE, LREE and depleted HFSE contents, carrying geochemical characteristics suggesting earlier subduction process. Some samples of the younger mildly alkaline lavas display geochemical characteristics of intraplate magmatism with enrichment of LILE contents with little or no HFSE depletion. Knowing that the Galatean volcanic rocks experienced syn-volcanic extensional tectonics during the Miocene, we think that the reactivation of the old suture zone produced first calc-alkaline series originated from a subduction-modified subcontinental lithospheric mantle, followed by more alkaline products. However, some volcanic rocks suggest penetration of small amounts of asthenospheric melts to this lithospheric mantle source. The regionally known last volcanic phase produced small amounts of alkaline basaltic rocks in Güvem area at about 10Ma. Volcanic activities ended possibly with, or just after the Güvem event, when the extensional tectonic regime switched to strike-slip faulting in the region, with the inception of one of the major faults of Turkey, the North Anatolian Fault Zone.

Alkaline series related to Early-Middle Miocene intra-continental rifting in a collision zone: An example from Polatlı, Central Anatolia, Turkey

Abstract A large volcanic area (∼7600 km2), the Galatean Volcanic Province (GVP), developed in northwest Central Anatolia during the Miocene along the Neo-Tethys Ocean suture zone possibly by post-collisional processes. The GVP mainly comprises 20–14 My old acid to intermediate volcanites with a geochemical signature indicating a mantle source modified by earlier (Late Cretaceous) subduction-related events. 100 km south of the GVP, near Polatli, Ankara, basaltic rocks that cover large areas are intercalated with the Miocene deposits of the Beypazari basin, an intra-continental subsidence zone at the southwest of the GVP. Field observations, geochemistry and K–Ar age dating of the Polatli volcanites show that they are Early (19.9 Ma) to mid (14.1 Ma) Miocene in age, covering an area as large as 215 km2. Variations in lava thickness and the thickness of the underlying silicified/baked zones suggest that the basaltic lavas erupted from a southern source, possibly from the Eskisehir fault zone, and flowed northwards. Most Polatli samples have chemical compositions that indicate derivation from a mantle source with crustal contamination during ascent. They do not display any characteristic to suggest a subductional component. Although the GVP and Polatli lavas formed close in time and space, they were derived from different mantle sources. Considering the positions of these two magmatic regions with regard to the Tethyan suture zone, we propose that the mantle beneath the GVP and near the suture zone memorised the earlier subduction while the mantle beneath Polatli that is located about 100 km further from the suture zone remained apparently unchanged. After a significant volume of magma was consumed in the GVP, a later (∼10 My) and last activity (Guvem activity) has produced quantitatively much less basaltic rocks where this subductional signature seems to completely disappear. Considering that the western Anatolian crust is proposed to undergo extension since the Late Oligocene–Early Miocene times, the Early Miocene intra-plate Polatli activity may have developed within this extensional tectonic regime. Combined with regional data, Polatli data also provide broad estimations on how long a subductional event continues to modify the mantle after the subduction ceased (at least ∼20 My), how long the subductional signature is preserved during significant magmatism (between 6 and 10 My) and how far the subductional effect disappears laterally on the mantle with respect to the collision zone (

Miocene spores and pollen from Pelitçik Basin, Turkey–environmental and climatic implications

The palynological investigation of the early Middle Miocene fluviolacustrine sedimentary rocks interfingering with volcanics of the Galatean Volcanic Province at Pelitçik Basin (Central Turkey) have yielded palynomorphs belonging to 51 spore and pollen taxa. The pollen record is dominated by Ulmus, Pinaceae , Quercus, Carpinus and Carya, and appears to reflect climatic conditions. Two pollen zones were established based on changing abundances of plant taxa. Zone 1 is characterized by dominance of Ulmus and Pinaceae. Zone 2 is differentiated and characterized by a dramatic increase in, and predominance of, Ulmus, Carya, deciduous Quercus, Carpinus, Salix and Pinaceae. Mixed mesophytic forests were widespread in the basin suggesting warm and temperate climate. The decreasing relative percentage of thermophilous taxa, with Engelhardia as the main component, and warm temperate taxa, such as Carya, at the upper part of Zone 2 generally indicates a climatic deterioration, probably related to the Middle Miocene cooling.

Vegetational and climatic investigations in the Early Miocene lacustrine deposits of the Güvem Basin (Galatean Volcanic Province), NW Central Anatolia, Turkey

The palynological analysis of the Burdigalian (Early Miocene) successions of the Güvem Basin (NW Central Anatoia, Turkey) has been carried out with the aim of reconstructing the palaeovegetation. The pollen spectra indicate a flora dominated by trees such as Quercus deciduous type, Carya, Carpinus, Ulmus/Zelkova, Engelhardia, Quercus ilex type and Pinaceae. Pterocarya, Juglans, Alnus, Salix, Liquidambar and Oleaceae are represented by lower percentages. Herbs and shrubs are represented by minor amounts of Poaceae, Amaranthaceae/Chenopodiaceae, Asteraceae/Asteroideae, Brassicaceae, and the aquatics Potamogeton, Sparganium and Typha. The Burdigalian flora reflects a mixed mesophytic forest with Quercus deciduous type, Quercus ilex type, pine species, Ulmus/Zelkova, Engelhardia, Carya, Carpinus, Pterocarya, etc., sparcely interspersed with open herbaceous areas. This flora reflects a warm-temperate climate. The fluctuations in abundances of broadleaved trees and xerophytes may represent fluctuations of relatively wet and dry periods. The overall composition of the flora of the Güvem Basin reflects cooler conditions compared with other Early Miocene floras in Europe, which is possibly due to intense volcanic activity of the area.

Use of tuffs from central Turkey as admixture in pozzolanic cements: Assessment of their petrographical properties

Tuffs from Galatean Volcanic Province were studied for their use as admixtures in pozzolanic cements. The effects of petrographical properties on the pozzolanic activity of mortar specimens were investigated by optical microscopy, X-ray powder diffraction (XRD), scanning electron microscope equipped with an energy dispersive X-ray system (SEM–EDX), and chemical analysis. The chemical compositions of tuffs conform well to the requirements of ASTM C 618 and the Turkish Standard TS 25, and SiO 2+Al 2O 3+total Fe 2O 3 exceeds 70%. Pozzolanic activities were determined according to their 7th day flexural and compressive strengths and vary between 1.7 and 3.0 MPa and 7.4 and 16.0 MPa, respectively. The mechanical strength of mortars is affected by alteration of tuffs used in the mixture. Clay minerals and zeolites form by the alteration of volcanic glass, which is the most reactive phase and has a reducing effect on mechanical strength. The alteration also causes the enrichment of tuffs with respect to K 2O+Na 2O. The methods used provided rapid evaluation of tuffs as potential admixtures in cements.

The Sarikavak Tephra, Galatea, north central Turkey: a case study of a Miocene complex plinian eruption deposit

The Sarikavak Tephra from the central Galatean Volcanic Province (Turkey) represents the deposit of a complex multiple phase plinian eruption of Miocene age. The eruptive sequence is subdivided into the Lower-, Middle-, and Upper Sarikavak Tephra (LSKT, MSKT, USKT) which differ in type of deposits, lithology and eruptive mechanisms.The Lower Sarikavak Tephra is characterised by pumice fall deposits with minor interbedded fine-grained ash beds in the lower LSKT-A. Deposits are well stratified and enriched in lithic fragments up to >50wt% in some layers. The upper LSKT-B is mainly reversely graded pumice fall with minor amounts of lithics. It represents the main plinian phase of the eruption. The LSKT-A and B units are separated from each other by a fine-grained ash fall deposit. The Middle Sarikavak Tephra is predominantly composed of cross-bedded ash-and-pumice surge deposits with minor pumice fall deposits in the lower MSKT-A and major pyroclastic flow deposits in the upper MSKT-B unit. The Upper Sarikavak Tephra shows subaerial laminated surge deposits in USKT-A and subaqueous tephra beds in USKT-B.Isopach maps of the LSKT pumice fall deposits as well as the fine ash at the LSKT-A/B boundary indicate NNE–SSW extending depositional fans with the source area in the western part of the Ovaçik caldera. The MSKT pyroclastic flow and surge deposits form a SW-extending main lobe related to paleotopography where the deposits are thickest.Internal bedding and lithic distribution of the LSKT-A result from intermittent activity due to significant vent wall instabilities. Reductions in eruption power from (partial) plugging of the vent produced fine ash deposits in near-vent locations and subsequent explosive expulsion of wall rock debris was responsible for the high lithic contents of the lapilli fall deposits. A period of vent closure promoted fine ash fall deposition at the end of LSKT-A. The subsequent main plinian phase of the LSKT-B evolved from stable vent conditions after some initial gravitational column collapses during the early ascent of the re-established eruption plume. The ash-and-pumice surges of the MSKT-A are interpreted as deposits from phreatomagmatic activity prior to the main pyroclastic flow formation of the MSKT-B.

Palaeomagnetic study of the Galatean Volcanic Province, north‐central Turkey: neogene deformation at the northern border of the Anatolian Block

A regional palaeomagnetic study is reported from 24 lavas of the (Late Miocene) Galatean Volcanic Province bordering the North Anatolian Fault Zone (NAFZ) in northern Anatolia. Rock magnetic studies show that the lavas have a ferromagnetic content dominated by low-Ti magnetite assemblages which have been subjected to variable degrees of high and low temperature oxidation. Although larger fractions of ferromagnetic grains are multidomain, significant fractions of single domain grains are always present and presumed to be responsible for the stable remanence at all sites. Magnetic remanence is interpreted to be essentially primary because it preserves a record of both polarities which has since been tectonically rotated. Fifteen sites define a coherent dipolar axis with a mean direction of D/I=16·8/56·5° (α95=6·9°). This is rotated clockwise by 10·2±7·2° from the Eurasian field at 10 Ma and is interpreted to record block rotation during westward expulsion of lithosphere along the northern margin of the Anatolian region late in the Neotectonic history. Upper Cretaceous rocks from the northern side of this sector of the NAFZ exhibit rotations relative to Eurasia; whilst these may have been imparted partly during Eocene collision of the İstanbul and Sakarya zones, consistent counterclockwise motions show that differential block rotations are occurring here with the Galatean region bounded at its northern margin by the NAFZ. Copyright © 1999 John Wiley & Sons, Ltd.

Palaeomagnetic study of the Galatean Volcanic Province, north-central Turkey: neogene deformation at the northern border of the Anatolian Block

A regional palaeomagnetic study is reported from 24 lavas of the (Late Miocene) Galatean Volcanic Province bordering the North Anatolian Fault Zone (NAFZ) in northern Anatolia. Rock magnetic studies show that the lavas have a ferromagnetic content dominated by low-Ti magnetite assemblages which have been subjected to variable degrees of high and low temperature oxidation. Although larger fractions of ferromagnetic grains are multidomain, significant fractions of single domain grains are always present and presumed to be responsible for the stable remanence at all sites. Magnetic remanence is interpreted to be essentially primary because it preserves a record of both polarities which has since been tectonically rotated. Fifteen sites define a coherent dipolar axis with a mean direction of D/I=16·8/56·5° (α95=6·9°). This is rotated clockwise by 10·2±7·2° from the Eurasian field at 10 Ma and is interpreted to record block rotation during westward expulsion of lithosphere along the northern margin of the Anatolian region late in the Neotectonic history. Upper Cretaceous rocks from the northern side of this sector of the NAFZ exhibit rotations relative to Eurasia; whilst these may have been imparted partly during Eocene collision of the Istanbul and Sakarya zones, consistent counterclockwise motions show that differential block rotations are occurring here with the Galatean region bounded at its northern margin by the NAFZ. Copyright © 1999 John Wiley & Sons, Ltd.

Structure of the Galatean Volcanic Province, Turkey

The Galatean volcanic province (GVP), located in northwestern Anatolia, is an ENE-WSW-oriented belt. The province as a whole corresponds to a depression filled with volcanic and sedimentary rocks. The northern margin of the GVP is truncated by the North Anatolian fault, whereas it is surrounded by a continental sedimentary pile interfingering with volcanics on the south. Field and aerial photographic studies reveal that the GVP consists of several volcanic complexes scattered throughout the province. Nine of these complexes are recognized, each covering an area of hundreds of km2 of circular or ellipsoidal form, with moderately to well-preserved morphology. They include calderas, stratovolcanoes characterized by central vent (s), and radial flows of both lava and volcaniclastics. Several continental basins are disposed between the major volcanic complexes. These basins are isolated from one another or are partly connected and may differ in age and lithology. Available radiometric and paleontologic age det...