Resin bonding surface treatment methods for conventional silica-based dental ceramics are not rel... more Resin bonding surface treatment methods for conventional silica-based dental ceramics are not reliable for glass infiltrated high alumina content In-Ceram ceramics. This study developed an alternative surface treatment to improve resin bonding of glass-infiltrated aluminum oxide ceramic blasting with diamond particles and then observed the efficiency of this treatment. Material and methods. In-Ceram test specimens were prepared and divided into 2 groups. All specimens were sandblasted with Al(2)O(3), and blasted with diamond particles and 2 adhesive resins were applied. After bonding and storage in humid conditions, shear bond strength values were measured with a universal testing machine. Surface roughness and fracture interfaces were determined with a perthometer and a SEM. The highest bond strength was obtained on the samples blasted with diamond particles (group II). The differences between the 2 groups and the 2 adhesive resin cements were both statistically significant. Panavia-Ex cement exhibited higher bond strength than Super-Bond cement. This higher bond strength was attributed to ceramic oxide and ester bond and the mechanical properties of Panavia-Ex cement.
The effect of residual stresses of CeO2 buffer layers on Ni substrate for YBCO coated conductors ... more The effect of residual stresses of CeO2 buffer layers on Ni substrate for YBCO coated conductors is considered. CeO2 films were fabricated on Ni tape substrate from the solutions prepared from alkoxide precursors, solvent, chelating agent and modifying liquid material by using a reel-to-reel sol–gel technique. SEM observation showed that CeO2 buffer layers had crack-free, pinhole-free and continuous structures and the characteristic feature of the films was grain boundary grooves. Finite element method (FEM) was used to compute the temperature and stress fields of the sample with CeO2/Ni configuration. The solution was obtained by ANSYS 5.4 analysis programme. The effect of time and residual stresses of the films with different thickness was examined in terms of the FEM results. It was found that the positions of the improved temperature and thermal stresses were considerably affected material properties, time and film thickness for CeO2 buffer layers and the thermal stresses values increased upon increasing the film thickness.
The Central Anatolian Plateau (CAP) displays a wealth of volcanoes of Miocene to Recent age with ... more The Central Anatolian Plateau (CAP) displays a wealth of volcanoes of Miocene to Recent age with different geochemical characteristics and is, therefore, a unique opportunity to derive information on the physical state of the Anatolian lithosphere during CAP development. Cappadocia is a part of the Anatolian block which is moving westward by lateral extrusion as a consequence of north-south convergence between Africa-Arabia and Eurasia (Sengör et al., 1985) and has developed extensive volcanism during the past 13My. Cappadocia hosts several stratovolcanoes such as Mt Erciyes and Mt. Hasan as well as numerous monogenetic vents and some andesitic dacitic relicts of lava fields intercalated within the ignimbritic sequence. The stratovolcanoes are strongly calcalkaline, although some young adventive basalts reflect a transitional character with their mildly alkaline nature. Petrology of those calcalkaline volcanics shows a decrease of subduction-related component and an increase of the intraplate signature through time (Deniel et al., 1998). We roughly distinguish two sequences of volcanism over the plateau as lavas sequence and ignimbrite sequence. Lavas Sequence: The volcanism of CAVP is started around 12-13 My with isolated Kecikalesi volcano which has typical characteristics of IAT (Island Arc Tholeiite). Similar volcanism is also represented by Erdas Dag Andesitic massive that initiated to erupt 11 My ago and continue till to 8 My. Early Erdas Dag lavas exhibit typical subduction related features with their adakitic nature (high Sr/Y and La/Yb ratios). Those ratios decrease with time. The lava sequence of CAVP continue with Damsa and Topuz Dag lavas that emplaced at around 10 and 8 My, respectively. Then lava sequence of Hodul Dag volcanism (5-6 My) is characterised by andesitic lavas domes and flows. At similar time span Keslik andesitic system also emplaced. Those lavas have relatively high (mildly high) Sr/Y ratios with their adakite-like nature. Following this episodes, scarce adakites emplaced over the plateau between 4-5 My. There is no adakit or adakite-like volcanism younger than 4 My. Around 3-4 My, some ordinary andesites extruded. Around 2 My, interestingly starts contemporenous Tholeiite-(mildly)Alkaline suite association. The CAVP witnesses Rhyolite-Basalt Bimodal volcanism since the last 1,5 My. Ignimbritic Sequence: The famous Cappadocian Ignimbrites are interstratified with either lavas or fluvio-lacustrine deposits. There is at least 9 different ignimbrite namely: Kavak, Zelve, Sarımaden, Sofular, Cemilkoy, Tahar, Gordeles, Kizilkaya, Valibabatepe ignimbrites (Le Pennec et al., 1994). All ignimbrites were individually produced over the plateau between 9-5 My, except Valibabatepe (2,5 My) which is related to Mt.Erciyes. There is no major incision/denudation process till to 5 My, than incision rate increased and was calculated around 450-500 meters as post-5 My, and 100-120 meters as post-2,5 My. We also tried to apply Sahagian&Maus,(1994) method to estimate the paleoaltimeter. 7 different lavas were sampled for this purpose but only two lavas gave some reliable result (lavas of 8,2 My and of 0,094 My). According to those rough estimations, the older lava that is actually located at 1430 meters was emplaced at around 410 meters from sea level and the younger one was solidified at 906 meters (actually 903 meters). It is important to quote that this method has ± 400 meters of uncertainty. Finally, a model of sub-crustal detachment-delamination of lower crust occured around 5 My is proposed as a responsible of CAP formation which is under the influence of extensional tectonic regime.
Cappadocian Ignimbrites, emplaced during Upper Miocene and cover approximately 40.000km2 area at ... more Cappadocian Ignimbrites, emplaced during Upper Miocene and cover approximately 40.000km2 area at central Anatolia (Le Pennec et al., 1994). Cappadocia hosts at least 9 Mio-pliocene aged ignimbrites. Although there is a debate on the stratigraphy of those ignimbrites, we uses terminology of Le Pennec et al., 1994 which is basing on Pasquaré 1968 proposition with some differences. So we use Cappadocian Ignimbrite terminology as Kavak, Zelve, Sarımadentepe, Cemilköy, Tahar, Gördeles, Sofular and Kızılkaya ignimbrites. Although, several works have been performed on these ignimbrites, the source areas are poorly known. In Le Pennec et al., 1994; it is proposed that the source vents of Kavak and Zelve ignimbrites might be Cardak village which is located in the South of Nevsehir. One of the important method used in the determination of paleoflow direction of ignimbrites is anisotropy of magnetic susceptibility (AMS). In the literature AMS method had been previously performed on Kizilkaya ignimbrite (Le Pennec et al,1998). In our study; oriented samples are taken from 8 ignimbrites, outcropping in the region, in order to determine the paleoflow directions. Totally; the samples from 70 different sites (dominantly Kavak and Zelve ignimbrites) have been taken. In the determination of the directions of the samples, magnetic and sun compasses are used in the field. Totally, 400 oriented core samples were prepared for magnetic measurement. Kavak and Zelve ignimbrites are unwelded and the oldest ignimbrites in the region. Because of their soft, unconsolidated state, it was difficult to take oriented samples from those ignimbrites at the site. For this purpose; special corers for our portable core logger were manufactured. So, unconsolidated, unwelded and brittle materials were sampled in situ. Preliminary data obtained at the end of our studies illuminate the possible source area of the ignimbrites, especially of Kavak and Zelve ignimbrites.
Direct observations have shown that most fine-grained particles fall from volcanic plumes as aggr... more Direct observations have shown that most fine-grained particles fall from volcanic plumes as aggregates (Gilbert and Lane, 1994). For instance, fine-ash particles up to 50 µm fell mainly as aggregates from Vulcanian explosions and co-pyroclastic flow plumes from dome collapses in the eruption of Soufriére Hills Volcano, Montserrat, during the 1995-1999 period (Bonadonna et al., 2002a). Aggregation is a major influence on tephra fallout and on the characteristics of the associated deposits causing premature fallout of fine particles as responsible for polymodal grain-size distributions (Carey and Sigurdsson, 1982; Brazier et al., 1983; Bonadonna et al., 2002a) and anomalous thicknesses of deposits (Carey and Sigurdsson, 1982; Hildreth and Drake, 1992; Bonadonna et al., 2002b). Careful investigation of different types of ash aggregates is important for interpretation of the origin of pyroclastic deposits which can be critically important in hazard assessments (Brown et al., 2010). Therefore, incorporation of ash aggregates into simulations and numerical modelling for hazard assessments are crucial. However, too little is known about the dynamics of aggregation (Gilbert and Lane, 1994; Bonadonna et al., 2002b) therefore detailed studies on ash aggregates may improve the results of modelling and enable interpretations to be made of atmospheric conditions within past eruption plumes (Gilbert and Lane, 1994). We found a new type aggregate in ash-fall deposits of Late Quaternary rhyolitic explosions from Acigol Complex, Central Anatolia, Turkey. This type of aggregate has not been described previously. They resemble to the cylindrical aggregates which were reported by Scolamacchia et al. (2005) for the first time in the volcanological literature. However, our new type aggregates are in ramiform with branches interconnecting to a main tubular void on the long axis of the aggregates. The main voids have maximum diameter of 1 mm. The branches are tubular voids having diameters smaller than the main void on the long axis of the aggregate. These aggregates are found within 1-4 mm grain size intervals of deposits. The inner structures of aggregates were observed after X-ray tomography imaging. Probably the particles which were the initial nucleus for aggregation are twigs or plant stems. The existence of any carbonaceous material in the main void and grains-size distribution in aggregates will be presented after SEM and X-ray spectroscopy analysis.
The Mt. Erciyes stratovolcano was built up in an intraplate tectonic environment as a consequence... more The Mt. Erciyes stratovolcano was built up in an intraplate tectonic environment as a consequence of Eurasian and Afro-Arabian continental collision. However, the volcanic products generally exhibit a calc-alkaline character; minor amounts of tholeiitic basalts are also present. Tholeiitic basalts show high Fe2O3, MgO, CaO, low K2O, and depleted Ba, Nb, and especially Rb (2.3-5.97 ppm) contents, low 87Sr/86Sr (0.703344-0.703964), and high 143Nd/144Nd (0.512920-0.512780) isotopic ratios. These compositional features show that they were derived from a depleted asthenospheric mantle source, possibly a MORB-like source component. In contrast, calc-alkaline basaltic rocks exhibit relatively high large-ion-lithophile and high-field-strength elements, high 87Sr/86Sr (0.704591-0.70507) and low 143Nd/144Nd (0.51272-0.512394) isotopic ratios.The bulk-rock chemistry of the tholeiitic basalts reflects the chemical composition of the extracted source component. Furthermore, trace-element concentrations may be calculated from an accepted mantle source component (starting composition) for different degrees of partial melting. These calculations also provide a sensitive approach to the origin of tholeiitic basalts. Modeled trace-element compositions of tholeiitic basalts are calculated from a primitive mantle composition. Calculated trace-element compositions imply that tholeiitic basalts are derived by minor fractional melting (1-1.5 %), in the absence of assimilation or deep-crustal melting. The calc-alkaline basalts were subsequently produced from initially tholeiitic basalts by the way of an AFC (assimilation-fractional crystallization) process, with a crustal assimilation of 10-15 %.The geochemical data, partial melting, and AFC modeling all indicate that basaltic products have a complex evolutionary history involving partial melting from a MORB-like mantle source. The assimilation and fractional crystallization processes are considered as providing an example for the chemical evolution of basaltic products, from tholeiitic to calc-alkaline, in an intraplate environment.
Two of the oldest known Cappadocian ignimbrites (Kavak and Zelve ignimbrites, ~ 9 Ma) are thought... more Two of the oldest known Cappadocian ignimbrites (Kavak and Zelve ignimbrites, ~ 9 Ma) are thought to have been originated from a caldera located in the vicinity of Acıgöl (Nevşehir) area. During Upper Miocene, volcanism of the region is characterized by andesitic/adakitic lavas and domes, whereas Quaternary volcanism is represented by bimodal basaltic and rhyolitic products. Quaternary rhyolitic volcanism is represented by domes, dome complexes, associated lava flows, phreatomagmatic eruption centers and ignimbrite flows with fall deposits. Quaternary rhyolitic products are mostly aphyric with minute plagioclase + orthopyroxene + magnetite ± amphibole microphenocrystic assemblage with apatite and zircon as accessory phases. They exhibit a marked geochemical evolution towards more differentiated compositions through time. Rhyolites older than 75 ka (74 -75% SiO2) have higher Al2O3, Fe2O3, CaO content than their younger counterparts. Moreover, younger rhyolites are strongly depleted in Ba and Sr, have lower LREE and higher HREE contents with a sharp negative Eu anomaly. Chondrite normalized REE and primordial mantle normalized patterns of both compatible and incompatible elements suggest the crystal fractionation of a plagioclase dominant assemblage with scarce orthopyroxene and amphibole would yield the youngest rhyolitic compositions. Besides, evident temporal transition from meta/peraluminous towards mildly peralkaline whole rock compositions (Agpaitic Index: 0,91 - 0,96) of Quaternary rhyolites would be linked to the intraplate rifting of the Central Anatolia.
Volcanic ash particles are important components of explosive eruptions and their surface texture ... more Volcanic ash particles are important components of explosive eruptions and their surface texture is the subject of intense research. Characterization of ash surfaces is crucial for understanding the physics of the volcanic plumes, remote sensing measurements of ash and aerosols, interfacial processes, modelling transportation and deposition of tephra and characterizing eruptive styles. A number of different methods have been used over the years to arrive at surface area estimates. The more common methods include estimates based on the geometric considerations (geometric surface area) and the physisorption of gas molecules on the surface of interest (physical surface area). In this study, micro computed tomography (micro-CT), a non-destructive method providing three-dimensional data enabled the measurement of surface areas and volumes of individual ash particles. Specific surface area estimates for ash particles were also obtained using nitrogen as gas adsorbent and the BET (Brunauer-Emmett-Teller) model. Results were compared with the values obtained from SEM stereoscopic imaging and geometric considerations. Surface area estimates of micro-CT and SEM stereoscopic imaging overlaps with mean specific surface area results of 0.0167 and 0.0214 m2/g, respectively. However, ash particle surface textures present quite a deviation from that of their geometric forms and approximation to sphere and ellipsoid both seemed to be inadequate for representation of real ash surfaces. The higher surface area estimate (> 0.4 m2/g) obtained from the technique based on physical sorption of gases (BET model here) was attributed to its capability for surface areas associated even with angstrom-sized pores. SEM stereoscopic and/or micro-CT imaging were suggested for characterization of textures on macro-pore regions of ash particles.
Journal of Volcanology and Geothermal Research, 2003
Mount Erciyes (3917 m) is the largest stratovolcano of Central Anatolia (Turkey). The volcanologi... more Mount Erciyes (3917 m) is the largest stratovolcano of Central Anatolia (Turkey). The volcanological evolution of Mount Erciyes from Pliocene-Quaternary to historical times exhibits two distinct stages: (1) Koç Dağ and (2) Erciyes. During the Koç Dağ stage, basaltic and andesitic lava flows were emitted from the cinder cones of Kızıl Tepe and Topakkaya Tepe. Then, Koç Dağ pyroclastics were emplaced, leading to a caldera collapse of 14×18 km in diameter with a volume estimated at 110 km 3. Two eruption phases separated by scoria fall and mud flow deposits are recognised associated with the caldera forming event. During Phase 1, plinian fall and pumice flows were emplaced on the eastern part of the volcano. Plinian fall deposits occur more than 50 km away from the source area. The volume of tephra is estimated at 63.3 km 3 (16 km 3 dense rock equivalent (DRE)), including 62 km 3 of plinian fall and 1.3 km 3 pumice flow deposits. Phase 2 mainly consists of pyroclastic flow deposits (two pumiceous flow units and Valibaba Tepe Ignimbrite (VTI)). The pumiceous flow deposits (4.2 km 3 DRE) extend 30 km from the inferred source area towards the north and northeast. The final pyroclastic flows of Phase 2 occurred 2.8 Ma ago and produced the VTI. The VTI is a low aspect ratio welded ignimbrite and its volume is estimated at 40 km 3 DRE. Plinian fall deposits (0.8 km 3 DRE) preceded the VTI and are only observed on the eastern part of the volcano, covering an area of 1500 km 2. During the Erciyes stage, two eruptive cycles are defined. The first cycle (2.6-0.17 Ma) is characterised by effusive, extrusive and weakly explosive activity with emplacement of andesitic lava flows, dacitic dome flows, basaltic andesite lava flows, and andesitic cones. The second cycle involved dacitic extrusive and explosive activity, located at the summit area, and produced block-and-ash flows derived from rhyodacitic domes. Plinian fall, surge and pumice flow deposits were emplaced prior to rhyodacitic dome extrusions. The last event was the emplacement of debris avalanche deposits related to sector collapse caldera.
Resin bonding surface treatment methods for conventional silica-based dental ceramics are not rel... more Resin bonding surface treatment methods for conventional silica-based dental ceramics are not reliable for glass infiltrated high alumina content In-Ceram ceramics. This study developed an alternative surface treatment to improve resin bonding of glass-infiltrated aluminum oxide ceramic blasting with diamond particles and then observed the efficiency of this treatment. Material and methods. In-Ceram test specimens were prepared and divided into 2 groups. All specimens were sandblasted with Al(2)O(3), and blasted with diamond particles and 2 adhesive resins were applied. After bonding and storage in humid conditions, shear bond strength values were measured with a universal testing machine. Surface roughness and fracture interfaces were determined with a perthometer and a SEM. The highest bond strength was obtained on the samples blasted with diamond particles (group II). The differences between the 2 groups and the 2 adhesive resin cements were both statistically significant. Panavia-Ex cement exhibited higher bond strength than Super-Bond cement. This higher bond strength was attributed to ceramic oxide and ester bond and the mechanical properties of Panavia-Ex cement.
The effect of residual stresses of CeO2 buffer layers on Ni substrate for YBCO coated conductors ... more The effect of residual stresses of CeO2 buffer layers on Ni substrate for YBCO coated conductors is considered. CeO2 films were fabricated on Ni tape substrate from the solutions prepared from alkoxide precursors, solvent, chelating agent and modifying liquid material by using a reel-to-reel sol–gel technique. SEM observation showed that CeO2 buffer layers had crack-free, pinhole-free and continuous structures and the characteristic feature of the films was grain boundary grooves. Finite element method (FEM) was used to compute the temperature and stress fields of the sample with CeO2/Ni configuration. The solution was obtained by ANSYS 5.4 analysis programme. The effect of time and residual stresses of the films with different thickness was examined in terms of the FEM results. It was found that the positions of the improved temperature and thermal stresses were considerably affected material properties, time and film thickness for CeO2 buffer layers and the thermal stresses values increased upon increasing the film thickness.
The Central Anatolian Plateau (CAP) displays a wealth of volcanoes of Miocene to Recent age with ... more The Central Anatolian Plateau (CAP) displays a wealth of volcanoes of Miocene to Recent age with different geochemical characteristics and is, therefore, a unique opportunity to derive information on the physical state of the Anatolian lithosphere during CAP development. Cappadocia is a part of the Anatolian block which is moving westward by lateral extrusion as a consequence of north-south convergence between Africa-Arabia and Eurasia (Sengör et al., 1985) and has developed extensive volcanism during the past 13My. Cappadocia hosts several stratovolcanoes such as Mt Erciyes and Mt. Hasan as well as numerous monogenetic vents and some andesitic dacitic relicts of lava fields intercalated within the ignimbritic sequence. The stratovolcanoes are strongly calcalkaline, although some young adventive basalts reflect a transitional character with their mildly alkaline nature. Petrology of those calcalkaline volcanics shows a decrease of subduction-related component and an increase of the intraplate signature through time (Deniel et al., 1998). We roughly distinguish two sequences of volcanism over the plateau as lavas sequence and ignimbrite sequence. Lavas Sequence: The volcanism of CAVP is started around 12-13 My with isolated Kecikalesi volcano which has typical characteristics of IAT (Island Arc Tholeiite). Similar volcanism is also represented by Erdas Dag Andesitic massive that initiated to erupt 11 My ago and continue till to 8 My. Early Erdas Dag lavas exhibit typical subduction related features with their adakitic nature (high Sr/Y and La/Yb ratios). Those ratios decrease with time. The lava sequence of CAVP continue with Damsa and Topuz Dag lavas that emplaced at around 10 and 8 My, respectively. Then lava sequence of Hodul Dag volcanism (5-6 My) is characterised by andesitic lavas domes and flows. At similar time span Keslik andesitic system also emplaced. Those lavas have relatively high (mildly high) Sr/Y ratios with their adakite-like nature. Following this episodes, scarce adakites emplaced over the plateau between 4-5 My. There is no adakit or adakite-like volcanism younger than 4 My. Around 3-4 My, some ordinary andesites extruded. Around 2 My, interestingly starts contemporenous Tholeiite-(mildly)Alkaline suite association. The CAVP witnesses Rhyolite-Basalt Bimodal volcanism since the last 1,5 My. Ignimbritic Sequence: The famous Cappadocian Ignimbrites are interstratified with either lavas or fluvio-lacustrine deposits. There is at least 9 different ignimbrite namely: Kavak, Zelve, Sarımaden, Sofular, Cemilkoy, Tahar, Gordeles, Kizilkaya, Valibabatepe ignimbrites (Le Pennec et al., 1994). All ignimbrites were individually produced over the plateau between 9-5 My, except Valibabatepe (2,5 My) which is related to Mt.Erciyes. There is no major incision/denudation process till to 5 My, than incision rate increased and was calculated around 450-500 meters as post-5 My, and 100-120 meters as post-2,5 My. We also tried to apply Sahagian&Maus,(1994) method to estimate the paleoaltimeter. 7 different lavas were sampled for this purpose but only two lavas gave some reliable result (lavas of 8,2 My and of 0,094 My). According to those rough estimations, the older lava that is actually located at 1430 meters was emplaced at around 410 meters from sea level and the younger one was solidified at 906 meters (actually 903 meters). It is important to quote that this method has ± 400 meters of uncertainty. Finally, a model of sub-crustal detachment-delamination of lower crust occured around 5 My is proposed as a responsible of CAP formation which is under the influence of extensional tectonic regime.
Cappadocian Ignimbrites, emplaced during Upper Miocene and cover approximately 40.000km2 area at ... more Cappadocian Ignimbrites, emplaced during Upper Miocene and cover approximately 40.000km2 area at central Anatolia (Le Pennec et al., 1994). Cappadocia hosts at least 9 Mio-pliocene aged ignimbrites. Although there is a debate on the stratigraphy of those ignimbrites, we uses terminology of Le Pennec et al., 1994 which is basing on Pasquaré 1968 proposition with some differences. So we use Cappadocian Ignimbrite terminology as Kavak, Zelve, Sarımadentepe, Cemilköy, Tahar, Gördeles, Sofular and Kızılkaya ignimbrites. Although, several works have been performed on these ignimbrites, the source areas are poorly known. In Le Pennec et al., 1994; it is proposed that the source vents of Kavak and Zelve ignimbrites might be Cardak village which is located in the South of Nevsehir. One of the important method used in the determination of paleoflow direction of ignimbrites is anisotropy of magnetic susceptibility (AMS). In the literature AMS method had been previously performed on Kizilkaya ignimbrite (Le Pennec et al,1998). In our study; oriented samples are taken from 8 ignimbrites, outcropping in the region, in order to determine the paleoflow directions. Totally; the samples from 70 different sites (dominantly Kavak and Zelve ignimbrites) have been taken. In the determination of the directions of the samples, magnetic and sun compasses are used in the field. Totally, 400 oriented core samples were prepared for magnetic measurement. Kavak and Zelve ignimbrites are unwelded and the oldest ignimbrites in the region. Because of their soft, unconsolidated state, it was difficult to take oriented samples from those ignimbrites at the site. For this purpose; special corers for our portable core logger were manufactured. So, unconsolidated, unwelded and brittle materials were sampled in situ. Preliminary data obtained at the end of our studies illuminate the possible source area of the ignimbrites, especially of Kavak and Zelve ignimbrites.
Direct observations have shown that most fine-grained particles fall from volcanic plumes as aggr... more Direct observations have shown that most fine-grained particles fall from volcanic plumes as aggregates (Gilbert and Lane, 1994). For instance, fine-ash particles up to 50 µm fell mainly as aggregates from Vulcanian explosions and co-pyroclastic flow plumes from dome collapses in the eruption of Soufriére Hills Volcano, Montserrat, during the 1995-1999 period (Bonadonna et al., 2002a). Aggregation is a major influence on tephra fallout and on the characteristics of the associated deposits causing premature fallout of fine particles as responsible for polymodal grain-size distributions (Carey and Sigurdsson, 1982; Brazier et al., 1983; Bonadonna et al., 2002a) and anomalous thicknesses of deposits (Carey and Sigurdsson, 1982; Hildreth and Drake, 1992; Bonadonna et al., 2002b). Careful investigation of different types of ash aggregates is important for interpretation of the origin of pyroclastic deposits which can be critically important in hazard assessments (Brown et al., 2010). Therefore, incorporation of ash aggregates into simulations and numerical modelling for hazard assessments are crucial. However, too little is known about the dynamics of aggregation (Gilbert and Lane, 1994; Bonadonna et al., 2002b) therefore detailed studies on ash aggregates may improve the results of modelling and enable interpretations to be made of atmospheric conditions within past eruption plumes (Gilbert and Lane, 1994). We found a new type aggregate in ash-fall deposits of Late Quaternary rhyolitic explosions from Acigol Complex, Central Anatolia, Turkey. This type of aggregate has not been described previously. They resemble to the cylindrical aggregates which were reported by Scolamacchia et al. (2005) for the first time in the volcanological literature. However, our new type aggregates are in ramiform with branches interconnecting to a main tubular void on the long axis of the aggregates. The main voids have maximum diameter of 1 mm. The branches are tubular voids having diameters smaller than the main void on the long axis of the aggregate. These aggregates are found within 1-4 mm grain size intervals of deposits. The inner structures of aggregates were observed after X-ray tomography imaging. Probably the particles which were the initial nucleus for aggregation are twigs or plant stems. The existence of any carbonaceous material in the main void and grains-size distribution in aggregates will be presented after SEM and X-ray spectroscopy analysis.
The Mt. Erciyes stratovolcano was built up in an intraplate tectonic environment as a consequence... more The Mt. Erciyes stratovolcano was built up in an intraplate tectonic environment as a consequence of Eurasian and Afro-Arabian continental collision. However, the volcanic products generally exhibit a calc-alkaline character; minor amounts of tholeiitic basalts are also present. Tholeiitic basalts show high Fe2O3, MgO, CaO, low K2O, and depleted Ba, Nb, and especially Rb (2.3-5.97 ppm) contents, low 87Sr/86Sr (0.703344-0.703964), and high 143Nd/144Nd (0.512920-0.512780) isotopic ratios. These compositional features show that they were derived from a depleted asthenospheric mantle source, possibly a MORB-like source component. In contrast, calc-alkaline basaltic rocks exhibit relatively high large-ion-lithophile and high-field-strength elements, high 87Sr/86Sr (0.704591-0.70507) and low 143Nd/144Nd (0.51272-0.512394) isotopic ratios.The bulk-rock chemistry of the tholeiitic basalts reflects the chemical composition of the extracted source component. Furthermore, trace-element concentrations may be calculated from an accepted mantle source component (starting composition) for different degrees of partial melting. These calculations also provide a sensitive approach to the origin of tholeiitic basalts. Modeled trace-element compositions of tholeiitic basalts are calculated from a primitive mantle composition. Calculated trace-element compositions imply that tholeiitic basalts are derived by minor fractional melting (1-1.5 %), in the absence of assimilation or deep-crustal melting. The calc-alkaline basalts were subsequently produced from initially tholeiitic basalts by the way of an AFC (assimilation-fractional crystallization) process, with a crustal assimilation of 10-15 %.The geochemical data, partial melting, and AFC modeling all indicate that basaltic products have a complex evolutionary history involving partial melting from a MORB-like mantle source. The assimilation and fractional crystallization processes are considered as providing an example for the chemical evolution of basaltic products, from tholeiitic to calc-alkaline, in an intraplate environment.
Two of the oldest known Cappadocian ignimbrites (Kavak and Zelve ignimbrites, ~ 9 Ma) are thought... more Two of the oldest known Cappadocian ignimbrites (Kavak and Zelve ignimbrites, ~ 9 Ma) are thought to have been originated from a caldera located in the vicinity of Acıgöl (Nevşehir) area. During Upper Miocene, volcanism of the region is characterized by andesitic/adakitic lavas and domes, whereas Quaternary volcanism is represented by bimodal basaltic and rhyolitic products. Quaternary rhyolitic volcanism is represented by domes, dome complexes, associated lava flows, phreatomagmatic eruption centers and ignimbrite flows with fall deposits. Quaternary rhyolitic products are mostly aphyric with minute plagioclase + orthopyroxene + magnetite ± amphibole microphenocrystic assemblage with apatite and zircon as accessory phases. They exhibit a marked geochemical evolution towards more differentiated compositions through time. Rhyolites older than 75 ka (74 -75% SiO2) have higher Al2O3, Fe2O3, CaO content than their younger counterparts. Moreover, younger rhyolites are strongly depleted in Ba and Sr, have lower LREE and higher HREE contents with a sharp negative Eu anomaly. Chondrite normalized REE and primordial mantle normalized patterns of both compatible and incompatible elements suggest the crystal fractionation of a plagioclase dominant assemblage with scarce orthopyroxene and amphibole would yield the youngest rhyolitic compositions. Besides, evident temporal transition from meta/peraluminous towards mildly peralkaline whole rock compositions (Agpaitic Index: 0,91 - 0,96) of Quaternary rhyolites would be linked to the intraplate rifting of the Central Anatolia.
Volcanic ash particles are important components of explosive eruptions and their surface texture ... more Volcanic ash particles are important components of explosive eruptions and their surface texture is the subject of intense research. Characterization of ash surfaces is crucial for understanding the physics of the volcanic plumes, remote sensing measurements of ash and aerosols, interfacial processes, modelling transportation and deposition of tephra and characterizing eruptive styles. A number of different methods have been used over the years to arrive at surface area estimates. The more common methods include estimates based on the geometric considerations (geometric surface area) and the physisorption of gas molecules on the surface of interest (physical surface area). In this study, micro computed tomography (micro-CT), a non-destructive method providing three-dimensional data enabled the measurement of surface areas and volumes of individual ash particles. Specific surface area estimates for ash particles were also obtained using nitrogen as gas adsorbent and the BET (Brunauer-Emmett-Teller) model. Results were compared with the values obtained from SEM stereoscopic imaging and geometric considerations. Surface area estimates of micro-CT and SEM stereoscopic imaging overlaps with mean specific surface area results of 0.0167 and 0.0214 m2/g, respectively. However, ash particle surface textures present quite a deviation from that of their geometric forms and approximation to sphere and ellipsoid both seemed to be inadequate for representation of real ash surfaces. The higher surface area estimate (> 0.4 m2/g) obtained from the technique based on physical sorption of gases (BET model here) was attributed to its capability for surface areas associated even with angstrom-sized pores. SEM stereoscopic and/or micro-CT imaging were suggested for characterization of textures on macro-pore regions of ash particles.
Journal of Volcanology and Geothermal Research, 2003
Mount Erciyes (3917 m) is the largest stratovolcano of Central Anatolia (Turkey). The volcanologi... more Mount Erciyes (3917 m) is the largest stratovolcano of Central Anatolia (Turkey). The volcanological evolution of Mount Erciyes from Pliocene-Quaternary to historical times exhibits two distinct stages: (1) Koç Dağ and (2) Erciyes. During the Koç Dağ stage, basaltic and andesitic lava flows were emitted from the cinder cones of Kızıl Tepe and Topakkaya Tepe. Then, Koç Dağ pyroclastics were emplaced, leading to a caldera collapse of 14×18 km in diameter with a volume estimated at 110 km 3. Two eruption phases separated by scoria fall and mud flow deposits are recognised associated with the caldera forming event. During Phase 1, plinian fall and pumice flows were emplaced on the eastern part of the volcano. Plinian fall deposits occur more than 50 km away from the source area. The volume of tephra is estimated at 63.3 km 3 (16 km 3 dense rock equivalent (DRE)), including 62 km 3 of plinian fall and 1.3 km 3 pumice flow deposits. Phase 2 mainly consists of pyroclastic flow deposits (two pumiceous flow units and Valibaba Tepe Ignimbrite (VTI)). The pumiceous flow deposits (4.2 km 3 DRE) extend 30 km from the inferred source area towards the north and northeast. The final pyroclastic flows of Phase 2 occurred 2.8 Ma ago and produced the VTI. The VTI is a low aspect ratio welded ignimbrite and its volume is estimated at 40 km 3 DRE. Plinian fall deposits (0.8 km 3 DRE) preceded the VTI and are only observed on the eastern part of the volcano, covering an area of 1500 km 2. During the Erciyes stage, two eruptive cycles are defined. The first cycle (2.6-0.17 Ma) is characterised by effusive, extrusive and weakly explosive activity with emplacement of andesitic lava flows, dacitic dome flows, basaltic andesite lava flows, and andesitic cones. The second cycle involved dacitic extrusive and explosive activity, located at the summit area, and produced block-and-ash flows derived from rhyodacitic domes. Plinian fall, surge and pumice flow deposits were emplaced prior to rhyodacitic dome extrusions. The last event was the emplacement of debris avalanche deposits related to sector collapse caldera.
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