The varto caldera (Bingöl, Eastern Anatolia) explosive eruption products and caldera formation

Varto Kaldera volkanı, Kuvaterner döneminde oluşumunu tamamlamasının ardından, Varto Fay Zonutarafından deforme edilerek günümüzde yarım Kaldera morfolojisi ile sonuçlanmıştır. VartoKaldera’sının oluşumu patlamalı püskürümler sonucu açığa çıkan piroklastik yoğunluk akıntı çökelleriyleyakından ilişkilidir. Bu çalışmada Kaldera çökmesine sebep olan püskürüm ürünlerinin fasiyes analizleriyapılarak bu ürünler detaylı olarak tanıtılmıştır. Kaldera çökmesiyle ilişkili beş farklı ignimbirittanımlanmıştır. Kaldera çökmesinin ardından patlamalı püskürümlerin devam ettiği ve Kaldera içindedepolandığı tespit edilmiştir. Ayrıca bu ignimbiritler ile eş yaşlı çökelen sedimanter kırıntılar arasındafasiyes ilişkileri de tespit edilmiştir. Volkano-sedimanter istifler içinde çeşitli yumuşak deformasyonyapıları ile kırılgan deformasyon yapıları tespit edilmiştir. Bu deformasyon yapılarının volkanikpatlamalar sırasında volkano-sismik aktiviteler sonucu oluştuğu sonucuna ulaşılmıştır.The Varto Caldera volcano has been deformed by the Varto Fault Zone after completing its formationthrough the Quaternary period, resulting in the recent morphology of the half caldera. The formationof the Varto Caldera is closely related to the pyroclastic density current deposits that were erupted asa result of explosive eruptions. In this study, facies analysis of the erupted materials that cause calderacollapse has been carried out, and these products have been introduced in detail. Five differentignimbrites related to the caldera collapse have been identified. After the collapse of the caldera, it wasdetermined that the explosive eruptions continue their volcanic activities and are deposited in thecaldera. In addition, facies relations were determined between these coeval ignimbrites andsedimentary deposits. Various soft deformation structures and brittle deformation structures havebeen identified through volcano-sedimentary sequences. It is concluded that these deformationstructures were formed as a result of volcano-seismic activities during volcanic eruptions

Uşak-Güre havzasının Volkano-sedimanter evrimi, Batı Anadolu

Uşak-Güre havzası Batı Anadolu'da Menderes Masifinin kuzeyinde yer alan KD?GB uzanımlı iyi korunmuş bir havzadır. Uşak-Güre havzası, Menderes Masifi Çekirdek Kompleksine (MMÇK) ait metamorfik kayaçlarının yüzeylemesine ait kayıtlar içeren Alt ve Üst Miyosen volcano-sedimanter istifler içermektedir. Yeni 40Ar/39Ar radyometrik yaş verileri Senezoyik volkanizmasının İnay grubuyla eş zamanlı olarak (17.29 My) Beydağı volkanın yerleşimiyle başladığını göstermektedir. En genç yaş verisi güneydeki Beydağı volkanından (12.15 My) elde edilmiş olup, volkanik aktivenin kuzeyden güneye doğru göçüne işaret etmektedir. Düşük açılı sıyrılma fay düzlemleri havzada ilk defa tanımlanmıştır. Simav Sıyrılma Fayının (SSF) taban bloğunda kalan Menderes Masifi Metamorfik kayaçlarına ait incekesit görüntüleri sünümlü-kırılgan deformasyon geçiş özelliklerini göstermektedir. Uşak-güre havzasında üç stratovolkan tanımlanmıştır. Stratovolkanlar karasal-yarı karasal ortam özellikleri sunarken volkanik istifler efüzif, ekstrüzif ve eksplozif faz özelliklerine sahiptir. Eksplozif volkanizma ürünleri ve bununla ilişkili magma-su etkileşimleri Batı Anadolu'da ilk defa tanımlanmıştır. Ayrıca, Uşak-Güre havzasında üç farklı volkanik birim sınıflandırılmıştır: bunlar (1) şoşonit, latit ve riyolitik lavlar ile dasitik ve andezitik piroklastik kayaçlardan oluşan Beydağı volkanik birimi; (2) potasik ortaç bileşimli lavlardan oluşan (trakit ve latitler) Payamtepe volkanik birimi ve (3) andezit ve latitik dayklardan oluşan Karaağaç daykları. Uşak-Güre havzasındaki volkanik kayaçlar MORB-normalize çoklu element diyagramlarında, Nb-Ta ve Ti tüketilmesi ile LILE ve LREE elementlerinin zenginleşmesiyle karakterize edilmektedir. Volkanik kayaçların jeokimyasal özellikleri, mafik ve feslik uç üyeleri ile aynı zamanda karışım özelliği gösteren magma bileşiminden baskın olarak piroksenlerin ve plajiyoklazların ayrımsal kristallenme süreçlerine maruz kaldıklarını göstermektedir. The Uşak-Güre basin is a well-preserved NE?SW-trending basin located on the northern part of the Menderes Massif, in western Anatolia. The basin contains a Lower to Upper Miocene volcano-sedimentary succession that records the un-roofing of the metamorphic rocks of the Menderes Massif. The new 40Ar/39Ar radiometric data demonstrate that Cenozoic volcanism commenced (17.29 Ma) with the emplacement of the Elmadağ volcano, synchronously with deposition of the İnay group. The youngest radiometric age is obtained from the Beydağı volcano (12.15 Ma) in the south, indicating that the volcanic activity migrated from north to south with time. Low-angle detachment surfaces are clearly defined in the basin for the first time. Photomicrographs of the metamorphic rocks of the Menderes Massif as a footwall unit of the Simav Detachment Fault (SDF), show that transition of the ductile to brittle deformation. Three stratovolcanoes has been described in the Uşak-Güre basin. These stratovolcanoes display the features of subaqueous-subaerial environments, and all volcanic sequences consist of complex successions of effusive-extrusive and explosive phases. The products of the explosive volcanism and related magma-water interactions have been described for the first time in the western Anatolia. Three distinct volcanic unit are classified 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. Volcanic rocks of the 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

Structural evolution of the Usak-Gure supra-detachment basin during Miocene extensional denudation in western Turkey

The Usak-Gure basin is a NE-SW-trending extensional basin located in the northern part of the Menderes Massif, in western Anatolia. The Usak-Gure basin contains a Lower to Upper Miocene volcano-sedimentary succession that records the unroofing of the metamorphic rocks of the Menderes Metamorphic Core Complex. We propose a new structural mechanism based on geological mapping and detailed kinematic fault analysis from each of the evolutionary phases. We also propose that north-to NE-dipping low-angle detachment surfaces define the basin boundaries and have identified three stages of deformation throughout the Miocene: the Early Miocene deformation phase (D-2) is characterized by low-angle normal faulting (Simav detachment fault) in the supra-detachment Usak-Gure basin, which marks the initiation of the extensional tectonics during the latest Oligocene; the Middle Miocene deformation phase (D-3) refers to volcano-tectonic activities during accumulation of the Inay Group; the Late Miocene deformation phase (D-4) is related to late Miocene tectonic activity widely responsible for deposition of the Asartepe Formations and uplift of the metamorphic rocks in the Usak basin margin. In addition, we propose that the eastern part of the Menderes Massif was delimited by the 'Usak-Mugla transtensional transfer zone' from Middle Miocene time throughout the eastern part of the Menderes Metamorphic Core Complex

Isotopic evidence for a transition from subduction to slab-tear related volcanism in western Anatolia, Turkey

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 0 isotopic analyses from the Miocene volcanic rocks of the Usak-Gure 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 Kirka-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 U Usak-Gure 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 Usak-Mugla 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 11 Ma), and possibly since the Early Miocene. (C) 2014 Elsevier B.V. All rights reserved

Growth, destruction and volcanic facies architecture of three volcanic centres in the Miocene Usak-Gure basin, western Turkey: Subaqueous-subaerial volcanism in a lacustrine setting

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 Usak and Cure basins accumulated a thick fluvio-lacustrine fill in which three distinct volcanic edifices (Elmadag, Itecektepe and Beydagi) 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

Stress fields around magma chambers influenced by elastic thermo-mechanical deformation: implications for forecasting chamber failure

© 2021, International Association of Volcanology & Chemistry of the Earth's Interior.Defining the conditions that lead to the rupture of a magma chamber is essential to forecast eruptions. So far, models simulating magma chamber dynamics have neglected the effects of elastic thermal expansion in the host rocks surrounding a new injection of magma, focusing instead primarily on elastic-plastic deformation and more recently, on visco-elastic deformation. Here we fill this gap by building a suite of elastic thermo-mechanical models to determine the stress field around a variably heated crustal magma chamber. We first consider linear elastic mechanical models with only the effect of magma pressure. We then present purely thermal models simulating heat distribution around a heated chamber. Finally, we present coupled linear elastic thermo-mechanical models that highlight the influence of temperature on the distribution of crustal stresses. Results show that thermal expansion–induced stresses generate two competing consequences: (1) they increase the level of shear stress around the magma chamber and (2) they partially suppress the level of tensile stress generated by the magmatic pressure. These competing effects influence the short-timescale conditions required for the failure of immature magmatic systems and hence the nucleation of dikes which may ultimately feed eruptions during unrest. Therefore, soon after a new magmatic recharge event, the contribution of temperature increase in the host rocks, following the new influx of magma into a crustal magma chamber, should be considered

Petrogenesis and Ar-40/Ar-39 geochronology of the volcanic rocks of the Usak-Gure basin, western Turkiye

In spite of much research over the past 30 years, the dynamic evolution, origin of the volcanism and geometrical-stratigraphical relations of the NE-SW-trending basins in western Anatolia are poorly understood. The Usak-Gure 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 Usak-Gure basin: (1) the Beydagi 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 Karaagac dikes composed of andesite and latite. The Beydagi volcanic unit occurs in three different NE-SW-trending volcanic centers Beydagi, Itecektepe and Elmadag calderas from southwest to northeast, respectively. The oldest radiometric ages for the Beydagi volcanic unit are from the Elmadag volcanic center in the north and range from 17 to 16 Ma. The data indicate that volcanism was active during the latest early Miocene. The youngest radiometric age for the Beydagi volcanic unit is obtained from the Beydagi caldera located (12 Ma) in the south. The data indicate that Beydagi volcanism was active in the late middle Miocene and migrated from north to south with time. Ar-40/Ar-39 ages of the Payamtepe volcanic unit are restricted to a short period between 16.0 and 15.9 Ma. Volcanic rocks of the Usak-Gure 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. (C) 2010 Elsevier B.V. All rights reserved

Van bölgesindeki Urartu merkezlerinde kullanılan kayaçlara ilişkin petrografik gözlemler

Urartu Krallığına ait yerleşimler, Van Gölü Havzası’nda Paleozoik yaşlı mermer türü temel kayaçlarından Kuvaterner yaşlı bazaltik kayaçlara kadar oldukça zengin bir kayaç grubu üzerinde yer almaktadır. Urartu kalelerinde yapı malzemesi olarak genellikle bazalt ve andezit türü volkanik kayaçlar ile yer yer kireçtaşı, traverten ve kumtaşı gibi farklı tip kayaçlar kullanılmıştır. Van Gölü’nün kuzeyinde ve batısındaki Pliyo-Kuvaterner yaşlı volkanik sahalar, bazalt ve andezitik gibi volkanik kayaçlar için doğusunda bulunan Paleosen-Eosen yaşlı sahalar kırıntılı ve kireçtaşları için ve güneydoğusunda bulunan Kuvaterner yaşlı sahalar traverten tipi karbonatlı kayaçlar için potansiyel alanları temsil etmektedir. Bu çalışmada Van Gölü Havzasındaki önemli Urartu merkezlerinden olan Van Kalesi, Çavuştepe, Ayanis, Toprakkale, Zivistan, Aliler, Keçikıran ve Körzüt kaleleri ile Minua Kanalı gibi tarihi yerleşimlere ait yapılardan örnekler alınmıştır. Alınan kayaç örneklerinin petrografik özelliklerini ayrıntılı inceleyerek, Urartu mimarisinde kullanılan kayaçların daha iyi tanınması amaçlanmıştır. Ana kayadan ve tarihi yapılardan alınan örneklerin karşılaştırılma yapılarak, yapı inşa malzemesinin kaynağını tespit edilmesinde ve taş ocakçılığı ile malzemelerin tarihi nakil yollarının belirlenmesinde önemli bilgiler sunacağı düşünülmektedir

Van bölgesindeki Urartu merkezlerinde kullanılan kayaçlara ilişkin petrografik gözlemler

Urartu Krallığına ait yerleşimler, Van Gölü Havzası’nda Paleozoik yaşlı mermer türü temel kayaçlarından Kuvaterner yaşlı bazaltik kayaçlara kadar oldukça zengin bir kayaç grubu üzerinde yer almaktadır. Urartu kalelerinde yapı malzemesi olarak genellikle bazalt ve andezit türü volkanik kayaçlar ile yer yer kireçtaşı, traverten ve kumtaşı gibi farklı tip kayaçlar kullanılmıştır. Van Gölü’nün kuzeyinde ve batısındaki Pliyo-Kuvaterner yaşlı volkanik sahalar, bazalt ve andezitik gibi volkanik kayaçlar için doğusunda bulunan Paleosen-Eosen yaşlı sahalar kırıntılı ve kireçtaşları için ve güneydoğusunda bulunan Kuvaterner yaşlı sahalar traverten tipi karbonatlı kayaçlar için potansiyel alanları temsil etmektedir. Bu çalışmada Van Gölü Havzasındaki önemli Urartu merkezlerinden olan Van Kalesi, Çavuştepe, Ayanis, Toprakkale, Zivistan, Aliler, Keçikıran ve Körzüt kaleleri ile Minua Kanalı gibi tarihi yerleşimlere ait yapılardan örnekler alınmıştır. Alınan kayaç örneklerinin petrografik özelliklerini ayrıntılı inceleyerek, Urartu mimarisinde kullanılan kayaçların daha iyi tanınması amaçlanmıştır. Ana kayadan ve tarihi yapılardan alınan örneklerin karşılaştırılma yapılarak, yapı inşa malzemesinin kaynağını tespit edilmesinde ve taş ocakçılığı ile malzemelerin tarihi nakil yollarının belirlenmesinde önemli bilgiler sunacağı düşünülmektedir