Vitric Tuff Research Articles

Middle Miocene volcanic flare up preceding and synchronous with the Langhian/Serravallian sea‐level decline in the North Pannonian Basin: Insights from 40Ar/39Ar dating, geo‐seismic analysis and 3D visualization of the subterranean Kráľová stratovolcano

AbstractThe Pannonian Basin System originated from the collision of the African and European tectonic plates, followed by the Miocene extensional collapse that led to the development of a back‐arc basins. Accurate dating is essential to comprehend the tectono‐volcanic evolution of the region, particularly in the under‐studied Danube Basin. Single‐grain 40Ar/39Ar dating has revealed that volcanic activity in the Danube Basin commenced around 14.1 million years ago, aligning with previous biostratigraphic and radioisotope data from nearby volcanic fields. The initial Middle Miocene pyroclastic deposits were generated by intermediate high K calc‐alkaline magmas, contributing significantly to the deposition of thick layers of fine vitric tuffs. The timing and chemistry of the volcanism are consistent with the Badenian rift phase in the Middle Miocene within the Carpathian–Pannonian region, suggesting an intraplate back‐arc volcanic environment. Three‐dimensional imaging has exposed the buried Kráľová stratovolcano, revealing its impressive scale with a thickness between 2620 and 5000 m and a base diameter of 18–30 km. Such dimensions place it among the ranks of the world's largest stratovolcanoes, indicating its substantial impact on the evolution of the Carpathian–Pannonian area. The complex formation history of the stratovolcano points to multiple phases of growth. Furthermore, the basin controlling Mojmírovce‐Rába fault's intersection with the stratovolcano implies that fault activity was subsequent to the volcanic activity, being younger than 14.1 million years. Regional age data consistently indicates that volcanic activity in the Danube Basin reached its zenith just prior to and during the lower/upper Badenian sea‐level fall (Langhian/Serravallian). K‐metasomatism is unique to the stratovolcanic structures and is not observed in the wider regional setting. This study supports the notion of an intricate, interconnected subterranean intrusive system within the stratovolcano, underscoring the complex interplay between geological structures and volcanic processes.

Short note. A new U-PB age for the Talampaya Formation: Stratigraphic and paleoclimatic implications

This paper presents a new U–Pb zircon age of 253.40 ± 1.06 Ma for the middle part of the Talampaya Formation, which is consistent with the previously reported dating of 252.38 ± 0.22 Ma at the top of the unit. The age herein presented was obtained from a tuff level intercalated into a fluvial sequence formed by finning-up cycles of massive conglomerates, cross-bedded sandstones, and laminated sandy mudstones interpreted as deposited by sandy meandering rivers with dominant sandy floodplains. In this context, a vitric tuff from a floodplain located 140 m from the base of the unit provided the zircons dated by the combination of LA-ICP-MS (Laser Ablation – Inductively Coupled Plasma – Mass Spectrometry).The radiometric age of 253.40 ± 1.06 Ma confirms the relocation of the Talampaya Formation in the Late Permian and demonstrates that at least the upper half and probably the whole of this unit was deposited during the Lopingian, a time interval scarcely represented in South America. This assumption is consistent with the age of 249.66 ± 0.11 Ma (early Triassic) reported in the overlying La Veteada Formation.The new age presented has paleoclimatic implications regarding the worldwide climatic aridification event that occurred at the end of the Late Paleozoic since it gives a relatively precise approximation to the onset of the aridization in this part of Gondwana during the Lopingian (circa 252.38 Ma).

A Unique Volcanic Jatibarang Reservoir: Facies Characterization and Fracture Calculation

Jatibarang structure, situated in Jatibarang low, one of the prolific sub-basin in the northwest Java basin, belongs to PT. Pertamina EP working area. One hundred seventy wells have been drilled, from which there were 56 production wells. Forty production wells were sunk on a volcanic reservoir. Since 1970, volcanic Jatibarang has faced disputed facies concepts, porosities heterogeneity, and permeability system. A fractured reservoir model was proposed. It was due to unique high-performance hydrocarbon in the early years, and then steeply depleted in the early next 3 years, and flat over 20 years. A unique petrophysical method was developed with various explosives and effusive facies. This study proposes a new facies determination concept related to unavailable default petrophysical plots usually used in the clastic-carbonate reservoir. The new concept of formation evaluation attempts to distinguish the fractured vitric tuff reservoir and non-reservoir zone, which is both effusive lava and explosive product. Reservoirs differed from common clastic-carbonate, typically high gamma-ray reservoir due to potassium feldspar composition. The fracture existence is reflected by a sonic overrunning density log aligned with a deep resistivity pattern. The width of the fracture apertures was measured, and spacing intensities were calculated. Finally, fracture permeability was estimated comprehensively to describe reservoir performance. Property models built with only sonic and triple combo have been debatable; however, advanced logging of JTB-211 has proven this accuracy method.

Characteristics and formation mechanism of the tight tuff reservoirs of the Upper Triassic Chang 7 member in the southern Ordos Basin, China

Organic-rich shales are commonly associated with tuff layers. Previous studies have mainly focused on the influence of water-laid tuffs on the primary productivity and enrichment of organic matter. Tuffs can also act as tight or low permeability reservoirs or as sweet spots in shales. However, the characteristics and formation mechanism of tight tuff reservoirs are poorly explored. The tuffs in the study area are divided into five lithologies: vitric tuff, crystal-vitric tuff, crystal tuff, tuffite, and tuffaceous sandstone. The pores in these tuffs have various types and sizes, and mainly include (1) intergranular pores, (2) intragranular pores, (3) dissolution pores, (4) seams around grains, (5) organic matter related pores, and (6) fractures. The tuffs form tight reservoir rocks with low porosity and permeability, ranging from 2.33% to 12.62% (average 7.2%) and from 0.000518 mD to 0.281mD (average 0.0783 mD), respectively. The average porosity and permeability of the tuffs are better than those of shales, and the pores in the tuff reservoirs are often filled with oil residues, which indicate that the tuff reservoirs may be favorable for oil and gas accumulations.The tuff reservoir qualities have strong heterogeneity, which are significantly controlled by lithology, grain size, components, devitrification, dissolution, and fluid pathway systems. Tuffs with large grain sizes commonly have high primary porosity with relatively more cracks and seams within and around grains, which can be conducive to the entry of late diagenetic fluids, which cause tuff reservoirs to be more prone to devitrification and dissolution. The devitrification of volcanic glass can produce abundant microcrystalline quartz, feldspars and intergranular pores, and can greatly improve the reservoir quality. Devitrification has generally occurred in the vitric tuffs and crystal-vitric tuffs, and the porosities have a positive covariation with the quartz contents in the two lithologies. The devitrification pores can be further enlarged by dissolution. Devitrification and dissolution were controlled by the tuff compositions and fluid actions. The fluid pathway systems, including scouring surfaces, bedding, fractures, and well-developed primary pores, controlled the fluid movement. Tuffs that contain high volcanic glass contents and coarse particles with abundant beddings and fractures are prone to intense devitrification and dissolution, which results in high reservoir quality.

The Engineering Characteristics and Classifications of Rock Masses along Road Section from Prambanan to Patuk, Yogyakarta, Indonesia

Several attraction places and agriculture area that essentials for tourism and villager to do their activities are located approximately 6 km along the road of Candi Ijo to Ngoro-Oro in between Prambanan and Patuk sub-districts, Yogyakarta, Indonesia. Many jointed rock masses along the road have the potential to fail. This paper describes the rock mass characteristic and quality determined using the Geological Strength Index (GSI) and Rock Mass Rating (RMR) classifications. The rock mass characteristic and quality were essentially the preliminary results of a study to evaluate stability of the rock slopes along the road of Candi Ijo to Ngoro-Oro. Field observation and laboratory tests were carried out to determine parameters of the GSI and RMR. The results show that the slopes in the study area consisted of tuffaceous sandstone, vitric tuff, lithic tuff, cemented tuffaceous sandstone, lapilli tuff, subarkose, laminated mudrock, and laminated tuffaceous sandstone. The intact rocks were classified as weak to very strong. The research area consisted of three rock mass qualities, namely fair rock mass quality having GSI between 30 and 45 and RMR between 41 and 60, good rock mass quality having GSI between 46 to 65 and RMR between 61 and 80, and very good rock mass quality having GSI > 65 and RMR between 81-100. The relationship between GSI and RMR obtained in this study was in good agreement with that proposed by Hoek et al. (1995).

Lithofacies and petrochemical characterization of volcano-sedimentary sequence of Chandil Formation around Kharidih-Bareda area, Seraikela-Kharsawan District, Jharkhand: implications for uranium mineralization

Mesoproterozoic Chandil Formation (ca. 1600 Ma) of North Singhbhum Mobile Belt record numerous features of felsic volcaniclastics and felsic to intermediate volcanics preserved in the central sector of the fold belt around Kharidih-Bareda area, Seraikela-Kharsawan district, Jharkhand. The felsic volcanic rocks exhibit flow bands, autoclasts and layering of crystal mushes revealing viscous nature of eruptives. The volcaniclastic sediments comprise of significant proportion of volcanic epiclasts and accidental lithic fragments. These volcaniclastics have been categorized into five prominent lithofacies viz, stratified lapilli tuff, banded tuff, tuff with penecontemporaneous deformation, welded lapilli stones, vitric tuff and volcanic bombs by field and petrographic studies of outcrops and subsurface borehole cores. The welded lapilli tuffs display fiamme and eutaxitic texture. Interlayering of the volcaniclastics, which are most often pyrite-rich, with psamo-pelitic lithology like carbonaceous phyllite, variegated phyllite, quartzite and minor limestone is suggestive of marine euxenic depositional environment. Petrographic study of the volcaniclastics indicated presence of glass shards, garnet phenocrysts, spherules of tremolite, ovoid to lenticular accretionary lapilli along with devitrified glassy material. Compositionally these felsic volcanics and volcaniclastics are rhyodacitic to andesitic in nature with peraluminous to meta aluminous in character. A/CNK values vary from 0.52 to 2.42 in felsic volcanics and from 0.12 to 1.63 in volcaniclastics. Signatures of arc magmatism is indicated by low concentration of HFS elements such as Nb (5-17 ppm), Ga (11-17 ppm) and Y (5-28 ppm). Elevated intrinsic content of uranium (3-8 ppm), Th/U ratio ranging from 1.2 to 13.2, presence of metamict allanite and zircon in volcanics and volcaniclastics reveal their suitability as a prospective source for search of uranium mineralization. The volcanic-volcaniclastic-clastic association of the Chandil Formation provides an ideal situation where provenance and province both are available. Thus, suitable litho-structural locales such as the concealed shear zones sympathetic to the Dalma thrust and South Purulia Shear Zone within the volcano-sedimentary package of Chandil Formation may be targeted as preferable sites for locating concealed uranium mineralization.

Time Defendability of Ground Resistance Properties and Its Application of Vitric Tuff on the Development of Ground Enhancement Material

Ground repair material is an essential part of the grounding system as a lightning rod to reduce the risk of lightning activity. Grounding repair materials consist of conductive and superconductive materials, commonly known as Ground Enhancement Materials (GEM). GEM has a low resistivity, very effectively supporting lightning shock energy to earth. Vitric tuff, a pyroclastic rock, is composed of an aluminosilicate (phyllosilicate) mineral group developed as a grounding improvement material. The primary purpose of this study was to determine the decrease in resistivity of vitric tuff in its development as a GEM. The research method consisted of field observations and laboratory experiments (treatment with chemical-physical activation and formulation with additives). The results showed that moisture content, SiO2/Al2O3 ratio (quartz and feldspar mineral/albite), clay mineral, crystal quality (impurities), carbon, and salt were influenced by vitric tuff resistivity. With the vitric tuff formulation and additives, the resistivity reduction is above 99%. Based on experiments, the best formulation of GEM made from tuff is 65% activated vitric tuff, 27% activated charcoal, 6% NaCl, and 2% Cement Material Cellulose. The formula produces a resistivity value of 0.0124 Ω-m, which is stable with time and meets GEM requirements (ρ ≤ 0.20 Ω-m).

Hydrothermal Alteration and Ore Metal Mineralisation at Temon, Pacitan, East Jawa, Indonesia.

Pacitan area is known as Tertiary volcanic arc in Java, as the result of subduction zone of the Indian-Australian Plate beneath the Eurasian Plate since Oligocene. It was superimposed volcanism which formed a wide area of hydrothermal alteration zone, resulting potential ore metals mineralization, such at Temon and its vicinities, Pacitan Regency, East Java Province, Indonesia. The aim of study was to analyze hydrothermal alteration and ore metal mineralization zones. Method was surface mapping, thin section analyses, mineragraphic analyses and X-Ray Diffraction (XRD) analyses. Field study observed denuded and deformed volcanic crater geomorphology. There are ore placer deposits within the sand dunes of Grindulu River, which it consists of andesitic lava and breccia of Early Oligocene Mandalika Formation; Early Miocene lithic and vitric tuffs; and dacitic intrusion. The dikes of dacite as the last of volcanism was the host rock controlling the zonation of alteration and mineralization stages. Oblique normal faults and shear faults were cross over dilating formed fractures, which were as bodies to depositing the ore metals. There are (zone 1st) the argillic clay consists of quartz+alunite+dickite+kaolinite±illite with vuggy structures, (zone 2nd) the argillic clay consists of quartz+montmorillonite±illite zone with quartz vents, brecciated and sulfide massive, and (zone 3rd) as the chloritized zone with low grade and supergene on the edge of hydrothermal alteration. It was fluid overprinted that very acid to the core of zone 1st (pH2-4) into more netral pH 4-6 (zone 2nd) and (pH5-6) in the edge zone 3rd. The potentials ore metal mineralization are Fe and Cu by pyrite, chalcopyrite, hematite, and covellite. Other potential ore metal mineralization was also from enargite by the supergene alteration.

Epithermal Zeolite Alteration Associated with Siliceous Sinters, Hydrothermal Eruption Breccias, and Gold-Silver Mineralization, Central Taupo Volcanic Zone, New Zealand

Abstract In the central Taupo Volcanic Zone, extensive zeolite (mordenite ± clinoptilolite) alteration occurs in late Quaternary rhyolitic vitric tuffs that were deposited in a lake formed by caldera collapse following the ~290 ka Ohakuri ignimbrite eruptions. Glass shards in lacustrine vitric tuffs of the Ngakuru Formation and in the underlying Ohakuri Formation ignimbrite are replaced by mordenite ± clinoptilolite, along with hydrothermal adularia, opal-A, opal-CT, and cristobalite. This mineral assemblage is also found in the outer alteration zones of the nearby Ohakuri and Tahunaatara epithermal gold prospects. Evaluation of whole-rock chemical analyses indicates that the zeolitized vitric tuffs show a slight gain in K, and Na, Ca loss relative to unaltered Ohakuri Formation pumice, which is reflected in the presence of hydrothermal adularia in the alteration assemblage. The mordenite ± clinoptilolite alteration is associated with siliceous sinters and hydrothermal eruption breccias that were formed in recently active (39–1.5 ka) geothermal systems. By analogy with geothermal systems elsewhere in the Taupo Volcanic Zone at Wairakei and Ohaaki, the mordenite ± clinoptilolite alteration was formed from dilute alkali-chloride aqueous liquid at 60° to 150°C. Based on the close association of the mordenite ± clinoptilolite alteration with siliceous sinters and hydrothermal eruption breccias in the central Taupo Volcanic Zone, it is classified as shallow, low-temperature, epithermal alteration. Mordenite ± clinoptilolite alteration has also been identified in Quaternary rhyolitic caldera settings in Japan and the United States, where it is termed “caldera-type zeolitization.” In exploration for epithermal Au-Ag deposits in rifted arc settings, such alteration may be overlooked, given its subtle appearance and distal location relative to veins that mark upflow areas.

Petrogenesis of Late Cretaceous volcanic-plutonic complex from Xiaoxiong caldera in East Zhejiang

破火山内出露的火山岩与浅成侵入岩为硅质岩浆演化研究提供了一个重要窗口，从而备受关注。小雄破火山内的火山-侵入杂岩是中国东南沿海晚白垩世岩浆活动的典型代表，包括小雄组火山岩（K₂x）与两类侵入岩（花岗斑岩、正长斑岩）。本文以小雄火山-侵入杂岩为研究对象，开展了系统的锆石U-Pb年代学、岩石学和地球化学研究，旨在深入探讨破火山内火山岩与侵入岩之间的成因联系和岩浆演化过程。系统的LA-ICP-MS 锆石U-Pb年代学研究表明，小雄组火山岩形成于98~88Ma，并具有多期次喷发的特点，可分为下段、中段和上段，年龄分别为98~96Ma（K₂x¹）、95~92Ma（K₂x²）、~ 88Ma（K₂x³）。小雄花岗斑岩形成年龄为90Ma；正长斑岩形成稍晚，约88Ma。与下段流纹质玻屑凝灰岩的Nd-Hf同位素组成[ε_Nd（t）=-8.3~-7.2， ε_Hf（t）=-11.8~-7.2]相比，中段流纹岩要更为亏损[ε_Nd（t）=-5.84~-5.32， ε_Hf（t）=-10.1~-0.5]。研究表明，小雄组流纹质火山岩的母岩浆可能起源于发生在深部岩浆房中渐进的壳幔相互作用，中段流纹岩的源区混入了更多的亏损幔源组分。中段流纹岩与花岗斑岩具有相似的Nd-Hf同位素组成，以及 互补的微量元素地球化学特征，由发生在浅部岩浆房的分离结晶作用和堆晶作用所制约。值得注意的是，正长斑岩与花岗斑岩并不存在直接的成因演化关系，两者应是不同的起源。不同的正长斑岩岩株具有高度一致的结晶年龄、微量元素特征以及Nd-Hf同位素组成，以上特征均表明小雄破火山内的正长斑岩具有相同的起源。正长斑岩母岩浆起源于富集岩石圈地幔的部分熔融，岩浆源区混入了来自亏损的软流圈地幔组分，其地球化学成分变化主要受普通辉石+磷灰石+钛铁矿的分离结晶所控制。;The association of volcanic and shallow plutonic rocks in calderas may provide important clues to the geochemical evolution of silicic magma systems, and thus it has received a lot of attention. The Xiaoxiong caldera, mainly composed of volcanic rocks of the Xiaoxiong Formation (K₂x) and two types of plutonic rocks (granite-porphyry and syenite-porphyry), is a typical product of Late Cretaceous magmatism in SE China. In this paper, we conducted petrological and geochemical studies, as well as zircon dating and trace element analysis for the coexisting volcanic and plutonic rocks from the Xiaoxiong caldera, aiming to constrain the magmatic origin and evolution processes and evaluate the petrogenetic relationship between the volcanism and plutonism. LA-ICP-MS zircon U-Pb dating results revealed that the Xiaoxiong Formation was formed in 98~88Ma with characteristics of multi-staged eruptions. The ages of the Ⅰ-, Ⅱ-, Ⅲ-cycle volcanic rocks are constrained at 98~96Ma (K₂x¹), 95~92Ma (K₂x²) and ~88Ma (K₂x³), respectively. Meanwhile, zircon U-Pb dating provides crystallization ages of ca. 90Ma for granite-porphyry and ca. 88Ma for syenite-porphyry. However, in terms of Nd-Hf isotopic compositions, the rhyolites from the middle section [ε_Nd(t)=-8.3~-7.2, ε_Hf(t)=-11.8~-7.2] record increasingly depleted characteristics to the rhyolitic vitric tuffs from the lower section [ε_Nd(t)=-5.84~-5.32, ε_Hf(t)=-10.1~-0.5], implying a progressive crust-mantle interaction, and more juvenile, Nd-Hf isotopically depleted materials were involved into the source of these rhyolites. The rhyolites from the middle section and the granite-porphyry show cogenetic and complementary geochemical signatures. Therefore, we suggest that they could be closely linked by fractional crystallization and crystal accumulation in a shallow magma chamber, i.e., these rhyolites are formed by the extraction of interstitial melt from crystal mush, while the granite-porphyry represents the residual crystal mush. It is worth to note that there is no directly evolutional relationship between granite-porphyry and syenite-porphyry, and they are more likely to have different magmatic origins. In addition, the syenite-porphyries of different stocks in the Xiaoxiong caldera have a highly consistent crystallization ages, trace element characteristics and Nd-Hf isotope compositions, which indicates that they have the same magmatic origins. The syenite-porphyry was generated probably by pyroxene+apatite+ilmenite -dominated fractional crystallization from basaltic magma that was produced by magma mixing between melts derived from depleted asthenosphere and subduction-related enriched lithospheric mantle.

Study on optimal selection of porosity logging interpretation methods for Chang 73 segment of the Yanchang Formation in the southwestern Ordos Basin, China

The physical properties of tight shale reservoirs have always been a hot topic of discussion, and the tuff reservoirs have also attracted more and more attention. Log predicting of the porosity is also important for the exploration and development of tight oil. Tight oil resources have been found in tight shale and tuff reservoirs in the Chang 7 Member of the Upper Triassic Yanchang Formation in the Ordos Basin, China. However, the logging method that effectively predicting porosity of the Chang 7 Member is lacking, and few people have discussed how to optimize the log interpretation methods. In this study, the characteristics of shale and tuff reservoirs were summarized by microscope and scanning electron microscope observation, X-ray diffraction, pore and permeability experiment, and the logging data. In order to find the optimal method of porosity prediction, four methods were performed: multiple regression fitting, multi-component volume model, porosity logging formula, and back propagation neural network method.The “Zhangjiatan Shale” of the Chang 7 Member is characterized by abundant sandy lamina and tuff lamina, compared with the tuff reservoir, the enrichment of pyrite (average 22.7 wt%) and total organic matter (>6%) increase the content of intercrystalline pores and organic matter related pores, the logging response is characterized by high natural gamma ray, low spontaneous potential and high acoustic. The tuff reservoir is mainly composed of vitric tuff and crystal-vitric tuff, hence, the rich in intergranular pore and micro-fracture can be explained by the dissolution and devitrification of vitric and crystal fragments, and the logging characteristic is opposite to that of the “Zhangjiatan Shale”. Four methods for predicting porosity are established. First, appropriate logging parameters are selected for regression fitting in the “Zhangjiatan Shale” (e.g., gamma ray, deep lateral logging resistivity, density and spontaneous potential) and tuff reservoir (e.g., acoustic, density, compensated neutron logging). Then, the rock multi-component volume model was established as rock skeleton, clay or tuff matter, organic matter, and pores. The logging parameters of the skeleton, clay and organic matter were obtained by intersection graphs, which were applied in the improved porosity logging formulas. The effect of organic matter on logging was considered into the traditional porosity prediction formula, a third prediction method was established. Finally, the BP method was introduced into the porosity prediction work, and the neural network parameters were adjusted according to the log and porosity data. The learning rate and the learning accuracy were set as 0.1 and 10−6 in the study area. The error analysis between the result predicted and measured shows that the multi-component volume model is suitable for the “Zhangjiatan Shale” (the correlative coefficient R>80%), while the back propagation neural network is the best method for the tuff reservoir (the correlative coefficient R>90%).

Permian sedimentary tuff tight reservoirs in the Santanghu Basin, NW China

Sedimentary tuffs comprise important tight oil reservoirs in the Middle Permian Tiaohu Formation in the Santanghu Basin. This paper describes three research advances made on these reservoirs. (1) There are many sets of sedimentary tuff in the second member of the Tiaohu Formation and they are the “sweet section” for tight oil exploration. Vitric, crystal-vitric, and argillaceous tuffs are the main reservoir types, of which the first two are more favorable. (2) A model was established to show how the volcanic edifice controls the type and distribution of the volcanic lacustrine tuff deposition. The crystal-vitric tuff is distributed in the lacustrine deposits nearest to the volcanic crater, and the vitric tuff is distributed on both sides of the active volcanic belt a certain distance from the crater, and this is the most favorable distribution area for sedimentary tuff. Later devitrification resulted in formation of a large number of micro-pores, and this is the main reason for the presence of favorable reservoirs. (3) The sedimentary tuff reservoir has undergone successive geological processes from formation of secondary dissolution pores, then hydrocarbon charge and accumulation, to compaction. The tight oil accumulation is the result of the coupling of the diagenetic evolution of the tuff in the Tiaohu Formation and the hydrocarbon generation and charging from the shale in the Lucaogou Formation.

Davut – Tazekent Civarındaki Kayaçların Stratigrafik ve Petrografik Özellikleri, Diyadin-Ağrı-Türkiye

The study is located in vicinity of Taşbasamak, Tazekent, Davut, Boyalan, Kuşburnu and Ulukent villages in the south of Diyadin district of Ağrı city. In the study area, Paleozoic aged Batıbeyli metamorphites which consist of crystallized limestones which contain calc-schist interlevels are observed at the bottom. The Upper Miocene aged Alibonca formation composed of conglomerate, trachyandesitic tuff-agglomerate, sandy limestone, marl, dolomite-dolomitic limestone and lacustrine limestone are located unconformably on these metamorphites. Upper Miocene aged Sekirdağ volcanites consisting of dacitic - rhyodacitic tuffs, agglomerates and lavas are observed by lateral - vertical transition over the Alibonca formation. Higher up, Lower Pliocene aged Solhan volcanites are composed of alkaline basaltic lavas are observed. The Solhan volcanites are covered by Upper Pliocene aged Hamur volcanites consisting of trachyandesitic lava and ignimbrite. Higher up, Upper Pliocene-Pleistocene aged Kale pyroclastics consisting of lapilli tuff, ash, volcanic bomb, slag and agglomerate with alkaline basalt composition are observed. These pyrolastics are covered by Upper Pliocene-Pleistocene aged Tutak volcanites which are composed of alkaline basalts. At the top, travertine and alluvium are found. Calcite + dolomite ± quartz ± muscovite mineral paragenesis is observed in metacarbonates belonging to Batıbeyli metamorphites. The tuffs belonging to the Kuşburnu pyroclastic member include quartz, plagioclase, sanidine, clinopyroxene (diopside/augite), biotite, amphibole (hornblende), sphene, opaque mineral, volcanic glass and litic fragment. These tuffs were named as lapillistone and ash tuff “according to grain size”, trachyandesite tuff “according to composition and grain size”, lapillistone, ash tuff and lapilli tuff “accoding to percentage distribution of grains” and vitric tuff “according to glass-crystals-lithic fragments composition”. The tuffs of Sekirdağ volcanites contain quartz, plagioclase, sanidine, biotite, amphibole (hornblende), opaque mineral, volcanic glass and litic fragment. The dacitic and rhyodacitic lavas belonging to these volcantecs include quartz, plagioclase, sanidine, biotite, amphibole (hornblende), opaque mineral, plagioclase microlites and volcanic glass. Tuffs belonging to Sekirdağ volcanites were named as lapillistone and ash tuff “according to grain size”, rhyodacitic tuff and dacitic tuff “according to composition and grain size”, lapillistone and ash tuff “according to percentage distribution of grains” and vitric tuff “according to glass-crystals-lithic fragments”. Alkaline basalts of Solhan volcanites include quartz, olivine, clinopyroxene (diopside/augite), apatite, opaque mineral and plagioclase microlites. Plagioclase, sanidine, amphibole (hornblende), clinopyroxene (diopside/augite), apatite, opaque mineral, plagioclase and sanidine microlites are observed in trachyandesites belonging to Tazekent trachyandesite member. Plagioclase, hornblende, clinopyroxene, sanidine, pumice fragments, litic fragments and volcanic glass are located in ignimbirites belonging to Dalören ignimbirite member. The tuffs of Kale pyroclastics include plagioclase, clinopyroxene (diopside/augite), olivine, opaque mineral, volcanic glass and litic fragment. Agglomerates of Kale pyroclastics include plagioclase, olivine, clinopyroxen (diopside/augite), orthopyroxen (enstatite), apatite, opaque mineral, volcanic glass and litic fragment. These tuffs were named as lapillistone “according to grain size”, basaltic tuff “according to composition and grain size”, lapilli tuff “according to percentage distribution of grains” and vitric tuff “according to glass-crystals-lithic fragments composition”. The agglomerate is in basaltic agglomerate composition “according to composition and grain size”. Alkali basalts belonging to Tutak volcanites include plagioclase, olivine, clinopyroxen (diopside/augite), orthoproxen (enstatite), apatite, opaque mineral and plagioclase microlites.

Mineralogy, chemistry, and genesis of zeolitization in Eocene tuffs from the Bayburt area (NE Turkey): Constraints on alteration processes of acidic pyroclastic deposits

Eocene vitric tuffs in the Bayburt area (NE Turkey) possess a dacite-rhyodacite composition and contain abundant altered glass shards and flattened fibrous pumice with lesser amounts of pyrogenic minerals (plagioclase, quartz, biotite, and sanidine). Zeolitization is common and generally develops in the glassy components. The main zeolite mineral found in the tuffs is clinoptilolite, with lesser amounts of analcime and mordenite (?). Smectite is the dominant clay mineral, with lesser amounts of kaolinite also present. Opal-CT, calcite, and dolomite occur as secondary minerals. Scanning electron microscopy studies reveal the dissolution of glass, with the development of popcorn-textured smectites and tabular clinoptilolites developed. The opal-CT spheres found on the clinoptilolite crystals appear to have crystallized simultaneously and are due to excess silica in the environment. Fibrous mordenite (?) also developed on the clinoptilolites. In the clinoptilolites Rr = 0.81–0.82, Si/Al = 4.20–4.70, and K+ is the dominant exchangeable cation (0.65–3.30) seen, together with lesser amount of Ca2+ (0.39–2.25) and Na+ (0.02–2.16). The degree of zeolitization increases with the content of glassy component in the tuffs. The formation of K-clinoptilolite is controlled by the SiO2/Al2O3 (4.9–7.0) and K2O/Na2O (0.8–10.8) ratios in the zeolitized tuffs. δ18OV-SMOW and δDV-SMOW values of clinoptilolite-rich tuffs range from 22 to 25.6‰ and from −96 to −111‰, respectively, which suggests that zeolitization occurred at low temperatures (30-55 °C) via fluid-rock interactions. Smectite was initially formed from the devitrification of glassy components and is associated with the increase in (Na++K++Ca2+)/H+ activity and the presence of high pH (~9–10) fluids. The zeolites subsequently developed within a saline-alkali shallow marine environment.

Geochemistry of the Zeolite-rich Miocene Pyroclastic Rocks from the Gördes, Demirci and Şaphane Regions, West Anatolia, Turkey

The western Anatolian Miocene volcano-sedimentary basins in the Gordes, Demirci and Şaphane regions host abundant heulandite/clinoptilolite (hul/cpt) bearing widespread zeolitized pyroclastic rocks. Lithostratigraphy of these zeolitic pyroclastic levels show comparable association. Petrography and geochemistry of all the samples show mainly rhyolithic and rhyodacitic character and ash size vitric tuffs. Polarized microscopy and X-ray diffraction determinations of the samples show composition of 55–95 wt % hul/cpt and accessory of smectite, illite/mica, opal–CT, quartz, K–feldspar, plagioclase and opaque minerals. Geochemical results obtained from the studied samples represent hul/cpt–rich facieses formed under the moderate alkaline conditions in these pyroclastic units. Correlation of geochemical results and concentration of hul/cpt in these pyroclastic rocks gives some chemical data on zeolitization process and on adsorption and ion-exchange character of hul/cpt type of zeolites. Depleted and enriched elements by zeolitization have similar ionic radii in general. Ca and H2O clearly increased, Si, Na and Si/Al ratio decreased in hul/cpt bearing Lower-Middle Miocene pyroclastic rocks of western Anatolia. Additionally, Sr, Nb, Th, Ni, Hf, Cs, Pb and Ta increased, and Zr, Co, W and most of the rare earth elements (REE) decreased in highly hul/cpt–rich pyroclastics.

The comparison of Qhv Tuff and Kasai Tuff characteristic based on petrography study of Batanghari Area, Ogan Komering Ulu District, South Sumatera

Tuff which located in Batanghari, South Sumatra, especially in the research area, interpreted comes from 2 different formation, which are Qhv (Quarter Holocene volcanic) and Kasai, mostly, the Tuff is dominated by Qhv which is the younger volcanic rock unit while tuff from Kasai deposited while orogeny at the Pliocene-Pleistocene, located in the northern part of research area. There are 2 kinds of method, which are field observation that consist of geological mapping, the surface observation and sample picking and we also did laboratory analysis which consist of remote sensing and petrography analysis. The field observation shows there is a different in the characteristic, Qhv tuff shows the rocks which is very weathered consist of feldspar, quartz and hornblende while Kasai tuff shows much resistant rocks with fresh colour of grey till choco brown, consist of feldspar, quartz and a bit of biotite. Petrography analysis shows that there is embayment texture on Qhv tuff it shows by the change of crystal shape meaning that erosion process is very high there also the appearance of included old crystal by the younger crystal meaning that this type of tuff is belong to crystal tuff (Schmid, 1981), while on the Kasai shows the appearance of glass which recrystallized meaning that the rock is having low to mid devitrification, Schmid, 1981 classified this rocks into type of Vitric Tuff.

Lithic-rich and lithic-poor ignimbrites and their basal deposits: Sovana and Sorano formations (Latera caldera, Italy)

Conceptual models explaining the characteristics of ignimbrites and their basal deposits have mainly focused on variations in particle concentration and speed of the parent pyroclastic currents. Here, we focus on the effects of relative proportions of clasts that are well coupled to the carrier gas phase and those that are poorly coupled, i.e., the proportions of fine and/or low-density clasts compared to coarse and/or dense clasts. We document facies and macroscopic clast populations of two ignimbrite-producing eruptive sequences of similar volume and composition, both erupted from Latera caldera (central Italy). The Sovana ignimbrite has 1–15 vol% dense lithic clasts and locally up to 70 vol% in lithic-rich domains. It preserves evidence of emplacement of multiple overlapping flow units with local internal channeling. The ignimbrite is underlain by two basal deposits: (1) a radially distributed, 20–80-cm-thick vitric tuff referred to as BUS (basal unit Sovana) that thins gradually with distance and shows evidence of emplacement by lateral currents; and (2) a fines-depleted, lenticular, massive lapilli tuff, up to 20 cm thick, with abundant lithic clasts. The Sorano ignimbrite, in contrast, has < 1 vol% dense lithic clasts. It contains multiple reverse coarse-tail graded emplacement units, but we observed no internal channeling. In most places, its basal deposits are 20–100 cm of dominantly planar-parallel, 5–10 cm-thick, reverse coarse-tail graded tuff beds. However, in local depressions near the tops of paleocanyons that were filled by Sorano ignimbrite, the basal deposits are up to 2 m thick and are clearly cross stratified. We interpret the different deposit characteristics in terms of recent modeling and experimental results. The Sovana eruption involved major caldera collapse that introduced abundant dense lithic clasts into the erupting mixtures. BUS may have partly resulted from expulsion of a dilute, fine-grained mixture at the site where the pyroclastic fountain(s) impacted the ground, which then propagated outward as a dilute pyroclastic current ahead of the main ignimbrite-producing currents; the expulsion process is promoted by collapsing mixtures rich in poorly coupled clasts. The fines-depleted layer overlying BUS was deposited by rapid sedimentation of abundant dense clasts from the head of the ash-cloud surge, which accompanied the concentrated underflow that deposited the ignimbrite. Spatial and temporal variations in dense-clast abundance, and likely other parameters, during eruption resulted in multiple flow units. The Sorano eruption lacked poorly coupled clasts and did not produce an expulsion-driven current. Its ash-cloud head deposited ash and small pumice lapilli that were able to move in traction carpets prior to being overridden by a concentrated underflow. The overriding ash-cloud bodies locally deposited cross-stratified horizons in depressions high on the canyon walls, before they were inundated as the concentrated underflows filled the canyons with ignimbrite. To summarize, the differences between the ignimbrites and their basal deposits can be largely attributed to the differences in proportions of poorly coupled relative to well-coupled particles in the collapsing eruptive mixtures; the resulting conceptual model simplifies the previous range of interpretations for basal deposits, and is consistent with recent modeling and experimental results.

Prospecting for Clinoptilolite-Type Zeolite in a Volcano-Sedimentary Terrain Using ASTER Data: A Case Study from Alborz Mountains, Northern Iran

Zeolites are hydrated alumino-silicates of alkali metals and alkaline earth cations which occur in sedimentary and volcano-sedimentary terrains. In this study, visible–near-infrared and shortwave infrared data of ASTER were evaluated in prospecting for zeolite in part of the green tuff belt of the Alborz Mountains, northern Iran. The study area is dominantly covered by sedimentary and volcano-sedimentary rocks, in which zeolite minerals occur only in the Late Eocene vitric tuff. Principal components (PC) analysis and spectral information divergence (SID) were used to discriminate and map the sedimentary and volcano-sedimentary units and the zeolite-rich areas, respectively. The X-ray diffraction and reflectance spectroscopy results indicated that clinoptilolite is the major type of zeolite mineral in this area. Comparing a color composite image, produced from PC images 1–3–5 as R–G–B, with the published geological map and the field investigations indicated that major sedimentary and volcano-sedimentary units as well as their alluvial deposits were discriminated efficiently. Results of the SID method, using an image-derived spectrum of clinoptilolite as a reference, showed good agreements with the field observations. The results of this study indicated that ASTER data are useful for discriminating various sedimentary and volcano-sedimentary units as well as clinoptilolite-type zeolite-rich areas in arid and semiarid terrains.

Adsorption of volatile organic compounds onto natural porous minerals.

The abundance of natural porous minerals and their low cost make them the potential adsorbents for VOCs (volatile organic compounds). In this paper, three natural minerals (diatomite, stellerite and vitric tuff) and their corresponding acid-treated minerals were used as adsorbents. The adsorption performances of minerals were investigated by the adsorption breakthrough curves of VOCs. The results indicated that the properties of organic compounds such as boiling point and polarity and the surface area and pore volume of minerals had obvious effects on the adsorption of VOCs over minerals. Increasing adsorption temperature and relative humidity would have negative effects on the VOC adsorption of minerals. The adsorption capacity of 2-heptanone over acid stellerite decreased by 7.2% as the temperature rose from 25°C to 45°C. The adsorption capacity of acid stellerite for 2-heptanone reduced by 60.9% when relative humidity increased from 0% to 75%. Minerals were tested for five adsorption-regeneration cycles to study the reusability. Better fittings of Thomas model, pseudo-first order kinetics model, and Freundlich model were showed in fitting the adsorption. Overall, porous minerals with high specific surface area and pore volume have promising prospect in VOCs adsorption.

Genetic analysis of bentonite—Permian Wangpo shale in Liangshan, Hanzhong, South Shaanxi Province

Fine pyroclastic materials form bentonites through subsidence, hydrolysis, and argillation in alkaline marine environments, which can further transform to K‐bentonite. Bentonites or K‐bentonites are quite popular with geologists because their formation often reflects geologic events. However, studies mainly focus on K‐bentonite, and research on ordinary bentonites in China is almost nonexistent. Recent research shows that the Wangpo shale consists of ordinary bentonites. Through thorough field investigations, indoor experimentation and analysis, and comparison of petrologic and geochemical characteristics of the Wangpo shale with K‐bentonites, this paper explores the nature and genesis of source rocks and provides a basis for the study of ordinary bentonites. The petrological study shows that the Wangpo shale is a montmorillonite vitric tuff, which is mainly composed of montmorillonite and small amounts of quartz, opal, and heulandite. These indicate that it is a typical bentonite. In addition, the rock contains an abundance of fossils reflecting a coastal–shallow sea depositional environment. We chose the elements with stable chemical characteristics for obtaining source rock characteristics, and the results showed that the Wangpo shale has a genetic relationship with neutral alkaline magma. As a boundary between the Upper Permian and the Middle Permian, the Wangpo shale has an internal connection with eruption of the Emeishan basalt in Southwest China. In combination with previous work, it can be inferred that studying the volcanic activity represented by the Wangpo shale plays an important role in studying Emeishan large igneous provinces and the end‐Guadalupian mass extinction.