Acid Volcanics Research Articles

Geochemistry and REE tetrad effect of the acidic volcanics and associated stream sediments, southeast G. El-Hadid area, Central Eastern Desert, Egypt

Geochemistry and REE tetrad effect of the acidic volcanics and associated stream sediments, southeast G. El-Hadid area, Central Eastern Desert, Egypt

Evidence of Siderian juvenile-like contribution to the continental arc magmatism in the Western Guanambi-Correntina block, São Francisco Craton (Brazil)

The Guanambi-Correntina Block, a basement relic within the São Francisco Craton, played a determining role in the stabilization of the South American plate during the Paleoproterozoic, preceding the formation of the Nuna-Columbia supercontinent. Despite its magnitude, the western part of the block is mainly hidden by Neoproterozoic to Phanerozoic sedimentary covers, limiting the exposition of a significant section of the craton. In the study area, the Correntina Complex and the Rio Corrente Suite crop out within the Paleoproterozoic basement in an erosional window showing a diverse assemblage of plutonic, volcanic, and metasedimentary lithologies interpreted as part of a continental arc setting. This study employs a comprehensive approach encompassing geological mapping, lithogeochemistry, whole rock Sm–Nd and Rb–Sr isotopic analyses, and zircon U–Pb-Hf data from metaplutonic and metavolcanic rocks aiming the investigation of the pre-stabilization tectonic stages of the São Francisco lithosphere. The U–Pb-Hf zircon data reveal a crystallization age of 2183 ± 9 Ma for the acid volcanism, characterized by a juvenile isotopic signature (εHf = +5.7 to +9.4) and TDMHf between 2.2 and 2.4 Ga. Nd–Sr whole rock geochemistry of a sanukitoid rock from the metaplutonic unit indicates εNd(t) of +3.05, TDMNd of 2.31 Ga, and 86Sr/87Sr(i) of 0.70173, for which a zircon U–Pb crystallization age of 2324 ± 9 Ma has been obtained, establishing it as the oldest known Paleoproterozoic occurrence in the São Francisco Craton basement. The results unveil the Correntina Complex as one of the oldest paleoproterozoic records of continental magmatic arc relics within the São Francisco Craton, recording one of the earliest Paleoproterozoic events in the eastern South American plate. A geological evolution model envisages juvenile crustal production during the Siderian to Rhyacian periods in the western Guanambi-Correntina Block, corroborating similar episodes documented for other regions of the craton. This study contributes to our understanding of the early tectonic processes and improves the knowledge of the paleoproterozoic terranes that shaped the São Francisco Craton.

Genesis of the rare metals mineralisation in Um Safi acidic volcanics, Central Eastern Desert, Egypt

The rare metals mineralisation in Um Safi area occurs in the acidic volcanics (mainly rhyolite and volcanogenic tuffs). The microscopic investigation revealed that they are highly altered and subjected to several alteration processes where the hydrothermal solution played the master role in redistribution of the rare metals. The mineralogical study configured three groups of rare metals mineralisation including: (a) rare metals of the radio-elements (thorite), (b) rare metals of the trace elements and REEs (zircon, xenotime, chernovite, ferro-columite, allanite, bastnäsite and cerianite) and (c) rare metals of the base metals (tungsten minerals and cassiterite). The assemblage of Wolframite–Heubnerite–cassiterite–copper and fluorite associated with sulfides indicating magmatic to hydrothermal transition mineralisation. The hydrothermal fluids rich in F and As cause the alteration of some primary minerals such as xenotime, allanite and wolframite into the secondary chernovite, bastnäsite and schellite, respectively. The study also clarified that the emplacement of granitic offshoots into rhyolite played an important role in the re-distribution of some rare elements.

Geochemistry and geochronology of early Triassic tephra from SW China: implications for biological evolution and tectonics

ABSTRACT Late Permian to middle Triassic volcanic activities were very strong, however, volcanic records in the early Triassic strata are less reported than those of the Permo-Triassic boundary and the Triassic Olenekian-Anisian boundary in the Yangtze plate, especially within the Sichuan basin. We conduct zircon U-Pb dating and geochemical analysis of the tephra which was first found in the early Triassic Jialingjiang Formation from the Maliuping section, Hechuan, Chongqing. The volcanic ash in the paper yields the new 248.5 ± 0.7 Ma U-Pb age consistent with those of volcanic ashes in these contemporaneous strata in the Yangtze plate. Geochemical characters of whole-rock samples show lower contents in SiO2, K2O and higher components in Al2O3, CaO, MgO, relatively enriched LREE and depleted HREE with distinct negative Eu anomaly, and conspicuous Ba, Nb, Ta, Sr, P, Ti depletion and Th, U, K, Nd enrichment, which is similar to those of the Mung Bean rock of the Triassic Olenekian-Anisian boundary, and those of acidic volcanics from the Sanjiang orogenic belt and Shiwandashan-Qiangfang suture zone during the Early-Middle Triassic. Trace elements of whole rock and analysed zircons of the tuff imply its primary magma derived from Rhyodacite/Dacite and its tectonic setting of volcanic arc granite with continental crust affinity. The early Triassic volcanism during the syn-collision stage of the Paleo-Tethys evolution was less active than those of the Permo-Triassic boundary and the Triassic Olenekian-Anisian boundary, while the volcanic event may have a crucial effect on prolonging fully biotic recovery and entirely ecosystem turnover soon after the Permian-Triassic mass extinction.

THE RELEVANCE OF THE STUDY OF THE PRIBREZHNY VOLCANIC COMPLEX IN THE CONTEXT OF THE HISTORY INVESTIGATIONS OF SOUTH KAMCHATKA

The present paper contains a review of publications, geological maps and reports on the study of the Pribrezhny volcanic complex of South Kamchatka. The Pribrezhny volcanic complex is comprised of a number of closeset volcanic massifs stretching chain-like along the narrow coastline of the Beregovoy ridge from the Avacha Bay to the Vestnik Bay. The relevance of the work is related to the necessity of revising the geodynamic history of formation of the study area which stems from emergence of some fragmentary, contradictory information about magmatic complexes of South Kamchatka. The paper presents the data on magmatic rocks penetrated in the coastal cliffs of South Kamchatka. Consideration is being given to their formation conditions in the context of a once-popular theory of geosynclines and in that of plate tectonics. Based on the review, several open research problems are formulated concerning the undetermined propagation limits of the Pribrezhny volcanic complex and unknown time intervals of its formation, and the lack of mineralogical and isotopic-geochemical studies of magmatic rocks. A separate research problem is the formation of transitional zone between the continental margin of Kamchatka and the Kuril Island Arc. The paper shows the relevance of the study of the Pribrezhny volcanic complex of South Kamchatka and proposes possible solutions to the research problems. A detailed mapping of the junction zone of Pribrezhny volcanic complex of South Kamchatka and the Kronotsky terrain near the Malko-Petropavlovsk zone of transverse dislocations will make it possible to refine the age and kinematics of their relationship. Determination of rare elements and strontium, neodymium and lead isotopes will provide a possibility to clarify the nature of magmatism as compared to heterochronous volcanic series of South Kamchatka. The data obtained will be needed to study magmogeneration conditions for acid volcanism of South Kamchatka and monogenic volcanism of the Malko-Petropavlovsk zone of transverse dislocations. The paleomagnetic studies, along with dating of rock absolute age, will help to reconstruct the paleolatitude of formation of the Pribrezhny volcanic complex and to restore the geodynamic evolution of formation of South Kamchatka.

How geoecological components of a terroir can be altered by spatial changes of vineyards – A case study from Eger Wine District (Hungary)

Terroir is a concept referring interactions of natural (topography, lithology, climate, soil etc.) and human (economic conditions, traditions, cultivation practices, etc.) factors; therefore, terroir is spatially delimited and subjected to environmental, socio-economic, and temporal changes. The geoecological background of wine districts are considered more stable among them, but, because of its natural diversity and the spatial changes of production sites, changes in abiotic terroir components might occur too. In this study the spatial changes of grape production sites in Eger Wine District (Hungary) across two and a half centuries (1784 to 2018), and their consequences on the composition of the geoecological factors (lithology, topography, soil characteristics) were analyzed. Modernization of cultivation, urbanization and increase of built-up areas around the central settlement resulted in decreased concentration, i.e. increased spatial dispersion to more remote vineyards further from Eger. It also has consequences on the lithological and topographical composition of the production sites. Besides the slightly increasing extent of vineyards (from 5346 ha to 7413 ha) we found a distinct decrease of vineyards at higher elevations and a substantial increase at lower elevations. Distribution according to slope gradient changed also remarkably, with the share of vineyards on <5 % slopes from 38 % to 65 %. These changes resulted in transformations of pedological characteristics according to the comparison of vineyard’s extent with soil map data: vineyards shifted to slightly acidic, more fertile (i.e. deeper soil layer with higher organic carbon content) soils. The share of vineyards with different lithology and parent material also changed: loose, calcareous Tertiary sediments decreased almost to half, and the share of vineyards over acidic volcanics and their weathered regoliths almost doubled. Comparing these two dominant lithological types and soil profiles derived from them, different pedological characters and taxonomic status were found (Phaeozems and Vertisols). However, comparison of these two lithological types based on main topsoil characteristics (pH, SOC, carbonates, depth of fertile soil layer, N, P, K content) according to 25 randomly chosen surficial soil samples at production sites, showed no significant differences.. In the case of this particular wine district, spatial changes of the production sites affected mostly the distribution by elevation, by slope gradient, but did not alter significantly the surface soil character of the terroir.

Eruption, transport mechanisms and deposition of Paleogene ignimbrites, southwestern North Patagonian Massif, Argentina

The Paleocene-Eocene Catán Lil Ignimbrite (CLI) is one of the few occurrences within the explosive acid volcanism of this age in the extra-Andean region of the North Patagonian Massif. It represents a small-scale explosive eruption covering an area of 214 km2, with an estimated volume of 1.27 km3 and consisting of three weakly-to densely welded cooling units. The maximum thickness of this sequence is 90 m. Its basal unit is the best preserved, and has allowed a lithofacial analysis that reveals different aspects of the eruption and the emplacement mode of the Catán Lil pyroclastic flows. The CLI ignimbrites are generally massive, poorly sorted, matrix-supported deposits (tuff and lapilli tuff) resulting from dense pyroclastic currents (PDCs). They are composed mainly of juvenile fragments, scarce lithoclasts and crystalloclasts, being a product of a purely magmatic fragmentation occurred at a shallow level. A pyroclastic fountaining eruptive model is interpreted, resulting from the collapse of a low eruptive column, and a rapid and high-temperature emplacement. The CLI PDCs generally respond to slow moving pyroclastic flows with low erosive energy. The morphology and stratigraphy indicate radial emissions with thicknesses decreasing towards the periphery that become evident in Central-South ignimbrites. These PDCs flowed over a planar terrain, giving rise to most of the CLI deposits (South-Central area and North- East). The Northwestern ignimbrites are deposits in the interior (south and middle part) of the Catán Lil creek, forming thick deposits within the latter valley and thin, veneer-like deposits over the flanking Lipetrén granitoids. In the North- East region, the ignimbrites show stratigraphic relationships that suggest that the PDCs would slightly postdate those of the South-Central area. The Catán Lil Ignimbrites represent the most eastern exposures of the Paleocene-Eocene Pilcaniyeu Belt, differing from the latter in that it lacks a conspicuous lava facies, and by the unimodal character and the tectonic signature of the Catán Lil sequence.

Geochronology, Eruption Sequence and Geochemistry of Mid–Late Jurassic Volcanics South of Manzhouli: Petrogenesis and Implications for Mesozoic Tectonic Regime Transformation

AbstractTo the south of Manzhouli, Hulunbuir, Inner Mongolia, experienced a tectonic regime transformation from compression to extension in the mid‐Mesozoic. Based on systematic research of the volcanics, petrology, volcanic facies, chronology and geochemistry of rocks in the Buridun area, two stages of volcanics are identified. The first stage named the trachyte series was formed in the late Middle Jurassic (167–163 Ma), its eruption rhythm is pyroxene trachyandesite–trachyandesite–trachyte, and its origin rock is basic volcanics from thickened lower crust, with a tectonic setting in the collision orogeny after the closure of the Mongolia Okhotsk Ocean (MOO). The second stage is a bimodal volcanic rock, formed in the early Late Jurassic (163–160 Ma). The eruption rhythm of basic volcanics in this stage is basaltic andesite–basalt–olivine basalt, which comes from the metasomatized lithospheric mantle, the acidic volcanics of which being characterized by the eruption rhythm of sedimentary‐explosive‐overflow facies, which came from the partial melting of newly formed lower crust, and this shows the characteristics of A‐type granite; the tectonic setting is extension of the lithosphere after collision and closure of the MOO. The changes in the formation age and tectonic setting of the two stages of volcanics demonstrate that the transition time from the compressive system to the extensional system south of Manzhouli is about 163 Ma.

Middle Permian basic and acidic volcanism in the Istanbul zone (NW Turkey): evidence for post-variscan extensional magmatism

ABSTRACT The Istanbul Zone (NW Turkey) forms the eastward extension of Avalonia and was subjected to deformation, uplift and erosion for a time period of 40–50 Ma following the collision with the Sakarya Zone during Early to Late Carboniferous. This paper deals with the petrology and age of the volumetrically minor basic and acidic volcanism at the lowermost horizons of Middle Permian continental red beds, which are overlain by Lower Triassic marine sedimentary rocks in the Kocaeli Peninsula. The volcanic activity is represented mainly by amygdaloidal basalt, rhyolite and minor trachydacite. The amygdaloidal basalt was derived from near-primary middle-K calc-alkaline mantle melts with negligible crystal fractionation. On the other hand, the rhyolite and trachydacite compositionally resemble A2-type rhyolites and underwent low-pressure crystal fractionation as indicated by the presence of a significant Eu anomaly. Initial ɛNd values of amygdaloidal basalt range from 0.0 to 1.5 and those of rhyolite-trachydacite are between −0.4 and −3.4. Amygdaloidal basalt and rhyolite-trachydacite are not directly related to each other by crystal fractionation. Amygdaloidal basalt probably represents the product of the near-primary mantle melts from low-degree melting of a spinel peridotitic source, and the rhyolite-trachydacite originated from highly-fractionated products of basic magmas that are slightly more alkaline than amygdaloidal basalt. However, basic and intermediate products of alkaline basic magmas are unknown in this region to date. U-Pb dating of zircons from a rhyolite sample yielded an igneous crystallization age of 261 ± 3 Ma (2σ), suggesting that the date of deposition of the continental red beds goes back to the latest Middle Permian. Based on the transgressive nature of the Permian-Triassic sequence that starts from the Middle Permian continental red beds and grades into Lower Triassic marine deposits, we suggest that the volcanism likely occurred in an extensional setting. This extension was concurrent with the northward subduction of the Palaeo-Tethys beneath the Sakarya and Istanbul zones after the Variscan orogeny. Therefore, the latest Middle to Late Permian volcanism might have occurred during the initial stage of a back-arc extensional setting

Geological Investigation of Lead Mineralization Associated with Silicified Zone in Büyük Kızılcık (Göksun-K.Maraş) Region

Doğu Toroslar'da farklı ortam ve tektonik koşullarda oluşmuş birbirinden farklı istifler yüzeylemektedir. Bu istifler tabandan tavana Üst Jura-Kretase yaşlı peridotitler, bantlı gabro, izotrop gabro, levha dayk karmaşığından oluşan Kömürhan Ofiyolitleri ve Bodrum Napı’na ait metamorfik kaya birimleri yer almaktadır. Kömürhan Ofiyolitleri ve Bodrum Napı Geç Kretase yaşlı Baskil Granitoyidleri tarafından kesilmiştir. Baskil Granotoyidinin kesmiş olduğu birimler içerisinde cevherleşmeye ilişkin alterasyon zonları gözlemlenmektedir. Cevher mikroskopi çalışmalarında pirit, sfalerit, galenit, arsenopirit, manyetit ve hematit tespit edilmiştir. Pirit üzerinde yapılan izotop analizinde δ 34S değeri -3 %o olarak belirlenmiştir. Kuvars mineralleri üzerinde yapılan sıvı kapanım analizinde 69-127 °C arasında ve ortalama olarak 103 °C epitermal oluşum sıcaklığı belirlenmiştir. Çalışma alanında cevherleşmelerin birincil kökeni Miyosen’den itibaren bölgeyi etkileyen asidik karakterli volkanizmanın etkisiyle metamorfik istifler içerisindeki fay ve kırık çatlak sistemlerinde yerleşmiş sülfürlü yataklanma şeklinde oluşurken, ikincil cevherleşmelerin birincil sülfürlü minerallerin çözünerek tektonik olaylar sonucu oluşan süreksizlik zonlarında depolandığı düşünülmektedir.

Environmental risk assessment associated with acidic volcanics in Egypt

The present work aims to study gamma rays emitted by radionuclides such as 238U, 232Th and 40K from acidic Monqul volcanics. The studied volcanics are represented by a thick stratified lava flows interbanded with their pyroclastics. They are composed of thick lava flows of andesite and, to a lesser extent of basalt, and acidic volcanics including rhyolite and dacite. The average values of 238U, 232Th and 40K are (46 ± 24 Bq kg-1), (62 ± 11 Bq kg-1) and (1227 ± 318 Bq kg-1) in the rhyolite-dacite samples are greater than the worldwide average. The variation of radioactive bearing minerals observed inside granite faults produced the great amounts of radioactivity perceived in the samples. Calculating radiological risks is used to assess the public's radioactive risk from radionuclides revealed in the studied Rhyolite-dacite samples. The acceptable limit for excess lifetime cancer (ELCR) evaluations has been exceeded. As a result, Rhyolite-dacite are inappropriate for apply in building materials.

Towards the fertility trend: Unraveling the economic potential of igneous suites through whole-rock and zircon geochemistry (example from the Tapajós mineral Province, Northern Brazil)

Magmatic hydrothermal mineral deposits axiomatically frame the hosting pluton and the given tectonic setting in which they are inserted. Unsurprisingly, pre-Cambrian porphyry deposits are different than Phanerozoic examples, as collisional or post-collisional deposits are different than arc-related mineralizing systems. As such, this contribution assesses the tectonic framework and the magmatic evolution of the igneous suites present in south-central Amazonian Craton (Tapajós Mineral Province, TMP), and how these parameters translate into metallogenetic potential for the formation of magmatic-hydrothermal copper and gold deposits. For this purpose we gathered whole-rock geochemistry data from selected TMP copper and gold deposits and present new in situ trace-element and U-Pb analyses in zircon grains.The host rocks of the selected mineralizing systems belong either to the older magmatic sequence (OMS, 2.00–1.95 Ga), or to the younger magmatic sequence (YMS, 1.90–1.86 Ga). Whereas OMS presents characteristics of arc-related rocks, YMS represents the evolution towards post-orogenic or collisional setting. OMS might be divided into groups I, II and III granitoids. Group I comprises granites and granodiorites that mark the onset of the arc-magmatism in the TMP at ca. 2011 Ma. In this stage rocks are peraluminous, ferroan, anhydrous, show a strong crustal component and fO2 values close to or below the fayalite-magnetite-quartz buffer (ΔFMQ), yielding metallogenetic unfertile pluton. These rocks correlate with the Cuiú-Cuiú Complex and comprise samples from the Patrocínio and Tocantinzinho deposits. Group II granitoids correlate with the Creporizão Suite and comprise Tocantinzinho, São Jorge, Chapéu do Sol and Patrocínio deposit samples (with extrusive equivalents in the Coringa deposit). Rocks are metaluminous to peraluminous, magnesian to ferroan and mark the evolution of the magmatism towards more oxidizing (0 ≤ ΔFMQ ≤ + 4), hydrous and metallogenetically fertile conditions at ca. 1986 Ma. Mineralized zones are defined by gold bearing sulfide veins and veinlets within the potassic or sericitic alteration halos. Group III comprises rarer high-K, metaluminous, ferroan, anhydrous and reduced syenites and monzonites dated at 1993 and 1974 Ma, generated by decompression melting of metasomatized mantle. By itself, group III rocks should be considered as unfertile batches of magma, however, its interaction with the coeval, more hydrous and oxidized group II melts, confer these magmas their metallogenetic potential. Mineralization in group III rocks is defined by disseminated pyrrhotite – pyrite ± gold within the sericitic, chloritic and/or carbonate alteration zones.YMS comprises intermediate and acid rocks that belong to the Parauari Intrusive Suite and to the Iriri Group. Whereas, intermediate volcanics from YMS evolved on a hydrous and reduced petrologic trend, acid volcanics and the Batalha and Palito granitoids evolved on a dry and reduced trend, reflecting a change on TMP’s tectonic context, from magmatic-arc to a post-orogenic or collisional tectonic setting. Despite the reduced and anhydrous characteristic of the magmas, YMS’s metallogenetic potential is related with remobilization or melting of SCLM or lower crustal Au-rich sulfides formed on the previous magmatic events. Hence, the first pulses of the YMS might be considered as potentially fertile for the formation of Au-rich magmatic-hydrothermal deposits.

Podrobnosti o počátcích sedimantace a vulkanické činnosti na začátku permu (asselu); rudnický obzor v sz. části podkrkonošské pánve

A succession of the early Permian (Asselian) Rudník member exposed at the locality Škodějov – Hrádecký potok in the northwestern part of the Krkonoše Piedmont Basin (eastern Bohemia) contains light-colored clastic rocks with macroscopically conspicuous lamination, overlying lacustrine bituminous claystones and siltstones (ʻblack shalesʻ). This work aims to constrain the origin of those laminated strata. They can be macroscopically described as heterolithic sequence formed by fine- to medium-, exceptionally coarse-grained sandstone with intraclasts of mudstone, calcified fine-grained sandstone, mudstone and claystone with interlayers of organic-rich laminae. Volcaniclastic rocks are also present. The heterolithic volcanosedimentary sequence comprises cyclic (up to 4 dm), mostly horizontally laminated rocks, in places with soft- sediment deformation structures. Diagenetic phenomena, related to calcification of volcaniclastic layers and growth of pyrite crystals and framboids, are common. Volcaniclastic rocks with a predominance of albitized volcanic glass fragments are interpreted as vitritic tuffs. Fragments of volcanic glass floating in silty to fine-grained sandy matrix contain vesicules and are locally brown- colored. They are reinterpreted as being derived from contemporary intermediate (andesitic) volcanism, most likely extrabasinal. Extensive alteration of volcanic material makes characterization of the original composition of volcaniclastic deposits difficult. Trace element analysis using a portable XRF spectrometer revelaed negligible concentrations of V, Ni and Ti, which are indicative of rather basic volcanism. Results of outcrop-scale gammaspectrometry are presented here as trends of Th/U ratio of relevant lithotypes from several localities of the Rudník member. Organic-rich laminae present within the heterolithic succession at Hrádecký potok section are commonly rich in pyrite clusters. Those are the most probably related to formation of algal mats stimulated by input of fine-grained volcaniclastic material into the Rudník Lake. However, elevated siliciclastic and volcaniclastic input, particularly during periods of intensified volcanic activity, with related seismic events (that may have triggered gravity flows), may have disturbed or punctuated growth of algae on the lake floor. Our work has shown that the volcanic activity at the onset of deposition of the Rudník member in the northwestern part of Krkonoše Piedmont Basin (Škodějov – Hrádecký potok) was probably of intermediate nature and that it influenced depositional environment. Particularly, the fluctuating input of clastic and volcanogenic material could have caused an alternation of oxic and dysoxic conditions in the lake lacustrine environment over time. The intermediate character of volcanism in this locality contrasts with confirmed acidic volcanism documented in volcaniclastic layers in another lacustrine succession at Vrchlabí – roadcut (Martínek et al. 2006) that probably represent a different eruptive phase recorded within the Rudník member.

The Kyrenia Terrane (Northern Cyprus): Detrital Zircon Evidence for Exotic Elements in the Southern Neotethys

AbstractThe Kyrenia terrane of northern Cyprus comprises a tectonic stack of Triassic to Eocene rock units interleaved with basic and acid volcanics and minor metamorphic inliers, alongside an Oligocene‐Miocene flysch. Our U‐Pb‐Hf detrital zircon investigation in the Kyrenia Triassic to Eocene section reveals Precambrian, Silurian (∼430 Ma), Carboniferous (∼300 Ma), Triassic (∼240 Ma), and Upper Cretaceous (∼85 Ma) zircons. The presence of 300 Ma zircons, as early as in Triassic sediments, is enigmatic because Carboniferous magmatism is confined to the Paleotethyan realm which is traced north of the Taurides. Deposition of the Kyrenia sequence closer to a Northern Tethyan province would better fit its detrital zircon signal. The detrital signal of the Kyrenia, indicative for derivation from areas north of the Mediterranean, also differs significantly from that of the Mamonia Complex (SW Cyprus) in which only Afro‐Arabian sources are distinguished. Thus, in view of its unusual detrital zircon content, the Kyrenia sequence stands out in the Eastern Mediterranean as an exotic rock pile that cannot be straightforwardly correlated with its neighboring geologic environment. We defined the metamorphic inliers of Kyrenia as an ophiolitic mélange and recognized blueschist‐greenschist facies metamorphism to which we infer an Upper Cretaceous age. A U‐Pb zircon age of 555 ± 9 Ma (Cadomian) was obtained for the crystallization of a metabasic rock in the mélange. These findings support the geodynamic linkage of the Kyrenia with the Alanya and Bitlis massifs that were also affected by Upper Cretaceous HP‐LT metamorphism and accreted to the southern Tauride.

Architecture of volcanic plumbing systems inferred from thermobarometry: A case study from the Miocene Gutâi Volcanic Zone in the Eastern Carpathians, Romania

The Gutâi Volcanic Zone (GVZ) in the Eastern Carpathians records one of the most complex and long-lasting periods of Miocene volcanic activity (15.4–7.0 Ma) in the Carpathian–Pannonian region. Two types of volcanism are documented: 1) caldera-related acidic volcanism (ca. 15.4 Ma); and 2) multiphase intermediate volcanism (13.4–7.0 Ma). Two composite volcanoes (Mogoşa - G5, Igniş - G7), six extrusive domes (Dăneşti - G2, Poiana Cremenei - G3, Breze - G6, Pleşca Mare - G9, Gutâi - G10 and Laleaua Albă - G11) and an intrusive complex (Firiza - G12) were selected for analysis to unravel the architecture of the volcanic plumbing systems (VPS) based on the pressure-temperature (P-T) conditions during crystallisation of amphiboles and clinopyroxenes. Using the reliable geothermobarometers for amphiboles, and for clinopyroxenes, P–T conditions were calculated for basalts, basaltic andesites, andesites, dacites/rhyolites, and mafic microgranular enclaves (MMEs) hosted by dacites. The calculated pressures vary from 0.4 to 1.8 kbar for low-Al amphiboles (7.5–9.3 wt% Al2O3, magnesio-ferri-hornblende) and from 6 to 9 kbar for high-Al amphiboles (11.2–15.6 wt% Al2O3, magnesio-hastingsite, ferri-sadanagaite and pargasite). The calculated temperatures vary between 800 and 860 °C for low-Al amphiboles and between 950 and 1010 °C for high-Al amphiboles. The P–T data acquired for the clinopyroxenes (augite and diopside with 62–85 Mg#) are 3.5–8.5 kbar (predominantly >5 kbar) and 1050–1150 °C. A difference of 4–5 kbar is observed between the pressures recorded by low-Al amphiboles and clinopyroxenes in the G2 dacites and G3, G6 and G10 high-silica andesites. The “at equilibrium” high-Al amphiboles and clinopyroxenes from the G5, G11 and G12 samples record similar high pressures (6.0–8.5 kbar) but differences in temperature of 90–140 °C. The different depths constrained by the P–T data for the crystallisation of the amphiboles and clinopyroxenes indicate the presence of magma storage reservoirs scattered throughout the entire thickness of crust, from very deep locations (27–33 km) near the lower crust–lithospheric mantle boundary (MOHO = 33–35 km), up to shallow levels in the upper crust (2–5 km). Most of the volcanic structures show complex, multi-level interconnected VPS. The presence of numerous very deep magmatic reservoirs in several volcanic structures across the entire time-interval of the volcanism (which have high isotopic signatures, such as 87Sr/86Sr values of 0.7070–0.7076, for even the most basic rocks) provides evidence for a main, deep magma reservoir (“deep hot zone”) that acted as a “MASH zone” at the crust–mantle boundary beneath the GVZ. The architecture of the magmatic plumbing systems controlled the geological evolution of the studied volcanic structures. The processes of assimilation fractional crystallisation and magma mingling and mixing were also controlled by the complex VPS, as recorded by a wide range of volcanological, mineralogical–petrographical, and geochemical features. Overall, the GVZ records a complex evolution of volcanic activity that reflects the intricate magmatic plumbing systems. The VPS models and their inferred architectures provide a better understanding of the complex and long-lasting volcanism in the GVZ, and are relevant to other areas of extinct volcanism globally.

Volcanic Tuffs, Red- and Usual-Colored Clayey Rocks in Upper Riphean–Vendian Deposits in the Middle and Southern Urals: Comparison of Lithochemical Characteristics

In the lower part of Upper Vendian deposits on the East European Platform, packs of chocolate-brown clayey rocks/tuff-argillites containing intercalations of volcanic tuffs (products of acid volcanism) are widespread. Upper Riphean–Vendian sections on the western slope of the Middle and Southern Urals include packs of the red-colored clayey rocks. Among them, volcanic tuffs (clay-type rocks) with the atypical anomalous coloration (light gray with a pinkish, cream, greenish or steel tint, light brown with a beige tint, and others) were found in the early 2000s. The purpose of the present work is to compare the lithogeochemical characteristics of volcanic ash tuffs, red- and usual-colored clayey rocks at different Upper Riphean–Vendian stratigraphic levels in the Middle and Southern Urals and to determine signs of the probable pyroclastic/tuffogenic material admixture in the red-colored clayey rocks.

Provenance constraints on the Cretaceous-Paleocene erosional history of the Guiana Shield as determined from the geochemistry of clay-size fraction of sediments from the Arapaima-1 well (Guyana-Suriname basin)

Recent studies have emphasized the role of the Equatorial Atlantic Ocean opening on the drainage reorganization and erosion of the West African and northeastern Brazilian cratons during the Cretaceous. However, such studies are lacking regarding the Guiana Shield. To fill this gap, we determined the provenance of sediments deposited in the Suriname-Guyana basin during the Cretaceous-Paleocene based on the total organic carbon (TOC) content, δ13CTOC, major and trace element concentrations, and Sr-Nd isotopic data of nineteen clay-size fraction samples from one industrial well (Arapaima-1). Overall, the absence of correlation between the TOC content, δ13CTOC and provenance proxies as well as the lack of Ce anomaly indicate that marine authigenesis, reducing conditions, and weathering have not markedly affected the trace element ratios (Eu/Eu*, Cr/Th, Th/Sc) and Sr-Nd isotopic compositions used as provenance proxies. Three samples (Early Cretaceous, Cenomanian and Late Campanian) have radiogenic εNd(0) values > − 2.2. The Early Cretaceous sample may have been sourced by Precambrian or Mesozoic mafic rocks of the Guiana Shield or contemporaneous basic volcanic rocks. The Cenomanian sample is likely to have been sourced by basic volcanic rocks of the Caribbean Large Igneous Province or the Takutu rift whereas the Late Campanian sample may have recorded more acid volcanism in the Takutu Rift. The other samples have an overall Guiana cratonic provenance with variable contributions of the Paleoproterozoic and Mesoproterozoic terranes and Jurassic or Precambrian mafic dykes. Increases in 87Sr/86Sr ratios and trace element ratios characteristic of more differentiated sources suggest an increasing contribution from the inner part of the Guiana Shield after the Coniacian. Because of the possible presence of active volcanism during the deposition of analyzed samples, post rift mantle upwelling under the equatorial margin is the favored mechanism to explain the increasing erosion of the Guiana Shield inner parts.

Late Mesozoic Eastern Mongolia Volcanic Area: Structure, Magmatic Associations, and Sources of Melts

The Eastern Mongolia Volcanic Area (EMVA) is the largest Late Mesozoic intracontinental volcanic area of East Asia. Its magmatic activity lasted from ~ 170 Ma to the beginning of Cenozoic, but the peak of activity occurred between 135 and 105 Ma. It was accompanied by rifting and formation of NE-trending grabens and troughs filled with thick volcanic sequence. The largest volcanic eruptions occurred in the first half of the Early Cretaceous. They were mainly represented by mafic lavas and were terminated by acid volcanism. The second half of the Early Cretaceous was marked by exclusively mafic volcanism, which was replaced by alkaline basaltic rocks since the end of the Early Cretaceous and in the Late Cretaceous. The mafic rocks of the EMVA are trachybasalt and basaltic trachyandesite, with subordinate alkaline basaltic rocks. The geochemical characteristics of these rocks indicate that they were derived from two magma types related to different mantle sources: (1) suprasubduction basalts (IAB) and (2) within-plate ocean-island basalts (OIB). The predominance of rocks with transitional characteristics testifies the interaction of magmas or their sources during their formation. The widest spread OIB-type rocks have (Th/Nb)PM ≤ 1. The IAB-type mafic rocks are of limited distribution and were formed mainly at the early stages of the EMVA evolution. The felsic igneous rocks of the EMVA were mainly derived by crustal anatexis, as well as by the interaction of anatectic melts with basaltic derivatives. A model is proposed, in which the EMVA was formed in a composite geodynamic setting, which was determined by the mantle plume impact on the active continental margin. The magmatic evolution is thought to be related to the interaction of plume-derived magmas with a subduction-modified mantle wedge.

A Review on Petrology and Geochemistry of the Neoproterozoic Malani Igneous Suite and Related Rocks (Northwestern Peninsular India)

This paper reports new mineral and whole-rock geochemical data on the acid volcano-plutonic rocks of the Tusham Ring Complex (TRC) from the Neoproterozoic Malani Igneous Suite (MIS), northwestern Peninsular India and discusses their magmatic evolution, tectonic implication, and geodynamic history. Geochemically, the investigated rocks have the characteristics of hypersolvus, high-K calc-alkaline to shoshonitic, peraluminous and A-type granitoids and they are enriched in SiO2, (Na2O + K2O), Fe/ Mg, Ga/Al, Th, U, REE (except Eu), LILE + HFSE, halogens (F and Cl) and depleted in CaO, MgO, Sr, Cr, Ni, P, Ti and Eu abundances. They also show high heat production (HHP) affinity and high mineralization potential. The high abundances of fluorine (0.80–7.11 wt %) and chlorine (0.44–1.56 wt %) in biotite and the geochemistry of the studied rock types indicate that the acid volcanics and granite massifs of TRC were derived from a halogen-enriched magmatic source under low degree partial melting of crustal protolith. The field, petrography, mineral chemistry, whole-rock geochemistry of the rocks under study, in combination with their tectonic and petrogenetic signatures have proposed that the rift-related Neoproterozoic magmatism of MIS has close linkage with geodynamic evolution of Nagarparkar, Seychelles and Madagascar A-type granitoids during Rodinia breakup.

Simulating the Conditions of Generation for Permeable Geyser Channels in Areas of Acid Volcanism

The geysers and paleo-geysers that exist in Kamchatka are situated in volcanogenic artesian basins composed of products of recent acid volcanism. This is in accord with the worldwide patterns for the occurrence of geyser fields. The results of a TOUGHREACT simulation of flow-through ascending circulation of thermal waters, which have chemical compositions in agreement with that of the water in Geyser Valley and which occurs in rhyolite host rocks, showed the generation of channels with high transmitting capacity and lateral self-isolation. This occurs due to the high rate of dissolution for volcanic glass in an axial ascending flow and deposition of silica in the annulus. Studies of mineral composition, as sampled at the surface of cones/gryphons at the Velikan, Bolshoi, and Pervenets geysers, showed them to be dominated by the zeolite mineral phase (heulandite, clinoptilolite, and mordenite) with some minor amounts of amorphous silica (opal).