Acid Volcanics Research Articles

A comparative study of indoor radon levels and inhalation dose in some areas of Punjab and Haryana, India

Indoor radon concentrations have been measured for two consecutive half-year periods in a wide range of dwellings of some regions of Punjab and Haryana states. The objective was to find correlation between the variations of indoor radon levels with the sub-soil, local geology, type of building materials, etc. of the two regions. So keeping this in view the indoor radon measurements have been carried out in the dwellings of different villages around the Tusham ring complex, Bhiwani District, Haryana, known to be composed of acidic volcanics and the associated granites along with some villages of Amritsar District, Punjab. The indoor radon concentration in the dwellings around Tusham (Haryana) have been found to be varying from 120.5±95 to 915.2±233 Bq m−3, whereas it ranges from 60.0±37 to 235.6±96 Bq m−3 for the dwellings of Punjab. The 222Rn concentration observed at most of locations particularly around Tusham ring complex region is higher than that of all the villages studied in Punjab region. Local geology including embedded granitic rocks, sub-soil, etc. as well as building materials having higher radioactive content are the major contributors for the higher indoor radon levels observed in the dwelling around Tusham, where few dwellings have higher radon concentrations than the ICRP, 1993 recommendations. The annual effective dose equivalent has also been estimated for each location of the both regions, which has been found to be varying from 1.0 to 17.2 mSv/y.

Melt and high-density fluid inclusions of magmatic water in phenocrysts of quartz from acidic volcanic rocks of the Verkhneural’sk ore district, South Urals

The location of the vast majority of the Ural VHMS deposits in central volcanic structures and their paragenetic relation to acidic volcanism are the most reliable attributes. According to the genetic models, the formation of the VHMS systems is related to shallow chambers of acidic magma. However, many aspects of such relation are discussed. On the basis of comprehensive study of melt inclusions in quartz phenocrysts in acidic volcanic rocks, we determined the composition of primary magmatic melts; the contents of trace elements, H 2 O, Cl, S; and the pressure and composition of magmatic fluid for the first time in the Verkhneural’sk ore district, South Urals. The Verkhneural’sk ore district located in the northern Magnitogorsk trough is attributed to the Uchaly‐Alexandrinka structural‐formation zone. Eight Cu‐Zn deposits are located in the district. The geology of the district, which has been described in numerous publications [1‐3], permits consideration of only some features that are important for our study. Acidic volcanic rocks occur in the upper part of the bimodal basalt‐rhyolite association of the Middle Devonian Karamalytash Formation. According to pertochemistry, the underlain basalts are tholeiitic, while acidic volcanics mainly pertain to calc-alkaline rock series. All economic deposits of the district are hosted in acidic volcanic rocks at the three lithostratigraphic levels corresponding to three rhythms of volcanism. Melt inclusions were studied in 150 samples of dacite, dacitic rhyolite, and rhyolite from these three rhythms. The inclusions range from 5‐10 to 100 µ m in size. Variably devitrified inclusions are the most abundant; vitreous inclusions locally with a gas phase are less frequent. Melt inclusions containing opaque crystals determined as magnetite and globules of pyrrhotite, pentlandite, chalcopyrite, and bornite are also observed. Glasses were soften at 600‐720 ° C and homogenized at 850‐1130 ° C. Initial melting of devitrified inclusions was observable at 780‐850 ° C, and total homogenization, at 950‐1210 ° C [4].

Hierarchical cluster analysis of hydrochemical data as a tool for assessing the evolution and dynamics of groundwater across the Ethiopian rift

The hydrochemical evolution and flow pattern of groundwater is analyzed in a complex closed rift basin on the basis of multivariate hierarchical statistical cluster analysis. The analysis was made on the basis of water samples collected from over 120 wells and limited surface waters. The result revealed dissimilar hydrochemical phases in the rift and highlands representing different groundwater flow regimes. Five groundwater zones with different hydrochemical facies were identified. Both the conventional hydrochemical and multivariate statistical analyses indicate that the central sector of the rift represents a complex groundwater system influenced by thermal waters and alkaline lakes. It also demonstrates that the close similarity of lakes and groundwater with high fluoride, sodium, Total Dissolved Solids (TDS) and pH. The waters associated with acidic volcanic rocks are characterized by a positive alkalinity residual of calcite. When they concentrate due to the effect of climate, the precipitation of calcite causes a decrease in the chemical activity of calcium and increase in alkalinity. These waters become NaHCO3-dominated with distinctly different from highland systems characterized by Ca-MgHCO3 type waters with low TDS. Alkaline waters are intimately linked to acidic volcanics while fresh waters are associated with dominantly basic volcanics. Waters with similar hydrochemical facies as highland waters are evident in local fractures of the rift floor. The zonation of hydrochemical facies on the basis of hierarchical cluster analysis indicates increase in ionic concentration and pH along the groundwater flow path. Key words: Ethiopian rift, groundwater evolution, hierarchical cluster analysis, hydrochemistry, volcanic rocks.

Petrogenesis and tectonic setting of bimodal volcanism in the Sakoli Mobile Belt, Central Indian shield

AbstractThe Sakoli Mobile Belt comprises bimodal volcanic rocks that include metabasalt, rhyolite, tuffs, and epiclastic rocks with metapelites, quartzite, arkose, conglomerate, and banded iron formation (BIF). Mafic volcanic rocks are tholeiitic to quartz‐tholeiitic with normative quartz and hypersthene. SiO2 shows a large compositional gap between the basic and acidic volcanics, depicting their bimodal nature. Both the volcanics have distinct geochemical trends but display some similarity in terms of enriched light rare earth element–large ion lithophile element characteristics with positive anomalies for U, Pb, and Th and distinct negative anomalies for Nb, P, and Ti. These characteristics are typical of continental rift volcanism. Both the volcanic rocks show strong negative Sr and Eu anomalies indicating fractionation of plagioclases and K‐feldspars, respectively. The high Fe/Mg ratios for the basic rocks indicate their evolved nature. Whole rock Sm–Nd isochrons for the acidic volcanic rocks indicate an age of crystallization for these volcanic rocks at about 1675 ± 180 Ma (initial 143Nd/144Nd = 0.51017 ± 0.00017, mean square weighted deviate [MSWD] = 1.6). The εNdt (t = 2000 Ma) varies between −0.19 and +2.22 for the basic volcanic rock and between −2.85 and −4.29 for the acidic volcanic rocks. Depleted mantle model ages vary from 2000 to 2275 Ma for the basic and from 2426 to 2777 Ma for the acidic volcanic rocks, respectively. These model ages indicate that protoliths for the acidic volcanic rocks probably had a much longer crustal residence time. Predominantly basaltic magma erupted during the deposition of the Dhabetekri Formation and part of it pooled at crustal or shallower subcrustal levels that probably triggered partial melting to generate the acidic magma. The influence of basic magma on the genesis of acidic magma is indicated by the higher Ni and Cr abundance at the observed silica levels of the acidic magma. A subsequent pulse of basic magma, which became crustally contaminated, erupted as minor component along with the dominantly acidic volcanics during the deposition of the Bhiwapur Formation.

Palaeoenvironmental change during the end-Guadalupian (Permian) mass extinction in Sichuan, China

The end-Guadalupian mass extinction has been investigated in Sichuan province, SW China. In the south of the province the platform carbonates of the Maokou Formation are overlain by the Emeishan flood basalts, a possible factor in the extinction event, and in the north of the province the formation is succeeded by shallow-marine carbonates of the Wuchiaping Formation (Late Permian). The extinction event is primarily recorded by the loss of fusulinaceans and possibly by species-level turnover amongst calcareous algae. The high-diversity, Middle Permian microfossil assemblages are last seen beneath a surface recording widespread emergence and karstification. In northern Sichuan emergence occurred early in the Capitanian Stage and the succeeding strata record restricted hypersaline deposition that preceded the deposition of a thick ash horizon, the Wangpo Bed. These mid-Capitanian arid conditions are replaced by humid conditions towards the end of the stage as indicated by the development of a widespread coal seam. In southern Sichuan only a thin development of this humid, coaly facies is seen developed atop the Maokou karstic surface and below the oldest flood basalt. The Guadalupian interval saw the development of large C isotope excursions in the carbonate record. These include a positive-then-negative swing late in the Capitanian and a newly discovered negative spike superimposed on an early Capitanian heavy interval. This spike may be a global phenomenon but the magnitude (8‰) may have been exaggerated by an increased contribution from light, respired C derived from soils during relative sea-level fall. A plethora of environmental factors approximately coincide with the extinction event, including regression, acidic volcanism and flood basalt volcanism making it difficult to unravel the relative significance of each.

Hydrogeological framework and occurrence of groundwater in the Ethiopian aquifers

Comprehensive hydrogeological investigations have been carried out in the Ethiopian volcanic terrain and associated quaternary sediments. The occurrence and distribution of groundwater are systematically analysed in relation to the geomorphological and geological setting within one of the world’s thickest volcanic provinces. The study starts from regional conceptualization to a more focussed analysis of four selected areas with distinct hydrogeological features. The chosen areas represent highland trap volcanic sequence characterized by multi-layer aquifers, intermountain sedimentary graben, fractured rift floor volcanics boarded by steep high-altitude plateau, and vast rift floor flood plain covered with alluvial sediment with adjoining gently-sloping pediments. The result revealed extreme variations in aquifer hydraulic characteristics and recharge rates. The flow and occurrence of groundwater is strongly controlled by the structure and geomorphological setup of the volcanic rocks and associated sediments. Groundwater flow in the rift and escarpment areas is largely controlled by faults. The recharge varies in a wide range between a few mm to 400 mm/yr. Despite the occurrence of permeable rocks and high recharge rates in some highlands adjacent to steep escarpments, the groundwater reserve is low due to the fast release of the recharged water to the rift plains through large open faults. Wide basic and acidic volcanics, alluvio-colluvial and lacustrine deposits form shallow unconfined aquifers, with transmissivity varying between 27 and 135 m 2/d. The thick trap series volcanics interbedded with river gravels and sands form deep confined and semi-confined aquifers locally with artesian conditions. Intermountain grabens and rift floor sediments associated with fractured volcanics form the largest aquifers under water table and semi-confined conditions. High well yields in deeper volcanic aquifers are often associated with regional fault lines and permeable sediments interbedded with the volcanics. Limited water quality analysis indicates that the groundwaters are Ca–MgHCO 3 type in the highlands, Na–HCO 3 type in the rift with local SO 4 and Cl enrichment. Hard waters are dominant in the basic volcanics. The highland waters have relatively lower ionic concentration (TDS ranging from 50 to 1200 mg/l). The rift waters have high salinity and fluoride, which is the major national water quality problem.

A combination study of indoor radon and gamma radiation levels in Tusham ring complex

The aim of the present study was to investigate a possible correlation between indoor radon and gamma radiation levels in a region of high heat producing rock formations. Since the natural occurring radionuclides are responsible for the major contribution to the total effective dose of the ionizing radiations received by the population, so keeping this in view the indoor radon and gamma radiation levels have been measured in the dwellings of different villages situated in and around the Tusham Ring Complex, Bhiwani district, Haryana, known to be composed of acidic volcanics and the associated granites. The radon concentration levels have not only been found to be varying with the mode of construction of houses and building materials utilized, but also especially on their location with respect to the nearby high heat producing granite rocks. The indoor radon concentration levels at some places, especially those on or close to granite rock formations have been found to be considerably higher and even at some places it also exceeds the upper limit of the proposed action level of the ICRP limits. A better correlation between indoor radon and gamma radiation levels has been observed particularly in case of the dwellings well exposed to the high heat producing granitic rock formations.

Radon exhalation rate and uranium estimation study of some soil and rock samples from Tusham ring complex, India using SSNTD technique

Besides uranium and radium, radon exhalation rate is also a crucial factor for radon emanation from ground or building material. In the present study uranium concentration and radon exhalation rate in the wide range of soil and rock samples collected from Tusham ring complex, Haryana, known to be composed of acid volcanics and the associated high heat producing granites, have been estimated. For comparative analysis, the soil samples from some districts of Punjab have also been analysed for uranium estimation and radon exhalation rate. The ‘can’ technique using plastic track detectors LR-115 type-II has been used for radon exhalation rate measurement, whereas the ‘Fission track registration’ technique has been employed for uranium content determination in these samples. The 222Rn exhalation rate in weathered granite area of the Tusham ring complex shows a maximum value of 63.76 Bq kg - 1 h - 1 , whereas the maximum value for uranium content has been found to be around 62.02 ppm. The corresponding values of exhalation rate and uranium content in the soil samples of this region are 11.54 Bq kg - 1 h - 1 and 13.41 ppm, respectively. A positive correlation between radon exhalation rate and uranium concentration has been observed for both soil and rock samples under the present investigation.

As rochas vulcânicas mesozóicas ácidas da Bacia do Paraná: litoestratigrafia e considerações geoquímico-estratigráficas

The mesozoic acidic volcanic rocks of Parana Basin: lithostratigraphy and geochemical stratigraphy aspects. The mesozoic acidic volcanics of Parana Basin covers an area of 64,000 km 2 or 2.5% of the total volume of Serra Geral Formation. Two main types are recognized and are named Palmas (aphyric rocks) and Chapeco (porphyritic rocks). The Palmas type (2% of total volume) dominate over the Chapeco (0.5% vol.) one. In the Parana State, it is possible to found the Chapeco overlaying the Palmas volcanic rocks. The geochemical data shows that Chapeco volcanics have distinctly higher Ba, Nb, La, Ce, Zr, P. Nd, Y, Yb, Lu e K and lower concentrations of Rb, Th and U relative to Palmas rocks. The Nb concentration in Chapeco rocks is 2.58 times higher than Palmas leading to the suggestion that the magmatic sources of Palmas and Chapeco rocks are different. The Rb/Ba of Chapeco (0,09-0,11) and Palmas rocks (0,27-0,31) indicates that crustal assimilation process is very important to explain the origin of these rocks, mainly the Palmas type. The geochemical data allow us to recognize five different types of Palmas volcanic rocks named Santa Maria, Cax- ias do Sul, Anita Garibaldi (Peate el al., 1997), Clevelândia and Jacui, and three different types of Chapeco volcanics, named Ourinhos, Tamarana (Peate el al., 1997) e Guarapuava, which are strongly correlated with their regional distribution in Parana Basin, and appear to have evolved from different magma-types. The re- gional and temporal relationships of the different acidic volcanic rocks point to diacronous stratigraphic units.

As rochas vulcânicas mesozóicas ácidas da Bacia do Paraná: litoestratigrafia e considerações geoquímico-estratigráficas

The mesozoic acidic volcanics of Paraná Basin covers an area of 64,000 km² or 2.5% of the total volume of Serra Geral Formation. Two main types are recognized and are named Palmas (aphyric rocks) and Chapecó (porphyritic rocks). The Palmas type (2% of total volume) dominate over the Chapecó (0.5% vol.) one. In the Paraná State, it is possible to found the Chapecó overlaying the Palmas volcanic rocks. The geochemical data shows that Chapecó volcanics have distinctly higher Ba, Nb, La, Ce, Zr, P. Nd, Y, Yb, Lu e K and lower concentrations of Rb, Th and U relative to Palmas rocks. The Nb concentration in Chapecó rocks is 2.58 times higher than Palmas leading to the suggestion that the magmatic sources of Palmas and Chapecó rocks are different. The Rb/Ba of Chapecó (0,09-0,11) and Palmas rocks (0,27-0,31) indicates that crustal assimilation process is very important to explain the origin of these rocks, mainly the Palmas type. The geochemical data allow us to recognize five different types of Palmas volcanic rocks named Santa Maria, Caxias do Sul, Anita Garibaldi (Peate el al., 1997), Clevelândia and Jacuí, and three different types of Chapecó volcanics, named Ourinhos, Tamarana (Peate el al., 1997) e Guarapuava, which are strongly correlated with their regional distribution in Paraná Basin, and appear to have evolved from different magma-types. The regional and temporal relationships of the different acidic volcanic rocks point to diacronous stratigraphic units.

Evolution and relationships between volcanism and tectonics in the central-eastern part of the Oligocene Borovitsa caldera (Eastern Rhodopes, Bulgaria)

The nested Borovitsa caldera emplaced during the collision-related Paleogene volcanism in the Eastern Rhodopes. The pre-caldera succession consists in Priabonian to Early Oligocene sediments and lavas (absarokites, shoshonites, latites). The caldera filling corresponds to an acid volcanism Early Oligocene in age. The tectono-magmatic evolution of the caldera can be divided into six main stages. (1) Ignimbritic units (more than 1.5 km thick) with a trachydacitic to trachytic composition deposited. The K–Ar method yields an age of 34–33.5 Ma. The volcanic products are either strongly or not welded in the western and eastern parts of the caldera, respectively. (2) An initial Murga caldera, 7–10 km in diameter, collapsed. This event was accompanied by the intrusion of a circular body consisting of lenses-bearing rocks of trachyrhyodacitic to rhyolitic composition within the border faults. (3) The emission of pyroclastic rocks continued and a large sub-volcanic body (33 Ma) of trachydacitic to trachyrhyolitic composition intruded in the western part of the circular body. (4) The Borovitsa caldera (15 km × 34 km) collapsed. Rhyolitic and trachydacitic dykes dated at 32.5 Ma intruded along its border faults. (5) High-Si trachyrhyolitic–perlitic domes intruded in the eastern part of the Borovitsa caldera at 30–32 Ma and the Dushka caldera collapsed within the Borovitsa structure. (6) Dykes of various compositions (from shoshonite to rhyolite) and trachydacitic to rhyolitic sub-volcanic stocks finally intruded within the caldera and along its rims at 27.5–29.5 Ma. Observations on radar and optical satellite imagery allowed both a new mapping of the structural pattern in the Borovitsa caldera and the understanding of the relationships between faulting and volcanism in this area. Horse-tail features accommodating the right-lateral throw component at the termination of NW–SE and N–S right-lateral strike–slip faults are superimposed upon the Murga caldera and the eastern part of the Borovitsa caldera respectively. WNW–ESE to NW–SE extension along the horse-tail patterns was responsible for the ascent of pressurized magma through the crust via vertical open fractures leading to volcanic activity and subsequent emplacement of domes and crypto-domes during the fifth magmatic stage. This extension was followed by a compression with various orientations, which may be interpreted as a switch of the tensile stress to a compressive one at the onset of subsidence of the Dushka caldera. The last tectonic event in the area is characterized by a N–S extension that led to the reactivation of part of the previous structures, the formation of NW–SE to E–W normal faults and the emplacement of dykes and stocks during the sixth magmatic stage.

Regional variations pattern of indoor radon levels in some areas of Punjab and Haryana

The indoor radon concentration levels and their regional variations pattern, for two consecutive half-year periods, in a wide range of dwellings of some regions of Punjab and Haryana states have been studied. The objective was to find the relation between the variations of indoor radon levels with the sub-soil and local geology, type of building materials utilised in the dwellings of the region. Keeping this in view, indoor radon measurements have been carried out in the dwellings of 30 villages around the Tusham Ring Complex, Bhiwani district, Haryana, known to be composed of acidic volcanics and associated granites, along with 11 villages of Amritsar District, Punjab. The indoor radon concentration in the dwellings around Tusham (Haryana) was found to vary from 120 +/- 95 to 915 +/- 233 Bq m(-3), whereas radon levels varied from 60 +/- 37 to 235 +/- 96 Bq m(-3) for the dwellings studied in Punjab. We believe that local geology including embedded granitic rocks, and sub-soil, as well as building materials having higher radioactive content, is the major contributor for the higher indoor radon levels observed particularly in the dwelling around Tusham Ring complex, where some dwellings are showing higher radon concentrations than the ICRP recommendations. The environmental samples from some areas of Punjab state and around the Tusham Ring Complex of Haryana state have also been analysed for radon exhalation studies. Higher values for radon exhalation rates have been observed for the Tusham's soil/rock specimens, as compared with soil samples of the Amritsar region of Punjab.

Geology, petrography and geochemistry of the acid volcanism of the Paraná Magmatic Province in the Piraju-Ourinhos region, SE Brazil

Geology, petrography and geochemistry of the acid volcanism of the Paraná Magmatic Province in the Piraju-Ourinhos region, SE Brazil

The Miocene granitoid rocks of Mt. Bukulja (central Serbia): evidence for pannonian extension-related granitoid magmatism in the northern Dinarides

The study presents evidence about the origin and evolution of the Miocene (20–17 Ma) granitoid pluton of Mt. Bukulja, situated within the southern Pannonian/northern Dinarides region (central Serbia, south-central Europe). The pluton is composed of slightly peraluminous two-mica granite (TMG), metaluminous hornblende-biotite and biotite-bearing (H-BG) granite and rare aplite granite. A lamprophyre dyke (BLD) similar in composition and age to other Serbian primitive minettes has been found in the vicinity of Mt. Bukulja. The available and newly determined radiometric age suggests that the TMG was emplaced around 20 Ma whereas the age of the H-BG is inadequately constrained. TMG and H-BG show similar petrographic characteristics but evidence of open system magma processes is found only in the H-BG. In comparison to the H-BG, the TMGs are less enriched in most trace elements, including REE, and have a more fractionated REE-pattern and stronger negative Eu-anomaly. The TMGs display a wider range of initial Sr-Nd isotope ratios (87Sr/86Sr20 Ma = 0.70652–0.71368 and 143Nd/144Nd20 Ma = 0.51223–0.51283) than the H-BG (87Sr/86Sr20 Ma = 0.70768–0.70781 and 143Nd/144Nd20 Ma = 0.51242–0.51256). Geochemical modeling suggests that the H-BG could have derived from a BLD-like melt by mixing plus fractionation processes assuming a batch of TMG-like magma as the acid end-member. On the other hand, the geochemical variability of the TMG is reproduced by an AFC model with an assimilation/fractionation ratio ( r ) of 0.5 and with high amount of crustal component (~20–50 %) starting from the least evolved TMG rocks. In the modeling, the average composition of the least evolved TMG samples was used to represent the parental magma composition whereas the composition of adjacent metamorphic rocks was adopted as possible contaminant. The composition of the least evolved TMG implies that the TMG parental magma likely originated by melting of a mafic lithology such as earlier basalts underplating in the lower crust. The high proportions of crustal assimilation along with other geochemical and geological evidence suggest that the Mt. Bukulja TMG originated within the same geotectonic setting as acid volcanics of the north Pannonian Basin. The results of this study support the hypothesis that the Mt. Bukulja pluton is related to tectonomagmatic events controlled by the early extensional phases in the opening of the Pannonian basin.

The distribution and hydrogeological controls of fluoride in the groundwater of central Ethiopian rift and adjacent highlands

Occurrence of fluoride (F) in groundwater has drawn worldwide attention, since it has considerable impact on human health. In Ethiopia high concentrations of F in groundwaters used for community water supply have resulted in extensive dental and skeletal fluorosis. As a part of a broader study, the distribution of F in groundwater has been investigated, and compared with bedrock geology and pertinent hydrochemical variables. The result indicates extreme spatial variations. High F concentration is often associated with active and sub-active regional thermal fields and acidic volcanics within high temperature rift floor. Variations in F can also be related to changes in calcium concentration resulting from dissolution of calcium minerals and mixing with waters of different chemical composition originated from variable hydrogeological environment across the rift valley. The concentration of F dramatically declines from the rift towards the highlands with the exception of scattered points associated with thermal springs confined in local volcanic centers. There are also interactions of F-rich alkaline lakes and the surrounding groundwater. Meteoric waters recharging volcanic aquifers become enriched with respect to F along the groundwater flow path from highland recharge areas to rift discharge areas. Locally wells drilled along large rift faults acting as conduits of fresh highland waters show relatively lower F. These areas are likely to be possible sources of better quality waters within the rift. The result of this study has important implications on site selection for water well drilling.

Changes in detrital garnet assemblages related to transpressive uplifting associated with strike–slip faulting: An example from the Cretaceous System in Kii Peninsula, Southwest Japan

The chemical characteristics of detrital garnet have served as relatively reliable and definitive indicators of the major tectonic settings of sedimentary units in many parts of the world. In Southwest Japan a multidisciplinary approach combining sandstone modal, heavy mineral and garnet compositional analyses of the Cretaceous upper continental slope to trench deposits of the Kurosegawa and Shimanto belts combined with a comparison of the detrital garnet features in and around Kii Peninsula revealed the following characteristics. The garnet assemblages show significant changes with age. The Lower Cretaceous Yuasa Formation is characterized by pyrope-rich almandine garnets derived from granulite-facies metamorphic rocks. These are associated with garnet grains that have pyrope–almandine compositions and high grossular contents suggesting an eclogite-origin. Garnet assemblages of the lower Upper Cretaceous Yukawa Formation are dominated by grains with chemical characteristics indicating an origin as low P/ T type metamorphic rocks. There are also spessartine–almandine garnets derived from acidic igneous rocks, some with a high P/ T type metamorphic origin and others with a grandite composition. Garnet assemblages of the upper Upper Cretaceous Miyama Formation are similar to those of the Yukawa Formation, with the exception that grandite garnets are absent. The above compositional changes of garnets in the deposits allow us to characterize the corresponding provenances and by combining these results with stratigraphic ages temporal changes of these provenances can also be determined. The source area for the granulite- facies metamorphic rocks that continuously supplied detritus throughout the Cretaceous might be Precambrian continental basement in East Asia. In early Late Cretaceous time, the detritus was derived from terranes distributed along the Median Tectonic Line, a major strike–slip fault stretching throughout Southwest Japan. The garnet compositions suggest the source area included eclogite in the Kurosegawa belt that forms the basement to the Cretaceous strata, and the low P/ T type metamorphic rocks and granitic rocks in the Paleo-Ryoke belt including the Higo belt. Studies of the Miyama Formation show that at this time widespread acidic volcanism began and this was the source for much of the volcanic sediment in the formation. The provenance change between the Lower and lower Upper Cretaceous Formations is likely to have been caused by uplifting and unroofing associated with Cretaceous transpression expressed by the strike–slip movement along the Median Tectonic Line and other lateral faults in the Chichibu belt.

Microbial Communities in the World's Largest Acidic Volcanic Lake, Kawah Ijen in Indonesia, and in the Banyupahit River Originating from It

A first study was made on the microbial community composition of the Indonesian crater lake Kawah Ijen (pH < 0.3) and the Banyupahit-Banyuputih river (pH 0.4-3.5) originating from it. Culture-independent, rRNA gene-based denaturing gradient gel electrophoresis was used to profile microbial communities in this natural and ancient, extremely acidic environment. Similarity in community profiles of the different sampling locations was low, indicating heterogeneity in community composition. Archaea were present at all sampling locations; archaeal diversity was low at the most acidic locations and increased at pH >2.6. Bacteria were not detected in the water column of the crater lake, but were found at all locations along the acidic river. Bacterial diversity increased with increasing pH. Eukarya were only present at pH >2.6. Retrieved rRNA gene sequences of Bacteria and Archaea were not closely related to known acidophilic species. It is concluded that tolerance to extreme acidity in this system is developed most extensively among Archaea. The acidity gradient of the Banyupahit-Banyuputih river has a clear effect on microbial community composition and biodiversity.

Basic magmatism in the geological history of the Elbrus Neovolcanic area, greater Caucasus: Evidence from K-Ar and Sr-Nd isotope data

The age and genesis of basic rocks in the magmatic evolutionary series are of principal significance for regions with predominant acid, mainly crustal volcanism. The appearance of basic volcanic rocks in the rhyolite‐dacite volcanic sequences is usually a sensitive indicator of a change in the conditions of magma generation, the involvement of different mantle and/or crustal reservoirs, or a change in the geotectonic and geodynamic settings of the volcanic activity. This is evident from the abundance of Neogene‐Quaternary acid and moderately acid volcanism in the Elbrus neovolcanic area, Greater Caucasus. The Neogene‐Quaternary magmatic centers of the Greater Caucasus are localized within three (Kazbek, Central Georgian, and Elbrus) neovolcanic areas. The Elbrus area located in the central part of the northern slope of the Greater Caucasus is bounded by the upper reaches of the Kuban River in the west, the Kuma River in the north, the Cherek River in the east, and the Main Caucasus Range in the south (Fig. 1). Evolution of the young magmatism in the Greater Caucasus is divided into three stages [1] with age boundaries determined by isotope‐geochronological investigations [2‐8]. The first (Late Miocene) stage (9.5‐8.3 Ma) is represented by subalkaline acid intrusive rocks of the Caucasian Mineral’nye Vody area of the Elbrus volcanic area [2, 3]. Products of the second (Pliocene) stage are found in the central sector (Chegem and Tyrnyauz regions). In the Chegem region, the products are represented by acid and moderately acid volcanic rocks of the Upper Chegem caldera and Lower Chegem highland (2.9‐2.7 Ma) [2, 5, 6], andesites of the postcaldera Kumtyube and

The Cambrian to Aquitanian geological record of the Longi-Taormina Unit (Calabria-Peloritani Arc, southern Italy): geodynamic implications

The Longi-Taormina Unit forms the “Dorsale calcaire” of the Peloritani Alpine Belt (southern Calabria-Peloritani Arc). It is made by a thick sedimentary cover of Meso-Cenozoic age overlying a Variscan weakly metamorphosed Cambrian to Carboniferous succession. The Palaeozoic series consists of pelitic to arenaceous sediments containing layers of acidic and basic volcanics. The acidic volcanics are affected by the “Caledonian” compressional deformations and are referred to Early Ordovician. The basic rocks belong to two different volcanic cycles; the first, not dated, is ascribed to the Caledonian cycle according to its geochemical signature; whereas the second, middle-late Devonian in age, is interpreted to have formed in the framework of pre-Variscan extensional tectonics. During the Variscan Orogeny (330 Ma), the area recorded metamorphism up to subgreenschist-to-greenschist facies and two main deformation phases, marked by syn-schistose early folds (Dv1), overprinted by dominantly NW-SE trending late folds (Dv2). During the Aquitanian, deformation related to the Alpine Orogeny led to imbrication of the Palaeozoic and Meso-Cenozoic series. The sedimentary cover was affected by a series of N090° to N130° trending folds. Detailed stratigraphical and structural investigations on the tectonic contact between the Longi-Taormina Unit, and the overlying Fondachelli Unit indicate that this structure is part of a frontal thrust ramp which developed during the Aquitanian. Our geological and structural studies on the Cambrian to Aquitanian rocks of the Longi-Taormina Unit of the Calabria-Peloritani Arc enable to unravel the complex geodynamic history of the central-western Mediterranean area.

Pre-industrial Metal Anomalies in Ice Cores: A Simplified Reassessment of Windborne Soil Dust Contribution and Volcanic Activity during the Last Glaciation

A major issue regarding pre-industrial accumulation of heavy metals such as Cu, Pb, Zn, or Hg in ice cores relates to the source(s) of the metals. We investigate the two possibilities that have been generally advocated for the origin of metal anomalies: (1) increased amounts of windborne dust during particularly cold periods; and (2) volcanic activity. We analyze the time span 35,000-14,000 yrs BP, which is characterized by extreme temperature deviations (ΔT: -2.1° to -9.8°C). Our findings show no definitive relationships between climate, dust, and metal contents, at least during the colder episodes. Thus, although dust deposition undoubtedly adds metals to the ice, it not clear whether climate can fully account for a direct relationship between these variables. In order to study the volcanic hypothesis, we analyze the case under a double perspective: (1) large explosive episodes related to acid magmatism; and (2) quieter mafic volcanic activity. Although the first one can introduce huge volumes of metal-rich aerosols to the stratosphere during single, catastrophic events, the latter is more continuous, accumulative, and far richer in sulfur. However, inasmuch as metals build volatile species with sulfur and halides, the chloride-rich character of the acid volcanism could easily compensate for its deficiency in sulfur. Thus, we suggest that the volcanic activity, via quiescent degassing and eruptive episodes, may account for an important part of the heavy metal contents present in the ice cores.