Acid Volcanic Rocks Research Articles

고속도로 건설현장의 산성배수 발생개연성평가 및 피해저감대책: ○○고속도로건설현장

<TEX>${\bigcirc}{\bigcirc}$</TEX>고속도로 건설현장 <TEX>${\bigcirc}$</TEX>공구에 분포하는 암석에 대하여 산성배수 발생개연성을 평가하고 피해 저감대책을 검토하였다. 고속도로건설구간의 지반은 이천리층에 해당하는 사암과 중성내지 산성 화산암으로 구성되어 있으며 이들은 주변의 화강암관입에 수반된 열수 용액에 의해 황화광물을 산점상으로 함유하고 있다. 황화광물의 함량이 높은 화산암과 사암은 산성배수 발생개연성이 높고 중금속(Zn, Pb, As)을 많이 함유한 산성배수가 주변지역으로 유출되어 환경오염을 유발할 개연성이 높은 것으로 나타났다. 건설공사과정중 산성배수가 발생될 개연성이 높은 구역에서 배출되는 배수는 중화 및 중금속 제거처리 후 배수가 이루어져야 하며, 절취면의 안정성 확보를 위하여 산성배수의 발생을 근원적으로 억제할 수 있는 코팅처리기술을 적용한 후 숏크리트, 앵커 등 사면보강공법이 적용되어야 할 것으로 판단된다. 화산암과 사암은 골재로서 활용이 어려우며 지반성토재로 사용할 경우 지하수와 우수의 접촉을 최소화할 수 있는 성토층의 구조를 갖춘 후 활용하여야 한다. Assessment and damage reduction strategy of acidic rock drainage were conducted in a section of <TEX>${\bigcirc}{\bigcirc}$</TEX> highway construction site. The geology of the studied section consists of Icheonri sandstone and intermediate to acidic volcanic rocks. Sulfides occur as a disseminated type in sandstone and volcanics which were altered by the hydrothermal solution of granite intrusion. Volcanics and sandstone with a high content of sulfide were classified as a potentially acid rock drainage(ARD) forming rock. The drainage originated from those rocks may acidify and contaminate the surrounding area during the highway construction. Therefore, the drainage should be treated before it is discharged. A slope landslide hazard due to the ARD was also expected and the coating technology was recommended for the reduction of ARD generation as a preemptive measure before reinforcement work for enhancing slope stability such as shotcrete and anchor. According to the ARD risk analysis, those rocks should not be used as cement aggregate, but only to be used as a bank fill material of a filling-up system that allows minimal contact with rainfall and groundwater.

El'gygytgyn impact crater, Chukotka, Arctic Russia: Impact cratering aspects of the 2009 ICDP drilling project.

The El'gygytgyn impact structure in Chukutka, Arctic Russia, is the only impact crater currently known on Earth that was formed in mostly acid volcanic rocks (mainly of rhyolitic, with some andesitic and dacitic, compositions). In addition, because of its depth, it has provided an excellent sediment trap that records paleoclimatic information for the 3.6 Myr since its formation. For these two main reasons, because of the importance for impact and paleoclimate research, El'gygytgyn was the subject of an International Continental Scientific Drilling Program (ICDP) drilling project in 2009. During this project, which, due to its logistical and financial challenges, took almost a decade to come to fruition, a total of 642.3 m of drill core was recovered at two sites, from four holes. The obtained material included sedimentary and impactite rocks. In terms of impactites, which were recovered from 316.08 to 517.30 m depth below lake bottom (mblb), three main parts of that core segment were identified: from 316 to 390 mblb polymict lithic impact breccia, mostly suevite, with volcanic and impact melt clasts that locally contain shocked minerals, in a fine-grained clastic matrix; from 385 to 423 mblb, a brecciated sequence of volcanic rocks including both felsic and mafic (basalt) members; and from 423 to 517 mblb, a greenish rhyodacitic ignimbrite (mostly monomict breccia). The uppermost impactite (316–328 mblb) contains lacustrine sediment mixed with impact-affected components. Over the whole length of the impactite core, the abundance of shock features decreases rapidly from the top to the bottom of the studied core section. The distinction between original volcanic melt fragments and those that formed later as the result of the impact event posed major problems in the study of these rocks. The sequence that contains fairly unambiguous evidence of impact melt (which is not very abundant anyway, usually less than a few volume%) is only about 75 m thick. The reason for this rather thin fallback impactite sequence may be the location of the drill core on an elevated part of the central uplift. A general lack of large coherent melt bodies is evident, similar to that found at the similarly sized Bosumtwi impact crater in Ghana that, however, was formed in a target composed of a thin layer of sediment above crystalline rocks.

Geological and geochemical characteristics in the paleo-weathering crust sedimentary type REE deposits, western Guizhou, China

A supergene REE deposit closely interrelated with the weathering of the Emeishan basalt formation was produced in the Xuanwei formation, the overlying stratum of the late Permian Emeishan basalt formation in West Guizhou, China. The host strata consist primarily of offwhite kaolinite clay rock and/or grayish black carbonaceous shale. Mineralogical analyses reveal that kaolinites are the major minerals in REE ores with small amounts of smectite, illite, boehmite, hornblende, pyrophyllite, calcite, dolomite and/or iron-bearing minerals, with a certain proportion of feldspar, quartz crystal debris and noncrystal debris. Geochemical analyses reveal high enrichment of trace elements like Cu, Nb, Ta, Zr and Hf. The host strata feature considerable lithological variability, close interrelation of the REE grade with the lithology and uneven spatial distribution of the REE ores, which are mostly found in Lufang, Maojiaping and Zhangsigou profiles of Weining County and can be as thick as 20m. Of the five stratigraphic profiles, 48% have their whole-rock ∑REE higher than 1000ppm. The REE in this framework consists primarily of ion adsorbed phases and REE-rich residual independent mineral phases. Comprehensive analyses suggest that the source may not only include the Emeishan basalt, but the intermediate acid volcanic rocks evolved from the Emeishan basalt in the later periods; the hydrothermal alteration subsequently imposed on the host strata might have boosted the mineralization of the rare earth. The preliminary genetic model should have been: the denudation product from the weathering of the parent rock was migrated to the sea-continental margin at the continent side carrying huge quantities of REE with it and was preserved by the quick marine transgression. The host strata consist primarily of kaolinite clay rock and/or carbonaceous shale, which are so far believed to be a sedimentary type REE deposit closely interrelated with weathering effect.

Chromium isotope anomaly in an impactite sample from the El'gygytgyn structure, Russia: Evidence for a ureilite projectile?

AbstractThe 3.6 Ma, 18‐km‐diameter El'gygytgyn impact structure (Arctic Russia) is unique among the currently known terrestrial impact craters in that it is the only one that was formed in acid volcanic rocks. Previous analyses of impactites from El'gygytgyn showed minor enrichments of the siderophile elements, including Ir, which, together with distinct Cr enrichments, gave rise to speculation that an achondritic projectile was involved. We studied the major and trace element composition in samples from the new ICDP drill core obtained near the center of the structure, as well as the chromium isotopic composition of an impact glass sample collected on the surface. Several suevitic breccias from the upper part of the suevite sequence in the drill core show higher Cr and Ni contents compared with felsic volcanic rocks in the lower part of the core and from surface samples. However, it is difficult to unambiguously establish a meteoritic component from trace element data, as input from (rare) mafic target rocks is a possibility. In contrast, the Cr isotopic composition of the impact glass sample yielded a nonterrestrial ε54Cr value of −0.72 ± 0.31 (2 std. err.). This negative ε54Cr is different from known carbonaceous chondrite values (ε54Cr of +0.95 to +1.65), but is nearly identical to reported values for ureilites (approximately −0.77). The value is, however, also within analytical error of eucrites (approximately −0.38) and ordinary chondrites (approximately −0.42). Given the chemical signatures found in previous analyses of El'gytgytgyn impactites and the similarity of our Cr isotopic data to ureilites, we suggest that the impacting asteroid could have been an F‐type asteroid of mixed composition, similar to the recent Almahata Sitta fall in Sudan.

Experience of petrochemical typification of acid volcanic rocks from different geodynamic settings

A classification diagram was empirically developed for acid volcanic rocks formed in modern geodynamic settings and reflects their peculiar chemical features. The testing of the binary diagram Al2O3/(CaO + MgO)−Fe2O 3 Tot /(CaO + MgO) for the Late Cretaceous (Pimorsky, Siyanovsky, Kamensky, and Levosobolevsky) and Paleogene (Bogopolsky) Volcanic Complexes of East Sikhote Alin demonstrated its high efficiency for deciphering the tectonic settings of ancient acid volcanism.

Litostratygrafia czerwonego spągowca w Wielkopolsce

Litostratygrafia czerwonego spągowca w Wielkopolsce

Geology, petrology and geochronology (Pb-Pb) of the Serra da Bocaina Formation: evidence of an Orosirian Amoguijá Magmatic Arc in the Rio Apa Terrane, south of the Amazonian Craton

This work presents the results of the geological mapping and the petrological characterization of the Serra da Bocaina Formation belonging to the Amoguija Magmatic Arc of the Rio Apa Terrain. In the Bocaina hills, the Serra da Bocaina Formation consists of intermediately to predominately acidic volcanic rocks, classified as andesites and rhyolites and subdivid- ed into five petrographic facies, which include four volcanoclas- tics and one effusive. In the studied rocks, tectonic structures are generated in two compressive ductile to ductile-brittle deforma- tional phases. The first phase, which is more intense, presents along the entire studied area and is responsible for the Santa Rosa Shear Belt, whereas the second phase is more localized. The geochemical study indicates a calc-alkaline magmatism of medium to high K, peraluminous, and generated in a volcanic arc environment. These volcanic rocks formed in an explosive environment related to the Amoguija Magmatic Arc, as indicat- ed by their Pb-Pb zircon age of 1877.3 ± 3.9 Ma.

Petrography of impact glasses and melt breccias from the El'gygytgyn impact structure, Russia

AbstractThe El'gygytgyn impact structure, 18 km in diameter and 3.6 Ma old, in Arctic Siberia, Russia, is the only impact structure on Earth mostly excavated in acidic volcanic rocks. The Late Cretaceous volcanic target includes lavas, tuffs, and ignimbrites of rhyolitic, dacitic, and andesitic composition, and local occurrence of basalt. Although the ejecta blanket around the crater is nearly completely eroded, bomb‐shaped impact glasses, redeposited after the impact event, occur in lacustrine terraces within the crater. Here we present detailed petrographic descriptions of newly collected impact glass‐bearing samples. The observed features contribute to constrain the formation of the melt and its cooling history within the framework of the impact process. The collected samples can be grouped into two types, characterized by specific features: (1) “pure” glasses, containing very few clasts or new crystals and which were likely formed during the early stages of cratering and (2) a second type, which represents composite samples with impact melt breccia lenses embedded in silicate glass. These mixed samples probably resulted from inclusion of unmelted impact debris during ejection and deposition. After deposition the glassy portions continued to deform, whereas the impact melt breccia inclusions that probably had already cooled down behaved as rigid bodies in the flow.

Hydrogeochemistry and arsenic contamination of groundwater in the Rayen area, southeastern Iran

High As contents in groundwater were found in Rayen area and chosen for a detailed hydrogeochemical study. A total of 121 groundwater samples were collected from existing tube wells in the study areas in January 2012 and analyzed. Hydrogeochemical data of samples suggested that the groundwater is mostly Na–Cl type; also nearly 25.62 % of samples have arsenic concentrations above WHO permissible value (10 μg/l) for drinking waters with maximum concentration of aqueous arsenic up to 25,000 μg/l. The reducing conditions prevailing in the area and high arsenic concentration correlated with high bicarbonate and pH. Results show that arsenic is released into groundwater by two major phenomena: (1) through reduction of arsenic-bearing iron oxides/oxyhydroxides and Fe may be precipitated as iron sulfide when anoxic conditions prevail in the aquifer sediments and (2) transferring of As into the water system during water–acidic volcanic rock interactions.

Preliminary Study on HFSE Mineralization in the Peralkaline Granites of Nusab El Balgum Area, South Western Desert, Egypt

Nusab El Balgum mass complex represents one of peralkaline volcanic activity phenomena in the south Western Desert of Egypt, which is typical for within-plate event, which formed in Mesozoic period. It consists of acidic volcanic (rhyolite and their pyroclastics) and sub-volcanic granitic rocks (incomplete ring, small stock and dyke of a peralkaline aphanites) as well as dykes (trachyte, bostonite, rhyodacite, rhyolite and porphyritic rhyolite) variable in thickness and the most of run in NNE-SSW trend. The peralkaline granitic rocks, especially those located at the southwestern part of this mass are characterized by extreme enrichments in HFSE (rare metals such as Zr, Nb, U and Th and REEs) which are the highest concentrations (e.g., >1% Zr, 0.5% Nb and 2.6% total REEs, Y up to 1%, eU up to 300 ppm and eTh up to 1100 ppm). The rare metal bearing minerals are thorite, uranothorite, autunite, amorphous secondary uranium, zircon and ferrocolumbite, while the REEs bearing minerals are bastnaesite, monazite and xenotime. The positive relations in all of the binary diagrams of Zr versus Nb, Y, eU and eTh, Nb versus Y, eU and eTh, Y versus eU and eTh in post magmatic intensely hematised peralkaline granites indicated that, this process is responsible for the enrichment in these HFSE. The chondrite-normalized pattern of high-altered peralkaline granites indicates: 1) higher LREEs enriched pattern (La/Gd = 11.34 and 12.25) means the alteration processes taking place under open system and these rocks evolved from magma of lithospheric rifting, 2) ΔCe 2O, and thus very low viscosity, despite its low temperature (ments, as indicated by strong negative Eu anomalies; and c) it had abundances of HFSE cations. Redistribution of elements took place by post magmatic hydrothermal solutions.

Sucessões vulcânicas, modelo de alimentação e geração de domos de lava ácidos da Formação Serra Geral na região de São Marcos-Antônio Prado (RS)

In the Sao Marcos (RS) and Antonio Prado (RS), the Serra Geral Formation exposes at the base basalts of pahoehoe type, covered by basalts of the ´a´ā type. The first succession was generated by a low rate of eruption in a closed flow system allowed the flow to reach distances >; 100 km of the source. The ´a´ā lava flow types were generated by higher rates of eruption and transported in open channels where rapid cooling prevented long distances from the source to be reached. The two types of basalts are low-TiO2 tholeiitic and the morphology of flows is not related to variations in SiO2 and MgO contents. Above these rock types outcrop acidic volcanic rocks geochemically of Caxias Group (Palmas Subgroup). Dimension stones extraction exposed the inner portions of the acidic feeder dikes with vertical magmatic foliations. The lava domes have exogenous characteristics and horizontal foliations. We propose a model for the generation of domes involving the diapirically rise of acids magmas that become vesicular and more viscous, that stop near the surface. New magmatic pulses extracted pieces of the vesicular fraction generating autobreccias in the conduit and vertical structures that extend laterally toward the surface organizing the lava domes with vitrophyres in the base and in the top, with a thin massive phaneritic core. Magmatic textures of the domes are typical of effusive units and the identification of the feeder dykes in the area allows the understanding of the emplacement process of acidic flows in the Serra Geral Formation.

The role of strike-slip faults in the displacement of the Palaeotethys suture zone in Southeast Thailand

Six N–S tectono-stratigraphic belts can be recognized in Southeast Thailand, each with a distinct stratigraphy and igneous history. The westernmost Belt (I) is thought to be part of the Sibumasu Block, and the easternmost (V) to include part of the Indochina Block. Between those, Belt III comprises acid volcanic rocks, volcaniclastics, and Carboniferous to Triassic sedimentary rocks with distinctive faunas, interpreted to be a volcanic arc; Belt IV comprises Triassic rocks of back-arc basin origin; Belt V is interpreted as a Permian accretionary complex on the western flank of Indochina; and VI is an unconformable cover of Jurassic–Cretaceous red-beds correlating with the Khorat Group. A history of the Triassic Indosinian Orogeny is proposed, leading to the cratonization of Southeast Thailand by the end-Triassic.The apparent absence in Southeast Thailand of rocks from the Devonian–Triassic Palaeotethys ocean (the Inthanon Zone of Northern Thailand) is suggested to have resulted from a phase of post-Indosinian, oblique to longitudinal, sinistral, strike-slip faulting. That phase is thought to have included displacement on the Mae Yuam Fault which bounds the Inthanon Zone in Northern Thailand. Then followed a phase of transverse, sinistral, strike-slip faulting which offset the tectono-stratigraphic belts and faults of the earlier phase.

Biogeochemical exploration using the Thola shrub in the Andean Altiplano, Bolivia

This study concerns the implementation of the most suitable geochemical prospecting methodology to explore for gold deposits in the Andean Altiplano, Bolivia. The main gold ore deposits in this area are associated with the ‘saddle reef antimony-gold type’ in low-grade metamorphic Ordovician–Silurian siliciclastic rocks, placer gold deposits of Miocene age and epithermal gold deposits related to acid volcanic rocks of Tertiary age. An orientation biogeochemical survey was carried out over these deposits by analysing a common plant (Thola shrub) for Au, Sb and pathfinder elements. Thola is widespread and abundant in this semi-arid highland terrain and includes different families such as Compositae ( Baccharis incarum/B. tola ) and Solanaceae ( Fabiana densa ) with deep roots (&gt;5 m) that are able to penetrate allochthonous rocks (acid tuffs) and mineralized zones. This orientation survey shows strong anomalies in gold and antimony over saddle reef antimony-gold deposits and anomalies over placer gold deposits where the bottom of the placer is exposed. High concentrations of Au and pathfinder elements were obtained in transects across acid volcanic rocks in the vicinity of abandoned mines. The Thola shrub therefore has the potential to be an excellent exploration medium throughout an area of 140 000 km 2 in the Bolivian Altiplano.

Uranium and arsenic dynamics in volcano-sedimentary basins – An exemplary study in North-Central Mexico

Abstract Uranium and As in deep groundwater of the volcano-sedimentary Villa de Reyes Graben around the city of San Luis Potosi in semi-arid North-Central Mexico (mean U: 7.6 μg L −1 , max. 138 μg L −1 ; mean As: 11.4 μg L −1 , max. 25.8 μg L −1 ) partly exhibit concentrations in excess of the WHO guideline values and thus endanger the quality of the most important drinking water source. To unravel the mechanisms for their enrichment in groundwater, the potential trace element sources, volcanic rocks and basin fill sediments, were characterized. A total of 131 solid and liquid samples were analyzed for major and trace element composition. The As/U hydrogeochemical signatures, their behavior during rock alteration and evidence from other major and trace element distributions, especially rare earth elements, strongly argue for dissolution of acid volcanic glass to be the dominating process of U and As release into groundwater. This natural baseline quality representing water–acid volcanic rock interaction is modified by additional trace element (preferentially As) mobilization from the sedimentary basin fill, representing a secondary source, in the course of decarbonatization of playa lake sediments and desorption from Fe-(hydr)oxide coated clastic material. The common behavior of both elements during magmatic differentiation and growing drift apart in sedimentary environments are important findings of this work. Comparison with recent findings in a similar environment suggests a common primary trace element source identification but significant differences in the evolution of As and U distribution. Geological and climatic similarity to numerous volcano-sedimentary basins makes the findings useful for water management purposes and transferable to other semi-arid regions facing challenges of geogenically impacted drinking water quality.

Field relation, geochemistry and origin of the Xinglonggou volcanic rocks in Beipiao area, Liaoning Province (China): Reappraisal on the foundering of lower continental crust of North China Craton

Our large scale geological mapping in the Beipiao area, western Liaoning Province, the North China Craton, shows that the exposed “Xinglonggou Formation” is not a monoclinal stratum, but a suit of strongly deformed volcanic rocks intruded by some small plugs. Consequently, two rock groups are categorized for the “Xinglonggou Formation” in the Beipiao area, according to their field relation, petrography, and geochemical characteristics. The group 1 rocks are blackish and fresh, and cut across the deformed group 2 volcanic rocks. Meanwhile, the group 1 rocks exhibit characteristics of higher magnesium number (Mg#⩾60), calcium content (CaO>5wt.%), and Sr/Y ratio (>60), but lower potassium (K2O<2wt.%) and Rb contents (<40ppm). Among these rocks, most of them have higher Cs but lower Li content. Geochemically, the group 1 rocks belong to high-SiO2 adakite (HSA). On the contrary, the group 2 is composed of intermediate and acid volcanic rocks, which are brownish or greenish and strongly folded. Compared with the group 1 rocks, they have higher potassium (K2O>2wt.%) and Rb contents, but lower Mg# (<60) and calcium content (most samples CaO<5wt.%); meanwhile, they have lower Sr/Y ratios (in general<60), and lower Cs but higher Li contents. According to their near zero εNd(t) value and radiogenic Pb isotopic compositions, as well as the enrichment of U and Th relative to LREE, neither the group 1 or the group 2 rocks result from the partial melting of the lower crust of North China Craton. The group 1 HSAs are generated by melting of the subducted oceanic crust of the Paleo-Pacific plate; otherwise, the group 2 rocks are derivatives of the magma originated from a slab-derived melt metasomatised mantle.

Petrography and major element geochemistry of the Permo-Triassic sandstones, central India: Implications for provenance in an intracratonic pull-apart basin

Detrital mode, composition of feldspars and heavy minerals, and major element chemistry of sandstones from the Permo-Triassic succession in the intracratonic Satpura Gondwana basin, central India have been used to investigate provenance. The Talchir Formation, the lowermost unit of the succession, comprises glacio-marine and glacio-fluvial deposits. The rest of the succession (base to top) comprising the Barakar, Motur, Bijori, Pachmarhi and Denwa formations, largely represent variety of fluvial depositional systems with minor fluvio-deltaic and fluvio-lacustrine sedimentation under a variety of climatic conditions including cold, warm, arid, sub-humid and semi-arid. QFL compositions of the sandstones indicate a predominantly continental block provenance and stable cratonic to fault-bounded basement uplift tectonic setting. Compositional maturity of sandstones gradually increases upwards from the Early Permian Talchir to the Middle Triassic Denwa but is punctuated by a sharp peak of increased maturity in the Barakar sandstones. This temporal change in maturity was primarily controlled by temporal variation in fault-induced basement uplift in the craton and was also influenced by climatic factors. Plots of different quartz types suggest plutonic source rocks for the Talchir sandstones and medium-to high-rank metamorphic plus plutonic source rocks for the younger sandstones. Composition of alkali feldspars in the Permo-Triassic sandstones and in different Precambrian rocks suggests sediment derivation from felsic igneous and metasedimentary rocks. Compositions of plagioclase in the Talchir and Bijori sandstones are comparable with those of granite, acid volcanic and metasedimentary rocks of the Precambrian basement suggesting the latter as possible source. Rare presence of high-K plagioclase in the Talchir sandstones, however, indicates minor contribution from volcanic source rock. Exclusively plagioclase-bearing metasedimentary rock, tonalite gneiss and mafic rocks are the probable sources of plagioclase in the Upper Denwa sandstones. Quartz-rich nature of the sandstones, predominance of K-feldspar over plagioclase and albite rich character of plagioclase in the sandstones is consistent with deposition in an intracratonic, pull-apart basin like the Satpura Gondwana basin. Composition of garnet and its comparison with that from the Precambrian basement rocks suggests mica-schist and amphibolite as possible sources. Predominance of dravite variety of tourmaline in the Permian sandstones suggests sediment supply from metasedimentary rocks. Presence of both dravite and schorl variety of tourmaline in subequal amount in the Triassic sandstones indicates sediment derivation from granitic and metasedimentary rocks. However, schorl-bearing rocks are absent in the basement complex of the study area. A–CN–K plot suggests granites, acid volcanic rock and meta-sediments of the basement as possible sources of the Talchir sandstones and metasedimentary rocks for the Barakar to Pachmarhi sandstones. The Denwa sandstones were possibly derived from K-feldspar-free, plagioclase-bearing metasediments, mafic rocks and tonalite gneiss. Chemical Index of Alteration (CIA) values suggest low intensity source rock weathering for the Talchir sandstones and higher intensity source rock weathering for the others. Various bivariate plots of major oxides composition of the sandstones suggest passive to active continental margin setting and even arc tectonic setting for a few samples.

The linkage between geological setting and human health in Ethiopia: a preliminary geo-environmental-health model

Tropical environments are known for their prevalence of a number of geo-chemical diseases. This is related to the very nature of their geo-environments. Little research is conducted in geo-sciences in Ethiopia to investigate the linkage between geo-environments and associated health risks. Fluoride and related diseases are the most widely studied from geological perspectives. Ethiopia is characterized by complex but regionally homogeneous geo-environment. Climate is under the influence of monsoon from two oceans and continental sources. Locally orography modifies the redistribution of rainfall in the lee and wind ward directions. This leads to any combination of warm to cold and wet to dry climate. Prominent geologic features are rifting, volcanism and uplifting. Combination of geology, climate, and topography results in a complex pattern of geo-environment which in turn results in belts of availability or scarcity of certain geo-chemical elements. This work shows the presence of linkage between geo-environmental setting and prevalence of geo-chemical diseases such as goiter, elephantiasis, flourisis, and trace element related health problems. South-western Ethiopia, which is under the influence of Indian Ocean monsoon and underlain by volcanic rocks shows the highest incidence of Iodine Deficiency Disorder (IDD). Regions of Ethiopia under the influence of Atlantic Ocean monsoon or areas underlain by sediments and sedimentary rocks show the lowest IDD. Elephantiasis prevalence is linked to laterite soils derived from chemical weathering of basalts, a typical process commonly taking place in humid plateau of south-western Ethiopia between altitudes of 1000 and 2000 masl. Flouride related diseases are common features in area where water supply for domestic water use depend on aquifers in acid volcanic rocks, commonly in the rift setting. Regardless of the prevalence of geo-chemical diseases, Ethiopia is also endowed with natural geo-chemical materials of significant health benefits ( e.g. , Mineral waters and mud volcanoes). The work proposes a preliminary geo-environmental health model for Ethiopia.

Seismic and geodetic evidence for the existence of hot materials beneath the Wakayama swarm activity, southwestern Japan

A remarkable seismic swarm area exists amid the Wakayama Plain on the western coast of the Kii Peninsula, in southwestern Japan, close to the Median Tectonic Line (MTL). The hypocenters of these swarm earthquakes are very shallow with a median of 6 km. This is exceptionally shallow for seismic activity in plain areas where the seismogenic layer is usually deep compared to that in mountainous regions ( Takayama et al., 2006). Also, the b-value below 8 km in the eastern part of this swarm region is anomalously high. In addition to these seismic features, GEONET data and leveling survey data obtained by the Geospatial Information Authority of Japan indicate that land around the swarm region are expanded and upheaved. Areas of the dilatation and upheaval almost overlap and their centers correspond to the site where the high b-value anomaly is observed. These facts strongly suggest that there are hot materials beneath the source region. In the Kii Peninsula acid volcanic rocks outcrop widely, and the Wakayama swarm area is located on the southern side of the MTL in the metamorphic belt below which the relatively young hot Philippine Sea plate is subducting and dehydration from a surpentinized forearc mantle is expected to occur. Based on the seismic and geodetic observations and the tectonic background of the area in which the swarm region is situated, we propose a hypothesis that a diorite or a serpentine diapir with plentiful hot fluids might be intruding beneath the source area.

Tectono-sequence stratigraphy and U–Pb zircon ages of the Rincón Blanco Depocenter, northern Cuyo Rift, Argentina

Extensional processes that followed the Gondwanan Orogeny rise to the development of a series of rift basins along the continental margin over older accreted Eopaleozoic terranes. Stratigraphic, structural, paleontological, and isotopic studies are presented in this work in order to constrain the ages of the sedimentary infilling and to analyze the tectosedimentary evolution of one of the Cuyo basin depocenters, known as Rincón Blanco. This asymmetrical half-graben was filled by continental sediments under a strong tectonic control. The infilling was strongly controlled by tectonics which in term produced distinctive features along the whole sedimentary sequence. Using a combination of lithological and structural data the infilling was subdivided into packages of genetically linked units bounded by regional extended surfaces. Several tuffs and acid volcanic rocks have been collected across the whole section of the Rincon Blanco sub-basin for SHRIMP and LA-MC-ICPMS U–Pb zircon dating. The ages obtained range from 246.4±1.1Ma to 230.3±1.5Ma which is the time elapsed for the deposition of three tectono-sequence units separated by regional unconformities and mainly constrained to the Middle Triassic. They are interpreted as a result of a reactivation of the extensional system that has evolved along strike as segments of faults that linked together and/or as laterally propagating faults. Regional correlation with coeval rift basins permits to establish north-south propagation in the extensional regime along the western margin of SW Gondwana. This trending started in the lowermost Triassic and extended until the latest Triassic. Two of them were precisely correlated with Cerro Puntudo and Cacheuta half-graben systems. The new data indicate that the three sequences were mostly deposited during the Middle Triassic (246 to 230Ma), with no evidence of sedimentation during Norian and Rhaetian, which is in conflict with some previous biostratigraphic studies.

Tectonic evolution of the Brusque Group, Dom Feliciano belt, Santa Catarina, Southern Brazil

The Dom Feliciano Belt constitutes the main geotectonic unit of the southeastern portion of Brazil and Uruguay. It was formed by the end of the Neoproterozoic as a result of the interaction among the Rio de La Plata, Paranapanema, Congo and Kalahari cratons during the formation of Western Gondwana. The Brusque Group represents the supracrustal units of the Dom Feliciano Belt that occur in its northernmost part, which ends in the Brazilian coast and probable continuity in the Kaoko Belt in southwestern Africa. It is possible to constrain the evolution of the Brusque Group paleobasin to the Neoproterozoic, with the rift phase starting in the Tonian (940–840 Ma) and the main sedimentation occurring until 640 Ma, as indicated by the ages of the acid volcanic rocks intercalated with the metasedimentary sequence. The supracrustal rocks can be grouped in three main units lithostratigraphically organized from the oldest to the youngest: Rio Oliveira Formation (rift phase, predominating metavolcanic units), Botuverá Formation (metasedimentary) and Rio da Areia Formation (metavolcano–carbonatic). Between 640 and 600 Ma several metamorphism and deformation phases affected the Brusque Group. Around 600 ± 10 Ma the three granitic suites (São João Batista, Valsungana and Nova Trento) were emplaced within regional metamorphites, producing post-foliation S2 metamorphic aureoles. S2 represents the main foliation observed in the metavolcanosedimentary rocks that constitute the Brusque Group. The tectonic model for the evolution of Brusque Group can be better achieved only when the geochemical, isotopic and geochronologic information available for the Dom Feliciano Belt in Santa Catarina, is considered as a whole. Therefore it is here suggested that the Brusque Group initially evolved in an independent peri-cratonic basin setting separated from the Florianópolis – Pelotas-Aiguá magmatic arc by the Adamastor ocean, having been juxtaposed to it only around 600 Ma, when Brusque Group and the Florianópolis Batholith collided.