Acidic Lava Flows Research Articles

Geochemical Characteristics of Quartzite in Parts of Paleoproterozoic Dhanjori Group, Singhbhum Craton, Eastern India: Implications for Provenance and Paleoweathering

Abstract Singhbhum craton preserves the records of sedimentation, magmatism, and tectono-thermal events from Mesoarchaean to Neoproterozoic. The Dhanjori Group (DG), located on the northeast margin of the Singhbhum craton, comprises of a variety of rocks including quartz pebble conglomerate, quartzite, schist, interlayered with mafic to intermediate and rarely acidic lava flows, tuff and agglomerate. Petrography and geochemical characteristics of the Dhanjori quartzite have been undertaken to interpret paleoweathering and provenance characteristics. Studied quartzites are made up of abundant quartz, feldspar, mica, and lithic fragments. With the help of geochemical data, the studied quartzites are classified as quartz-arenites and sub-arkoses. In addition to the A-CN-K plot, various chemical indices such as the chemical index of weathering (CIW), chemical index of alteration (CIA), and plagioclase index of alteration (PIA) indicate moderate to intense chemical weathering of the provenance under semi-humid climatic conditions. Rare earth element (REE) chondrite normalized patterns of the studied samples illustrate enriched light rare earth elements (LREEs) (LaN/SmN = 3.11 – 6.19), depleted heavy rare earth elements (HREEs) (GdN/YbN = 0.35 – 3.12) and negative Eu anomaly (Eu/Eu* = 0.55 - 0.87, ~ 0.68). Such patterns are similar to that of the upper continental crust (UCC). In the discrimination function diagram, studied samples of the Dhanjori Group fall in quartzose sedimentary field. In addition, La/Sc vs. Th/Co and La-Th-Sc diagrams, various ratios like Th/Sc (~0.61), La/Sc (~4.42), Th/Co (~0.03), La/Co (~0.11), and Cr/Th (~141.62) imply a mixed provenance for the studied samples. Hence, it has been inferred that the meta-sediments and orthoamphibolites of the older metamorphic group, Singhbhum granitoid complex, as well as associated Archaean metavolcanic suites, would have acted as the probable source rocks for the studied Dhanjori quartzites.

Investigação geotécnica de taludes rochosos por meio da análise estrutural: estudo de caso da BR-116, Rio Grande do Sul

A BR-116, localizada no nordeste do estado do Rio Grande do Sul, atravessa a Escarpa da Serra Geral, composta de derrames ácidos e básicos da Formação Serra Geral. Diversos movimentos de massa são observados na rodovia, relacionados com a queda e os deslizamentos de blocos dos taludes rochosos. Como hipótese, pretendeu-se verificar se as famílias de fraturas tectônicas regionais causam os movimentos de massa nos taludes da BR-116. O objetivo desta pesquisa foi aperfeiçoar os métodos de investigação geotécnica, correlacionando a Geologia Estrutural com a estabilidade de taludes rochosos. Entre os métodos utilizados estão o sensoriamento remoto e a análise de lineamentos estruturais, a análise estrutural geométrica e a análise geotécnica dos maciços rochosos (identificação de possíveis planos de ruptura e cálculo de seus fatores de segurança). Os resultados dos lineamentos estruturais regionais indicam o predomínio da direção ENE, seguida pelas direções subordinadas NE e WNW. Em relação às fraturas de alto ângulo analisadas em campo, caracterizou-se um máximo com direção N50-70E, similar ao observado regionalmente. A interpretação do diagrama de movimentos de massa indica que 75% dos movimentos que podem ocorrer na BR-116 seriam causados por deslizamentos em cunha, e o restante são planares, com predomínio de descontinuidades de alto ângulo. A direção máxima dos lineamentos (N70-90E) pode causar movimentos em seis dos sete taludes estudados, e o segundo máximo (N60-80W) condiciona deslizamentos em quatro dos sete pontos. Essa evidência mostra que as estruturas provenientes dos lineamentos regionais são as que mais podem gerar movimentos de massa.

Monte Amiata volcano (Tuscany, Italy) in the history of volcanology: 2—its role in the definition of “ignimbrite” concepts and in the development of the “rheoignimbrite” model of Alfred Rittmann

The explosive eruptions that occurred between nineteenth and twentieth centuries produced a fundamental cultural impact on the development of Volcanology. Pyroclastic products and ignimbrites features start to be at the base of an international debate. Various descriptions of explosive eruptions, and a new terminology of their products, such as nuee ardente and ignimbrite, were presented and extensively discussed in the framework of the International Association of Volcanology conferences held in 1961 at Catania and in 1963 at Tokyo. Ignimbrite deposits are first assimilated to welded tuffs. That attention to explosive volcanism of the first half of the twentieth century was the context in which has matured the Alfred Rittmann model of rheoignimbrite as welded ignimbrite showing secondary flowage structures. This term introduced by Rittmann in 1958, and shared by Giorgio Marinelli in 1961, was intended to describe the extensive sheet of acidic vitrophyric volcanic rocks of Monte Amiata volcano, interpreted as lava flows by all previous authors. Rheomorphic ignimbrites, in the Rittmann model, have features that strongly differentiate them from normal ignimbrites and that are very similar to what shown by acidic lava flows, as fluidal structures and wrinkles. The concept of rheomorphic ignimbrite is still in use into the volcanological literature, even if not for the Monte Amiata volcanics, nowadays definitively considered to be lava flows and domes. However, the Rittmann and Marinelli authoritative assumptions inhibited, up to present times, new volcanological interpretation of Monte Amiata acidic lavas.

Feeder systems of acidic lava flows from the Paraná-Etendeka Igneous Province in southern Brazil and their implications for eruption style

In the Rio Grande do Sul State, southern Brazil, the volcanic sequence of the Paraná-Etendeka Igneous Province consists of pahoehoe and rubbly pahoehoe lava flows with basaltic and basaltic andesitic composition respectively, overlaid by acidic volcanic rocks. The acidic volcanic rocks of the Paraná-Etendeka Igneous Province exhibit textures and structures that can be related to effusive and/or explosive eruptions generating predominantly rheoignimbrites. The huge lava volume related to the emplacement of large igneous provinces implicates on efficient feeder systems that are more commonly observed in continental environments. In the Paraná-Etendeka Igneous Province, feeders of basaltic rocks are exposed in several dyke swarms (Ponta Grossa NW trending, Florianópolis/Skeleton Coast (NW Namibia) N-S trending, Serra do Mar NE trending and Henties Bay/Outjo NE trending). In contrast, the only feeder system proposed to the acidic rocks of the Paraná-Etendeka Igneous Province is the Messum complex in Namibia (Milner et al. 1995). In the study area, the opening of three quarries for the extraction of dimension stones has exposed impressive structures/textures that show the effusive emplacement and the ductile to fragile-ductile magma transition along the acidic feeder dykes. Besides that, magma mixing/mingling processes between two acidic magmas are observed along the dykes. Here we describe new occurrences of acidic feeder dykes, correlate the dykes with acidic flows and discuss their importance to understand the emplacement of the Palmas type acid units in southern Brazil.

Mafic subvolcanic intrusions and their petrologic relation with the volcanism in the south hinge Torres Syncline, Paraná-Etendeka Igneous Province, southern Brazil

The hypabyssal intrusions investigated in this study are located in the east-central region of the state of Rio Grande do Sul, in the south hinge of the Torres Syncline. The intrusions comprise twenty-four dikes and ten sills, intruding in ponded pahoehoe, compound pahoehoe, rubbly and acidic lava flows of the south sub-Province of the Paraná Igneous Province and the sedimentary rocks of the Botucatu, Pirambóia, Santa Maria and Rio do Rasto Formations, on the edge of the Paraná Basin. The intrusive dikes in the flows have preferred NNW-SSE direction and the intrusive dikes in the sedimentary rocks have preferred NE-SW direction. Regarding the morphology, the dikes were separated into two different groups: symmetrical and asymmetrical. The small variation in facies is characterized by fine to aphanitic equigranular rocks. The rocks were divided into two types: Silica Supersaturated Tholeiite (SST) – dikes and sills consisting of plagioclase and clinopyroxene as essential minerals, with some olivine and felsic mesostasis, predominant intergranular texture and subordinate subophitic texture; and Silica Saturated Olivine Tholeiite (SSOT) – dikes consisting mainly of plagioclase, clinopyroxene and olivine, and predominant ophitic texture. The major and trace element geochemistry allows classifying these hypabyssal bodies as basalts (SSOT), basaltic andesites and trachyandesites (TSS) of tholeiitic affinity. The mineral chemistry data and the REE behavior, combined with the LILE and HFSE patterns, similar to the flows and low-Ti basic intrusions of southern Brazil and northwestern Namibia allow suggesting that these dikes and sills were part of a feeder system of the magmatism in the Paraná-Etendeka Igneous Province. The preferred direction of the intrusive dikes in the sedimentary rocks of the Paraná Basin coincides with tectonic-magmatic lineaments related to extensional processes and faulting systems that served as vents for dike swarms parallel to the Brazilian coast, with the same direction as the Namibia coast dike swarm. This suggests that these dikes were part of the triple junction system related to the opening of the South Atlantic Ocean. The preferred directions of the intrusive dikes in the lava flows are similar to the directions of the Ponta Grossa and Rio Grande Arcs and the Torres Syncline. They may have been a part of, or been caused by one or more geotectonic cycles that originated these structures. The emplacement process of the asymmetric dikes suggests they were enclosed under the hydraulic fracture model, since they do not follow a pre-existing fracture filling pattern. The emplacement of the sills conforms to the weakness zones of the sedimentary units. Regarding the intrusive dikes in the flows, divided by lithofacies associations, also taking into account the geochemical and petrographic similarities, it is observed that these dikes are part of a supply system of the basic lava flows, stratigraphically positioned above the host lava flows.

Vesicle distribution in acidic lava flow units in the rift basins of NE China: implications for petroleum reservoir exploration

AbstractAcidic lava flows comprise a large proportion of the total volcanic succession in the rift basins of northeast China. The objective of this study was to explore the vesicle distribution in the acidic lava flows in those basins. Two representative areas with acidic lava flow outcrops in NE China were selected for study. These lava flows share similar magma sources and chemistries. The types and inner structures of the acidic lava flows were determined in detail by measuring the shape of the flows (thickness and lateral extent) and the vertical sequences in the outcrops and shallow coring well Y1D1 in the two outcrop areas. Furthermore, the interpretation of deep borehole data and 3D seismic data from the Changling Graben of the Songliao Basin provided additional thickness and geometry data as a robust complement to the outcrop data. This study revealed that the shapes of the acidic lava flows transition from dome to tabular to braided with decreasing size. Furthermore, the vertical sequences can be classified into three zones: the upper vesicle zone, the massive core zone and the basal zone. The borehole thickness data indicate a trend in the maximum proportions occupied by the upper vesicle zone: thick flows have a relatively low proportion occupied by upper vesicle zones, whereas thin flows display a wide range in the proportion represented by upper vesicle zones. Therefore, braided acidic lava flows are more likely to have a high proportion of upper vesicle zones. Upper vesicle zones usually have high porosity and permeability and represent the primary effective gas reservoir system. The greatest lateral extents of gas reservoirs are usually in the tabular acidic lava flows, but the largest proportions occupied by gas reservoirs are usually in stacked braided lava flows. This study can help us to better understand the distribution of volcanic petroleum reservoirs in acidic lava successions where hydrocarbons are encountered but borehole data are limited. Furthermore, this study is useful for interpreting acidic lava flows in logs and seismic data from basins. Copyright © 2016 John Wiley & Sons, Ltd.

Geology, Geochemistry and Radioactivity of Granitic and Volcanic Rocks at Hadarba Area, South Eastern Desert, Egypt

The present work deals with geology, geochemistry, radioactivity and tectonic environment of the granitic and volcanic rocks at Hadarba area, South Eastern Desert of Egypt. The granitic rocks comprise tonalite-granodiorite and monzogranite, while volcanic rocks include rhyolite, rhyodacite anddacite. These rocks are characterized by high concentrations of SiO2, Na2O, Fe2O3, K2O, Zr, Nb and Y but low in MgO, CaO, Cr, Ni, Sr, Ga and V. Field studies indicate that Dokhan volcanics extrude both tonalite-granodiorite and monzogranite with sharp contact forming a thick successive sequence of laminated acid lava flows, crystal lapilli tuffs and agglomerates. They range in composition from rhyolite, rhyodacite to dacite. Shear zone comprise lines–arranged intrusions trending NE-SW direction were recorded north Gabal Hadarba and extends for about 2.3 km in length with a width reaches up to 10 meter. These lines–arranged intrusions include quartz vein, microgranite and basic dykes. These shear zones cut through monzogranite. Petrochemical studies and tectonic discrimination diagrams for the monzogranite reveal that it is classified as granite developed in the within-plate tectonic environment, while Dokhan volcanics are classified as rhyolite and dacite developed in the immature island arcs and active continental margin environments.Field radiometric measurements of these granitic and volcanic rocks reveal low uranium and thorium contents. Uranium contents range from 1.2 to 2.7 ppm in the tonalite-granodiorite, from 1.1 to 8.5 ppm in the monzogranite, from 1.3 to 9.3 ppm in the Dokhan volcanic and from 1.4 ppm to 15.4 ppm in the felsite dyke.

GEOLOGY, GEOCHEMISTRY AND RADIOACTIVITY OF GRANITIC AND VOLCANIC ROCKS ATHADARBA AREA, SOUTH EASTERN DESERT, EGYPT

The present work deals with geology, geochemistry, radioactivity and tectonic environment of the granitic and volcanic rocks at Hadarba area, South Eastern Desert of Egypt. The granitic rocks comprise tonalite-granodiorite and monzogranite, while the volcanic rocks include rhyolite, rhyodacite and dacite. These rocks are characterized by high concentrations of SiO2, Na2O, Fe2O3, K2O, Zr, Nb and Y but low in MgO, CaO, Cr, Ni, Sr, Ga and V. Field studies indicate that Dokhan volcanics extrude both tonalite-granodiorite and monzogranite with sharp contact forming a thick successive sequence of laminated acid lava flows, crystal lapilli tuffs and agglomerates. They range in composition from rhyolite, rhyodacite to dacite. Shear zone comprise lines–arranged intrusions trending NE-SW direction were recorded north Gabal Hadarba and extends for about 2.3 km in length with a width reaches up to 10 meter. These lines–arranged intrusions include quartz vein, microgranite and basic dykes. These shear zones cut through monzogranite.Petrochemical studies and tectonic discrimination diagrams for the monzogranite reveal that it is classified as granite developed in the within-plate tectonic environment, while Dokhan volcanics are classified as rhyolite and dacite developed in the immature island arcs and active continental margin environments. Field radiometric measurements of the granitic and volcanic rocks reveal low uranium and thorium contents. Equivalent uranium content ranges from 1.2 to 2.7 ppm in the tonalite-granodiorite, from 1.1 to 8.5 ppm in the monzogranite, from 1.3 to 9.3 ppm in the Dokhan volcanic and from 1.4 to 15.4 ppm in the felsite dyke.

The role of viscosity in the emplacement of high-temperature acidic flows of Serra Geral Formation in Torres Syncline (Rio Grande do Sul State, Brazil)

The acidic flows from Serra Geral Formation in Torres Syncline, Rio Grande do Sul, Brazil, are on the top of a volcanic sequence composed by a complex facies association of compound, simple and rubbly pahoehoebasic flows, acidic lava domes, and tabular acidic lava flows. The origin and emplacement conditions of the acidic volcanic rocks are discussed in this paper based on petrology, on calculated apatite saturation thermometry temperatures, and on estimated viscosity data. The liquidus temperatures for metaluminous rhyodacite to rhyolite samples are about 1,067.5 ± 25oC in average. The viscosity (η) values vary from 105 to 106 Pas for anhydrous conditions, suggesting the emplacement of high-temperature - low-viscosity lava flows and domes. The occurrence of acidic lava domes above simple pahoehoe flows as flow-banded vitrophyres was under low effusion rates, in spite of their high temperature and low viscosities, which are reflected in their small height. The emplacement of lava domes has continued until the eruption of rubbly pahoehoe flows and the geometry of these deposits rugged the relief. Presence of tabular acidic lava flows covering the landscape indicates that it was under high effusion rates conditions and such flows had well-insulated cooled surface crusts. The capacity to attain greater distances and overpass relief obstacles is explained not only by high effusion rates, but also by very low viscosities at the time of emplacement.

The role of geodiversity on the groundwater resource potential in the upper Blue Nile River Basin, Ethiopia

Groundwater has been the main source of water supply for large cities and towns over the last few decades in the upper Blue Nile River Basin, Ethiopia. However, provision is often unsuccessful because of poor well productivity, difficult drilling conditions, poor well positioning, or sometimes due to poor water quality. The growing pressure of urban population and industrial development is focusing unprecedented attention on the groundwater potential of the basin. The purpose of this work is to spatially characterize the groundwater potential of the upper Blue Nile River Basin with respect to variable recharge and geodiversity. The study shows that from the annual recharge obtained using the base flow separation method, the renewable groundwater potential in the basin was estimated to be in the range of 1.2 and 2 billion m3/year. The aquifers in the area are divided into three categories: low to moderate productivity (≈3.5 l/s) which includes crystalline basement rocks, acidic lava flows and domes, and very fine alluvial sediments; moderate to high productivity (≈5.5 l/s) that includes Mesozoic sedimentary rocks (sandstone, limestone, gypsum, dolomite); and high to very high productivity (≈20 l/s) which includes basic lava flows of the Trap series, Quaternary lava flows and alluvial sediments.

Petrography and Geochemistry of St. Mary Islands, near Malpe, Dakshina Kannada District, Karnataka

The present paper documents the petrography, mineral chemistry and petrochemistry of the acid volcanics of St.Mary group of islands. These are essentially characterized by pyroxene bearing rhyolites with average 73.49 wt.% SiO 2 . All the rhyolites from these islands are acmite normative, hence peralkaline with phenocrysts of zoned plagioclase and sometimes hypersthene/augite. There is depletion of LREE with moderate negative Eu anomaly. The enhancement of HFSE elements indicates their compatibility with continental crust. These rhyolites have high equilibrium temperature (915°C) at relatively lower oxygen fugacity (10 -16 ). The acidic lava flows are anorogenic, within plate rhyolites, generated during northern migration of Indian plate over Marion hotspot.

Volcanic cycles and setting in the Neoproterozoic III to Ordovician Camaquã Basin succession in southern Brazil: characteristics of post-collisional magmatism

The Camaquã Basin comprises a volcano-sedimentary succession, located in southernmost Brazil, and represents a molasse basin formed at the post-collisional stage of the Brasiliano/Pan-African orogenic cycle in the Neoproterozoic III to Ordovician period. This basin is one of the most well-preserved ancient volcano-sedimentary sequences undeformed and unmetamorphic in the world, dominantly developed on a continental setting under subaerial conditions. It is composed of five major stratigraphic units, four of them with a distinct volcanic character from the bottom to the top, as: (1) Maricá; (2) Bom Jardim; (3) Acampamento Velho; (4) Santa Bárbara; and (5) Guaritas Allogroups. A concise sight of geochemical and isotopic rock data is presented, as well as stratigraphic correlation and description of rock structures and textures that lead to the identification of their genetic processes, the aim of this paper, indicating a relation with a coeval plutonism, and volcanism that evolved from high-K calc-alkaline to shoshonitic and ended with a silica-saturated sodic alkaline magmatism, with a crustal component represented by peraluminous granites. Volcanic deposits from bottom to top are made mostly of volcanogenic sedimentary deposits, succeeded by basic to intermediate lava and pyroclastic flows of shoshonitic affinity, followed by intermediate and acid lava flows and ignimbrites of sodic alkaline affinity. The last volcanic event is represented by basalt pahoehoe flows, probably of mildly alkaline sodic affinity.

Palaeoceanography and tectonic setting of the Jurassic Coast Range ophiolite, central California: evidence from the extrusive rocks and the volcaniclastic sediment cover

The primary thesis of this paper is that the character of sedimentary rocks within or directly on top of an ophiolite complex can be used to constrain tectonic models of oceanic crustal genesis. Late Jurassic ( c. 169-161 Ma) Coast Range ophiolite remnants are exposed E and W of the San Andreas Fault in central California. Ophiolite volcanic rocks are mainly sub-alkaline tholeiitic basalts, but include subordinate intermediate and silicic flows and breccias. Available ‘immobile’ major and trace element data indicate that the Coast Range ophiolite formed above a subduction zone, possibly in a fore-arc setting, as suggested by the presence of high magnesian andesites and boninites. The ophiolite extrusives mainly comprise pillow lava and lava breccia formed on a rugged fault-controlled ocean floor. Interlava pelagic sediment is restricted to very small amounts of interstitial red chert and nannoplankton limestone. Widespread occurrence of vesicular lavas probably reflects high primary volatile contents rather than eruption in shallow water. Local interbeds of arc-derived silicic tephra in the uppermost extrusives suggest that the ophiolite and cover sediments formed together in a single tectonic setting. Depositionally overlying deep-water successions up to 600 m thick comprise radiolarian-rich tuffaceous and volcaniclastic sediments of ?Callovian-mid-Tithonian age (165-148 Ma). Depositional processes included airfall, turbidity currents, mass flow and current reworking. Small SiFeMn lenses along the lava-sediment contact formed by hydrothermal replacement of basal siliceous tuffaceous sediments or by direct chemical precipitation. At one locality (Llanada), the ophiolite is overlain by up to 1.8 km of younger (?Tithonian) basic-intermed, and acid lava flows, submarine lahars and mainly silicic pyroclastic sediments, of inferred volcanic arc origin. The volcaniclastic cover passes conformably upwards into late Tithonian and younger terrigenous deep-water clastic sediments of the Great Valley Group, deposited in a fore-arc setting. The Coast Range ophiolite and its cover are interpreted as an incipient intraoceanic volcanic arc, possibly developed above an eastward (continent-ward)-dipping subduction zone within the equatorial Pacific Ocean. In this scenario, short-lived (5–8 Ma) supra-subduction zone spreading to form the ophiolite was followed by ?Callovian-Tithonian arc volcanism, shedding tuffaceous debris onto the adjacent fore-arc. Subduction was active separately along the western American continental margin with the result that the Coast Range arc-ophiolite complex eventually collided with North America, triggering the Late Jurassic Nevadan orogeny and initiating Franciscan subduction-accretion. The Coast Range ophiolite remnants, at least those west of the San Andreas Fault, were apparently translated northwards to their present positions after Late Cretaceous.

Petrografia das rochas ácidas da Formação Serra Geral na região do Rio Paranapanema - São Paulo

The northernmost occurrences of acid lava flows outpourings of the Serra Geral Formation, described up to the moment, occur in the Paranapanema River region, near the Xavantes and Armando Laydner Dams and were classified as dacite and rhyolite granophyric.

Acid lava flow structure

Properties of four acid lava flows are described to evaluate typical distinctive characters from ignimbrite flows. The lamination due to fluidal structure of the acid lavas, indicating viscous flow, is the main feature to distinguish lava from ignimbrite.