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Search Results: 1 - 10 of 181 matches for " volcanism "
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Timing of Onset of Volcanic Centers in the Campanian of Western North America as Determined by Distal Ashfalls  [PDF]
Janet L. Bertog
Open Journal of Geology (OJG) , 2013, DOI: 10.4236/ojg.2013.32016
Abstract:

Strata of the Late Cretaceous Niobrara Formation and Pierre Shale Group include bentonites that provide a distal record of volcanic activity taking place to the west. Detailed stratigraphic analysis combined with mineralogy and geochemistry of the bentonites indicates the following timing of events: 1) Eustatic sea level fall as a result of the end of the Niobrara Cycle; 2) Tectonic deformation of the Western Interior Seaway coincident with tectonism on the Absoroka Thrust in Wyoming and Late Canyon Range Thrust in Utah; 3) Backarc volcanism in Montana associated with the Little Elkhorn Mountain volcanic complex; 4) Forearc volcanism in the Cascades area indicates subduction of a hot oceanic crust where plagioclase in the oceanic crust is being incorporated into the melt; 5) Cessation of tectonic activity results in a return of sedimentation patterns to north-south trending belts with the Boyer Bay and Burning Brule members of the Sharon Springs Formation deposited to the east and the Mitten Black Shale Formation deposited in the basin.

La Formación Cerros de Aguirre: Evidencias de Magmatismo Vendiano en el Uruguay
Campal,Néstor; Schipilov,Alejandro;
Latin American journal of sedimentology and basin analysis , 2005,
Abstract: this paper deals with the stratigraphy, petrography, geochemistry and structural relationships of the cerros de aguirre formation, which is located in the cuchilla dionisio terrane in eastern uruguay (bossi et al., 1998; bossi and gaucher, 2004) (fig. 1). detailed mapping at 1:20,000 scale, thin section petrography and geochemistry of major and trace elements were applied in this study. the cerros de aguirre formation is mainly composed of pyroclastic rocks with some interbedded volcanic layers, cropping out with a roughly elliptical outline 16 x 4 km in size, with a major axis oriented northsouth (fig. 2). the cerros de aguirre formation unconformably overlies granulites of the chafalote suite (masquelín et al., 2001). to the east, it is in tectonic contact along a regional shear zone with the greenschist-facies metasediments of the rocha group (hasui et al., 1975). the cerros de aguirre formation is subdivided here into three units: a) volumetrically dominant, finegrained fall deposits; b) concordant lavas, intercalated with the fall deposits, and c) pyroclastic flows. pyroclastic rocks include finely banded tuffs, massive tuffs, lapilli tuffs and tuffites with geochemical compositions ranging from andesites to rhyolites. lava flows are represented by basalts, andesi-basalts and rhyolites. pyroclastic flows are 20 to 100 m thick and up to 2 km wide, showing andesitic to rhyolitic compositions. the whole assembly exhibits open folding showing n20-30e oriented, sub-vertical axial planes (figs. 2 and 3). deformation increases in intensity toward the east, the main structure being an asymmetric syncline truncated in its eastern flank by a shear zone that also constitutes the western boundary of the rocha group (fig. 3). geochemistry and field work, both supports a syngenetic origin for lavas and fall deposits. the pervasive carbonation affecting the unit is analyzed, showing evidences that suggest that the process is simultaneous with volcanism. measured loi values of
Geomorphic investigations in the Medves Area, North Hungary
Horváth Gergely,Pintér Zoltán
Chinese Science Bulletin , 2001, DOI: 10.1007/BF03187237
Abstract: The Medves Area lies close to the Hungarian-Slovak boundary in North Hungary. Having “horstgraben-type” geological structure it can be characterised by steeply emerging horst-like hills and between them narrow trenches and deeply dissected erosional valleys. The recent morphology of the Medves Area is determined by four main elements: the structure, the petrographic setting, the exogenic processes and the anthropogenic effects. In spite of the domination of the Oligocene-Miocene sedimentary rocks great part of the area is covered by Pliocene basalts having either stratovolcanic structure or consisting of only lavas, forming lavaplateaus, small cones, dykes or necks. In spite of the strong denudation their original form dominates yet. The decrease of the sheet of the Medves Plateau was considerable only on the rims by parallel retreat. In the southern part of the Medves Area the evolution of the landscape was determined mainly by exogenic processes. The great density of the valleys is very significant, but it is interesting that many tributary valleys are dry valleys, which can be explained by neotectonic movements and young captures. Anthropogenic forms are very frequent in the Medves Area, where the change of the natural environment caused by human activity is above average. Especially the landscape forming effects of the mining of basalt and browncoal and that of the related industry and infrastructure changed the surface. Very interesting are the depressions on the surface caused by collapse of underground galleries, moreover sometimes trench-like deep fissures came into being.
Degassing of volatiles in the geological history of Mars
Héctor Javier Durand-Manterola
Geofísica internacional , 2003,
Abstract: I obtain an estimate of the total mass of degassed volatiles on Mars and the distribution of degassing in time. The amount of volatiles degassed in all the history of Mars is of the order of 3.73x1020 kg, i.e. 16 000 times the current Martian atmosphere. The bulk of the degassing occurred in Early, Middle, and Late Noachian, and in Early Hesperian. Degassing was monotonically decreasing in the last five epochs, from Early Hesperian to Late Amazonian. The amount of liquid water at the surface in the past was very little or none, thus the existence of life is doubtful.
COMPLEX STUDY OF THE LACUSTRIAN ECOSYSTEMS OF MOHO SWAMP
Daniel Constantin DIACONU,Emanuel MAILAT
Lakes reservoirs and ponds , 2010,
Abstract: Moho Swamp is an oligotroph swamp, formed in a volcanic crater on the site of a former lake, which permanently changes. Using a series of modern methods such as ultrasound bathymetry, we want to set up a reference base so that in the future one can be able to determine the rhythm and direction of the development of this complex ecosystem, both in terms of morph metrics and chemical hydrology parameters point of view. Bathymetry and geomorfological study represents the most important stage because it makes it possible to establish the concrete characteristics of the investigated lakes as well as their placement.
Evidence of historical seismicity and volcanism in the Armenian Highland (from Armenian and other sources)
A. Karakhanian,Y. Abgaryan
Annals of Geophysics , 2004, DOI: 10.4401/ag-3335
Abstract: This work presents a summary on the development of studies of historical earthquakes in Armenia and adjacent parts of Turkey and Iran. Since ancient times, this region has been an arena where active geodynamic and seismic history intermingled with no less active and dynamic evolution of human cultures and societies. A long-term historical record in this region beginning as early as the 8th century B.C. provides abundant evidence that can make an inestimable contribution to studies of historical seismicity and volcanism in the area. We discuss the main research methodology and sources used, and dwell on the principal catalogues of historical earthquakes compiled to date.
Influence of volatile degassing on initial flow structure and entrainment during undersea volcanic fire fountaining eruptions  [PDF]
P. D. Friedman, S. Carey, M. Raessi
Natural Science (NS) , 2012, DOI: 10.4236/ns.2012.412129
Abstract: Release of dissolved volatiles during submarine fire fountaining eruptions can profoundly influence the buoyancy flux at the vent. Theoretical considerations indicate that in some cases buoyant magma can be erupted prior to fragmentation (~75% vesicle volume threshold). Laboratory simulations using immiscible fluids of contrasting density indicate that the structure of the source flow at the vent depends critically on the relative magnitudes of buoyancy and momentum fluxes as reflected in the Richardson number (Ri). Analogue laboratory experiments of buoyant discharges demonstrate a variety of complex flow structures with the potential for greatly enhanced entrainment of surrounding seawater. Such conditions are likely to favor a positive feedback between phreatomagmatic explosions and volatile degassing that will contribute to explosive volcanism. The value of the Richardson number for any set of eruption parameters (magma discharge rate and volatile content) will depend on water depth as a result of the extent to which the exsolved volatile components can expand.
VULCANISMO NEóGENO EN EL SUROCCIDENTE ANTIOQUE?O Y SUS IMPLICACIONES TECTóNICAS
LóPEZ C.,ADRIANA?; SIERRA L.,GLORIA M.; RAMíREZ S.,DIEGO A.;
Boletín de Ciencias de la Tierra , 2006,
Abstract: the combia formation outcrops in northweat colombiano, end of the w:st="on"> cauca basin which lies between the central and western cordillera, approximately 6 °n, 75° w as corresponds to a volcano sedimentary sequence originated by several volcanic-magmatic pulses recorded between 10 and 6 ma and deposited under fluvial and lacustrine conditions. it appears that these magmatic events occurred under a transpresional regime associated with the accretion of oceanic material (the choco block) in the northwester margin of south america and the development of pull-apart or backarc basins related to pre-existing structures associated with the romeral system fault that acted as channels through which magmas ascended and emplaced. the presence of garnet crystals of pyrope type along with some piroclastic flows and the tholeitic affinity suggests a mantle origin for the first pulses of this volcanism. as magma evolved and basins closed, the magma underwent crustal contamination and volcanism turned calc-alkaline in affinity and explosive, as a result, several volcanic cones formed along the cauca basin.
Lavas Las Pataguas: volcanismo alcalino en el antearco andino del Mioceno Inferior, Chile central
Wall,Renate M; Lara,Luis E;
Revista geológica de Chile , 2001, DOI: 10.4067/S0716-02082001000200006
Abstract: the presence of lower miocene volcanic rocks in the coastal range of central chile is unique in that the westernmost outcrops of the oligocene-miocene volcanic arc occur 80 km to the east. the las pataguas lavas (llp; 33,8°s) consists of a total exposed area of 1.15 km2 without evidence of feeder conduits nor the construction of a volcanic edifice. the presence of east-west aligned and elongated flow-lobe tumuli suggests a flow from the west, over a gently sloping surface. this suggests a fissure-type eruptive system. the proposed age of the llp, of ca. 18 ma is intermediate between abanico formation (34-20 ma) and farellones formation (20-10 ma), and is coeval with littoral facies of the navidad formation, exposed 20 km to the west. llp consists of basaltic trachiandesites with 52.8-54.5 weight % silica, however their high total alkali contents (6.21-6.26 weight % k2o + na2o) place these rocks in the alkaline series of differentiation. this is a clear difference with the tholeiitic products of the abanico formation, and those typical calc-alkaline of the farellones formation. the rare earth element patterns are significantly enriched in light rare earth elements, with a la/sm ratio of 3.4 and the heavy rare earth elements, present a flat pattern. the silica and mgo contents indicate an advanced differentiation state dominated by fractional crystallization of olivine, clinopiroxene and magnetite. the content of ba and nb indicate a significant contribution from the lithospheric mantle. th and the ta-nb trough show a crustal signal as well. the particular petrogenesis and isolated westward forearc setting of the llp can be explained as a response to the slowing of convergence acceleration at the end of the extensional regime in place until the late early miocene, related to the abanico formation volcanism. therefore, the alkaline basaltic andesites of the llp represent a single, intermediate, volcanic episode between two characteristic tectonomagmatic regimes
Geochronology (40Ar/39Ar, K-Ar and He-exposure ages) of Cenozoic magmatic rocks from Northern Chile (18-22°S): implications for magmatism and tectonic evolution of the central Andes
W?rner,Gerhard; Hammerschmidt,Konrad; Henjes-Kunst,Friedhelm; Lezaun,Judith; Wilke,Hans;
Revista geológica de Chile , 2000, DOI: 10.4067/S0716-02082000000200004
Abstract: k-ar and ar/ar ages from magmatic rocks of northern chile (18-22°s) describe duration and extent of the tertiary and quaternary magmatic evolution and date major tectonic events in northernmost chile. this paper summarizes new k-ar and ar-ar mineral and whole rock ages for intrusive rocks from the precordillera, tertiary ignimbrites and andesitic stratovolcanoes from the western andean escarpment at 18°s (warp) and the volcanic front. intrusive rocks of the precordillera (quebrada paguana, quebrada blanca, quebrada choja, quebrada guatacondo, cerro chandacolla) represent the cretaceous to eocene magmatic arc system and gave ages between 45 and 35 ma. younger ages on intrusive rocks are invariably caused by deuteric alteration. ignimbrites of the putani and oxaya formations gave ar-ar sanidine ages around 24.2 to 24.8 ma and 22.8 to 19.4 ma, respectively. andesitic stratovolcanoes, which directly overlie oxaya ignimbrites east of the western cordillera gave ages of 20.3 ma (cordon quevilque) to 9.0 ma (cerro margarita). samples from the miocene to pleistocene arc system on the chilean altiplano underlying the volcanoes of the active volcanic front have been dated between 10.5 to ~3 ma. a widespread ignimbrite can be correlated from the lauca basin to the pacific coast and to the east to occurrences of near pérez. repeated ar-ar sanidine dating of the lauca-pérez-ignimbrite resulted in highly concordant ages of 2.71±0.25 ma, 2.72 ma±0.01 ma, and 2.73±0.11 ma. rocks from the active chain (volcanic cordillera) gave ages younger than 0.9 ma (volcán irruputuncu, volcán olca, volcán aucanquilcha, volcán ollagüe, volcán poru?ita). these new data are used to constrain miocene stratigraphy and tectonic movements as well as the timing of uplift and sedimentary response at the western andean escarpment within the framework of the tectonic evolution of the central andes
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