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911.
Kowalski Andrew S. Serrano-Ortiz Penélope Miranda-García Gabriela Fratini Gerardo 《Boundary-Layer Meteorology》2021,179(3):347-367
Boundary-Layer Meteorology - An analysis based on the law of linear momentum conservation demonstrates unequivocally that the mass fraction is the scalar whose gradient determines gas diffusion,... 相似文献
912.
New microthermometric data combined with stable isotope geochemistry and paragenetic relationships support a previously suggested
cooling–mixing model for the iron oxide–copper–gold mineralization in the Mantoverde district. Fluid inclusions show characteristics
of a CO2-bearing aqueous NaCl ± CaCl2 salt system. The evolution of the Mantoverde hydrothermal system is characterized by (1) an early hypersaline, high to moderate
temperature fluid; (2) a moderate saline, moderate temperature fluid; and (3) a low saline, moderate to low temperature fluid.
Early magnetite formation took place at median temperatures of 435.0°C, whereas hematite formed at median temperatures of
334.4°C. The main sulfide mineralization texturally post-dates the iron oxides and occurred before late-stage calcite, which
developed at a median temperature of 244.8°C. Boiling occurs only locally and is of no relevance for the ore formation. The
microthermometric and stable isotope data are supportive for a fluid cooling and mixing model, and suggestive for a predominantly
magmatic–hydrothermal fluid component during the iron oxide and main sulfide mineralization. Thereafter, the incursion of
a nonmagmatic fluid of ultimately meteoric or seawater gains more importance. 相似文献
913.
The Horní Slavkov–Krásno Sn–W ore district is hosted by strongly altered Variscan topaz–albite granite (Krudum granite body) on the northwestern margin of the Bohemian Massif. We studied the fluid inclusions on greisens, ore pockets, and ore veins from the Hub Stock, an apical expression of the Krudum granite. Fluid inclusions record almost continuously the post-magmatic cooling history of the granite body from ~500 to <50°C. Rarely observed highest-temperature (~500°C) highest-salinity (~30?wt.% NaCl eq.) fluid inclusions are probably the result of secondary boiling of fluids exsolved from the crystallizing magma during pressure release which followed hydraulic brecciation of the gneissic mantle above the granite cupola. The greisenization was related to near-critical low-salinity (0–7?wt.% NaCl eq.) aqueous fluids with low amount of CO2, CH4, and N2 (≤10?mol% in total) at temperatures of ~350–400°C and pressures of 300–530 bar. Crush-leach data display highly variable and negatively correlated I/Cl and Br/Cl values which are incompatible with both orthomagmatic and/or metamorphic origin of the fluid phase, but can be explained by infiltration of surficial and/or sedimentary fluids. Low fluid salinity indicates a substantial portion of meteoric waters in the fluid mixture that is in accordance with previous stable isotope data. The post-greisenization fluid activity associated with vein formation and argillitization is characterized by decreasing temperature (<350 to <50°C), decreasing pressure (down to ~50–100 bar), and mostly also decreasing salinity. 相似文献
914.
Juan Carlos Carracedo Francisco Pérez Torrado Alejandro Rodríguez González Vicente Soler José Luis Fernández Turiel Valentin R. Troll Sebastian Wiesmaier 《Geology Today》2012,28(2):53-58
Forty years after the Teneguía Volcano (La Palma, 1971), a submarine eruption took place off the town of La Restinga, south of El Hierro, the smallest and youngest island of the Canarian Archipelago. Precursors allowed an early detection of the event and its approximate location, suggesting it was submarine. Uncertainties derived from insufficient scientific information available to the authorities during the eruption, leading to disproportionate civil protection measures, which had an impact on the island's economy—based primarily on tourism—while residents experienced extra fear and distress. 相似文献
915.
Ignacio Díaz-Martínez José María Hernández Salvador García Fernández Xabier Murelaga Félix Pérez-Lorente 《Proceedings of the Geologists' Association. Geologists' Association》2012,123(3):464-470
A new bird ichnotaxon found in Cenicero (La Rioja, Ebro Basin, Spain) is described here. The footprints are preserved in sandstone beds in a central-distal alluvial fringe with a mud-dominated floodplain, located in the transition unit between the Nájera and Haro formations. This level is positioned between the Y and Z local Agenian biozones (lower Miocene). The footprints were preliminarily studied in another work and considered as an indeterminate ichnotaxon. Uvaichnites riojana ichnogen. nov. and ichnosp. nov. is a tridactyl footprint characterized by a prominent central pad, very large to enormous sized, with unjointed toes at the proximal end. These features differ from Aquatilavipes, Aviadactyla, Avipeda, Ludicharadripodiscus, Fuscinapeda, and Ornithotarnocia of the Avipedidae morphofamily. U. riojana is considered to be similar to common crane (Grus grus) footprints in the Gruidae family. There are a few references about this family in the Iberian Peninsula and Balearic Islands and this find could confirm the presence of Gruidae since at least the lower Miocene. 相似文献
916.
José Bandeira Ben McGee Afonso C.R. Nogueira Alan S. Collins Ricardo Trindade 《Gondwana Research》2012,21(2-3):323-340
Final Gondwana amalgamation was marked by the closure of the Neoproterozoic Clymene ocean between the Amazonia craton and central Gondwana. The events which occurred in the last stage of this closure were recorded in the upper Alto Paraguai Group in the foreland of the Paraguay orogen. Outcrop-based facies analysis of the siliciclastic rocks of upper Alto Paraguai Group, composed of the Sepotuba and Diamantino Formations, was carried out in the Diamantino region, within the eastern part of the Barra dos Bugres basin, Mato Grosso state, central-western Brazil. The Sepotuba Formation is composed of sandy shales with planar to wave lamination interbedded with fine-grained sandstone with climbing ripple cross-lamination, planar lamination, swaley cross-stratification and tangential to sigmoidal cross-bedding with mud drapes, related to marine offshore deposits. The lower Diamantino Formation is composed of a monotonous, laterally continuous for hundreds of metres, interbedded siltstone and fine-grained sandstone succession with regular parallel lamination, climbing ripple cross-lamination and ripple-bedding interpreted as distal turbidites. The upper part of this formation consists of fine to medium-grained sandstones with sigmoidal cross-bedding, planar lamination, climbing ripple cross-lamination, symmetrical to asymmetrical and linguoid ripple marks arranged in lobate sand bodies. These facies are interbedded with thick siltstone in coarsening upward large-scale cycles related to a delta system. The Sepotuba Formation characterises the last transgressive deposits of the Paraguay basin representing the final stage of a marine incursion of the Clymene ocean. The progression of orogenesis in the hinterland resulted in the confinement of the Sepotuba sea as a foredeep sub-basin against the edge of the Amazon craton. Turbidites were generated during the deepening of the basin. The successive filling of the basin was associated with progradation of deltaic lobes from the southeast, in a wide lake or a restricted sea that formed after 541 ± 7 Ma. Southeastern to east dominant Neoproterozoic source regions were confirmed by zircon grains that yielded ages around 600 to 540 Ma, that are interpreted to be from granites in the Paraguay orogen. This overall regressive succession recorded in the Alto Paraguai Group represents the filling up of a foredeep basin after the final amalgamation of western Gondwana in the earliest Phanerozoic. 相似文献
917.
Ana Luisa Outa Mori Paulo Alves de Souza Juliana Charão Marques Ricardo da Cunha Lopes 《Gondwana Research》2012,21(2-3):654-669
Index species useful for correlations with the International Stratigraphical Column are rare or absent in the Pennsylvanian–Permian strata of the Paraná Basin in Brazil, preventing accuracy in geochronologic assignments. Besides, absolute datings are very scarce in comparison with other Gondwana basins. This paper presents palynological data from an outcrop on the surroundings of the Candiota coal mine, southmost Brazil, from several levels of the Rio Bonito and Palermo formations. The presence of certain index species of spore–pollen allowed the recognition of two Permian palynozones: the Vittatina costabilis and the Lueckisporites virkkiae zones. Furthermore, U–Pb in zircons from a volcaniclastic level interbedded in the coal strata of the former unit was analyzed through LA-MC-ICP-MS method, providing a new absolute age dating of 281.4 ± 3.4 Ma (Cisuralian, Early Permian). This dating is assumed as the oldest occurrence of the L. virkkiae Zone in Paraná Basin, which contains index species that are widespread in other Gondwana basins. A well distributed surface boundary occurs in this section also, allowing local and regional correlations. These new biostratigraphical and geochronological data are integrated, in order to offer a deep analysis on the stratigraphical significance for correlations across the Occidental Gondwana. 相似文献
918.
Silvia Barredo Farid Chemale Claudia Marsicano Janaína N. Ávila Eduardo G. Ottone Victor A. Ramos 《Gondwana Research》2012,21(2-3):624-636
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 ± 1.1 Ma to 230.3 ± 1.5 Ma 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 230 Ma), with no evidence of sedimentation during Norian and Rhaetian, which is in conflict with some previous biostratigraphic studies. 相似文献
919.
José R. Martínez Catalán 《International Journal of Earth Sciences》2012,101(5):1299-1314
An arcuate structure, comparable in size with the Ibero-Armorican arc, is delineated by Variscan folds and magnetic anomalies in the Central Iberian Zone of the Iberian Massif. Called the Central Iberian arc, its sense of curvature is opposite to that of the Ibero-Armorican arc, and its core is occupied by the Galicia-Trás-os-Montes Zone of NW Iberia, which includes the Rheic suture. Other zones of the Iberian Massif are bent by the arc, but the Ossa-Morena and South Portuguese zones are not involved. The arc formed during the Late Carboniferous, at final stages of thermal relaxation and collapse, and an origin related with right-lateral ductile transpression at the scale of the Variscan belt is proposed. The Central Iberian arc explains the width of the Central Iberian Zone, clarifies the position of the allochthonous terranes of NW Iberia, and opens new perspectives for correlations with the rest of the Variscan belt, in particular, with the Armorican Massif, whose central zone represents the continuation of the southwest branch of the arc detached by strike-slip tectonics. 相似文献
920.
W. Siebel C. K. Shang E. Thern M. Dani?ík J. Rohrmüller 《International Journal of Earth Sciences》2012,101(8):2105-2123
Correct interpretation of zircon ages from high-grade metamorphic terrains poses a major challenge because of the differential response of the U–Pb system to metamorphism, and many aspects like pressure–temperature conditions, metamorphic mineral transformations and textural properties of the zircon crystals have to be explored. A large (c. 450?km2) coherent migmatite complex was recently discovered in the Bohemian Massif, Central European Variscides. Rocks from this complex are characterized by granulite- and amphibolite-facies mineral assemblages and, based on compositional and isotopic trends, are identified as the remnants of a magma body derived from mixing between tonalite and supracrustal rocks. Zircon crystals from the migmatites are exclusively large (200–400?μm) and yield 207Pb/206Pb evaporation ages between 342–328?Ma and single-grain zircon fractions analysed by U–Pb ID-TIMS method plot along the concordia curve between 342 and 325?Ma. High-resolution U–Pb SHRIMP analyses substantiate the existence of a resolvable age variability and yield older 206Pb/238U ages (342–330?Ma, weighted mean age?=?333.6?±?3.1?Ma) for inner zone domains without relict cores and younger 206Pb/238U ages (333–320?Ma, weighted mean age?=?326.0?±?2.8?Ma) for rim domains. Pre-metamorphic cores were identified only in one sample (206Pb/238U ages at 375.0?±?3.9, 420.3?±?4.4 and 426.2?±?4.4?Ma). Most zircon ages bracket the time span between granulite-facies metamorphism in the Bohemian Massif (~345?Ma) and the late-Variscan anatectic overprint (Bavarian phase, ~325?Ma). It is argued that pre-existing zircon was variously affected by these metamorphic events and that primary magmatic growth zones were replaced by secondary textures as a result of diffusion reaction processes and replacement of zircon by dissolution and recrystallization followed by new zircon rim growth. Collectively, the results show that the zircons equilibrated during high-grade metamorphism and record partial loss of radiogenic Pb during post-peak granulite events and new growth under subsequent anatectic conditions. 相似文献