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71.
Grajales-Nishimura José Manuel Ramos-Arias Mario Alfredo Solari Luigi Murillo-Muñetón Gustavo Centeno-García Elena Schaaf Peter Torres-Vargas Ricardo 《International Journal of Earth Sciences》2018,107(3):1005-1031
International Journal of Earth Sciences - The Juchatengo complex (JC) suite is located between the Proterozoic Oaxacan complex to the north and the Xolapa complex to the south, and was amalgamated... 相似文献
72.
Linking geomorphology and hydrodynamics: a case study from Península Valdés, Patagonia, Argentina 总被引:1,自引:0,他引:1
A case study is presented to assess the relevance of geomorphology in hydrogeological phenomena in an arid coastal area in the Argentinean extra-Andean Patagonia (Península Valdés) with an average rainfall of 232 mm/year and a soil moisture deficit of about 472 mm/year. Various geomorphic units were identified by interpreting Landsat 7 satellite images processed with ER Mapper software and then surveyed in the field, as well as by geological characterization. The hydrodynamic analysis was based on a survey of 89 wells, the construction of equipotential maps, and the interpretation of pumping-test results by a non-equilibrium method. The hydrochemical characterization was based on chemical tests analyzed with the Easy_Quim 6.0 application. The combination of geomorphological, geological, hydrodynamic and hydrochemical elements allowed the definition of hydromorphological units that are typical of recharge, circulation and discharge areas, the latter both for coastal and inland areas in wetlands (salt pans) with elevations to ?40 m relative to sea level. These units and the criteria used for their definition allow immediate recognition of hydrogeological phenomena in arid regions such as the extra-Andean Patagonia, with low information density but with near-optimal satellite imaging of landforms due to the lack of vegetation cover. 相似文献
73.
Two sedimentary units are recognized by means of stratigraphic and sedimentological analyses at Monte Verde, a late Pleistocene archeological site with stone tools and well-preserved wood artifacts and botanical remains, that lies southwest of Lago Llanquihue and north of the Golfo de Reloncavi in the southern end of the Chilean Central graben. the geological evidence shows that at no time after 33,000 yr B.P., and perhaps since the first Llanquihue advance (before 56,000 yr B.P.), was the Monte Verde area covered by ice. Influences of two glacial advances at 20,000 and 15,000-14,500 yr B.P. are recognized at the site; effects of the Varas Interstade, however, are not identified. Rapid climatic change took place after the end of the Llanquihue Glaciation. It was shortly interrupted by a cool, wet period around 10,000 yr B.P., after which a well-documented Hypsithermal (8270-4750 yr B.P.) accompanied by pyroclastic vulcanism followed. The evidence indicates that around 13,000 yr B.P. 1) the site occupants settled on the sandy point bars and beaches of the old creek channel and 2) the area was habitated during cool and wet conditions similar to those that prevail in the area today. Evidence for reconstruction of the paleo-environment and climate of the terminal Pleistocene and the preliminary implications of these findings for understanding the human occupation at Monte Verde are discussed. 相似文献
74.
Mario Costa Giorgio Ferrara Rosalino Sacchi Sonia Tonarini 《International Journal of Earth Sciences》1992,81(2):487-500
The Proterozoic basement of the Province of Zambezia (Mozambique) is located near the southern end of the so called Mozambique Belt. Rb-Sr data derived from the analyses of 66 whole rocks and a few mineral samples bear witness of a magmatic and metamorphic episode referable to the Kibaran (ca. 1000 Ma) and helped to model the late-Proterozoic evolution as follows. At 1100–1050 Ma a pre-orogenic, calc-alkaline magmatism was responsible for the emplacement of now deformed granite and granodiorite. This phase was accompanied by rhyolitic volcanism. A subsequent peak of deformation and metamorphism occurred at 1000-950 Ma and was associated with a second generation of substantially post-tectonic granites. A thermal event resulting in the emplacement of a final generation of granites and pegmatites can be dated to around 500-450 Ma.The metamorphic basement has not preserved its protolith age, probably as a result of extensive isotopic homogeneization of Sr in Kibaran times. Its maximum time of differentiation from the mantle should be around 1600 Ma.The very low values of initial Sr isotopic ratios suggest the absence of Archean crustal precursors and support the rather young, yet pre-Pan-African evolution of the southernmost Mozambique Belt.
Zusammenfassung Das proterozoische Grundgebirge der Provinz Zambesi (Mosambique) befindet sich in der Nähe des südlichen Endes des sogenannten Mozambique Belt. Rb/Sr Daten aus 66 Ganzgesteins- und einigen Mineralanalysen zeugen von einer magmatischen und metamorphen Episode die sich dem Kibaran (ca. 1000 Ma) zuordnen läßt, und wie sich im folgenden zeigt, hilfreich bei der Modellisierung der spätproterozoischen Entwicklung ist. Um 1100 bis 1050 Ma erfolgte ein präorogener kalkalkalischer Magmatismus, bestehend aus Graniten und Granodioriten, die heute deformiert vorliegen. Diese Phase wurde von rhyolithischem Vulkanismus begleitet. Von 1000 bis 950 Ma folgte der Höhepunkt der Deformation und Metamorphose, begleitet von einer bedeutenden 2. Generation posttektonischer Granite. Bedingt durch ein weiteres thermales Ereignis intrudierte die letzte Granit- und Pegmatitgeneration vor 500 bis 450 Ma.Im metamorphen Grundgebirge ist das Eduktalter vermutlich aufgrund der starken isotopischen Homogenisierung von Sr während der Kibara-Zeit nicht erhalten. Seine maximale Differentiationszeit vom Mantel muß vor 1600 Ma gewesen sein.Die sehr niedrigen Gehalte der initialen Sr-Isotopenverhältnisse lassen die Abwesenheit von archaischen Krustenvorläufern vermuten, und unterstützen die sehr junge, bis jetzt Prä-Pan-Afrikanische Entwicklung des südlichsten Mozambique Belts.
Résumé Le socle protérozoïque de la province du Zambèze, au Mozambique, se trouve à proximité de l'extrémité sud du «Mozambique Belt». Des mesures Rb/Sr effectuées sur 66 roches totales et sur quelques minéraux témoignent d'un épisode magmatique et métamorphique attribuable au Kibarien (environ 1.000 Ma), ce qui permet de se représenter comme suit l'histoire de cette région au Protérozoïque supérieur. Il y a 1.100 à 1.050 Ma, la région a connu une phase de magmatisme calco-alcalin qui s'est traduite par la mise en place de granites et granodiorites, aujord'hui déformés. Cette phase s'est accompagnée d'un volcanisme rhyolitique. Elle a été suivie, entre 1.000 et 950 Ma, d'une activité tectono-métamorphique majeure, à laquelle est associée une deuxième et importante génération de granites, post-tectoniques. Ultérieurement, la région a connu encore un épisode thermique, daté à 500-450 Ma, responsable de la mise en place d'une dernière génération de granite et de pegmatite.Le socle métamorphique n'a pas gardé de témoins de l'âge de son protolithe, en raison probablement de la forte homogénisation isotopique du Sr à l'époque kibarienne. Lâge maximal de sa différenciation à partir du manteau doit se situer autour de 1.600 Ma.La valeur très basse des rapports isotopiques initiaux du Sr suggère l'absence de précurseurs crustaux archéens et incite à admettre une évolution relativement jeune — bien que pré-panafricaine — du «Mozambique Belt» méridional.
() .. . , Rb/Sr 66 , , Kibara, 1000 , , , . 1100 1050 - - , , . . 1000 950 , - . , 500 450 . , , , Kibara. , , 1600 my . - .相似文献
75.
M. H. Ort Beatriz L. Coira Mario M. Mazzoni 《Contributions to Mineralogy and Petrology》1996,123(3):308-322
Cerro Panizos, a large caldera in the central Andes Mountains, produced two large dacitic ignimbrites at 7.9 Ma and 6.7 Ma
and many andesitic and dacitic lava flows and domes. The older rhyodacitic Cienago Ignimbrite represents the most silicic
magma erupted by the system. The younger, much larger volume dacitic Cerro Panizos Ignimbrite is very crystal-rich, containing
up to 50% biotite, plagioclase, and quartz crystals in the pumice. It is weakly zoned, with most of the zoning apparent between
two main cooling units. Major and most trace elements show little variation through the Cerro Panizos Ignimbrite, but the
small range of composition is consistent with typical fractionation trends. Sr, Nd, and Pb isotopic ratios are very “crustal”,
with initial 87Sr/86Sr values of 0.711 to 0.715, ɛNd values of –7.5 to –10.2, and nearly invariant Pb isotopic ratios (206Pb/204Pb=18.85, 207Pb/204Pb=15.67, and 208Pb/204Pb=38.80). The limited zonation observed in the Cerro Panizos Ignimbrite is explained by impeded crystal settling due to high
crystal content. The magma body was a crystal-liquid mush before ascent to the pre-eruption crustal levels. Crystals formed,
but did not separate easily from the magma. Limited fractionation of plagioclase and biotite may have occurred, but the composition
was largely controlled by lower crustal MASH processes. AFC modeling shows that the Cerro Panizos magmas resulted from a mixture
of roughly equal proportions of late Miocene mantle-derived basalts and melts from ∼1.0 Ga (Grenville age) lower crust. This
occurred in a MASH zone in the lower crust, and set the crustal isotopic ratios observed in the Cerro Panizos magmas. The
great thickening of the crust beneath the central Andes Mountains sent upper and middle crustal rock types to lower crustal
(and deeper) depths, and this explains the “upper crustal” isotopic signatures of the Cerro Panizos rocks. Minor upper crustal
assimilation of early Miocene volcanic or subvolcanic rocks produced much of the isotopic variation seen in the system. The
nearly invariant high Pb isotopic values and high Pb concentrations indicate that Pb came almost entirely from the crustal
source, and was little altered by any subsequent upper crustal assimilation. This Pb signature is isotopically similar to
that of the southern Bolivian Tin Belt, suggesting a widely distributed Pb source. The great difference between compositions
of Miocene and Quaternary central Andean volcanic rocks is explained by crustal thickening in early Miocene time leading to
abundant lower crustal water and associated fluxed melting during the time of the earlier eruptions. The lower crust dried
out considerably by Quaternary time, so less crustal component is present.
Received: 22 December 1994 / Accepted: 13 September 1995 相似文献
76.
Mario Bossolasco 《Pure and Applied Geophysics》1947,10(1-2):41-53
Riassunto Si espongono i risultati delle osservazioni sulle correnti telluriche eseguite a Mogadiscio nel 1933 con misure delle due componenti NS ed EW, traendone alcune deduzioni che permettono di precisarne le caratteristiche, specie nei confronti del relativo andamento diurno.
Summary The paper deals with the results of the earth-current-observations made at Mogadiscio during 1933. The analysis reveal elements for a new picture of the distribution of the earth-currents in the equatorial regions, particularly concerning the daily variation.
Zusammenfassung Die Ergebnisse des Erdstrom-Beobachtungen durchgeführt in einigen Monaten des Jahres 1933 in Modagiscio sind angegeben. Aus des Diskussion folgen einige Elemente die eine Neubearbeitung des Darstellung des Erdstrom-Verteilung in dem äquatorialem Gürtel nötig machen und dazu dienen werden sollen. besonders in Beziehung auf den täglichen Gang.相似文献
77.
78.
Quantifying Organization of Atmospheric Turbulent Eddy Motion Using Nonlinear Time Series Analysis 总被引:3,自引:0,他引:3
Using three methods from nonlinear dynamics, we contrast the level of organization inthe vertical wind velocity (w) time series collected in the atmospheric surface layer(ASL) and the canopy sublayer (CSL) for a wide range of atmospheric stability ()conditions. The nonlinear methods applied include a modified Shannon entropy, waveletthresholding, and mutual information content. Time series measurements collected overa pine forest, a hardwood forest, a grass-covered forest clearing, and a bare soil, desertsurface were used for this purpose. The results from applying all three nonlinear timeseries measures suggest that w in the CSL is more organized than that in the ASL, and that as the flows in both layers evolve from near-neutral to near-convective conditions, the level of organization increases. Furthermore, we found that the degree of organization in w associated with changes in is more significant than the transition from CSL to ASL. 相似文献
79.
80.
We present an analysis of a regional simulation of present-day climate (1981–1990) over southern South America. The regional
model MM5 was nested within time-slice global atmospheric model experiments conducted by the HadAM3H model. We evaluate the
capability of the model in simulating the observed climate with emphasis on low-level circulation patterns and surface variables,
such as precipitation and surface air mean, maximum and minimum temperatures. The regional model performance was evaluated
in terms of seasonal means, seasonal cycles, interannual variability and extreme events. Overall, the regional model is able
to capture the main features of the observed mean surface climate over South America, its seasonal evolution and the regional
detail due to topographic forcing. The observed regional patterns of surface air temperatures (mean, maxima and minima) are
well reproduced. Biases are mostly within 3°C, temperature being overestimated over central Argentina and underestimated in
mountainous regions during all seasons. Biases in northeastern Argentina and southeastern Brazil are positive during austral
spring season and negative in other seasons. In general, maximum temperatures are better represented than minimum temperatures.
Warm bias is larger during austral summer for maximum temperature and during austral winter for minimum temperature, mainly
over central Argentina. The broad spatial pattern of precipitation and its seasonal evolution are well captured; however,
the regional model overestimates the precipitation over the Andes region in all seasons and in southern Brazil during summer.
Precipitation amounts are underestimated over the La Plata basin from fall to spring. Extremes of precipitation are better
reproduced by the regional model compared with the driving model. Interannual variability is well reproduced too, but strongly
regulated by boundary conditions, particularly during summer months. Overall, taking into account the quality of the simulation,
we can conclude that the regional model is capable in reproducing the main regional patterns and seasonal cycle of surface
variables. The present reference simulation constitutes the basis to examine the climate change simulations resulting from
the A2 and B2 forcing scenarios which are being reported in a separate study. 相似文献