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CASTRO ANTONIO; CORRETGE L. GUILLERMO; DE LA ROSA JESUS D.; FERNANDEZ CARLOS; LOPEZ SUSANA; GARCIA-MORENO OLGA; CHACON HELENA 《Journal of Petrology》2003,44(7):1309-1344
The Sanabria appinitic rocks and host migmatites form an unusual,non-peri-batholithic complex in which all the typical membersof the appinite suite are present. It differs from most appiniticcomplexes in the deeper level of emplacement and the close temporaland spatial association with migmatites. Consequently, manyin situ relationships that resulted from the invasion of maficmagma into a crustal anatectic zone are extremely well preserved.The complex shows unequivocal relations between members of theappinitic suite and between these and migmatites derived byanatexis of a gneissic formation (Ollo de Sapo gneiss). Theserelations point to derivation of monzodiorites and biotite dioritesby hydrous basalt fractionation combined with fluid-assistedmelting of the crustal rocks surrounding the appinitic intrusions.This hydrous basic magma may be derived from an enriched regionof the mantle associated with subduction. Petrogenetic modelshave been tested using a combination of field relations andgeochemical data. Despite the complexity of the processes involved,it is concluded that water played an important role in the petrogenesisof the intermediate and mafic magmas. Reaction between monzodioritemelts and the host migmatites was responsible for the generationof a range of intermediate rocks within the complex. The needfor water to facilitate magma generation in both the mantleand the crust suggests that melting is linked with subduction.This interpretation has important implications because appiniticmagmatism may be considered as indicative of subduction processesinvolved not only in the generation of the mafic end-membersof the suite, but also in the generation of batholiths withwhich the appinitic rocks are spatially and temporally associated. KEY WORDS: appinite; monzodiorite; migmatite; Variscan orogen; Iberian massif 相似文献
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CASTRO ANTONIO; GUILLERMO CORRETGE L.; EL-BIAD MOHAMMED; EL-HMIDI HASSAN; FERNANDEZ CARLOS; PATINO DOUCE ALBERTO E. 《Journal of Petrology》2000,41(10):1471-1488
We have studied experimentally the melting relationships ofthe Ollo de Sapo gneiss (OSG), an important crustal protolithfor the Iberian leucogranites, of possible volcanoclastic origin.The results of this study are compared with previously determinedPTt paths, allowing us to interpret the mechanisms of meltingand granitoid production during the Hercynian orogenic cycle.Phase relationships determined in fluid-absent experiments indicatethat the OSG is a fertile source for peraluminous leucogranites.The slope of the fluid-absent solidus is strongly controlledby the breakdown of Ms in the presence of Qtz, Pl and Kfs. Thissolidus curve has a positive slope ranging from dP/dT = 30 bar/°Cat low P (<6 kbar) to dP/dT = 70 bar/°C at higher P (6–15kbar). The relationships between the Ms vapour-absent solidusand the PTt metamorphic paths in different sectors of the Iberianmassif have two important implications: (1) melt productivityis strongly favoured at low P; (2) anatexis in the Iberian massifprobably took place by decompression associated with crustalthinning and extension. These results are in agreement withthe relationships between granite production and tectonic deformationphases observed in the Iberian massif. Our results emphasizethat anatexis is a process that is strongly controlled bothby the phase relationships of the crustal protoliths and bythe thermal structure of the continental crust. Consequently,one must be careful when assigning potential crustal protolithsto particular granite associations exclusively on the basisof geochemical comparisons. KEY WORDS: anatexis; Hercynian orogen; Iberian massif 相似文献
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VIKA G. EDER AGUSTÍN MARTÍN-ALGARRA† ANTONIO SÁNCHEZ-NAVAS‡ YURI N. ZANIN ALBINA G. ZAMIRAILOVA YURI N. LEBEDEV§ 《Sedimentology》2007,54(6):1365-1387
This study examines textural inhomogeneity and variable chemical composition of Upper Jurassic glaucony in relation to small‐scale synsedimentary and postsedimentary authigenic processes controlled by the palaeonvironmental and palaeogeographical context. Four glaucony types with complex textural and compositional features have been recognized in cores of the Georgiev Formation of the West Siberian Basin. Samples exclusively made of light green type 1 glaucony (K2O < 6·5%: the less mature type, richer in glauconite–smectite mixed layer) formed under dysoxic conditions in the deepest distal marine environments of the northern sectors of the West Siberian Basin. Dark green type 2 glaucony is the most mature (richest in glauconitic mica: K2O up to 8·5%), is sometimes associated with type 1 glaucony, and is typical of high bottom areas with a low sedimentation rate within the central sectors of the basin. Type 3 glaucony is formed by brown grains, poorer in K and Fe but richer in Al and Si than type 2 glaucony, and is only present in strongly condensed successions of the central‐eastern sectors of the West Siberian Basin. Type 4 glaucony is much richer in Fe than any other type, shows fresh yellowish green cores slightly less mature than type 2 glaucony, and brown rims and cracks with composition similar to that of type 3 grains; it was formed in western sectors of the West Siberian Basin, close to Urals. Weathering under a subtropical to temperate climate, and erosion of badly drained peneplaned lowland areas around the basin, provided Al‐rich terrigenous clays as substratum for glauconitization, which explains Al and Si enrichment in Siberian glaucony. Maturation from glauconite–smectite to glauconitic mica is monitored by a change from light to dark green colour related to decrease in Al, Si, Mg, Ca and Na, and to increase in K and Fe. Brown rims of type 4 glaucony, and brown type 3 grains formed after leaching of Fe and K from mature glauconite, with formation of clays and Fe oxyhydroxides as reaction products, as a result of free oxygen exposure related to a hydrodynamic regime and temporary sea‐level fall. Glauconitization stopped and diagenetic pyrite formed due to basin deepening and burial under black shales during the latest Jurassic–earliest Cretaceous transgression. This study demonstrates that, due to the complex nature of glaucony, the authigenesis of glauconitic minerals in the rock record cannot be correctly understood if the palaeoenvironmental context and the palaeogeographical context of glaucony‐bearing sediments are not considered. 相似文献
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ISABELLA BORDI ALESSANDRO DELL'AQUILA ANTONIO SPERANZA† ALFONSO SUTERA 《地球，A辑:动力气象学与海洋学》2002,54(3):260-272
Recently, a theory relating baroclinic neutrality and midlatitudes tropopause height has been proposed. However, GCM results have shown that the dependence of the theory on external parameters is not consistent with that displayed by these numerical experiments. In the present paper we suggest an analytic formula for baroclinic adjustment to the neutrality of Eady waves through tropopause modification. This formula extends considerably the abovementioned theory by taking into account both a simple representation of the stratosphere and the topography. These modifications alter the tropopause condition for a baroclinically neutral state and its sensitivity to the external parameters. In particular, the topography introduces a dependence on the tropospheric vertical wind shear of the neutrality condition. This feature is not present in other models that assume a background state with a zero potential vorticity gradient in the troposphere. We show, furthermore, that the modified neutrality condition has sensitivities that may resemble those displayed by GCM simulations, with respect to the parameters defining the background flow. 相似文献
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DUNCAN M. FitzGERALD WILLIAM J. CLEARY JOAO THADEU
De MENEZES ANTONIO H. da F. KLEIN 《Sedimentology》2013,60(2):469-502
Clastic, depositional strandplain systems have the potential to record changes in the primary drivers of coastal evolution: climate, sea‐level, and the frequency of major meteorological and oceanographic events. This study seeks to use one such record from a southern Brazilian strandplain to highlight the potentially‐complex nature of coastal sedimentological response to small changes in these drivers. Following a 2 to 4 m highstand at ca 5·8 ka in southern Brazil, falling sea‐level reworked shelf sediment onshore, forcing coastal progradation, smoothing the irregular coastline and forming the 5 km wide Pinheira Strandplain, composed of ca 500 successive beach and dune ridges. Sediment cores, grab samples and >11 km of ground‐penetrating radar profiles reveal that the strandplain sequence is composed of well‐sorted, fine to very‐fine quartz sand. Since the mid‐Holocene highstand, the shoreline prograded at a rate of ca 1 to 2 m yr?1 through the deposition of a 4 to 6 m thick shoreface unit; a 1 to 3 m thick foreshore unit containing ubiquitous ridge and runnel facies; and an uppermost beach and foredune unit. However, the discovery of a linear, 100 m wide barrier ridge with associated washover units, a 3 to 4 m deep lagoon and 250 m wide tidal inlet within the strandplain sequence reveals a period of shoreline transgression at 3·3 to 2·8 ka during the otherwise regressive developmental history of the plain. The protected nature of Pinheira largely buffered it from changes in precipitation patterns, wave energy and fluvial sediment supply during the time of its formation. However, multiple lines of evidence indicate that a change in the rate of relative sea‐level fall, probably due to either steric or ice‐volume effects, may have affected this coastline. Thus, whereas these other potential drivers cannot be fully discounted, this study provides insights into the complexity of decadal‐scale to millennial‐scale coastal response to likely variability in sea‐level change rates. 相似文献
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ARÁNZAZU LUZÓN JUAN PEDRO RODRÍGUEZ‐LÓPEZ ANTONIO PÉREZ MARÍA ASUNCIÓN SORIANO HÉCTOR GIL ANDRÉS POCOVÍ 《Sedimentology》2012,59(7):2199-2225
Meltwater flows emanating from the Pyrenees during the Pleistocene constructed a braided outwash plain in the Ebro Basin and led to the karstification of the Neogene gypsum bedrock. Synsedimentary evaporite dissolution locally increased subsidence rates and generated dolines and collapses that enabled the accumulation and preservation of outwash gravels and associated windblown deposits that were protected from erosion by later meltwater flows. In these localized depocentres, maximum rates of wind deceleration resulted from airflow expansion, enabling the accumulation of cross‐stratified sets of aeolian strata climbing at steep angles and thereby preserving up to 5 m thick sets. The outwash plain was characterized by longitudinal and transverse fluvial gravel bars, channels and windblown facies organized into aeolian sand sheets, transverse and complex aeolian dunes, and loess accumulations. Flat‐lying aeolian deposits merge laterally to partly deformed aeolian deposits encased in dolines and collapses. Synsedimentary evaporite dissolution caused gravels and aeolian sand deposits to subside, such that formerly near‐horizontal strata became inclined and generated multiple internal angular unconformities. During episodes when the wind was undersaturated with respect to its potential sand transporting capacity, deflation occurred over the outwash plain and coarse‐grained lags with ventifacts developed. Subsequent high‐energy flows episodically reached the aeolian dune field, leading to dune destruction and the generation of hyperconcentrated flow deposits composed in part of reworked aeolian sands. Lacustrine deposits in the distal part of the outwash plain preserve rhythmically laminated lutites and associated Gilbert‐type gravel deltas, which developed when fluvial streams reached proglacial lakes. This study documents the first evidence of an extensive Pleistocene proglacial aeolian dune field located in the Ebro Basin (41˙50° N), south of what has hitherto been considered to be the southern boundary of Pleistocene aeolian deposits in Europe. A non‐conventional mechanism (evaporite karst‐related subsidence) for the preservation of aeolian sands in the stratigraphic record is proposed. 相似文献
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A non-hydrostatic, fully compressible, regional-scale numerical model of the atmosphere that includes parameterization of cloud microphysics is run in a two-dimensional mode. It uses two different observed vertical profiles of temperature, relative humidity and wind to simulate the local circulation evolution and impact on convection and nocturnal fog occurrence in São Paulo, Brazil. Theatmospheric behaviour generated by the model is similar to the observations of the two summer days with and without sea breeze progression over the plateau. The convective development occurs in the afternoon of the two experiments but with different features and intensities. In the experiment with sea-breeze progression, there is fog formation over the plateau during the following night, in accordance with the observations. A strong northwesterly flow acting in the lower troposphere, with intensity varying between 7 and 10 m s-1,appears as an inhibiting agent of the sea-breeze progression over the plateau and of convective development in the afternoon and of the nocturnal fog occurrence. In this case, observed gusts during the night are well simulated and appear to be related to the topography. 相似文献
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Significance of MORB-derived Amphibolites from the Aracena Metamorphic Belt, Southwest Spain 总被引：2，自引：0，他引：2
CASTRO ANTONIO; FERNANDEZ CARLOS; DE LA ROSA JESUS D.; MORENO-VENTAS IAKI; ROGERS GRAEME 《Journal of Petrology》1996,37(2):235-260
The Aracena metamorphic belt, in the southwest Iberian Massif,is characterized by the presence of MORB-derived amphibolitesand continental rocks deformed and metamorphosed during theHercynian orogeny. Geochemical relationships of these amphibolitesindicate the existence of a multiple fractionation process froma set of parental magmas, implying the existence of a multi-chambersystem beneath the ridge where the basalt protolith was extruded.Neodymium isotopic ratios are typical of MORB, and oxygen isotopesindicate that these amphibolites have been derived from theuppermost part of the oceanic crust. Thermal evolution, revealedfrom the study of chemical variations in the amphibole chemistry,is interpreted as resulting from subduction in a low-pressureregime in which the thermal structure of the continental hanging-wallplayed an important role. This continental wall was previouslyheated by subduction of a slab window resulting from migrationof a triple junction along the continental edge during plateconvergence. Three petrologic arguments support this tectonicmodel. These are: (1) the low-pressure inverted metamorphicgradient of amphibolites of the oceanic domain; (2) the high-temperature-low-pressure metamorphism of the continental hanging wall; (3)the early intrusion of boninites into the continental domain.
*Corresponding author. 相似文献