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121.
122.
The distribution of Ti, Zr, Y, Sr, K, P and Nb has been investigated at 55 sample sites within a single basaltic flow, the Cliefden Outcrop, which has adjusted to low-grade metamorphism of the prehnite-pumpellyite facies. The cluster of points in the plot of Ti, Zr and Y as proposed by Pearce and Cann shows that the ratio of these elements has remained relatively constant after metamorphism and would therefore have significance in attempts at classification of magma type. Likewise a plot involving Nb, Y, Zr and P as proposed by Floyd and Winchester shows only restricted scatter and appears useful. However, plots involving Sr or K show a scatter that is clearly related to metamorphic processes. Consequently, plots involving these two elements are likely to be of little use in classification in this case.Low-grade metamorphism is common, variable and not always recognized. The study concerned one style of alteration and revealed problems in the application of some classification schemes. Consequently it is apparent that much more rigorous testing is needed before classification schemes can be generally applied to sequences of basaltic rocks. 相似文献
123.
Stephen E. Kesler John F. Lewis Lois M. Jones Raymond L. Walker 《Contributions to Mineralogy and Petrology》1977,65(1):91-99
Reconnaissance studies of early island-arc intrusions in the Cordillera Central of the Dominican Republic demonstrate that these rocks are mainly hornblende tonalite with lesser amounts of hornblende diorite, quartz diorite, granodiorite and quartz monzonite. Two plutons (El Bao, Medina) are petrographically and chemically homogeneous, whereas two others (El Rio and Loma de Cabrera) are compositionally heterogeneous. Samples from these intrusions range in SiO2 from 49 to 70% with most rocks in the 59 to 62% range. K2O ranges from 0.24 to 3% and averages 1.2%. Cu, Zn, Co, Ni, V and possibly Cr decrease with increasing SiO2. Rb/Sr values for the intrusions are low but variable. Present-day 87Sr/86Sr values range from 0.7031 to 0.7045 for the El Bao and Loma de Cabrera batholiths and 0.7033 to 0.7091 for the Medina stock. These data do not generate isochrons. The Cordillera Central tonalite intrusions are the most abundant plutonic rock type in the Greater Antilles, although small, younger granodiorite and quartz monzonite stocks are present. The Cordillera Central intrusions are lower in SiO2, K2O, Rb, and Sr than the average composition of the Sierra Nevada batholith, but they are similar to the tonalites and trondjhemites from the western margin of the Sierra Nevada batholith. The low Rb/Sr ratios and low initital Sr87/Sr86 ratios for the Cordillera Central intrusions combined with the high liquidus temperatures required for the generation of tonalite magmas strongly favor a subcrustal source for these magmas in an island-arc setting. 相似文献
124.
Raymond Capdevila François Mégard Jorge Paredes Philippe Vidal 《International Journal of Earth Sciences》1977,66(1):434-446
Résumè Le batholite de San Ramon est constitue par un granite à gros grains ou porphyroïde, à biotite et parfois hornblende, de teinte rouge à grise. Il s'étend sur 90 km du Nord au Sud à la bordure est de la Cordillère Orientale du Pérou Central. Il recoupe des terrains carbonifères et on le retrouve en galets dans des conglomérats rouges sous-jacents aux calcaires triasico-liasiques. Son âge est précisé par une isochrone Rb/Sr en roches totales qui le fixe à 238±10 MA. Il s'agit donc d'un granite d'âge permien supérieur à trias inférieur en partie contemporain du volcanisme rhyolitique à andésitique qui accompagne le dépôt des molasses rouges Mitu post-léonardiennes et pré-ladiniennes. Avec d'autre granitoïdes tardi-hercyniens de la Cordillère Orientale, il témoigne de l'importance insuffisamment reconnue jusqu'alors du plutonisme associé à ce volcanisme »permo-triasique«.
The batholith of San Ramon is made of a coarse-grained to porphyritic granite that bears biotite and also hornblende at some places. It extends over 90 km from north to south along the eastern boundary of the Eastern Cordillera of Central Peru. It intrudes Carboniferous and Lower Permian strata and is included as cobbles into the red conglomerates that underlie Triassic to Liassic carbonates. A Rb/Sr whole-rock isochron gives a Late Permian to Early Triassic age of 238±10 m. y. Thus the San Ramon granite appears to be in part coeval with the andesite to rhyolitic volcanism associated to the red Mitu molasses, that as a whole were deposited after the Late Leonardian and before the Lower Ladinian. Some other radiometric ages from the Eastern Cordillera granitoïds stress the extension of this Late Variscan plutonism.
Zusammenfassung Der Batholit von San Ramon besteht aus einem grobkörnigen bis porphyrartigen Granit mit Biotiten und bisweilen Hornblenden von rötlicher bis grauer Farbe. Er erstreckt sich über 90 km in N—S-Richtung längs dem Ostrand der östlichen Cordillere von Zentralperu. Er durchschneidet Karbon- und Permablagerungen und findet sich in Gerollen des triadisch-liassische Kalke unterlagernden Konglomerats. Aus der Rb/Sr-Gesamtisochrone ergibt sich ein Alter von 238±10 M. J. Es handelt sich also um einen Granit aus dem Grenzbereich Perm—Trias, der zum Teil gleichaltrig mit dem rhyolitischen bis andesitischen Vulkanismus ist, der die Ablagerung der postleonardischen und praeladinischen roten Molasse Mitubegleitet. Im Verein mit anderen spätvariszischen Granitoïden weist er auf die bisher ungenügend erkannte Bedeutung des diesen permo-triadischen Vulkanismus begleitenden Plutonismus hin.
Resumen El batolito de San Ramón esta localizado a lo largo del limite este de la Cordillera Oriental en el Perú Central. Esta compuesto por un granito de grano grueso que puede tambien ser porfiroide, contiene biotita y tambien hornablenda y su color varia de rojo a gris. Dicho granito intruye terrenos carboniferos y eo-pérmicos y se le encuentra formando parte de los cantos en los conglomerados rojos infrayacentes a la serie carbonatada triásico-liásica. Una isocrona Rb/Sr en rocas totales le da una edad de 238±10 m. y. es decir del Permico terminal o de la base del Triásico. Por lo tanto, el granito de San Ramón es contemporáneo con parte del volcanismo riolitico a andesítico asociado a la sedimentacion de las molasas rojas del grupo Mitu, la cual ocure entre el Leonardiano superior y el Ladiniano inferior. Junto con otros granitoïdes de la Cordillera oriental, el batolito de San Ramón demuestra la importancia del plutonismo asociado a este volcanismo »permo-triásico«.
- , , . 90 - . , , . — Rb/Sr — 238± 10 , .. - . .. , - - «». , , , - .相似文献
125.
Raymond Joesten 《Geochimica et cosmochimica acta》1977,41(5):649-670
Metamorphic reaction bands consist of mineral assemblage layers, that separate incompatible mineral assemblages, and grow by reaction at their contacts and by precipitation within the layer. The stoichiometry of these reactions is determined by the relative diffusion fluxes within adjacent layers. Using the local equilibrium-steady diffusion model of Fisher (1973), the stoichiometric coefficients of layer growth reactions can be computed from the mass balance at each layer contact and independent ratios of instantaneous fluxes within each layer.Model calculations in a ternary system show that (1) variation in bulk composition across a reaction band, expressed in terms of layer sequence, mineral formulae of phases that comprise monomineralic layers and modal proportions of phases in multimineralic layers is largely determined by the relative fluxes of components that diffuse in the same direction; (2) the fraction of the width of a reaction band produced by replacement of each of the initial reactant assemblages is largely determined by the relative fluxes of components that diffuse in opposite directions; (3) the fraction of the width of a layer produced by internal precipitation is determined by temperature and the relative fluxes of components that diffuse in opposite directions; (4) in a multilayer reaction band, only one layer can grow by reaction at both contacts, and that layer contains the initial contact between initial reactants; and (5) a reaction band cannot grow by constant volume replacement of both reactant assemblages, if the system is closed to diffusion beyond layer contacts with the initial reactant rock masses. 相似文献
126.
A shallow lattice dome subjected to three independent sets of step or impulse loads is investigated. Symmetric and asymmetric loading distributions are considered. The dynamic response is determined by numerical integration, and critical loads are defined by the Budiansky-Roth criterion. Interaction curves for fixed maximum response and for snap-through instability are obtained, and a comparison is made with previous results for static loading. 相似文献
127.
Raymond G. Giese 《Ground water》1982,20(5):526-530
128.
An analysis of the flow in layered viscous fluids at small, but finite amplitude is illustrated in an application to the shortening of two different viscous fluids parallel to their interface. The analysis extends the familiar infinitesimal amplitude analysis, which retains terms to first-order in the surface slope, to second-order in this quantity. To second-order accuracy, the asymmetry in interface form characteristic of the finite-amplitude lobe-and-cusp structure emerges. Additional results for mullion structures are derived and used to interpret some natural structures. 相似文献
129.
L.M. Jones Raymond L. Walker S.E. Kesler John F. Lewis 《Earth and Planetary Science Letters》1979,43(1):112-116
Initial87Sr/86Sr ratios have been determined for a representative suite of Upper Cretaceous granodiorites and associated rocks from the Above Rocks composite stock in central Jamaica and the Terre-Neuve pluton in northwestern Haiti. The average initial87Sr/86Sr ratio for severn samples of the Terre-Neuve intrusion is 0.7036, with a range of 0.7026–0.7047. For two samples of the Above Rocks the initial ratios are 0.7033 and 0.7034. A third sample from this intrusive has an initial ratio of 0.7084, which is tenatively attributed to contamination. The initial87Sr/86Sr ratios indicate that neither ancient sialic crust nor sediments carried down a Benioff zone can be the primary source of the granodioritic magma. K/Rb ratios for these rocks range from 178 to 247, which are much lower than the average values (≥1000) for tholeiitic basalts. It is concluded that the magmas originated primarily by melting of downthrust oceanic crust or adjacent mantle material. 相似文献
130.