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Geodynamic Information in Peridotite Petrology 总被引：12，自引：1，他引：12
Systematic differences are observed in the petrology and majorelement geochemistry of natural peridotite samples from thesea floor near oceanic ridges and subduction zones, the mantlesection of ophiolites, massif peridotites, and xenoliths ofcratonic mantle in kimberlite. Some of these differences reflectvariable temperature and pressure conditions of melt extraction,and these have been calibrated by a parameterization of experimentaldata on fertile mantle peridotite. Abyssal peridotites are examplesof cold residues produced at oceanic ridges. High-MgO peridotitesfrom the Ronda massif are examples of hot residues producedin a plume. Most peridotites from subduction zones and ophiolitesare too enriched in SiO2 and too depleted in Al2O3 to be residues,and were produced by melt–rock reaction of a precursorprotolith. Peridotite xenoliths from the Japan, Cascades andChile–Patagonian back-arcs are possible examples of arcprecursors, and they have the characteristics of hot residues.Opx-rich cratonic mantle is similar to subduction zone peridotites,but there are important differences in FeOT. Opx-poor xenolithsof cratonic mantle were hot residues of primary magmas with16–20% MgO, and they may have formed in either ancientplumes or hot ridges. Cratonic mantle was not produced as aresidue of Archean komatiites. KEY WORDS: peridotite; residues; fractional melting; abyssal; cratonic mantle; subduction zone; ophiolite; potential temperature; plumes; hot ridges 相似文献
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CLAUDE FROGET 《Sedimentology》1981,28(6):793-804
The study of clays from sites 338 to 343 enables the main lines of the palaeogeographical evolution of the Vøring plateau, off Norway, to be determined. The following stages are proposed: (1) In early Eocene sediments, clays provide evidence of erosion of the Scandinavian shield; detrital primary minerals (illite, chlorite) derived from crystalline rocks are dominant. This erosion results from tectonic movements coeval with the opening of the Norwegian basin. The rejuvenation of marginal relief hinders pedogenesis, which is only indicated by the presence of minerals coming from the few soils which are developed. (2) From the Middle Eocene, primary minerals decrease while smectite becomes dominant. This trend increases through the late Eocene and at the beginning of the Middle Oligocene, where only smectite is present. During this period the basin margins are stabilized after the initial movements. In essentially pelagic marine sediments, the smectite seems to be derived from volcanic rocks. (3) During the Middle Oligocene and early to Middle Miocene, smectite is always dominant, but primary minerals reappear, with mixed-layers indicating a moderate continental alteration. This composition suggests a modification of the climate, mainly marked by an increase in humidity. (4) In Pliocene and Plio-Pleistocene sediments, primary minerals are dominant, while smectite decreases. The glacial climate is responsible for this mineralogy. Detrital minerals would come from the erosion of Scandinavian moraines and from rafting by icebergs. 相似文献
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JEAN-CLAUDE CLAUDE 《水文科学杂志》2013,58(6):815-831
Résumé Parmi les objectifs assignés au barrage de Manantali sur le Bafing, le soutien de pointe de crue, indispensable pour le maintien des cultures traditionnelles de décrue dans la vallée du Sénégal, concurrence gravement les autres besoins lors des années déficitaires en eau: baisse de production électrique et diminution des réserves d'eau destinées à l'irrigation. On propose ici des règles permettant de réaliser un soutien de crue mobile relativement économique en eau, coïncidant avec une pointe de débit sur les affluents non contrôlés pour lesquels on envisage une prévision à l'horizon 10 jours. On montre par simulation numérique au pas de temps journalier que le soutien mobile, comparé au soutien à date fixe, permet de faire en période sèche un gain important de production électrique, tout en conservant une fréquence de crue “correcte”, supérieure à celle du régime naturel. 相似文献
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Abstract Flood forecasting is of prime importance when it comes to reducing the possible number of lives lost to storm-induced floods. Because rainfall-runoff models are far from being perfect, hydrologists need to continuously update outputs from the rainfall-runoff model they use, in order to adapt to the actual emergency situation. This paper introduces a new updating procedure that can be combined with conceptual rainfall-runoff models for flood forecasting purposes. Conceptual models are highly nonlinear and cannot easily accommodate theoretically optimal methods such as Kalman filtering. Most methods developed so far mainly update the states of the system, i.e. the contents of the reservoirs involved in the rainfall-runoff model. The new parameter updating method proves to be superior to a standard error correction method on four watersheds whose floods can cause damage to the greater Paris area. Moreover, further developments of the approach are possible, especially along the idea of combining parameter updating with assimilation of additional data such as soil moisture data from field measurements and/or from remote sensing. 相似文献
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The actinic flux is the only radiometric quantity suitable for photolysisfrequency determination. It is derived from solar spectral irradiancemeasurements performed by a portable spectroradiometer in the 300–850nm wavelength range. The spectral irradiance is first divided into a directpart and a diffuse part, according to the atmospheric conditions, and thenconverted into the corresponding actinic flux quantity. As an intermediary,the ratio
of diffuse actinic flux to diffuseirradiance is calculated by the spherical harmonics radiative code withrespect to wavelength, solar zenith angle, surface albedo, and aerosolproperties.The results of extensive sensitivity studies of
asa function of the main atmospheric parameters are discussed and lead to theconclusion that aerosol optical depth is the major critical value for aprecise
determination. The global algorithm totransform spectral irradiance into actinic flux is finally applied forphotodissociation rate calculations by convolution of the obtained actinicflux spectra with the absorption cross-sections and quantum yields of themolecule studied. Photolysis rates of different atmospheric photooxidants havebeen measured with this spectroradiometric method during the summers of 1993and 1994 in Brittany and in Portugal. The ozone and nitrogen dioxidephotodissociation rates obtained present a good agreement with thej(O3) and j(NO2) actinometerresults, for the same experimental conditions in Brittany. 相似文献
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The evolution and architecture of a set of retreating Lower Frasnian patch reef outcrops in the Canning Basin of Western Australia were evaluated, and their depositional and stratigraphic contacts spatially recorded using digital surveying tools. The geological data, together with high‐resolution digital elevation models, were assembled in three‐dimensional visualization and modelling software and subsequently used for building two‐dimensional surface models and three‐dimensional volumetric models. Numerical data on geometry and shape were extracted from these models and used to quantitatively assess the retrogradation motif of patch reef development. The development of the patch reefs comprises three stages. During stages 1 and 2, the patch reefs exhibited an overall retrogradational escarpment‐type configuration displayed by, on average, 60° steep reef‐margin walls that lacked the support of coeval slope deposits. The subdivision between stages 1 and 2 is based on minor backstepping reducing less than 10% of the platform‐top area. The onset of stage 3 is recognized by stromatolite development fringing reef‐margin walls. During stage 3 an aggrading accretionary reef‐margin developed, comprising allochthonous and autochthonous slope deposits. Both types of slope deposit onlap the previous stages and are distributed unevenly with allochthonous slope deposits being noticeably absent around the smaller and more elongate patch reefs. The variation in distribution of slope sediment type can be explained by the amount, linked to platform size, of platform‐top shedding. Small patch reefs were unable to fill the available accommodation adjacent to escarpments with allochthonous slope sediments and were thus encroached by autochthonous slope sediments. The variation, which cannot be explained by the size difference in the platform‐top factory, has been related to the difference in perimeter length. For patch reefs with similar platform‐top production areas, a more elongate patch reef inherits a longer perimeter and a proportionally smaller volume of allochthonous slope sediment per margin length will be transported to the flanks. Thus, the more elongate patch reef intrinsically contained more sites within which autochthonous slope sediments developed. Digital outcrop modelling and numerical evaluation of the evolution of the patch reefs revealed the major differences in retrogradation motif. The quantified variations in progressive decline of platform‐top area with height were confirmed by hypothetical decline curves for ellipse‐shaped carbonate systems for which aspect ratio (ratio between length and width) varied. This mathematical model demonstrates that the progressive decline of the production area is highly sensitive to shape and can be used to numerically assess and predict the relative timing of drowning, i.e. when the platform‐top production area becomes nil, of retrogradational isolated carbonate platforms that are controlled by high accommodation. Wider implications can be surmised for highstand systems tracts and prograding carbonate systems. For example, for equally sized platforms with hypothetically similar carbonate factories and identical external forces, the potential to prograde by platform‐top shedding is higher with a smaller aspect ratio because the shorter perimeter implies less accommodation space needing to be filled up to commence slope progradation. Clearly, there are intrinsic effects of shape on the development of carbonate platform systems. 相似文献
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Rapid Temporal Changes in Ocean Island Basalt Composition: Evidence from an 800 m Deep Drill Hole in Eiao Shield (Marquesas) 总被引：1，自引：1，他引：1
CAROFF MARTIAL; MAURY RENE C.; VIDAL PHILIPPE; GUILLE GERARD; DUPUY CLAUDE; COTTEN JOSEPH; GUILLOU HERVE; GILLOT PIERRE-YVES 《Journal of Petrology》1995,36(5):1333-1365
The Dominique drill hole has penetrated the volcanic shieldof Eiao island (Marquesas) down to a depth of 800 m below thesurface and 691•5 m below sea-level with a percentage ofrecovery close to 100%. All the lavas encountered were emplacedunder subaerial conditions. From the bottom to the top are distinguished:quartz and olivine tholeiites (800–686 m), hawaiites,mugearites and trachyte (686–415 m), picritic basalts,olivine tholeiites and alkali basalts (415–0 m). The coredvolcanic pile was emplaced between 5•560•07 Ma and5•220•06 Ma. Important chemical changes occurred during this rather shorttime span (0•34 0•13 Ma). In particular, the lowerbasalts differ from the upper ones in their lower concentrationsof incompatible trace elements and their Sr, Nd and Pb isotopicsignature being closer to the HIMU end-member, whereas the upperbasalts are EM II enriched. The chemical differences betweenthe two basalt groups are consistent with a time-related decreasein the degree of partial melting of isotopically heterogeneoussources. It seems unlikely that these isotopic differences reflectchanges in plume dynamics occurring in such a short time span,and we tentatively suggest that they result from a decreasingdegree of partial melting of a heterogeneous EM II–HIMUmantle plume. Some of the intermediate magmas (the uppermost hawaiites andmugearites) are likely to be derived from parent magmas similarto the associated upper basalts through simple fractionationprocesses. Hawaiites, mugearites and a trachyte from the middlepart of the volcanic sequence have Sr–Nd isotopic signaturessimilar to those of the lower basalts but they differ from themin their lower 206Pb/204Pb ratios, resulting in an increasedDMM signature. Some of the hawaiites-mugearites also displayspecific enrichments in P2O5, Sr and REE which are unlikelyto result from simple fractionation processes. The isotopicand incompatible element compositions of the intermediate rocksare consistent with the assimilation of MORB-derived wall rocksduring fractional crystallization. The likely contaminant correspondsto Pacific oceanic crust, locally containing apatite-rich veinsand hydrothermal sulphides. We conclude that a possible explanationfor the DMM signature in ocean island basalts is a chemicalcontribution from the underlying oceanic crust and that studiesof intermediate rocks may be important to document the originof the isotopic features of plume-derived magmas. KEY WORDS: alkali basalt; assimilation; mantle heterogeneity; Marquesas; tholeiile
*Corresponding author 相似文献
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THOMAS B. KELLOGG JEAN CLAUDE DUPLESSY NICHOLAS J. SHACKLETON 《Boreas: An International Journal of Quaternary Research》1978,7(1):61-73
BOREAS Kellogg, T. B., Duplessy, J. C. & Shackleton, N. J. 1978 03 01: Planktonic foraminiferal and oxygen isotopic stratigraphy and paleoclimatology of Norwegian Sea deep-sea cores. Boreas. Vol. 7, pp. 61–73. Oslo. ISSN 0300–9483.
Three Norwegian Sea deep-sea cores, which penetrate to sediments at least 200,000 years old, were analyzed for oxygen isotope content, total calcium carbonate, and planktonic foraminifera. The oxygen isotopic stratigraphy was used to refine the time control for paleoclimatic and paleo-oceanographic events previously described for the region. Two pulses of relatively warm subpolar water entered the region between 124,000 B.P. and 115,000 B.P. (the last interglacial), and since about 13,000 B.P. The remaining portion of the last 150,000 years was characterized by extensive ice cover. The magnitude of the change in isotopic composition between peak glacial and peak interglacial conditions is larger than can be explained by the changing isotopic content of the oceans alone suggesting that large temperature and salinity effects are recorded in isotope curves from Norwegian Sea isotope curves. The magnitude of the isotopic change from substage 5e to 5d (greater than 1%) is attributed to a combination of changing oceanic isotopic composition combined with a large temperature effect due to a sudden sea-surface temperature decrease of about 6o C. The persistence of heavy isotope values throughout substages 5d through 5a may be related to the sea-ice cover which prevented dilution of the isotopically heavy waters by isotopically light run-off. Sedimentation rates calculated for each of the isotope stages show large changes from one stage to another with some tendency for odd numbered stages to have higher rates. 相似文献
Three Norwegian Sea deep-sea cores, which penetrate to sediments at least 200,000 years old, were analyzed for oxygen isotope content, total calcium carbonate, and planktonic foraminifera. The oxygen isotopic stratigraphy was used to refine the time control for paleoclimatic and paleo-oceanographic events previously described for the region. Two pulses of relatively warm subpolar water entered the region between 124,000 B.P. and 115,000 B.P. (the last interglacial), and since about 13,000 B.P. The remaining portion of the last 150,000 years was characterized by extensive ice cover. The magnitude of the change in isotopic composition between peak glacial and peak interglacial conditions is larger than can be explained by the changing isotopic content of the oceans alone suggesting that large temperature and salinity effects are recorded in isotope curves from Norwegian Sea isotope curves. The magnitude of the isotopic change from substage 5e to 5d (greater than 1%) is attributed to a combination of changing oceanic isotopic composition combined with a large temperature effect due to a sudden sea-surface temperature decrease of about 6