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691.
692.
Magnesiocarpholite has been synthesized on its own composition between 15 and 25 kb water pressure and 415°–600° C. Best conditions are 25 kb-550° C, starting from a mixture of oxides and synthetic cordierite. Within the MgO-Al2O3-SiO2-H2O system, possible substitutions appear to be very limited in magnesiocarpholite. Cell-parameters are a=13.706(3), b= 20.075(3), c=5.107(l) Å, space group Ccca. The larger cell, as compared with the most magnesian natural carpholites, is tentatively ascribed to structural disorder. Preliminary stability data confirm the low-temperature character of this mineral which is shown to be a high-pressure equivalent of sudoite+quartz. 相似文献
693.
Bruno Goffe 《Contributions to Mineralogy and Petrology》1977,62(1):23-41
The Southern Vanoise is localized in the internal part of the Western Alps, in the Briançonnais zone. In Vanoise the following units can be distinguished (Fig. 1): a pre-hercynian basement (micaschists, glaucophanites, basic rocks), a permian cover (micaschists) and a mesozoic-paleocene cover (carbonate rocks). This area has been affected by the alpine metamorphic event characterized here by high and intermediate pressure facies. The rocks paragenesis are often unbalanced.The paleozoic rocks (Table 1) contain mainly: quartz, albite, paragonite, phengite, blue amphibole, chlorite, green biotite, garnet (Table 2). These minerals were analysed by an electron microprobe (Tables 3, 4 and 5). Mineral composition is highly variable: glaucophane is zoned (Table 5), white micas are more or less substituted with phengite (3.22O3/FeO + MgO)<0.53] whereas the Al rich chlorites [(Al2O3/FeO + MgO)>0.6] are associated with the less substituted white micas (Si=3.2) (Tables 3 and 4). The phengites with a Si content 3.2 occur in rocks where the retromorphic evolution is the most pronounced and penetrative. A metamorphic evolution is characterized by the disappearance of glaucophane which corresponds to the appearance of Al rich chlorite and to the decrease of phengitic substitution.The samples analysis are plotted in the tetraedric diagram: K2O-Al2O3-Na2O, Al2O3-FeO, MgO, on which a special mathematical treatment was applied. This method calculates the location of rocks composition in the four minerals space. This location is internal when the per cent amounts of all four relevant minerals are positive, if any of them is negative, the point is external (Tables 6–9).In Southern Vanoise micaschists, 2 subfacies are successively present (Fig. 3):Subfacies I: glaucophane-chlorite-phengite (Si4+ 3.5)-paragonite. Then subfacies II: chlorite-albite-phengite (Si4+ 3.2)-paragonite.In basic rocks is found essentially: Subfacies III: glaucophane-garnet-phengite-paragonite or IV: glaucophane-garnet-phengite-albite. Then subfacies V: green biotite-chlorite-albite-paragonite.The assemblages I and II proceed through reaction: 2 glaucophane +1 paragonite+2 H2O4.2 albite + 1 chlorite.The assemblage V appears with reactions: 1.8 glaucophane +2 phengite0.4 chlorite+2 green biotite + 3.6 albite +0.4 H2O or 2 glaucophane +2 phengite +0.5 garnet+ 6 H2O2 green biotite +1 chlorite+4 albiteThese reactions are controlled by hydratation: the composition variation of phengite and associated chlorite during the metamorphic evolution determines the stability of some minerals (particularly the glaucophane in Na2O poor rocks).In same rocks the results of mathematical treatment is not consistent with the data (Tables 2, 6–9). This discrepancy corresponds to a desequilibrium between chlorite and phengite.These results imply a continuous metamorphic evolution between two stages (Fig. 6): a first stage (1) at 8 kb, 350 ° C; a second stage (2) at 2 to 3 kb, 400–450 ° C. 相似文献
694.
Bruno d'Anglejan 《Estuaries and Coasts》1981,4(1):2-15
The suspension transport away from the extensive turbidity zone of the St. Lawrence estuary is largely determined by the channel topography. The suspended sediments are advected downstream by a 40 km long turbid plume which takes its source in a turbidity maximum at the head of the estuary and flows downstream partly confined by the South Channel. During the ebbing phase of tidal cycles, the turbid waters of the plume are forced downstream through narrow converging sections of the channel, and slowed down through more opened diverging regions, particularly down-stream of the St. Roch Traverse. These, large fluctuations in stratification modulate the vertical transport of suspended material from the bottom to the surface layer. Midway down the estuary, dispersion of the plume occurs along a frontal zone which seasonally migrates 30 km or more in response to changes in fresh water discharge. The plume is reinforced and the turbidity gradient is intensified by local injections of inshore waters from Ste. Anne Bay, a subtidal platform highly enriched in suspended material by intertidal exchanges with large mudllats. Lateral erosion of the plume and cross-channel transport of suspended matter from the South into the North Channel is made possible by large horizontal shears developing in the central part of the middle estuary during the early flood. These are created by a one-hour tidal phase difference between the North and the South Channel. 相似文献
695.
Bénédicte Cenki‐Tok James R. Darling Yann Rolland Bruno Dhuime Craig D. Storey 《地学学报》2014,26(1):29-37
Dating the timing of motion on crustal shear zones is of tremendous importance for understanding the assembly of orogenic terranes. This objective is achieved in this paper by combining petrological and structural observations with novel developments in in situ U‐Th‐Pb geochronology of allanite. A greenschist facies shear zone within the Mont Blanc Massif is documented. Allanite is synkinematic and belongs to the mylonitic assemblage. LA‐ICP‐MS U‐Th‐Pb isotope analyses of allanite reveal high contents and highly radiogenic isotopic compositions of the common‐Pb component. The use of measured Pb‐isotope compositions of associated minerals (feldspars and chlorite) is critical for accurate common‐Pb correction, and provides a powerful mechanism for linking allanite growth to the metamorphic assemblage. A mean 208Pb/232Th age of 29.44 ± 0.95 Ma is accordingly taken for synkinematic allanite crystallisation under greenschist facies conditions. This age reflects the timing of the Mont Blanc underthrusting below the Penninic Front and highlights the potential of directly dating deformation with allanite. 相似文献
696.
The objective of this study was to investigate the removal mechanism of U(VI) from groundwater by magnetite as the main product of anoxic steel corrosion. For this purpose, a systematic sequence of batch experiments was conducted to focus the active role of magnetite in the reduction of U under different conditions. Results indicated that under anoxic conditions U(VI) was sorbed at the magnetite surface, whereas under reducing conditions at different H2(g) pressures, U was present in tetravalent form as amorphous UO2. 相似文献
697.
Guillermo Booth-Rea José Miguel Azañón Bruno Goffé Olivier Vidal José Miguel Martı́nez-Martı́nez 《Comptes Rendus Geoscience》2002,334(11):857-865
We present the first occurrences of high-pressure, low-temperature ferro-magnesiocarpholite-bearing mineral assemblages associated to quartz segregations in the Alpujarride units of southeastern Betics (Sierra de Almagro, Sierra de los Pinos and Sierra Cabrera). Thermobarometric results show that the carpholite-bearing rocks underwent the same P–T conditions in the three outcrops, i.e. 8–10 kbar, 350–400 °C. Metamorphic and structural data allow us to conclude that these rocks belong to the same Alpujarride unit. In the Sierra de Almagro, tectonic units with carpholite-bearing rocks overlie low-pressure, low-temperature Alpujarride units, then forming a stack with an inverted tectono-metamorphic sequence, as observed in the central and western part of the Alpujarride complex. The preservation of carpholite-bearing assemblages in these rocks implies that no significant temperature increase occurred during the exhumation history. To cite this article: G. Booth-Rea et al., C. R. Geoscience 334 (2002) 857–865. 相似文献
698.
Slah Boulila Bruno Galbrun Linda A. Hinnov Pierre-Yves Collin 《Sedimentary Geology》2008,203(1-2):54-63
High-resolution magnetic susceptibility (MS) analysis was carried out on a Lower Kimmeridgian alternating marl–limestone succession of pelagic origin that crops out at La Méouge (Vocontian Basin, southeastern France). The aim of the study was to characterize the strong, dm-scale sedimentary cyclicity of the succession at a very high resolution, and to analyze the cycles for evidence of astronomical forcing. From marl to limestone, MS varies progressively and closely tracks the highest frequency cyclicity corresponding to the basic marl–limestone couplets. Long-term wavelength cycling modulates the high-frequency cyclicity (couplets), and appears to be controlled by clay content. Spectral analysis of the MS record reveals the presence of the complete suite of orbital frequencies in the precession, obliquity, and eccentricity (95–128 ka and 405 ka) bands with very high amplitude of the precession index cycles originating from dm-scale couplets. 405 ka-eccentricity cycles are very pronounced in the MS maxima of the marl members of the couplets, suggesting eccentricity-driven detrital input to the basin. 405 ka-orbital tuning of the MS maxima further sharpens all of the orbital frequencies present in the succession. These results are similar to those of previous studies at La Méouge that used carbonate content observed in field. Our results are also in accordance with cyclostratigraphic studies in Spain and Canada that report dominant precession index forcing. By contrast, in the Kimmeridge Clay (Dorset, UK), obliquity forcing dominates cyclic sedimentation, with weaker influence from the precession index. Ammonite zone duration estimates are made by counting the interpreted precession cycles, and provide an ultra-high resolution assessment of geologic time. In sum, this study demonstrates the power of the MS as a proxy in characterizing the high-resolution cyclostratigraphy of Mesozoic sections, particularly in alternating marl–limestone successions, and for high-resolution correlation and astronomical calibration of the geologic time scale. 相似文献
699.
Saskia Erdmann Rucheng Wang Fangfang Huang Bruno Scaillet Kai Zhao Hongsheng Liu Yan Chen Michel Faure 《Comptes Rendus Geoscience》2019,351(8):551-561
Constraining crystallization pressure and thus intrusion depth of granites in various geodynamic settings remains challenging, yet important to further our understanding of magma system and crustal evolution. We propose that titanite, which is a common accessory in metaluminous and weakly peraluminous granites, can be used as a barometer if it crystallized in magmatic, near-solidus conditions and in equilibrium with amphibole, plagioclase, K-feldspar, quartz, biotite, and magnetite ± ilmenite. Titanite Al2O3 increases with pressure (P) according to: P (in MPa) = 101.66 × Al2O3 in titanite (in wt%) + 59.013 (R2 = 0.83) with estimated uncertainties of ~±60 to ~±100 MPa for crystallization between ~150 and 400 MPa. We highlight that the current calibration dataset is limited, and that systematic experimental studies are needed to rigorously quantify the relation. The most important use of this empirical barometer will be for rocks in which amphibole is present but significantly altered, or in combination with amphibole barometry, as titanite can be easily dated by LA-ICP-MS. 相似文献
700.
Raymond Gèze Isabelle Veltz Jean-Claude Paicheler Bruno Granier Roland Habchi Dany Azar Sibelle Maksoud 《Arabian Journal of Geosciences》2016,9(19):730
A dinosaur tracksite was discovered in Batha on the side of the road from Harissa to Ghosta (Keserwan, Lebanon). About ten trackways are exposed at the top of two beds of Lower Cretaceous limestones over an area of approximately 1000 m2. These footprints were probably made by at least two dinosaur species, Sauropoda and either Theropoda or Ornithopoda. The site, which is the first record from Lebanon, should be protected to allow further scientific investigations. 相似文献