Regional oxygen isotope systematics of felsic volcanics; a potential exploration tool for volcanogenic massive sulphide deposits in the Iberian Pyrite Belt     

C. Lerouge  Y. Deschamps  M. Joubert  E. Bchu  A. -M. Fouillac  J. A. Castro 《Journal of Geochemical Exploration》2001,72(3)

Regional oxygen isotopic sytematics have been performed mainly on the felsic volcanic footwall rocks of the orebodies but also on purple schist characteristic of the hanging wall series, around two giant VMS deposits in the Spanish Iberian Pyrite Belt, Riotinto and La Zarza. As the terranes of the Iberian Pyrite Belt, these two giant deposits have been affected by the Hercynian tectono-metamorphic events, strongly modifying their geometry. About 60 and 40 samples were collected over a 10×4 km² area at Riotinto and a 3×2 km² area at La Zarza, respectively. Whole-rock powders were analysed for oxygen by CO₂-laser fluorination. At both sites, a same type of low-δ¹⁸O anomaly down to +3.6‰, well differentiated from the regional background (up to 20‰), was identified near the orebodies. The lowest δ¹⁸O values (+4 to +11‰) correspond to the chlorite hydrothermal halo, essentially restricted to the feeder zones of the orebody. Intermediate δ¹⁸O values (+9 to +15‰) correspond to the sericite hydrothermal halo, mostly developed laterally to the orebody until 0.5–1 km. The regional background (+16 to +20‰) is represented by spilitised volcanic rocks. A same kind of low anomaly, but with less contrast, was defined in purple schist in the immediate hanging wall of the orebodies. All these results demonstrate that, despite high geometrical modifications of the orebodies related to the Hercynian tectonics, oxygen isotopic anomalies recorded by volcanic host rocks during the emplacement of the mineralising hydrothermal systems are still identified. This strongly suggests that oxygen isotopic systematics could be useful to identify target areas in the Iberian Pyrite Belt, as already demonstrated on other VMS targets in the world.  相似文献   

Book Reviews     

Anne-Marie de Grosbois  Dale Easley  Fakhry A Assaad 《Environmental Geology》2006,49(3):494-496

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Species composition and dietary relationships in a brackish shallow water fish assemblage in the Bothnian Sea,Sweden     

Staffan Thorman  Anne-Marie Wiederholm 《Estuarine, Coastal and Shelf Science》1984,19(3):359-371

A nearshore fish assemblage inhabiting a shallow bay in the southern Bothnian Sea, Sweden, with demanding environmental conditions (c. 5‰; >15°C during 4 months 1980 and 1 month 1981) was studied during a two-year period, in 1980 and 1981. Seasonal distribution patterns, dietary relationships, and growth rates were studied in Pungitius pungitius (L.), Pomatoschistus minutus (Pallas.), Gasterosteus aculeatus (L.), Phoxinus phoxinus (L.), Pomatoschistus microps (Krøyer) and Gobius niger L. The structure of the juvenile populations changed both over seasons and years but the adult populations remained constant. Lower water temperature, fewer individuals, lower and delayed fish growth, and lower interspecific food overlaps were found in 1981 compared to 1980. Few significant correlations were found in both years between the following community parameters: diversity, niche width, food overlap, and the proportion of each species in the fish assemblage.According to these results it is suggested that food competition and resource partitioning were of minor importance for the structuring of the fish community in the present area. Rather, the extreme salinity and the fluctuations in temperature regulated the fish populations. One may conclude that the populations of juveniles were more influenced by short-term changes in the environment than those of the adults.  相似文献   

Climate and environmental change at the end of the Holocene Humid Period: A pollen record off Pakistan     

Sarah J. Ivory  Anne-Marie Lézine 《Comptes Rendus Geoscience》2009,341(8-9):760-769

Pollen studies from core SO90-56KA recovered from the Arabian Sea off the Makran Coast (24° 509N, 65° 559E; 695 m depth) show that the end of the Holocene Humid Period, linked to the weakening of Indian monsoon fluxes, took place between 4700 and 4200 BP. Two periods of strong summer monsoon activity are identified between 5400–4200 BP and 2000–1000 BP during which the montane pollen taxa coming from the Himalayas reached the Makran coast due to increased fluvial activity of the Indus River. A contrasting period, dominated by the winter monsoon between 4200 and 2000 BP, is identified based on the presence of pollen taxa from the Baluchistan plateaus. The regional vegetation of the low- and midaltitudes, arid and semiarid, are remarkably stable from 4500 BP to the present.  相似文献   

The crystal and melt structure of spinel and alumina at high temperature: An in-situ XANES study at the Al and Mg K-edge     

Daniel R. Neuville  Dominique de Ligny  Grant S. Henderson  Anne-Marie Flank 《Geochimica et cosmochimica acta》2009,73(11):3410-2801

We present structural information obtained on spinel and alumina at high temperature (298-2400 K) using in-situ XANES at the Mg and Al K-edges. For spinel, ^[4](Al_x,Mg_1−x)^[6](Al_2−x,Mg_x)O_4, with increasing temperature, a substitution of Mg by Al and Al by Mg in their respective sites is observed. This substitution corresponds to an inversion of the Mg and Al sites. There is a significant change in the Al K-edge spectra between crystal and liquid, which can be attributed to a change of the ^[6]Al normally observed in corundum at room temperature, to a mixture of ^[6]Al-^[4]Al in the liquid state. This conclusion is in good agreement with previous ²⁷Al NMR experiments. Furthermore, both experiments at the Al and Mg K-edges are in good agreement with XANES calculation made using FDMNES code.  相似文献   

Upcoming International Events     

Anne-Marie de Grosbois 《Environmental Geology》2007,52(8):1667-1672

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Textural evidence for recent co-seismic circulation of fluids in the Nojima fault zone, Awaji island, Japan     

Anne-Marie Boullier  Koichiro Fujimoto  Tomoyuki Ohtani  Gabriela Roman-Ross  ric Lewin  Hisao Ito  Philippe Pezard  Benoît Ildefonse 《Tectonophysics》2004,378(3-4):165

The Hirabayashi borehole (Awaji Island, Japan) was drilled by the Geological Survey of Japan (GSJ) 1 year after the Hyogo-ken Nanbu (Kobe) earthquake (1995, M_JMA=7.2). This has enabled scientists to study the complete sequence of deformation across the active Nojima fault, from undeformed granodiorite to the fault core. In the fault core, different types of gouge and fractures have been observed and can be interpreted in terms of a complex history of faulting and fluid circulation. Above the fault core and within the hanging wall, compacted cataclasites and gouge are cut by fractures which show high apparent porosity and are filled by 5–50 μm euhedral and zoned siderite and ankerite crystals. These carbonate-filled fractures have been observed within a 5.5-m-wide zone above the fault, but are especially abundant in the vicinity (1 m) of the fault. The log-normal crystal size distributions of the siderite and ankerite suggest that they originated by decaying-rate nucleation accompanied by surface-controlled growth in a fluid saturated with respect to these carbonates. These carbonate-filled fractures are interpreted as the result of co-seismic hydraulic fracturing and upward circulation of fluids in the hanging wall of the fault, with the fast nucleation of carbonates attributed to a sudden fluid or CO₂ partial pressure drop due to fracturing. The fractures cut almost all visible structures at a thin section scale, although in some places, the original idiomorphic shape of carbonates is modified by a pressure-solution mechanism or the carbonate-filled fractures are cut and brecciated by very thin gouge zones; these features are attributed to low and high strain-rate mechanisms, respectively. The composition of the present-day groundwater is at near equilibrium or slightly oversaturated with respect to the siderite, calcite, dolomite and rhodochrosite. Taken together, this suggests that these fractures formed very late in the evolution of the fault zone, and may be induced by co-seismic hydraulic fracturing and circulation of a fluid with a similar composition to the present-day groundwater. They are therefore potentially related to recent earthquake activity (<1.2 Ma) on the Nojima fault.  相似文献   

Early Cretaceous megaspore assemblages from southeastern Australia     

Anne-Marie P. Tosolini  Stephen McLoughlin  Andrew N. Drinnan 《Cretaceous Research》2002,23(6):807

Twenty-nine megaspore species including six new taxa (Bacutriletes otwayensis sp. nov.,Erlansonisporites cerebrus sp. nov., Erlansonisporites decisum sp. nov., Hughesisporites coronatus sp. nov., Hughesisporites dettmanniae sp. nov., and Verrutriletes depressus sp. nov.) are documented from Aptian and Albian strata of the Gippsland and Otway basins, southeastern Australia. Together with six taxa known only from underlying Neocomian strata, these megaspores are used to establish four provisional biozones for the Lower Cretaceous that complement existing biostratigraphic schemes based on miospores and plant macrofossils. Megaspores are best represented in silty floodbasin facies and it is likely that the parent plants predominantly occupied moist understorey to fully aquatic habitats on the floodplain. Megaspores are sparsely represented in most other fluvial facies chiefly due to reworking of floodbasin sediments into higher energy channel and crevasse deposits. The relatively high diversity of lycophyte and fern megaspores contrasts with the scarcity of these plant groups in macrofossil assemblages. The megaspore record suggests that heterosporous cryptogams may have been significantly more prominent in the vegetation of this region than previously suggested. Several megaspores from southeastern Australia are closely comparable to forms from India and Argentina indicating broad similarities between Early Cretaceous heterosporous fern and lycophyte communities across Gondwana. These similarities also suggest that megaspores may be useful for inter-continental biostratigraphic correlation.  相似文献   

Sensitivity of UT1 determined by single-baseline VLBI to atmospheric delay model, terrestrial and celestial reference frames     

Jan Hefty  Anne-Marie Gontier 《Journal of Geodesy》1997,71(5):253-261

 At the present time, the daily VLBI observations on the Westford-Wettzell baseline is the only continually running VLBI project for studies of high-frequency Earth rotation variations. An analysis of this experiment with regard to the potential errors in the atmospheric delay model and in adopted celestial and terrestrial reference frames is presented in the paper. A new VLBI geometric delay model is applied and an algorithm for global adjustment for this specific single-baseline VLBI developed. The results over three years show discrepancies at the milliarcsecond level between the daily observations and the adopted atmospheric model as well as the combined celestial reference frame. A significant number of these discrepancies are removed by the global adjustment. Received: 19 August 1996; Accepted: 13 September 1996  相似文献   

Etude de l''acquisition d''éléments dissous par les eaux de lessivage des roches granitiques sous climat tempéré     

Grard Sarazin  Christian Fouillac  Gil Michard 《Geochimica et cosmochimica acta》1976,40(12):1481-1486

Using chemical potential diagrams and budget calculations, we show that the acquisition of solutes by surface water in granitic rocks under temperate climate corresponds with transformation of primary minerals into kaolinite or halloysite. This mineral controls aluminium solubility.  相似文献