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1.
O. Maurel P. Moniè R. Pik N. Arnaud M. Brunel M. Jolivet 《International Journal of Earth Sciences》2008,97(3):565-584
Vertical displacements on the SW–NE Têt fault (Eastern Pyrenees Axial Zone, France), which separates the Variscan Canigou-Carança and Mont-Louis massifs, were constrained using a thermochronologic multi-method approach. 40Ar/39Ar data from the granitic Mont-Louis massif record its Variscan cooling history and reveal no ages younger than Early Cretaceous, while the Canigou-Carança gneiss massif records systematically younger 40Ar/39Ar ages. These younger 40Ar/39Ar ages in the Canigou-Carança gneiss massif are the result of partial to total rejuvenation of argon isotopic systems related to a thermal flow coeval with the Cretaceous HT-BP metamorphism in the North Pyrenean Zone. Only the deepest rocks from the Canigou-Carança suffered this extensive Mid-Cretaceous thermal overprint probably due to differential burial around 4 km at that time. The post Mid-Cretaceous vertical displacements along the Têt fault are recorded by “low” temperature thermochronology using K-feldspar 40Ar/39Ar, zircon and apatite fission track and (U–Th)/He datings. The Mont-Louis granite samples experienced a long period of protracted cooling reflecting a lack of thermo-tectonic activity in this area from Late Palaeozoic to Early Cenozoic, followed by cooling from 55–60 Ma to Late Eocene at a mean rate of 15–20°C/Ma in the final stage. This cooling stage corresponds to Têt fault reactivation with a reversed component, promoting exhumation of the Mont-Louis roof zone contemporaneously with the south-vergent Pyrenean thrusting. In the Canigou-Carança massif, the main cooling event occurred from 32 to 18 Ma at a maximum rate of 30°C/Ma during Early Oligocene followed by a more moderate rate of 3°C/Ma from Late Oligocene to Early Burdigalian, coeval with the normal reactivation of the Têt fault in brittle conditions that accommodated the final exhumation of the massif during the opening of the Gulf of Lion. 相似文献
2.
Alexandra Guedes Fernando Noronha Marie-Christine Boiron David A. Banks 《Chemical Geology》2002,190(1-4):273-289
In order to identify and characterise fluids associated with metamorphic rocks from the Chaves region (North Portugal), fluid inclusions were studied in quartz veinlets, concordant with the main foliation, in graphitic-rich and nongraphitic-rich lithologies from areas with distinct metamorphic grade. The study indicates multiple fluid circulation events with a variety of compositions, broadly within the C–H–O–N–salt system. Primary fluid inclusions in quartz contain low salinity aqueous–carbonic, H2O–CH4–N2–NaCl fluids that were trapped near the peak of regional metamorphism, which occurred during or immediately after D2. The calculated P–T conditions for the western area of Chaves (CW) is P=300–350 MPa and T500 °C, and for the eastern area (CE), P=200–250 MPa and T=400–450 °C. A first generation of secondary fluid inclusions is restricted to discrete cracks at the grain boundaries of quartz and consists of low salinity aqueous–carbonic, H2O–CO2–CH4–N2–NaCl fluids. P–T conditions from the fluid inclusions indicate that they were trapped during a thermal event, probably related with the emplacement of the two-mica granites.
A second generation of secondary inclusions occurs in intergranular fractures and is characterised by two types of aqueous inclusions. One type is a low salinity, H2O–NaCl fluid and the second consists of a high salinity, H2O–NaCl–CaCl2 fluid. These fluid inclusions are not related to the metamorphic process and have been trapped after D3 at relatively low P (hydrostatic)–T conditions (P<100 MPa and T<300 °C).
Both the early H2O–CH4–N2–NaCl fluids in quartz from the graphitic-rich lithologies and the later H2O–CO2–CH4–N2–NaCl carbonic fluid in quartz from graphitic-rich and nongraphitic-rich lithologies seem to have a common origin and evolution. They have low salinity, probably resulting from connate waters that were diluted by the water released from mineral dehydration during metamorphism. Their main component is water, but the early H2O–CH4–N2–NaCl fluids are enriched in CH4 due to interaction with the C-rich host rocks.
From the early H2O–CH4–N2–NaCl to the later aqueous–carbonic H2O–CO2–CH4–N2–NaCl fluids, there is an enrichment in CO2 that is more significant for the fluids associated with nongraphitic-rich lithologies.
The aqueous–carbonic fluids, enriched in H2O and CH4, are primarily associated with graphitic-rich lithologies. However, the aqueous–carbonic CO2-rich fluids were found in both graphitic and nongraphitic-rich units from both the CW and CE studied areas, which are of medium and low metamorphic grade, respectively. 相似文献
3.
Cécile Fabre Marie-Christine BoironJean Dubessy Aliouka ChabironBernard Charoy Tomas Martin Crespo 《Geochimica et cosmochimica acta》2002,66(8):1401-1407
Lithium is an important geochemical tracer for fluids or solids. However, because the electron microprobe cannot detect Li, variations of Li abundance at the micrometric scale are most often estimated from bulk analyses. In this study, the Li intense emission line at 670.706 nm in optical emission spectroscopy was used to perfect the analysis of Li at the micrometric scale by means of laser-induced breakdown spectroscopy (LIBS). To estimate lithium content for different geological materials, LIBS calibration of the emission line at 670.706 nm was achieved by use of synthetic glasses and natural minerals. The detection limit for this method is ∼5 ppm Li. Three applications to geological materials show the potential of LIBS for lithium determination, namely for Li-bearing minerals, melt inclusions, quartz, and associated fluid inclusions.For spodumene and petalite from granite pegmatite dikes (Portugal), the Li2O concentrations are 7.6 ± 1.6 wt% and 6.3 ± 1.3 wt%, respectively, by use of LIBS. These values agree with ion microprobe analyses, bulk analyses, or both. For eucryptite crystals, the Li concentrations are scattered because grain size is smaller than the LIBS spatial resolution (6 to 8 μm). Lithium concentrations of melt inclusions from the Streltsovka U deposit (Siberia) are in the range of 2 to 6.2 wt% (Li2O) for Li-rich daughter minerals. Lithium estimations on silicate glasses display values between 90 and 400 ppm.Lithium was also analyzed as a trace element in quartz. Transverse profiles were performed in hydrothermal barren quartz veins from the Spanish Central System (Sierra de Guadarrama). The highest Li concentrations (250 to 370 ppm) were found in specific growth bands in conjunction with the observed variation in optical cathodoluminescence intensity. Considering the fluid inclusion analysis, the source of fluid responsible to the Li enrichment in quartz is probably high-salinity fluids derived from sedimentary basins. 相似文献
4.
Ahmed Barakat Christian Marignac Marie-Christine Boiron Mohamed Bouabdelli 《Comptes Rendus Geoscience》2002,334(1):35-41
The gold showings at Bleida are hosted in Late Pan-African N50–80 °E quartz–hematite–chlorite 1 tension lenses that are related to the activity of major sinistral sub-east–west thrusts. Ores result from three superimposed stages of fluid migration. Gold occurs in microcracks offsetting the earlier minerals. Fluids evolved from COHN compositions with a saline component to boiling aqueous fluids. Pressure and temperature decreased from 50 MPa and 300 °C to less than 4 MPa and 150 °C. Thus, the gold showings at Bleida were formed in a typical geothermal (epithermal) setting, likely controlled by the Late Pan-African magmatism. To cite this article: A. Barakat et al., C. R. Geoscience 334 (2002) 35–41 相似文献
5.
Christian Montenat Marie-Christine Janin Pascal Barrier 《Comptes Rendus Geoscience》2004,336(14):1301-1310
The WNW–ESE trending Toulourenc Fault Zone (TFZ) is the western segment of the major Ventoux–Lure Fault Zone, which separates the Provençal platform from the Baronnies Vocontian Basin. The TFZ was subject to polyphased Mid-Cretaceous movements, during the Early Aptian and Middle–Late Albian times. The latter faulting episode generated conglomerates and olistoliths resulting from dismantled faultscarps cutting Barremian–Bedoulian limestones. The deformation is related to compressional wrench faulting (NE–SW sinistral faults; dextral component for the TFZ). It induced the uplift of the northwestern corner of the platform, as indicated by a mid-Cretaceous hiatus (Early Aptian pro parte to Early Albian) narrowly delimited in space. The opening of submeridian grabens within the platform favoured the northward transit of channelised coarse-grained Albian sands originating from a southern area. To cite this article: C. Montenat et al., C. R. Geoscience 336 (2004). 相似文献
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André Burnol Francis Garrido Philippe Baranger Catherine Joulian Marie-Christine Dictor Françoise Bodénan Guillaume Morin Laurent Charlet 《Geochemical transactions》2007,8(1):12
High levels of arsenic in groundwater and drinking water are a major health problem. Although the processes controlling the
release of As are still not well known, the reductive dissolution of As-rich Fe oxyhydroxides has so far been a favorite hypothesis.
Decoupling between arsenic and iron redox transformations has been experimentally demonstrated, but not quantitatively interpreted.
Here, we report on incubation batch experiments run with As(V) sorbed on, or co-precipitated with, 2-line ferrihydrite. The
biotic and abiotic processes of As release were investigated by using wet chemistry, X-ray diffraction, X-ray absorption and
genomic techniques. The incubation experiments were carried out with a phosphate-rich growth medium and a community of Fe(III)-reducing
bacteria under strict anoxic conditions for two months. During the first month, the release of Fe(II) in the aqueous phase
amounted to only 3% to 10% of the total initial solid Fe concentration, whilst the total aqueous As remained almost constant
after an initial exchange with phosphate ions. During the second month, the aqueous Fe(II) concentration remained constant,
or even decreased, whereas the total quantity of As released to the solution accounted for 14% to 45% of the total initial
solid As concentration. At the end of the incubation, the aqueous-phase arsenic was present predominately as As(III) whilst
X-ray absorption spectroscopy indicated that more than 70% of the solid-phase arsenic was present as As(V). X-ray diffraction
revealed vivianite Fe(II)3(PO4)2.8H2O in some of the experiments. A biogeochemical model was then developed to simulate these aqueous- and solid-phase results.
The two main conclusions drawn from the model are that (1) As(V) is not reduced during the first incubation month with high
Eh values, but rather re-adsorbed onto the ferrihydrite surface, and this state remains until arsenic reduction is energetically
more favorable than iron reduction, and (2) the release of As during the second month is due to its reduction to the more
weakly adsorbed As(III) which cannot compete against carbonate ions for sorption onto ferrihydrite. The model was also successfully
applied to recent experimental results on the release of arsenic from Bengal delta sediments. 相似文献
9.
Jean?VallanceEmail author Marie-Christine?Boiron Michel?Cathelineau Serge?Fourcade Michel?Varlet Christian?Marignac 《Mineralium Deposita》2004,39(3):265-281
The Moulin de Chéni orogenic gold deposit is the only granite-hosted deposit of the Saint-Yrieix district, French Massif Central. It occurs in 338±1.5 Ma-old peraluminous leucogranites and is characterized by intense microfracturing and bleaching of the granite in relation to pervasive sulfide crystallization. Formation of quartz veins and gold deposition occurred in two successive stages: an early mesozonal stage of quartz-sulfide (Fe-As-S) deposition, usually devoid of gold and a late epizonal stage of base metal and gold deposition. Both stages postdate peak metamorphism and granite intrusion. The genesis of the deposit is the result of four successive fluid events: (1) Percolation of aqueous-carbonic metamorphic fluids under an assumed lithostatic regime of 400–450 °C, at a maximum depth of 13 km; (2) Formation of the main quartz lodes with coeval K-alteration and introduction of As and S from aqueous-carbonic fluids percolating along regional faults. Arsenopyrite and pyrite deposition was linked to the alteration of Fe-silicates into K-feldspar and phengite at near-constant iron content in the bulk granite. Temperature was similar to that of the preceding stage, but pressure decreased to 100–50 MPa, suggesting rapid uplift of the basement up to 7.5 km depth; (3) The resulting extensional tectonic leads to the deposition of gold, boulangerite, galena and sphalerite in brecciated arsenopyrite and pyrite from aqueous fluids during a mixing process. Temperature and salinity decrease from 280 to 140 °C and 8.1 wt% eq. NaCl to 1.6 wt% eq. NaCl, respectively; (4) Sealing of the late fault system by barren comb quartz which precipitated from dilute meteoric aqueous fluids (1.6 wt% eq. NaCl to 0.9 wt% eq. NaCl) under hydrostatic conditions at 200–150 °C.Editorial handling: B. Lehmann 相似文献