Origine des grenats des roches calco-alcalines du Sud-Est de l’Espagne     

J. Lopez-Ruiz  E. R. Badiola  L. Garcia Cacho 《Bulletin of Volcanology》1977,40(3):141-152

Tertiary dacites and rhyodacites in SE Spain contain garnets, both as phenocrysts in the lavas and within their enclosed metamorphic venoliths. Microprobe analyses show that calc-alkaline and metamorphic rocks garnets are quite similar in composition (almandine-rich). However, the zoning patterns displayed in the two types of garnets differ. Garnets included in lavas show normal zoning (or a slight enrichment of Mn at the borders), while garnets in xenoliths have Mn-enriched rims or reverse zoning. The differences in zonation, as well as in petrographic features, indicate that the garnets in volcanic rocks crystallized directly from the calc-alkaline magma at an early stage of its crystallization. On the other hand, the uniform composition of dacitic and rhyodacitic garnets, as well as its low pyrope and grossular content, suggest that the conditions in which the garnets crystallized were rapidly exceeded.  相似文献   

Chemical variations of muscovites from the Sierra de Guadarrama metamorphic area,Sistema Central,Spain     

J. López Ruiz  A. Aparicio  L. García Cacho 《International Journal of Earth Sciences》1980,69(1):94-106

Muscovites in metapelites belonging to the Chloritoid, Staurolite, Kyanite, Sillimanite-K feldspar and Sillimanite-K feldspar-Cordierite zones of the Sierra de Guadarrama metamorphic area, have a chemical composition close to the end member Ms (mean value around Ms 92); nevertheless, they show definite variations in Al₂O₃, K₂O and Na₂O contents and, to a lesser extent, in FeO and MgO.These chemical variations (i. e., a progressive decrease of celadonite content, a increase followed by a decrease in paragonite solid solution towards compositions close to the endmember muscovite) may be regarded as in a close relationship with metamorphic grade in the upper metamorphic zones (Chloritoid, Staurolite and Kyanite zones), but the corresponding variations in the remaining lower zones (that is, a slight increase in Fe and Mg coupled with a slight increase in Al^VI and Ti, and more or less abrupt changes in Na and K contents) can only be explained considering the interference of anatectic phenomena, which modificate the normal trends due to changes in metamorphic grade.As a consequence of these observations, it has been concluded that muscovite composition in metapelites can only be used as an indicator of metamorphic grade in conditions where partial melting phenomena are absent.

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Zusammenfassung Muskovite in Metapeliten, die zu den Chloritoid, Staurolit, Cyanit, Sillimanit-K-Feldspat und Sillimanit-K-Feldspat-Cordierit Zonen der Sierra Guadarrama Metamorphgebiet gehören, zeigen einen Chemismus, der sich dem Endglied Muskovit nähert (Durchschnitt etwa Ms 92). Es wurden trotzdem bestimmte Veränderungen in den Gehalten von hauptsächlich Al₂O₃, K₂O und Na₂O und in geringerem Ausmaß in FeO und MgO festgestellt.Diese chemischen Veränderungen (d. h. ein progressives Abnehmen des Keladonitgehaltes, gefolgt von einer Abnahme der Paragonitmischungsreihe in einer Richtung, die sich dem Endglied Muskovit annähert) können in einem engen Zusammenhang mit der höher metamorphen Zone (Chloritoid-, Staurolit- und Cyanitzonen) gesehen werden. Die entsprechenden Veränderungen in den tieferen Zonen (d. h. eine minimale Abnahme von Fe und Mg begleitet von einer ebenfalls geringen Abnahme von Al und Ti und einer mehr oder weniger abrupten Veränderung im Na- und K-Gehalt) können jedoch nur unter Berücksichtigung der Interferenz von anatektischen Phänomenen gesehen werden. Solche Phänomene modifizieren den normalen Trend durch eine Veränderung des Metamorphosegrades.Daraus folgt, daß die Muskovitzusammensetzung als Indikator des Metamorphosegrades nur in Abwesenheit von partiellen Schmelzphenomen gebraucht werden kann.

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Résumé Les muscovites des métapélites de la Sierra de Guadarrama, appartenant aux zones à chloritoïde, staurotide, disthène, sillimanite-feldspath potassique et sillimanite-feldspath potassique-cordierite, ont une composition chimique très proche de la valeur theorique (valeur moyenne Ms 92); néanmoins elles présentent une certaine variation dans les teneurs en Al₂O₃, K₂O et Na₂O et, à une moindre échelle, en FeO et MgO.Ces variations chimiques (diminution progressive en céladonite, augmentation suivie d'une diminution de la paragonite vers des compositions proches de la muscovite sensu stricto) que présentent les muscovites des zones à chloritoïde, staurotide et disthène sont étroitement liées aux zones métamorphiques superieures. Au contraire, les variations (legère augmentation des teneurs en Fe et Mg, legère diminution en Al^VI et Ti, et plus ou moins brusques variations en Na et K, respectivement) correspondantes des muscovites des zones de la sillimanite-feldspath potassique et de la sillimanite-feldspath potassiquecordiérite, ne peuvent s'expliquer que si l'on admis que, dans les niveaux plus métamorphiques, les muscovites souffrent une série de changements chimiques dûs au début de l'anatexie, laquelle modifie les tendances normales liées à l'intensité du metamorphisme.En conséquence, seules les muscovites des métapélites situées au-dessus de l'isograde du feldspath potassique, en dehors de toute fusion partielle peuvent être utilisées pour déterminer le degré de métamorphisme des roches qui les contiennent.

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, , , , -K- -- - , , 92 % . ₂₃, K₂ Na₂O FeO MgO. (.. , , , ) — , . (.. , ) , . . , .

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Behind the scenes at the Nationaal Natuurhistorisch Museum, Leiden, and the Teyler Museum, Haarlem, The Netherlands: report of a visit by the Geologists' Association, 30 November and 1 December, 2002     

Stephen K. Donovan  Willem Renema  Isabel M. van Waveren  Cor F. Winkler Prins 《Proceedings of the Geologists' Association. Geologists' Association》2003,114(3):279-288

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Synchroneity between marine and terrestrial responses to millennial scale climatic variability during the last glacial period in the Mediterranean region     

M. Sánchez Goñi  I. Cacho  J. Turon  J. Guiot  F. Sierro  J. Peypouquet  J. Grimalt  N. Shackleton 《Climate Dynamics》2002,19(1):95-105

Land-sea climatic proxies have been obtained from the Last Glacial section of IMAGES core MD95-2043 (western Mediterranean Sea). Vegetation and alkenone derived SST curves indicate rapid (~150 years) and synchronous terrestrial and marine climatic changes, paralleling the Dansgaard-Oeschger (D-O) climatic variability over Greenland. This frequency of climate change can be related to shifts between the two modes of operation of the North Atlantic Oscillation (NAO). Transfer functions applied to the pollen data indicate that there was an amplification of the climatic signal during Heinrich events (HEs) in comparison with other D-O stadials. The development and persistence of both Scandinavian and Atlantic Mobile Polar Highs over southwestern Europe may explain the extreme cooling (~10 °C) and dryness (400 mm) during Heinrich events 5 and 4 in the Mediterranean region. Comparison of the results of core MD95-2043 with similar climatic data from IMAGES core MD95-2042, located off Portugal, indicates that thermal and precipitation gradients occurred between the Mediterranean and the Atlantic sides of Iberia within HEs. HEs 4 and 5 are associated with more humid conditions in the Atlantic (by 200 mm) than in the Mediterranean site, as is the case at the present time. This comparison also illustrates the different behaviour of these areas during the D-O stadials. In contrast with the Mediterranean site, the Atlantic site shows similar precipitation and temperature drops for all the D-O stadials, including those related to the HEs. Here we propose the operation of different Mobile Polar Highs (MPH) as the driving mechanism for this difference in behaviour between the Atlantic and Mediterranean sides of Iberia. HEs are related to a stronger influence of the Scandinavian MPH, forcing a severe aridification and cooling of the full Iberian Peninsula. The Atlantic MPH may have been dominant during the other stadials, which would preferentially affect Southwestern Iberia.  相似文献   

Évolution thermique des séries sédimentaires de la Marge ardéchoise : étude pétrographique de la matière organique et des argilesThermal evolution of the sedimentary series of the Ardèche Margin: petrological studies of organic matter and clays     

Luis Martinez  Joëlle Duplay  Isabel Suarez-Ruiz  Jean Robert Disnar  Geneviève Farjanel  Philippe Larqué  Nicole Liewig 《Comptes Rendus Geoscience》2002,334(14):1021-1028

Two wells, Balazuc (BA1) and Morte-Mérie (MM1), located in a confined area (1200 m apart) and separated by the Uzer fault (a Liassic structure with a dip fault of 1300 m) were analysed using conventional methodologies and techniques (PRV, TAI, XRD, STEM) in order to compare the diagenetic evolution of clays and organic matter. The thermal convective process allows the circulation of hot fluids and the oxidation of organic matter. The conductive process allows the maturation of the organic matter, the expulsion of hydrocarbons and the deposit of pyrobitumes in the migration channels. To cite this article: L. Martinez et al., C. R. Geoscience 334 (2002) 1021–1028.  相似文献   

Petrographic and trace element analysis of uranium-rich tufa calcite, middle Miocene Barstow Formation, California, USA     

Jennifer M. Cole  E. Troy Rasbury†  Isabel P. Montañez‡  Vicki A. Pedone§  Antonio Lanzirotti¶  Gilbert N. Hanson† 《Sedimentology》2004,51(3):433-453

An integrated petrographic and spectroscopic (X‐ray diffraction, phosphor imaging and synchrotron X‐ray absorption spectroscopy) study of tufas from the Miocene Barstow Formation, California, relates sample morphology, mineralogy and geochemical composition. The tufas, composed mainly of calcite that formed at the interface between an ancient alkaline lake and ground or spring waters, have textures similar to those of microbially mediated terrestrial stromatolites and travertines. The tufas have elevated concentrations of a number of trace elements including Mn, Fe, Sr and U. Synchrotron X‐ray fluorescence analyses show that U concentrations can exceed 500 p.p.m. X‐ray absorption spectroscopy indicates that the U in these samples is incorporated as U(IV). It is suggested here that alkaline lake waters had a high U/Ca ratio and tufa calcite formed where groundwater or (possibly epithermal) springs brought in Ca and trace elements such as Sr. The rapid, and possibly microbially mediated, precipitation of calcite allowed for incorporation of high concentrations of trace metals as either structural substitutes or extremely fine‐scale inclusions.  相似文献   

Decades of Drought, Years of Hunger: Archival Investigations of Multiple Year Droughts in Late Colonial Chihuahua     

Georgina H. Endfield  Isabel Fern´ndez Tejedo 《Climatic change》2006,75(4):391-419

Unusually severe or prolonged drought ranks among the most devastating and calamitous of all extreme climate events, contributing to wildfires, crop failure, livestock death, food shortages and famine. The response of human activities and the natural environment to such historical weather perturbations provides a guide to where the most critical sensitivities to future climate changes may lie (McCarthy et al., 2001, ‘Climatic change 2001: Impact adaptation, and vulnerability’, from 3rd Assesment Report of IPCC). The reconstruction of regional climatic histories and investigations of the impacts of – and social response to – extreme droughts in history are thus of crucial significance if we are to understand and anticipate the potential repercussions of future events (Wigley, 1985, Nature 316, 106–107; Grove and Conterio, 1995, Clim. Change 30, 223). Chihuahua, in the arid Northwest of Mexico, is one of the most seriously and frequently drought affected regions of the country (Garcia, 2000, available at www.sequia.edu.mx/proyectos/vulnera.html). Prolonged drought in the 1930s, 1950s and 1990s contributed to water scarcity, harvest failure, illness, livestock disease, abandonment and water conflict and served to highlight the particular vulnerability of agrarian society in this region to climatic variability (Sandoval, 2003, Ingeneria Hidraulica en Mexico 18(2), 133–155). Recent investigations using tree ring analysis have identified several phases of such prolonged drought over the last seven centuries. In this paper we use archival documents to investigate the impacts of such periods in late colonial Chihuahua and to explore how society in the region responded to and coped with them.  相似文献   

Long-term neutralisation potential of red mud bauxite with brine amendment for the neutralisation of acidic mine tailings     

M. Paradis  J. Duchesne  A. Lamontagne  D. Isabel 《Applied Geochemistry》2007

Acid mine drainage is an environmental problem produced when sulphide in mine tailings dams comes in contact with O₂, bacteria and water. Oxidation occurs and a succession of reactions is responsible for producing acid and metals in the environment. One solution proposed is to use red mud bauxite (RMB) that is very alkaline to neutralise acidic tailings. Previous experiments showed that RMB has a good neutralisation capacity for a short time, but the long-term neutralisation potential is uncertain. So brine was added to RMB to verify if it can improve long-term alkalinity retention of RMB. Some authors have presented results where seawater or other natural or artificial Ca- and Mg-rich brines were used with RMB to convert the basicity (mainly NaOH) and other soluble alkalinity into low solubility hydroxide, carbonate and hydroxycarbonate minerals. Results showed that neutral pH conditions were maintained over the entire test for RMB and a mixture of RMB with brine. Addition of brine to RMB slightly lowered the pH compared to RMB alone. RMB alone lost a lot of dissolved alkalinity at the beginning of the test. Most of the alkalinity was lost in water after a few flushes for RMB samples. The addition of brine helped to keep neutralisation potential over more cycles of leaching.  相似文献   

ISPRS Commission Iii Symposium: Photogrammetric Computer Vision 2006     

Isabel  Sargent Sarah  Smith-Voysey 《The Photogrammetric Record》2007,22(117):88-90

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Morphometrical analysis of torrential flows-prone catchments in tropical and mountainous terrain of the Colombian Andes by machine learning techniques     

Arango  María Isabel  Aristizábal  Edier  Gómez  Federico 《Natural Hazards》2021,105(1):983-1012

Natural Hazards - Assessment of susceptibility to torrential flows at the catchment scale is a necessary step for prioritising zones that can be identified by hazard and risk maps. In the Andean...  相似文献