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Synthèse de nucléosides à aminosucre et d'un nucléoside à sucre ramifié
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Foraminifères de carottes méditerranéennes et d’une carotte nord-atlantique: taxonomie et paléoclimatologie
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Essai d’application de la méthode des traces de fission à la datation de quelques massifs éruptifs du sud des Alpes
No full textSpontaneous fission of U238 nuclei dispersed in rock minerals leaves tracks which can be observed with an ordinary microscope after an appropriate chemical attack. These tracks are straight, isotropically oriented in space and fairly easy to distinguish from usual mineral imperfections.
The density of these tracks per unit of surface is proportionnal to the amount of uranium in the mineral and to the time elapsed since latter's formation. Hence they constitute a means of measuring rock ages. Approximately 2000 tracks per cm2 are formed per million years and per 1 ppm of uranium.
Using this method, we have measured a certain number of ages on several young granitic massivs of the southern Alps : Traversella, Biella, Bergell and Adamello massivs. Their ages are known to range between 30 and 40 m.y.
Apatite and titanite were extracted by the usual crushing and separating methods. One fraction was mounted on a thick dise of epoxy resin, polished to expose the mineral's internal surfaces and finally chemically attacked to enlarge the tracks. The track density was measured under 500 manification with an ordinary microscope equiped with a graticule eyepiece. When possible several hundred tracks were measured for each sample.
The quantity of uranium contained in the mineral was evaluated by an indirect method. Another fraction of the initial separation was heated to 700° C for 12 hours to anneal fossil spontaneous tracks. The samples were then irradiated by thermal neutrons in the heavy water canal of "Melusine" Reactor at Centre de recherches nucléaires in Grenoble.
This irradiation induces fission in a certain number of U235 nuclei. Whith the value of the flux, the cross section of U235 and the isotopie ratio of U238 /U235, it is possible to calculate ages by an equation in which age is a function of spontaneous and induced fission track density and neutron flux.
Ages measured whith titanite are always greater than those with apatite. This difference can be explained by the fact that during initial cooling of rocks, titanite starts to conserve fission tracks at about 450° compared to 150° for apatite. Their age differences can be increased by metamorphism which affect apatite well before titanite. Hence these age discrepencies can furnish precious information about their thermal history.
The mean ages in million years found respectively for apatite and titanite for these massivs are Biella 29 and 37, Traversella 31 and 40, Bergell 20 and 37, Adamello 26 and 48. These results confirm the tarditectonic apparition of these massivs. The tonalite facies appears slightly older. This method of dating by fission tracks is useful however it does not replace the other more precise classical radiometric methods. Nevertheless it can be used when other methods are unapplicable. Moreover it contributes interesting information on rock's thermal evolutions.</p
Étude minéralogique et pétrographique de la région située à l’est de Çelikhan (Taurus Oriental, Turquie)
No full textThe region under study is situated in the Taurus mountain range, approximately 30 kilometers East of the town of Celikhan, in the department of Adiyaman. This region belongs to the overthrust zone which separates the Taurides from the border folds.
The rocks encountered in the region are of metamorphic, monzodiorit,ic and ophiolitic nature, with their associated sediments. Younger sediments of Tertiary age are well represented.
The metamorphic basement, of probable Paleozoic age, is the core of the Eastern Taurus range. In the region under study, it shows a prealpine metamorphism of green schist to amphibolite facies. This basement is intruded by rocks of acid, intermediate and basic composition. It is overthrusted over Tertiary sediments towards the South.
A circumbscribed, fairly heterogeneous and posttectonic monzodioritic stock of pre-Lutetian age is rich in inclusions which belong partly to the basement and are partly of unknown origin. The inclusions are of melamonzonitic, melamonzodioritic, dioritic, meladioritic and ultrabasic (phlogopite-bearing) composition.
The presence of a biotite-rich zone is noticeable in the metamorphic rocks at the contact with the intrusive rocks mentioned above. This contact zone is approximately 20 meters wide.
The ophiolitic suite, which was studied in detail, is formed of ultrabasic rocks, gabbro-diorites and diabases, with their associated rocks.
Harzburgites, lherzolites, wehrlites, pyroxenites and serpentinites are the main rock types of ultrabasic nature. In the northeastern part of the region under study, relatively weakly serpentinized harzburgites and wehrlites are associated with ortho-amphibolites. These ortho-amphibolites can be interpreted as older intrusive rocks of intermediate to basic composition which originate from the Upper mantle in association with the ultrabasites, or as rocks which have been transformed with the basement during a Pal eozoic phase of regional metamorphism in the amphibolite facies.
In the southern part of the region under study, the serpentinisation is more advanced, and rodingitic inclusions are frequent. These inclusions are probably formed from gabbros through calcic metasomatic processes which took place during the serpentinisation phase. Prehnite, hydrogarnet, clinopyroxene, actinote and chlorite are characteristic minerals in the rodingites.
Gabbro-diorites are the rarest rocks belonging to the ophiolitic suite and are found only in the southern part of the region.
Diabases (pillow lavas and dykes) and their associated rocks (particularly diabase breccias, locally devitrified hyaloclastites and tuffs) are extremely common. The dykes could be interpreted as the filling of fissures through which the submarine lavas reached the sea bottom.
Geological evidence seems to indicate that the volcanic activity took place in two main phases of Upper Cretaceous and Lower Eocene age. The sediments deposited after the first submarine volcanic phase are not fossiliferous, and thus their age remains unknown. However, the volcano-sedimantary complex is similarto other ophiolitic sequences of probable Upper Cretaceous age well known in other parts of Turkey.
The second phase of volcanic activity took probably place at the time of deposition of Lower Eocene sediments, transgressing on those deposited after the first volcanic phase. (...)</p
Étude géologique et pétrographique du complexe ophiolitique de la région située au sud-ouest de Malatya (Taurus Oriental, Turquie) et de sa couverture volcano-sédimentaire
No full textA geological and petrographical study has been made of the ophiolite complex and volcano-sedimentary cover of the eastern Taurus mountain belt NE of Malatya.
The paleozoic crystalline substratum of the ophiolite complex demonstrates paragenesis of the typical greenschist facies of the pelitic sequence. For the entire length of the region studied the basement is overthrust by an ophiolite mass. The latter forms a recumbent fold whose overturned limb fills a large portion of the map.
A younger volcano-sedimentary cover overlies the ophiolites with a transitional layer of volcanic breccias and agglomerates. The sedimentary series from bottom to top consists of red schists (argilites), greenschists containing more calcareous units, and finally a nummulitic limestone. Since the entire ophiolite volcano-sedimentary series lies in an inverted position, the latter occurs in thrust contact with the paleozoic basement.
In the Malatya region, thrusting in general has been southward in the southern part of the massif of Bitlis and northward in the northern part.
We propose the term "Lower Malatya Nappe" (Nappe de Malatya inférieure) for the abnormal superposition of the ophiolite complex and its volcano-sedimentary cover on the paleozoic substratum.
Lithologies of the ophiolitic sequence are described in separate chapters. Topics thus discussed include spilitic diabases, submarine lavas (sensu lato), pyroclastic products, albite syenites and various types of gabbros. The presence of epidote, pumpellyite and prehnite in these rocks is due to phenonena of deuteric alteration posterior to their emplacement.
Some examples of chemical reactions which are characteristic of both the deuteric late-magmatic processes and metamorphic processes are discussed in the chapter on metamorphism. Each of these reactions results in paragenesis of spilitic nature.
All of the units, from picritic basalt and olivine basalt to dacite and rhyolite, do not result from a "normal" magmatic evolution. Such a magmatic evolution probably exists to a certain extent. However, late-magmatic differentiation by fractional crystallization "in situ" followed by hydrothermal phases must have played a very important role. This would explain the great chemical diversity observed in these ophiolites.
The spilito-keratophyric series of Malatya is considered to represent the last products of differentiation of a tholeiitic magma of calcic-pacific type rich in aluminium and silica. The chemical composition of these ophiolites is analogous to that of many midocean ridge lavas.Ce travail est consacré à l'étude géologique et pétrographique d'un complexe ophiolitique et de sa couverture volcano-sédimentaire. Cet ensemble affleure dans la partie orientale de la chaine du Taurus au NE de Malatya.
Le substratum cristallophyllien paléozoïque de ce complexe ophiolitique montre des paragenèses du faciès schiste vert typiques de la séquence pélitique. Sur toute l'étendue de la région étudiée, ce soubassement est chevauché par le complexe ophiolitique. Ce dernier, en position renversée, forme un pli couché dont le flanc inverse occupe la plus grande partie de la carte.
La couverture volcano-sédimentaire, plus jeune, surmonte les roches ophiolitiques par l'intermédiaire d'un niveau formé de brèches volcaniques et d'agglomérats. La série stratigraphique de cette couverture est constituée, de bas en haut, par des schistes rouges (argilites), des schistes verts passant graduellement à des niveaux plus calcaires et, en dernier lieu, par un calcaire nummulitique. Cette série, également en position renversée, apparaît donc en contact avec le substratum paléozoïque.
Dans la région de Malatya, les charriages se sont faits, en général, vers le sud dans la partie méridionale du massif de Bitlis et vers le nord dans la partie septentrionale de ce dernier.
Nous proposons l'emploi du terme "Nappe de Malatya inférieure" pour désigner la superposition anormale du complexe ophiolitique et de sa couverture volcano-sédimentaire sur le substratum paléozoïque.
Plusieurs chapitres sont consacrés à l'étude des roches du cortège ophiolitique; mentionnons parmi les plus caractéristiques : les Diabases spilitiques, les laves sous-marines (sensu lato), les produits pyroclastiques, les syénites à albite et divers types de gabbros. La présence, dans ces roches d'épidote, de pumpellyite et de préhnite est due à des phénomènes d'altération deutérique postérieurs à leur mise en place.
Quelques exemples de réactions chimiques caractérisant aussi bien des processus deutériques tardimagmatiques que métamorphiques sont mentionnés dans le chapitre consacré au métamorphisme. Ces réactions, les unes et les autres, aboutissent à des paragenèses de nature spilitique.
Tous les termes allant du basalte picritique et du basalte à olivine aux dacites et rhyolites ne semblent pas résulter d'une évolution magmatique simple. Une telle évolution existe vraisemblablement dans une certaine mesure; cependant une différenciation par cristallisation fractionnée tardi-magmatique "in situ" se poursuivant par des phases hydrothermales doit avoir joué un rôle très important. Cela permettrait d'expliquer la grande diversité de compositions chimiques observées.
La série spilito-kératophyrique de Malatya est considérée comme représentant probablement les derniers produits de différenciation d'un magma tholéiitique de caractère pacifique calcique à tendance alumineuse et relativement riche en silice. Le chimisme de ces ophiolites est analogue à celui de certaines laves des crêtes médio-océanique.</p
Petrology of the Precambrian Crystalline and Associated Paleozoic Rocks of the Monroe Area, Hudson Highlands, New York, United States of America
No full textLa région étudiée dans ce travail couvre la feuille topographique entière au 1:25.000e de Monroe, dans l'état de New York, (Etats-Unis). Elle est située au sud-est de l'état de New York dans les Hudson Highlands du Reading Prong, à peu près 65 km au NW et 10 km à l'ouest du fleuve Hudson. Les roches cristallophylliennes précambriennes, fortement métamorphisées couvrent presque la moitié de la région de Monroe. Dans l'autre moitié se trouvent les roches sédimentaires paléozoiques (Cambrien Inférieur au Dénovien Moyen), relativement peu métamorphisées. Les dykes lamprophyriques abondent ils occupent les diaclases de tension de direction NW. Les lamprophyres coupent les roches précambriennes, cambriennes, et cambro-ordoviciennes mais pas les roches les plus jeunes. Une date radiométrique de 398 ma (méthode K40 -A40) obtenue sur l'amphibole kaersutite, qui forme les pheno-cristaux d'une lamprophyre, est légèrement trop jeune par rapport aux observations de terrain.
Les roches précambriennes se divisent en trois séries stratigaphiques. Du plus vieux au plus jeune ce sont 1) gneiss à cordiérite-sillimanite-almandine-biotite-feldspath-quartz, leptynite à grenat, et gneiss à biotite et mésoperthite: ceux-ci ont pour origine présumée des argiles marines et des grauwackes ou des tufs zéolitisés; 2) amphibolite, pyribolite, gneiss à biotite-hypersthène-quartz-antiperthite (enderbite), et gneiss à calc-silicate: ceux-ci ont pour origine présumée des roches volcaniques (basaltes et dacites) intercalées avec des grès calcaires et des marnes; et 3) gneiss granitique à ferrohastingsite ayant pour origine présumée une série épaisse de roches volcaniques rhyolitiques.
Il y a 1150 ma, cet ensemble eugeosynclinal de roche pélitiques, siliceuses, et volcaniques a été complètement recristallisé et en partie refondu lorsque la région a subi un métamorphisme de faciès à granulite à hornblende. Les températures et les pressions pendant cet événement étaient d'à peu près 700° - 800°C et 4 - 2 kb, avec la pression de l'eau inférieure à la pression environnante (PH2O < PS). Beaucoup de ces roches ont été migmatisées par l'anatexie partielle. Les effets des diaphtorèses paléozoiques dans cette région sont faibles et apparemment les assemblages métamorphiques se sont formées pendant une seule orogenèse précambrienne.
Plusieurs réactions ont pu produire ces assemblages.
Dans les roches pélitiques ayant un excès de quartz, la sillimanite et l'orthose se forment aux dépens de la muscovite, et, en plus, la cordiérite et l'orthose peuvent se former aux dépens de la sillimanite et de la biotite.
Les gneiss charnockitiques se sont formés de deux façons différentes: 1) La charnockite, sensu stricto, s'est formée de la décomposition de la biotite à fer ferreux en présence du quartz pour produire l'hypersthène et l'orthose. 2) L'enderbite et les granulites à pyroxènes (les charnockites intermédiaires et basiques) se sont formées de la décomposition de la hornblende en présence du plagioclase pour produire l'hypersthène, l'augite, et un plagioclase plus calcique.
(...)The area covered by this report is the entire 1:25,000 scale topographic map of the Monroe quadrangle of New York state, U.S.A. It is located in southeastern New York in the Hudson Highlands of the Reading Prong, about 65 km NW of New York City and about 10 km west of the Hudson River. Strongly metamorphosed Precambrian crystalline rocks underlie about one-half of the Monroe quadrangle. The other half is underlain by relatively unmetamorphosed Paleozoic sedimentary rocks of Lower Cambrian to Medial Devonian age. Lamprophyre dikes are abundant and occupy northwest-trending tension joints. The dikes intrude Precambrian, Cambrian, and Cambro-Ordovician strata but not the younger rocks. A radiometric K40 -A40 age of 398 M.Y. obtained on the amphibole, kaersutite, which forms phenocrysts in a lamprophyre, is slightly younger than that indicated by field geologic relations.
The Precambrian rocks are divided into three stratigraphic sequences. From oldest to youngest, these are 1) cordierite-sillimanite-biotite-almandine-feldspar-quartz gneiss, garnet leucogneiss, and biotite-mesoperthite gneiss, believed to have originated from marine shales and zeolitized graywackers or truffs; 2) amphibolite, pyribolite, biotite-hypersthene-quartz-antiperthite gneiss(enderbite), and calc-silicate gneiss, believed to be derived from basaltic and dacitic volcanic intercalated with calcareous quartzite and marlstone; and 3) ferrohastingsite granite gneiss believed to have originated from the metamorphism of a thick pile of rhyolitic volcanic rocks.
About 1150 M.Y. ago, this eugeosynclinal assemblage of pelitic, siliceous, and volcanic rocks was completely recrystallized and partly melted when the region underwent hornblende granulite facies metamorphism. Tempratures and pressures during this event were on the order of 700° - 800°C and 4 - 2 kb, with water pressure lower than load pressure (PH2O < PS). Many of these rocks were migmatized as a result of partial anatexis. The effects of Paleozoic retrograding are minimal, and it appears that the metamorphic assemblages are the result of one Precambrian orogeny.
Several reactions which may have produced these assemblages are as follows:
In pelitic rocks with an excess of quartz, sillimanite andorthoclase formed at the expense of muscovite, and, in addition, cordierite and orthoclase formed at the expense of sillimanite and biotite.
(...)</p
Étude micropaléontologique du Dogger du Jura méridional (France)
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Beobachtung ultravioletter Sternspektren mit Hilfe einer Stratosphaerengondel
No full textVon einer mit Hilfe des Erdmagnetfeldes stabilisierten Stratosphärengondel aus wurden die Ultraviolettspektren von mehreren heissen Sternen des ORION Sternbildes photographiert. Das Beobachtungsinstrument ist ein Schmidtteleskop, welches mit einem schwach auflôsenden Objektivprisma versehen ist. Die grundsätzlichen Bedingungen für die Wahl dieses Teleskops werden beschrieben. Probleme der Eichung im nahen Ultraviolett werden behandelt. Für die Zuordnung der Wellenlängen zu einem prismenerzeugten Spektrum wird eine Lôsung angegeben. In einem letzten Kapitel wird die Auswertung der Spektren diskutiert und als erstes astrophysikalisches Resultat ein Gesetz über die interstellare Absorption präsentiert