Reflectance spectrophotometry extended to u.v. for terrestrial,lunar and meteoritic samples

Extension of remote sensing of planetary bodies to the ultraviolet is now feasiable up to 2000 Å from earth-orbiting telescopes and spacecraft. The benefits of this extension is analysed on the basis of laboratory spectra taken on a large variety of terrestrial, lunar and meteoritic samples. Knowledge of the albedo for two wavelengths at 2300 and 6500 Å permits classification of a surface into one of the following types: lunar, carbonaceous chondrites, ordinary chondrites, achondrites or acidic rocks, basaltic rocks, irons. For lunar-type surfaces, a simple albedo measurement at 6500 Å can be converted into quantitative abundance determinations of silicate, aluminium oxide and iron; a large amount of telescopic lunar photometry data is available for mapping these abundances. Extension of the photometry to 2300 Å permits quantitative measurement of TiO₂ abundances. For asteroids and non-icy satellites, rock-type classification and constraints in chemical abundances of Si, Al, Fe and Ti can be derived from photometry at 2300 and 6500 Å. The IUE telescope already orbiting the earth, the Space Telescope to come, the lunar polar orbiter and other spacecraft under prospect are potentially available to provide the photometric observations at 6500 and 2300 Å required.     

Variación secular geomagnética en Sudamérica y alrededores con relación a todo el Hemisferio Sur

Resumen Se aplica el análisis de energía de espectro a los datos de la variación secular geomagnética para tres observatorios del Hemisferio Sur: Pilar, Amberley, Mauritius. Las figuras 2–10 indican generalmente tres tipos de picos: a) de periodos de menos de 10 años; b) del periodo aproximado de la actividad solar de 10–11 años; c) de una fluctuación de 40–60 años. Los coeficientes de la expansión esférico-armónica de la variación secular muestran también una fluctuación del último tipo.

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Summary The power spectrum analysis is applied to geomagnetic secular variation data of three southern magnetic observatories: Pilar, Amberley, Mauritius. The figures 2–10 indicate in general three types of peaks: a) of periods less than 10 years; b) of approximately solar activity cycle; c) of 40–60 years fluctuation. Also the coefficients of spherical harmonic expansion of SV show the last type fluctuation.

     

Cloud processes associated with past and future climate changes

 To investigate the cloud response during cold and warm periods, we have performed simulations of the Last Glacial Maximum (LGM-21ky BP) and of double CO₂ concentration using the LMD AGCM model. We observe that the thermal characteristics of these two climates are opposite, but the cloud response is more complex and does not display the same symmetry When doubling the CO₂, the warming of the troposphere and the cooling of the stratosphere are clearly linked with a reduction in low-level clouds and an increase of high-level clouds associated with relative humidity changes. For the LGM, the cloud response is more complex. In the inter tropical region, we show that the Hadley cell is reinforced during LGM (+20%) whereas it is reduced (−10%) for the double CO₂ experiments. The most important feature is that we observe an enlarged Hadley cell for LGM climate which strongly modifies the atmospheric dynamics and water transport. For LGM conditions, the cloud response is then mostly driven by these dynamical changes at low latitudes though at high latitudes the thermal changes explain a large part of the cloud response. Two different versions of the model, using different parametrizations for the precipitation show that cloud feedbacks may act differently for cold and warm climates; and that the cloud response may be more complex that previously expected, but also indicate that the details of these effects are model dependent.     

白云鄂博REE-Nb-Fe矿床成因的氧、碳和锶同位素及微量元素地球化学证据

根据白云鄂博赋矿白云石大理岩的岩石学特征及地质产状将其分为两类：粗粒和细粒白云石大理岩．它们的氧、碳和锶同位素及微量元素地球化学特征显然有别于分布在宽沟背斜以北典型的沉积石灰岩和白云岩,而和幢源火成碳酸岩十分相似．与矿床进行对比研究说明,成矿流体和矿质主要起源于碳酸岩浆的分异作用,其放射性成因同位素和微量元素保持了地但指纹,而氧和碳同位素组成却向壳源方向漂移,证实碳酸岩浆侵位过程中受大陆地壳的混染作用非常微弱,但是由碳酸岩浆活动所引起的成矿热液体系中却有一定的地表水混人认为白云鄂博REE-Nb-Fe超大型矿床的成因应归属于火成碳酸岩型矿床．     

Low-degree partial melting trends recorded in upper mantle minerals

The study of glass inclusions inside mantle minerals provides direct information about the chemistry of naturally occurring mantle-derived melts and the fine-scale complexity of the melting process responsible for their genesis. Minerals in a spinel lherzolite nodule from Grande Comore island contain glass inclusions which, after homogenization by heating, exhibit a continuous suite of chemical compositions clearly distinct from that of the host basanitic lava. The compositions range from silicic, with nepheline–olivine normative, 64 wt% SiO₂ and 11 wt% alkali oxides, to almost basaltic, with quartz normative, 50 wt% SiO₂ and 1–2 wt% alkali oxides. Within a single mineral phase, olivine, the inferred primary melt composition varies from 54 to 64 wt% SiO₂ for MgO content ranging from 8 to 0.8 wt%. An experimental study of the glass and fluid inclusions indicates that trapped melts represent liquids that are in equilibrium with their host phases at moderate temperature and pressure (T≈1230°C and P≈1.0 Gpa for melts trapped in olivine). Quantitative modelling of the compositional trends defined in the suite shows that all of the glasses are part of a cogenetic set of melts formed by fractional melting of spinel lherzolite, with F varying between 0.2 and 5%. The initial highly silicic, alkali-rich melts preserved in Mg-rich olivine become richer in FeO, MgO, CaO and Cr₂O₃ and poorer in SiO₂, K₂O, Na₂O, Al₂O₃ and Cl with increasing melt fractions, evolving toward the basaltic melts found in clinopyroxene. These results confirm the connection between glass inclusions inside mantle minerals and partial mantle melts, and indicate that primary melts with SiO₂ >60 wt%, alkali oxides >11%, FeO <1 wt% and MgO <1 wt% are generated during incipient melting of spinel peridotite. The composition of the primary melts is inferred to be dependent on pressure, and to reflect both the speciation of dissolved CO₂ and the effect of alkali oxides on the silica activity coefficient in the melt. At pressures around 1 GPa, low-degree melts are characterized by alkali and silica-rich compositions, with a limited effect of dissolved CO₂ and a decreased silica activity coefficient caused by the presence of alkali oxides, whereas at higher pressures alkali oxides form complexes with carbonates and, consequently, alkali-rich silica-poor melts will be generated.     

Relations entre contraintes tectoniques et propriétés magnétiques des roches volcaniques permiennes de la vallée du Guil (briançonnais,Alpes Françaises)

Résumé Les roches volcaniques permiennes de la vallée du Guil présentent une ARN de direction voisine du plan de la schistosité alpine qui les affecte. Leur aimantation permienne a probablement été modifiée, lors de l'orogénèse alpine, par les efforts tectoniques (modification d'origine purement mécanique, ou acquisition d'une nouvelle aimantation par effet de pression). L'ARN des roches du Guil ne peut donc pas être prise en référence pour une étude géotectonique de l'arc alpin.

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Summary The Guil valley permian volcanic rocks have NRM whose direction is very near to the plane of alpine schistosity affecting these rocks. During the alpine orogeny, their permian magnetization was probably modified by tectonic stresses (mechanical modification, or new magnetization by piezo-magnetic effect). The NRM of the Guil valley rocks cannot be used as a reference for geotectonic study of the Alps.

     

The conditions for biodegradation of petroleum hydrocarbons at sea

The hydrocarbon degradation potential of seawater appears higher in zones chronically polluted by these materials; they are characterized by an abundant bacterial development. The salinity of the effluent from a refinery and also its hydrocarbon content are factors affecting the speed of degradation.     

Petrogenesis of garnet lherzolite, Cima di Gagnone, Lepontine Alps

Garnet lherzolite at Cima di Gagnone has chemical and mineralogical properties similar to those of other garnet lherzolites in the lower Pennine Adula/Cima Lunga Nappe (Alpe Arami, Monte Duria). The Cima di Gagnone occurrence encloses mafic boudins that belong to an eclogite-metarodingite suite common in the numerous neighboring ultramafic lenses. The ultramafic rocks at Cima di Gagnone, including the garnet lherzolite, are interpreted as tectonic fragments of an originally larger lherzolite body that underwent at least partial serpentinization prior to regional metamorphism. This lherzolite body cycled through at least three metamorphic facies: greenschist or blue-schist (as antigorite serpentinite) → eclogite (as garnet lherzolite), pre-Alpine or early Alpine → amphibolite facies (as chlorite-enstatite-tremolite peridotite), Lepontine metamorphism. Relics of titanoclinohumite in the garnet peridotite, as also recorded by Möckel near Alpe Arami, are consistent with this metamorphic history, since they indicate a possible connection with Pennine antigorite serpentinites, e.g., Liguria, Piedmont, Zermatt-Saas, Malenco, Pustertal, all of which have widespread titanoclinohumite belonging to the antigorite paragenesis. Estimated pressures in excess of 20 kbar and temperatures of 800°±50°C for the garnet lherzolite assemblage are not inconsistent with conditions inferred for Gagnone and Arami eclogites. These conditions could have been reached during deep subduction zone metamorphism. It is shown by calculation that the effects of Fe and Cr on the location of the garnet lherzolite/spinel lherzolite phase boundary largely counter-balance each other.     

The fit of the continents around the North Atlantic Ocean

A new reassembly of the continents around the North Atlantic Ocean is presented. The first criterion used for this reassembly is the identification of the structural framework related to the opening which consists of marginal fracture zones generated by offsets of the Rift. The Africa—North America, Eurasia—Greenland, Greenland—North America and Eurasia—North America adjustments are successively discussed. It is argued that the adjustments are best made at the 3000-meters isobath between Africa and North America and at the 2000-meters isobath for the younger rifts. The difference is attributed to subsidence and modification of continental margins with time. The importance of the Late Paleozoic tectonic phase in determining the subsequent pattern of Mesozoic rifting is emphasized.