2,381 research outputs found
Geochemistry and preliminary Sr-Nd isotopic data on the Neoproterozoic granitoids from the Bantoum area, west Cameroon: evidence for a derivation from a Paleoproterozoic to Archaean crust
The Bantoum area in west Cameroon is composed of migmatitic gneisses associated with parallel strips of amphibolites,quartz-monzonites,biotite-granites, two-mica leucogranites and granitic dikes.Quartz-monzonites are metaluminous (A/CNK=0.8-0.9)I-type,biotite-granites are peraluminous (A/CNK=1.0-1.10)I-type, leucogranites are peraluminous (A/CNK=1.14)S-type granitoids.All are hyper-potassic rocks defining a calc-alkaline trend.Quartz-monzonites gave an Rb-Sr isochron age of 720+-61 Ma assumed to be a mixing age.The thermometry estimated from major elements and zircon saturation indicate that the biotite-granites crystallized from high temperature melts (812-866゜C) whereas leucogranites crystallized from low temperature melts (719-745゜C). The trace element distribution diagrams are characterized by an enrichment in LILE and LREE (5<La_N/Sm_N<17),with negative Nb,Ta,Sr and Ti anomalies. Model initial ^87Sr/^86 Sr ratios (620 Ma)are 0.707614-0.708363 for quartz-monzonites,0.711242-0.713784 for biotite-granites,and 0.715835 for leucogranites.They have highly negative ε_Nd (620 Ma)(-19~-11) and T_DM model ages ranging from 1.9 to 2.9 Ga. These geochemical and isotopic features imply that the granites are generated at different temperatures and from different crustal materials;they are the witnesses of the recycling of a Paleoproterozoic to Archean crust with minor inputs of juvenile magmas during the Pan-African orogeny. Chemical similarities between gneisses and some biotite-granites suggest that the partial melting of these gneisses may have contributed to the formation of granites
Continuum and line modelling of discs around young stars. I. 300000 disc models for Herschel/GASPS
We have combined the thermo-chemical disc code ProDiMo with the Monte Carlo
radiative transfer code MCFOST to calculate a grid of ~300000 circumstellar
disc models, systematically varying 11 stellar, disc and dust parameters
including the total disc mass, several disc shape parameters and the
dust-to-gas ratio. For each model, dust continuum and line radiative transfer
calculations are carried out for 29 far IR, sub-mm and mm lines of [OI], [CII],
12CO and o/p-H2O under 5 inclinations. The grid allows to study the influence
of the input parameters on the observables, to make statistical predictions for
different types of circumstellar discs, and to find systematic trends and
correlations between the parameters, the continuum fluxes, and the line fluxes.
The model grid, comprising the calculated disc temperatures and chemical
structures, the computed SEDs, line fluxes and profiles, will be used in
particular for the data interpretation of the Herschel open time key programme
GASPS. The calculated line fluxes show a strong dependence on the assumed UV
excess of the central star, and on the disc flaring. The fraction of models
predicting [OI] and [CII] fine-structure lines fluxes above Herschel/PACS and
Spica/SAFARI detection limits are calculated as function of disc mass. The
possibility of deriving the disc gas mass from line observations is discussed.Comment: accepted by MNRAS. 5 pages, 4 figures, 3 table
Photon momentum anisotropies from the late stages of relativistic heavy-ion collisions
The photon emission from the late stages of the dynamical evolution of
heavy-ion reactions at the highest RHIC and LHC energies is investigated. A
comparison between a calculation from hadronic rates from a fluid dynamic
evolution down to temperatures of 120 MeV and a full non-equilibrium hadronic
transport approach is performed. The photon yields are very similar in both
cases while the elliptic flow is slightly smaller in the non-equilibrium
scenario. This study is important, since it is crucial to apply the same
dynamical evolution model for hadronic and electromagnetic observables.Comment: 6 pages, 4 figures, accepted in PoS for Hard Probes 202
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