Search results for "rock"
showing 10 items of 1160 documents
An analytical model of heat transfer and fluid dynamic performances of an unconventional NTR engine for manned interplanetary missions
2009
Abstract An analytical model of fluid flow and heat transfer of a Nuclear Thermal Rocket (NTR) engine concept is presented. The engine is based on the direct conversion of the kinetic energy of the fission fragments (FFs) into the propellant enthalpy. The FFs can escape from an extremely thin layer of fissionable material: a sufficiently large surface coated with few micrometers of Americium 242m, confined by a neutron moderator–reflector, may become a critical reactor. Three dimensional coupled CFD-Monte Carlo simulations have already been presented in Di Piazza and Mulas (2006) . In this paper, an analytical integral 1-D model of fluid dynamics and heat transfer is built in order to fores…
Geochronology of the medium to high-grade metamorphic units of the Peloritani Mts., Sicily
2003
The Peloritani Mountains are a fragment of an orogen variably attributed to the Alpine or Hercynian orogeny. On the basis of 39 Ar- 40 Ar, U-Pb and Rb-Sr dating, the main metamorphism of the two medium-high grade metamorphic units, the Mela and Aspromonte Units, and most of the thrusting responsible for stacking the orogenic edifice are seen to be Hercynian. The main thrusting of the Aspromonte Unit over the lower grade units took place at 301€2 Ma. Brittle deformation during Tertiary reactivation of Hercynian thrust planes did not generate any rejuvenation of white micas in the studied sector. Our dataset shows a great complexity and we propose to unravel it by considering different levels…
Modeling of retrograde diffusion zoning in garnet: evidence for slow cooling of granulites from the Highland Complex of Sri Lanka
2003
¶Diffusion modeling of zoning profiles in garnet rims from mafic granulites is used to estimate cooling rates in the Proterozoic basement of Sri Lanka, which represents a small, but important fragment of the Gondwana super-continent. Metamorphic peak temperatures and pressures, estimated with two-pyroxene thermometry and garnet–clinopyroxene–plagioclase–quartz (GADS) barometry, yield 875±20 °C and 9.0±0.1 kbar. These peak metamorphic conditions are slightly higher than results obtained by garnet-biotite Fe–Mg exchange thermometry of 820±20 °C. Reset flat zoning profiles were observed in most garnets. Only narrow garnet rims touching biotite exhibit retrograde zoning in terms of Fe and Mg ex…
TeV particle direct detection in space - Recent results from the DAMPE mission
2019
Since its successful launch to a Low Earth Orbit in December 2015, the DAMPE (DArk Matter Particle Explorer) satellite mission has been preforming excellently, which allows the experiment to collect a large high quality data sample of high energy cosmic rays directly in space. With a relatively large acceptance, a thick BGO homogeneous calorimeter, and a precise silicon tracker, DAMPE is designed to measure multi-TeV particles in space with unprecedented precision. A first measurement of electron plus positron total flux up to 4.6 TeV based on the first 18 months of data has been published. Other results, including proton and Helium fluxes up to 100 TeV/nucleon, are becoming available. In t…
A Mineralogical, Chemical and Isotopic Investigation of Shales from the Barberton Greenstone Belt, South Africa, To Constrain Source Materials and Po…
2015
Major, trace and rare-earth elements were determined, together with their Rb-Sr, Sm-Nd and Pb-Pb isotopic systems, on shales from the ~3.5 to 3.1 Ga old Barberton Greenstone Belt in South Africa, to constrain their source materials and post-depositional evolution, on the basis of successive potential alteration impacts. A progressive change in the chemical composition has been identified from a dominant ultramafic-mafic (such as a komatiite end-member) source for the Fig Tree Group to a progressively felsic-plutonic (such as a granite end-member) provenance for the Moodies Group. The SiO 2 , K 2 O, U, Rb, Ba, and Sr contents, and the Zr/Y ratio increase upwards the stratigraphy, while the M…
Sinistral transport along the Trans-European Suture Zone: detrital zircon–rutile geochronology and sandstone petrography from the Carboniferous flysc…
2010
AbstractThe Lower Carboniferous flysch of the Istanbul Zone in Turkey is an over 1500 m thick turbiditic sandstone–shale sequence marking the onset of the Variscan deformation in the Pontides. It overlies Lower Carboniferous black cherts and is unconformably overlain by Lower Triassic continental sandstones and conglomerates. The petrography of the Carboniferous sandstones and the geochronology and geochemistry of the detrital zircons and rutiles were studied to establish the provenance of the clastic rocks. The sandstones are feldspathic to lithic greywackes and subgreywackes with approximately equal amounts of quartz, feldspar and lithic clasts. The amount of quartz and lithic fragments d…
40Ar/39Ar laser probe dating of detrital white micas from Cretaceous sedimentary rocks of the Eastern Alps: Evidence for Variscan high-pressure metam…
1997
The detritus of Cretaceous synorogenic sandstones of the northern margin of the Austroalpine microplate contains evidence for a high-pressure metamorphic basement and obducted oceanic crust exposed in early Alpine time. 40 Ar/ 39 Ar laser-probe data of detrital white micas give excellent plateau ages in a narrow range from 320 to 360 Ma. White micas cover the whole range from muscovites up to phengites (3.04 to 3.48 Si per formula unit). Heavy mineral spectra contain chrome spinel, glaucophane, chloritoid, epidote, and garnet, as well as zircon, tourmaline, and rutile. Glaucophane, chloritoid, and phengite correlate in their abundance. These minerals also correlate positively with the stabl…
Indo-Antarctic derived detritus on the northern margin of Gondwana: evidence for continental-scale sediment transport
2013
Provenance studies from Cambro-Ordovician sediments of the North Gondwana passive margin typically ascribe a North African source, a conclusion that cannot be reconciled with all observations. We present new U-Pb ages from detrital rutile and zircon from Late Ordovician sediments from Saxo-Thuringia, Germany. Detrital zircons yield age populations of 500–800 Ma, 900–1050 Ma and 1800–2600 Ma. The detrital rutile age spectra are unimodal with ages between 500 and 650 Ma and likely represent, together with the 500–800 Ma and 1800–2600 Ma zircon populations, detritus sourced predominantly from North Africa. In contrast, the c. 950 Ma zircons, which are persistently found in Cambro-Ordovician se…
Rutile chemistry and thermometry as provenance indicator: An example from Chios Island, Greece
2008
Abstract In the present study we focused on detrital rutile separated from 12 psammitic samples that belong to three different sedimentary successions (Carboniferous, Permo-Carboniferous, Permo-Triassic) occurring on Chios Island, Greece. The Ti, Cr, Al, Fe, Nb, Zr, Si, and V contents of the rutiles were obtained by electron-microprobe analyses to trace their provenance. The Cr and Nb concentrations of the analysed rutile grains show a wide range and indicate that this mineral in the Carboniferous succession is mainly derived from metamafic rocks, whereas in the Permo-Carboniferous and Permo-Triassic successions stem from a metapelitic source. The calculated formation temperatures using the…
Mise en évidence de corps d'origine cosmique probable au sein de la formation de Carnot (République Centrafricaine)
1992
Resume Deux etudes realisees independamment l'une de l'autre, ont permis de mettre en evidence, au sein de la Formation de Carnot, formation fluviatile mesozoique, d'une part des spherules magnetiques recuperees dans les residus d'un forage (zone de Boyali), d'autre part une anomalie magnetique tres localisee (sur 270 metres de long) traduisant la presence d'un corps decametrique a forte magnetisation remanente (zone de Gambondo). Ces deux elements magnetiques ont une origine cosmique probable. Ils correspondent a des micrometeorites et a une meteorite ayant atteint l'ouest de la Republique Centrafricaine entre l'Albien et le Maastrichtien.