Highly siderophile elements in ureilites Rankenburg, K.; Humayun, M.; Brandon, A.D. ...
Geochimica et cosmochimica acta,
09/2008, Letnik:
72, Številka:
18
Journal Article
Recenzirano
The abundances of the highly siderophile elements (HSE) Ru, Pd, Re, Os, Ir, and Pt were determined by isotope dilution mass spectrometry for 22 ureilite bulk rock samples, including monomict, ...augite-bearing, and polymict lithologies. This report adds significantly to the quantity of available Pt and Pd abundances in ureilites, as these elements were rarely determined in previous neutron activation studies. The CI-normalized HSE abundance patterns of all ureilites analyzed here except ALHA 81101 show marked depletions in the more volatile Pd, with CI chondrite-normalized Pd/Os ratios (excluding ALHA 81101) averaging 0.19
±
0.23 (2
σ). This value is too low to be directly derived from any known chondrite group. Instead, the HSE bulk rock abundances and HSE interelement ratios in ureilites can be understood as physical mixtures of two end member compositions. One component, best represented by sample ALHA 78019, is characterized by superchondritic abundances of refractory HSE (RHSE—Ru, Re, Os, Ir, and Pt), but subchondritic Pd/RHSE, and is consistent with residual metal after extraction of a S-bearing metallic partial melt from carbonaceous chondrite-like precursor materials. The other component, best represented by sample ALHA 81101, is RHSE-poor and has HSE abundances in chondritic proportions. The genesis of the second component is unclear. It could represent regions within the ureilite parent body (UPB), in which metallic phases were completely molten and partially drained, or it might represent chondritic contamination that was added during disruption and brecciation of the UPB. Removal of carbon-rich melts does not seem to play an important role in ureilite petrogenesis. Removal of such melts would quickly deplete the ureilite precursors in Re/Os and As/Au, which is inconsistent with measured osmium isotope abundances, and also with literature As/Au data for the ureilites. Removal of
26Al during silicate melting may have acted as a switch that turned off further metal extraction from ureilite source regions.
We report noble gas data (helium (He), neon (Ne), argon (Ar), krypton (Kr) and xenon (Xe)), nominal gas retention ages (K–Ar, U–Th–He) and cosmic ray exposure (CRE) ages for the ten howardites EET ...83376, EET 99408, LEW 85313, MET 00423, MET 96500, PCA 02066, PRA 04401, QUE 94200, QUE 97002, and SCO 06040, in research to better understand the regolith of the HED parent body – Vesta – through a combined petrological, compositional and noble gas study. Our main aim is to determine which howardites are truly regolithic – as defined by the presence of solar noble gas components (e.g. solar wind (SW), fractionated solar wind (FSW)) and/or by the presence of planetary components (e.g. Q, HL) associated with foreign clasts of carbonaceous chondrite material within the breccias.
Of our ten howardites, four (LEW 85313, MET 00423, PRA 04401 and SCO 06040) show evidence for a regolithic origin, with noble gas ratios indicating the presence of trapped components. Howardites PRA 04401 and SCO 06040 contain significant amounts of CM type carbonaceous chondrite material, and these samples are dominated by a planetary component similar to that observed in CM meteorites Murchison and Maribo. Overall, we find evidence for two regolithic groups with different release trends: (1) SW/FSW component dominated howardites (LEW 85313 and MET 00423), where SW/FSW is dominant at low temperature releases, and less pronounced at higher temperatures; (2) Planetary component dominated howardites (PRA 04401 and SCO 06040) that also contain SW/FSW – the planetary component is associated with incorporated carbonaceous chondrite material, and is dominant at the mid-temperature release. The remaining six howardites EET 83376, EET 99408, MET 96500, PCA 02066, QUE 94200, and QUE 97002, are dominated by cosmogenic noble gases, and are not considered regolithic.
Previous work by Warren et al. (2009) suggested that high siderophile element contents (specifically nickel (Ni)>300μg/g) were a regolith indicator for howardites, in addition to restricted Al2O3 contents (8–9wt.%) representing a eucrite/diogenite mixing ratio of 2:1 as indicative of an ancient well-mixed regolith. These parameters were based on five ‘gas-rich’ howardites. However, we find no obvious correlation between these parameters and SW/FSW or planetary noble gas content in our howardite samples. We conclude that howardite regolith parameters are not as simple as those defined by Warren et al. (2009), where three of the five howardites used contained foreign CM material, which may have caused a bias in their defined parameters. We conclude that sideophile abundances alone cannot be used to determine the regolithic nature of a sample: noble gas analysis remains a key parameter, where it is important to distinguish between planetary-dominated and SW-dominated regolithic howardites.
Silicic rocks occur in the uppermost units of the longest volcanic succession (~5000m thick) in the Binchuan area of the Permian Emeishan flood basalt province of SW China. They are predominantly ...rhyolites and to a lesser extent trachytes, both containing potassium feldspar megacrysts as the dominant phenocryst phase up to approximately 20mm in size. These megacrysts contain domains of albite arranged in vein-like networks, likely formed by post-magmatic alteration. Crystal size distributions (CSD) suggest that these megacrysts grew in a stable magmatic system, consistent with relatively uniform core-to-rim compositional (K2O: ~14–16wt%) and isotopic profiles 208Pb/206Pb ratios (~2.06–2.08±0.005). Both whole-rock trace elements and Pb isotope ratios of these silicic rocks are similar to the Emeishan basalts, suggesting a common source for both mafic and felsic units and a limited role of crustal melting in genesis of the felsic units. Major and trace element models further indicate that these rocks could not have formed exclusively by re-melting of old crust or solidified basaltic rock, but must have formed through crystal fractionation from the flood basalts or possibly partial melting of basaltic rock followed by fractional crystallization. K-feldspar-bearing rhyolites are also observed in the last stages of other large igneous provinces. We suggest that they represent final melt fractions and their appearance in the magmatic system coincides with waning of voluminous magmatic activities.
•K-feldspar megacrysts grow in static magma chamber.•K-feldspar megacrysts-bearing rhyolites have formed through crystal fractionation form the flood basalts or possibly partial melting of basaltic rock followed by fractional crystallization.•They represent final melt fractions and their appearance in the magmatic system coincides with waning of magmatic activities.
To present a case of conservatively managed calcific trochanteric bursitis and discuss differential diagnosis and treatment alternatives.
A 53-yr-old obese female presented with acute severe lateral ...hip and posterolateral thigh pain. Examination findings were consistent with trochanteric bursitis and radiographs demonstrated calcific infiltration of the trochanteric bursa.
An intensive 2-wk course of pulsed ultrasound, ice massage, interferential current and chiropractic lumbopelvic manipulation resulted in symptomatic relief, abolishment of palpatory tenderness and return of pain-free passive and resisted range of motion of the hip.
Trochanteric bursitis is a common cause of hip pain. A trial of conservative measures is warranted for this condition, even when calcinosis is present, before more invasive therapies are considered.
– We performed a battery of analyses on 17 samples of the Almahata Sitta meteorite, identifying three main lithologies and several minor ones present as clasts. The main lithologies are (1) a ...pyroxene‐dominated, very porous, highly reduced lithology, (2) a pyroxene‐dominated compact lithology, and (3) an olivine‐dominated compact lithology. Although it seems possible that all three lithologies grade smoothly into each other at the kg‐scale, at the g‐scale this is not apparent. The meteorite is a polymict ureilite, with some intriguing features including exceptionally variable porosity and pyroxene composition. Although augite is locally present in Almahata Sitta, it is a minor phase in most (but not all) samples we have observed. Low‐calcium pyroxene (<5 mole% wollastonite) is more abundant than compositionally defined pigeonite; however, we found that even the low‐Ca pyroxene in Almahata Sitta has the monoclinic pigeonite crystal structure, and thus is properly termed pigeonite. As the major pyroxene in Almahata Sitta is pigeonite, and the abundance of pigeonite is generally greater than that of olivine, this meteorite might be called a pigeonite‐olivine ureilite, rather than the conventional olivine‐pigeonite ureilite group. The wide variability of lithologies in Almahata Sitta reveals a complex history, including asteroidal igneous crystallization, impact disruption, reheating and partial vaporization, high‐temperature reduction and carbon burning, and re‐agglomeration.
We studied the degradation of MOCVD-grown InGaN LEDs on Si substrates under constant current stressing. Characterisations using Deep Level Transient Spectroscopy and Electron Energy Loss Spectroscopy ...on active areas showed that the stressing had generated defects that have trap states at 0.26eV below the conduction band edge (Ec – 0.26eV) and that correlated with the active area's lower nitrogen content as compared to unstressed samples. The combination of Current-Voltage, Electroluminescence, Cathodoluminescence, and device simulations indicate that an increase in the density of these defects is correlated with an increase in the non-radiative carrier recombination that causes degradation in light emission. Preventing formation of these defects will be critical for improving InGaN-on-silicon LED reliability.
•InGaN-on-Silicon LED degradation is associated with the formation of nitrogen vacancies in the active area.•Formations of nitrogen vacancies cause an increase in non-radiative carrier recombination that decreases the light emission.•Nitrogen vacancy density is low around threading dislocations, suggesting TDs might enhancing the defect formation rate.
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