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Six C1 chondrite samples and a C2 xenolith from the Plainview H5 chondrite were analyzed by radiochemical neutron activation for the elements Ag, Au, Bi, Br, Cd, Ce, Cs, Eu, Ge, In, Ir, Lu, Nd, Ni, Os, Pd, Pt, Rb, Re, Sb, Se, Sn, Tb, Te, Tl, Yb, and Zn. The data were combined with 9 earlier analyses from this laboratory and examined for evidence of chemical fractionation in C1 chondrites.A number of elements (Br, Rb, Cs, Au, Re, Os, Ni, Pd, Sb, Bi, In, Te) show small but correlated variations. Those of the first 8 probably reflect hydrothermal alteration in the meteorite parent body, whereas those of Sb, Bi, In, and Te may at least in part involve nebular processes. Br and Au show systematic abundance differences from meteorite to meteorite, which suggests hydrothermal transport on a kilometer scale. The remaining elements vary from sample to sample, suggesting transport on a centimeter scale.There is no conclusive evidence for nebular fractionation affecting C1 's. Though C1 chondrites have lower and ratios than do other chondrite classes, these ratios vary in other classes, suggesting that those classes rather than C1's are fractionated. Three fractionation-prone REE—Ce, Eu, and Yb have essentially the same relative abundances in C1's and all other chondrite classes, and hence apparently are not fractionated in C1's. We did not confirm the large Tb and Yb variations in C1's reported by other workers.We present revised mean C1 abundances for 35 elements, based on the new data and a critical selection of literature data. Changes are generally less than 10%, except for Br, Rb, Ag, Sb, Te, Au, and the REE.The Plainview C2 xenolith has normal trace element abundances, except for 3 elements falling appreciably above the C2 range: Rb, Cs, and Bi. Hydrothermal alteration may be the reason for all 3, though nebular fractionation remains a possibility for Bi. 相似文献
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This study is concerned with the influence of the glacial-isostatic adjustment caused by the last Pleistocene deglaciation
on the present-day sea level. The viscoelastic deformation caused by the time-variable ice and ocean loads is simulated by
computing the resulting perturbations for a spherical, self-gravitating, incompressible, Maxwell-viscoelastic earth model.
The associated variation of the earth rotation is described in terms of the Liouville equation, which is solved by means of
the MacCullagh formulae. This allows the determination of the vertical displacement and geoid height and, thus, the solution
of the sea-level equation. We test several viscosity and ice models and evaluate them by comparison of the computed response
with the Holocene relative sea-level record. Using the optimum combination of viscosity and ice models, we then estimate the
influence of the last Pleistocene deglaciation on the tide-gauge measurements. A comparison between the observational and
residual linear trends for the tide-gauge measurements shows a significant reduction of the variance and geographical variability
for the latter, in particular for the formerly ice-covered regions of North America and Scandinavia. The favoured value determined
for the global mean sea-level rise is (1.46±0.2) mm a−1. 相似文献
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Helmut Wolf 《Journal of Geodesy》1963,37(2):149-163
Ohne Zusammenfassung
Communication présentée à l'Assemblée générale de l'Association Internationale de Géodésie (Helsinki 1960). 相似文献
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