摘要:

40Ar/39Ar incremental heating analyses were performed on phlogopite mica from the DK‐7 kimberlite pipe in southern Botswana. No age plateau was obtained, as the spectrum yielded a step‐wise increase in age with increasing temperature. The ages appear to be anomalously high, suggesting the presence of excess radiogenic argon components that have been partially released by diffusion during cooling of the kimberlite.The pattern of data points on an39Ar/40Ar vs.39Ar/40Ar correlation plot, however, delineates two types of excess argon, one which is radiogenic‐rich, and one with a40Ar/36Ar ratio of 366. The latter component may reflect the contamination of the kimberlite xenocrysts by fluid originating from an undegassed mantle s

ISSN:0094-8276    

DOI:10.1029/GL013i007p00689

年代:1986

数据来源: WILEY

摘要:

Rheological parameters for ice II and ice III, needed in tectonic models of the icy satellites of the major planets, are obtained from extrusion experiments and compared with the rheology of ice I at pressures ∼2 kbar and temperatures ∼240K. Ice II has a higher effective viscosity (by a factor ∼10) than ice I at similar stress levels, whereas ice III has a lower viscosity (by a factor ∼0.01). The Rheological contrasts among the ice phases are related to differences in the dielectric relaxation behavior and state of proton order/disorder in the structures in a way that sheds light on the nature of dislocation motion in ice. A striking transformation plasticity accompanies the ice I‐III transition and could have large tectoni

ISSN:0094-8276    

DOI:10.1029/GL013i007p00693

年代:1986

数据来源: WILEY

摘要:

A comparison is made between GEOS‐3 and SEASAT altimeter data with regard to noise power spectral density (PSD), derived geoid PSD, and short wavelength resolution. At wavelengths greater than 450 km the noise PSDs for GEOS‐3 and SEASAT are essentially the same and are attributed to mesoscale oceanographic effects. At shorter wavelengths the noise spectra diverge because of the higher GEOS‐3 instrument noise. The average along‐track geoid PSDs are nearly identical between wavelengths of 4500 and 72 km. The spectral coherence between repeat tracks shows that the short wavelength resolution of SEASAT data is ≈32 km, and for GEOS‐3 i

ISSN:0094-8276    

DOI:10.1029/GL013i007p00697

年代:1986

数据来源: WILEY

摘要:

It is unlikely that the dust mantles of small comets (cometary mass ∼105kg, earth impact rate ∼20 per minute) suppress the evaporation of gases into the solar wind. An order‐of‐magnitude argument based on comet sizes, densities, and meteoritic dust influx indicate a maximum thickness for the mantles of ∼200µm. A much more reasonable estimate gives a thickness of ∼0.2µm. The mantles must be considered too thin to prevent the enrichment of the solar wind b

ISSN:0094-8276    

DOI:10.1029/GL013i007p00701

年代:1986

数据来源: WILEY

ISSN:0094-8276    

DOI:10.1029/GL013i007p00703

年代:1986

数据来源: WILEY