摘要:

This article summarizes information relevant to the interpretation of Lukanga Swamp — a depression some 52 km in diameter in central Zambia — as a considerably eroded astrobleme. The results of reconnaissance geological mapping, an airborne magnetic survey and petrological study of a small set of samples of impact rocks are presented. Circular topographic features coincide with a remarkably subdued magnetic field. A circular set of tangential faults indicates a diameter of the outer rim approximately 110 km. Polymict breccia occur, carrying marble megaclasts (klippes) up to 50 m long. Strongly shocked quartz clasts with several sets of decorated planar features are present as well as devitrified, flow‐banded silica glass exhibiting decarbonation textures around marble clasts. Provisional correlation of the brecciation event with the local geological record suggests a Paleozoic age of the astro

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1985.tb00852.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Separated fractions from the Mayo Belwa aubrite have been analysed for the rare earth elements (REE). The data show no ytterbium anomalies but the feldspar and magnetic fractions show complementary europium anomalies. The separated phases together account for the total REE abundances in the bulk meteorite which are about 0.5 times chondritic. The REE content of the feldspar is greater than that of the bulk meteorite. The partition coefficients for the REE between feldspar and orthopyroxene are about 10 times (in favour of the feldspar) those of the nearest equivalent terrestrial feldspar/orthopyroxene pairs, implying that the distribution of the REE which would result from equilibrium co‐crystallisation from a single liquid has been disturbed by a later event. This occurred more recently than 4.33 b.y. ago and resulted in a redistribution of the REE between the feldspar and a REE enriched residue. However, the REE patterns of the minerals are very like those of terrestrial equivalents and appear to be the result of igneous cumulus processes on a parent body rather than condensation of dust from a nebular ga

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1985.tb00853.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1985.tb00854.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1985.tb00855.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1985.tb00858.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY