Geology
Permanent URI for this community
Browse
Browsing Geology by Subject "Balaka"
Now showing 1 - 1 of 1
Results Per Page
Sort Options
Item Open Access A mineralogical and geochemical study of seven meteorites from Malawi, Namibia and Lesotho(University of the Free State, 2010-06) Lombard, Annegret; Tredoux, M; Schoch, A. E.English: Seven meteorites from Malawi, Namibia and Lesotho were studied using optical microscopy, scanning electron microscopy with energy dispersive X-ray spectrometry and electron microprobe analysis of mineral phases. Induced coupled plasma spectrometry and X-ray fluorescence techniques were used to obtain chemical information. The Thuathe meteorite from Lesotho is a H4 ordinary chondrite according to major element chemistry and mineralogy. The shock features were classified as S2/3 and the weathering grade as W0. It contains Sb sulphides, which had not been previously reported in any chondritic meteorite. Berthierite and stibnite was observed under the SEM and confirmed by electron microprobe analyses. The chondrite normalised REE pattern is relatively flat with no significant LREE/HREE variation. Very slight enrichment of Ta and U compared to H-group chondrites are noted. In this study the Machinga meteorite from Malawi is classified as an E6 ordinary chondrite according to major element chemistry and mineralogy, and the shock features were classified as S4, moderately shocked. Previously it had been classified as an L6 chondrite (Graham et al, 1984 and Koeberl et al, 1990). The rare earth element pattern is relatively flat with slight LREE/HREE variation from the norm. Slight enrichment of W, Pb and U is noted. The Balaka meteorite from Malawi is a L6 ordinary chondrite that is weakly shocked (S2). These classifications were done with major element chemistry as well as the mineralogy of the meteorite. The rare earth element pattern is flat with nearly no variation between LREE and HREE. The normalised trace element diagram mirrors the trends of the trace element diagram of the L-group chondrites with respect to ordinary chondrites. The Chisenga meteorite from Malawi is an IIIAB medium octahedrite according to chemistry and the bandwidth of kamacite (~1.5 mm) and taenite. Kamacite is the dominant Fe/Ni phase and Widmanstätten texture is prominent. The unreported specimens from Asab in Namibia prove to be L6 ordinary chondrites according to major element chemistry and mineralogy. The shock features are classified as moderately shocked (S4) and the weathering grade is W2. The rare earth element spectrum for the sample 1 from Asab shows enrichment of LREE. Enrichment of Ba, Sr, Th and U is shown in this sample. Sample 2 from Asab shows slight La enrichment compared to L-group chondrites. Enrichment in Ba, Sb, Sr and U is shown in the chondrite normalised trace element diagram. Sample 3 from Asab displays a flat chondrite normalised REE pattern with nearly no variation between LREE and HREE. Chemical variation in these meteorite samples in the chondrite normalised trace element diagram shows enrichment of Ba, Sb and Sr. The general trends of the diagrams are similar indicating that the three unknown specimens are of the same fall.