A mineralogical and geochemical study of seven meteorites from Malawi, Namibia and Lesotho
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Date
2010-06
Authors
Lombard, Annegret
Journal Title
Journal ISSN
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Publisher
University of the Free State
Abstract
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.
Afrikaans: Sewe meteoriete van Malawi, Namibië en Lesotho is bestudeer met behulp van optiese mikroskopie, skandeer elektron mikroskopie met energiedispersie X-straal spektrometrie en elektrone mikrosonde vir mineral fase analises. Induktief gekoppelde plasma spektrometrie en X-straal fluoressensie tegnieke is gebruik om chemiese inligting in te win vir die geochemiese interpretasie van die meteoriete. Die Thuathe meteoriet van Lesotho is ‘n H4 gewone chondriet soos bepaal met hoofelement chemise samestelling en mineralogy. Die skok-eienskappe is as S2/3 geklassifiseer en the ververings grad as W0. Dit bevat Sb sulfiedes, wat nooit voorheen beskryf is in enige chondritiese meteoriete nie. Berthieriet en stibniet is met behulp van die SEM opgespoor en met behulp van die elektrone mikrosonde geanaliseer. Die chondriet genormaliseerde SAE patroon is relatief plat met geen merkbare variasie in LSAE en HSAE. Effense verryking van Ta en U in vergelyking met H-groep chondriete kom voor. In hierdie studie is die Machinga meteoriet van Malawi geklassifiseer as ‘n E6 gewone chondriet met matige skok (S4), na aanleiding van hoofelement chemise samestelling en minerlogie. Vorige outeurs het dit as ‘n L6 chondriet geklassifiseer (Graham et al, 1984 en Koeberl et al, 1990). Die raar aard element patron is relatief plat met effense variasie van die LSAE/HSAE. Effense verryking van W, Pb en U is teenwoordig. Die Balaka meteorite van Malwi is ‘n L6 gewone chondriet met swak skok eienskappe (S2). Hierdie klassifikasies is met behulp van hoofelement chemiese samestelling asook mineralogie verkry. Die seldsame aard element patron is plat met feitlik geen variasie tussen die LSAE en HSAE. Die genormaliseerse spoorelement diagram vir die Balaka meteorite is ‘n spieëlbeeld van die van L-groep chondriete. Die Chisenga meteoriet van Malawi is ‘n tipe IIIAB medium oktahedriet na aanleiding van chemise samestelling en die bandwydte van kamasiet (~1.5 mm) en taeniet. Kamasiet is die dominante Fe/Ni fase en Widmanstätten tekstuur is prominent. ix Die drie onbekende voorbeelde vanaf Asab is L6 gewone chondriete na aanleiding van hoofelement chemise samestelling en mineralogie. Die skok-klassifikasie vir hierdie meteoriete is matig (S4) en die verwerings grad is W2. Die seldsame aard element patron vir monster 1 van Asab is verryk in LSAE. Ba, Sr, Th en U is verryk in hierdie monster. Monster 2 van Asab is effens verryk in La asook Ba, Sb, Sr en U. Die seldsame aard element patroon vir Monster 3 van Asab is plat met geen variasie tussen LSAE en HSAE. Ba, Sb en Sr is verryk in hierdie monster. Die algemene tendens van die diagramme is baie eenders wat aandui dat die monsters deel is van dieselfde gebeurtenis
Afrikaans: Sewe meteoriete van Malawi, Namibië en Lesotho is bestudeer met behulp van optiese mikroskopie, skandeer elektron mikroskopie met energiedispersie X-straal spektrometrie en elektrone mikrosonde vir mineral fase analises. Induktief gekoppelde plasma spektrometrie en X-straal fluoressensie tegnieke is gebruik om chemiese inligting in te win vir die geochemiese interpretasie van die meteoriete. Die Thuathe meteoriet van Lesotho is ‘n H4 gewone chondriet soos bepaal met hoofelement chemise samestelling en mineralogy. Die skok-eienskappe is as S2/3 geklassifiseer en the ververings grad as W0. Dit bevat Sb sulfiedes, wat nooit voorheen beskryf is in enige chondritiese meteoriete nie. Berthieriet en stibniet is met behulp van die SEM opgespoor en met behulp van die elektrone mikrosonde geanaliseer. Die chondriet genormaliseerde SAE patroon is relatief plat met geen merkbare variasie in LSAE en HSAE. Effense verryking van Ta en U in vergelyking met H-groep chondriete kom voor. In hierdie studie is die Machinga meteoriet van Malawi geklassifiseer as ‘n E6 gewone chondriet met matige skok (S4), na aanleiding van hoofelement chemise samestelling en minerlogie. Vorige outeurs het dit as ‘n L6 chondriet geklassifiseer (Graham et al, 1984 en Koeberl et al, 1990). Die raar aard element patron is relatief plat met effense variasie van die LSAE/HSAE. Effense verryking van W, Pb en U is teenwoordig. Die Balaka meteorite van Malwi is ‘n L6 gewone chondriet met swak skok eienskappe (S2). Hierdie klassifikasies is met behulp van hoofelement chemiese samestelling asook mineralogie verkry. Die seldsame aard element patron is plat met feitlik geen variasie tussen die LSAE en HSAE. Die genormaliseerse spoorelement diagram vir die Balaka meteorite is ‘n spieëlbeeld van die van L-groep chondriete. Die Chisenga meteoriet van Malawi is ‘n tipe IIIAB medium oktahedriet na aanleiding van chemise samestelling en die bandwydte van kamasiet (~1.5 mm) en taeniet. Kamasiet is die dominante Fe/Ni fase en Widmanstätten tekstuur is prominent. ix Die drie onbekende voorbeelde vanaf Asab is L6 gewone chondriete na aanleiding van hoofelement chemise samestelling en mineralogie. Die skok-klassifikasie vir hierdie meteoriete is matig (S4) en die verwerings grad is W2. Die seldsame aard element patron vir monster 1 van Asab is verryk in LSAE. Ba, Sr, Th en U is verryk in hierdie monster. Monster 2 van Asab is effens verryk in La asook Ba, Sb, Sr en U. Die seldsame aard element patroon vir Monster 3 van Asab is plat met geen variasie tussen LSAE en HSAE. Ba, Sb en Sr is verryk in hierdie monster. Die algemene tendens van die diagramme is baie eenders wat aandui dat die monsters deel is van dieselfde gebeurtenis
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Keywords
Chondrite, Mineralogy, Geochemistry, Classification, Thuathe, Machinga, Balaka, Chisenga, Asab, Chondrites (Meteorites), Meteorites--Classification, Electron microscoby, Dissertation (M.Sc. (Geology))--University of the Free State, 2010