Bilanga meteorite, Bilanga-Yanga, Gnagna Province, East Region, Burkina Faso
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|Latitude & Longitude (WGS84):||12° 27' North , 0° 5' West|
|Latitude & Longitude (decimal):||12.45000,-0.08333|
|Non-native locality type:||Meteorite|
|Meteorite Class:||Diogenite meteorite|
|Meteoritical Society Class:||Diogenite|
|Metbull:||View entry in Meteoritical Bulletin Database|
|Köppen climate type:||Aw : Tropical savanna, wet|
|Name(s) in local language(s):||, Est Région, République de Haute-Volta|
Diogenite, severely brecciated
Fell 27 Oct1999; 25 kg
A number of black stones covered with fresh fusion crusts were collected after a widely observed meteorite shower fell near the villages of Bilanga-Yanga and Gomponsago. The meteorite is one of only 11 witnessed diogenite falls recorded before 2014 and is the second most massive of all recovered diogenites. Like the great majority of diogenites, Bilanga is a plutonic pyroxenite compositionally dominated by orthopyroxene which crystallized well below (10-25 km??) the surface of its original parent body. Bilanga is somewhat unusual among diogenites as it contains significant amounts of accessory plagioclase (mostly bytownite), diopside, and silica which appear to have crystallized somewhat later than the predominant orthopyroxene. Bilanga is even more unusual because it is one of the most severely brecciated diogenites. Brecciation features include chemically related diogenite lithologies of varying grain size, partially recrystallized melt pockets, and some Si-,K-rich glass. It is also somewhat richer in its entourage of minor phases which have apparently crystallized in the interstices between the various assemblages and comminuted clasts which were partially reequilibrated and reassembled after brecciating events. Minor phases include K-Feldspar, Co-containing kamacite, tetrataenite, pentlandite, native copper, a light rare earth element-bearing phosphate, and several quench phases.
As an apparently 'geochemically normal' member of the HED Clan (Howardites-Eucrites-Diogenites) Bilanga may very well be a fragment of the asteroid 4 Vesta. However, more definitive work with O-isotope and Fe-Mn ratios and other geochemical and chronological markers is apparently needed before we can confidently declare which specific HED meteorites are fragments of Vesta and which are exceptions. O-isotope and Fe/Mn ratios clearly indicate that a few anomalous HED meteorites (e.g., Ibitira, Pasamonte) are from separate homeworlds, but definitive evidence for a putative 'main group' of HED meteorites derived only from Vesta is a work still in progress.
8 valid minerals.
Meteorite/Rock Types Recorded
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Grossman, J. N. & Zipfel, J. (2000). The Meteoritical Bulletin, No. 84, 2000 September. Meteoritics & Planetary Science 35, #9 (Suppl.): A199-A225. (Sept 2000).
Kolar, S. E., Domanik, K. J., Musslewhite, D. S. & Drake, M. J. (2002) Bilanga: A Unique Diogenite. Lunar and Planetary Science Conference XXXIII: pdf.1338 (Mar 2002)
Domanik, K. J., Shearer, C. K., Hagerty, J., Kolar, S. E. & Drake, M. J. (2003) Trace Elements in High-Ca Pyroxene & Plagioclase in the Bilanga Diogenite: Implications for the Magmatic Evolution of Diogenites. Annual Lunar and Planetary Science ConferenceXXXIV: abstract no.2042. (March 2003)
Domanik, K., Kolar, S., Musselwhite, D. & Drake, M. J. (2004) Accessory silicate mineral assemblages in the Bilanga diogenite: A petrographic study. Meteoritics & Planetary Science 39(4): 567-579. (April 2004)
Scott, E. R. D., Greenwood, R. C., Franchi, I. A. & Sanders, I. S. (2009) Oxygen isotopic constraints on the origin and parent bodies of eucrites, diogenites, and howardites. Geochimica et Cosmochimica Acta73 (19): 5835-5853. (Oct 2009)