Show simple item record

dc.creator
dc.date.accessioned2023-06-05T17:48:19Z
dc.date.available2023-06-05T17:48:19Z
dc.date.issuedn.d.
dc.identifier.urihttps://repository.tcu.edu/handle/116099117/58932
dc.descriptionNotes on three fragments found in the Libyan Desert and the Dar al Gani meteorites. From Dweir's Studies.
dc.relationOscar Monnig Papers (MS 124)
dc.rightsPrior written permission from TCU Special Collections required to use any document or photograph.
dc.sourceSeries III, Box 06, Dar al Gani meteorites folder
dc.subjectMeteorite
dc.subjectDar al Gani meteorites
dc.subjectLunar meteorite
dc.subjectAnorthositic breccia
dc.subjectChondrules
dc.subjectChondrite
dc.subjectDiamonds
dc.titleDar al Gani meteorites Found 1997 27º 01.68' N., 16º 21.52' E.
dc.typeDocument
dc.description.transcriptionThree fragments totaling 740 g were found in the Libyan Desert. Two other stones that were recovered later, DaG 665 (363 g) and DaG 874 (64.6 g), are possibly paired. Dar al Gani meteorites is one of only a handful of polymict members among a mostly monomict ureilite population. This particular meteorite has a brecciated structure and contains solar type rare gases, suggesting a surface residence on the ureilite parent body. Diamonds and many types of inclusions have been found in this meteorite. The diverse clasts have been categorized into seven groups: 1. ??coarse-grained mafic lithic clasts 2. ??fine-grained mafic lithic clasts 3. ??felsic lithic clasts and gabbroic class 4. ??dark clasts 5. ??sulfide or metal-rich lithic clasts 6. ??chondrule and chondrite fragments 7. ??isolated mineral clasts, mostly single crystals The main clast type present in polymict ureilites is the common Type I, monomict ureilite, containing mainly olivine, pigeonite, and carbon. Type I ureilites crystallized from the residues that remained after the extraction of a partial melt component, and probably represent mantle material. Type II ureilite clasts, which contain mainly olivine, augite, and orthopyroxene, with minor sulfide and metal, are present in lower abundance. Magmatic inclusions, usually containing a feldspathic glass component, are present in olivine and orthopyroxene grains of the Type II clasts. Type II ureilites are magmatic cumulates formed by fractional crystallization of basaltic magmas derived from alkali-rich chondritic precursor material. They crystallized within shallow magma chambers at high cooling rates. The abundant felsic clasts present in polymict ureilites are mainly composed of plagioclase and pyroxene phenocrysts in an alkali-rich groundmass. These clasts were formed through rapid fractional crystallization of felsic magmas reflecting 20-30% partial melting. They have an O-isotopic composition consistent with the missing basaltic component of the ureilite parent body, and may represent a primary igneous lithology. The crystallization age of one of these felsic clasts, determined by 53Mn-53Cr systematics, was found to be a very old 4,562.3 (=0.4) my. This age infers that the petrogenesis of the ureilite parent body occurred within ~ 10 m.y. of the formation of the solar system. The dark carbonaceous clasts have been linked to CI matrix material. Since the O-isotopic compositions of the chondrule and chondrite fragments are similar to those of ordinary and R chondrites, they likely represent impactors onto the ureilite parent body. The other clasts share a similar O-isotopic composition to the ureilites, indicating formation on a common parent body. Even though O-isotopic deviations among the various ureilite groups preclude them from being related by igneous processes, the heterogeneity of the polymict ureilites suggests there was a common parent body for all groups. The ureilite parent body was just large enough to reach partial melting temperatures, experiencing low degrees of basaltic melt migration. Due to this low degree of melting it has retained the chemical and isotopic heterogeneity of the original carbonaceous chondrite-like asteroid, represented by the dark class present in polymict ureilites. The parent body can be inferred to be intermediate in size between undifferentiated chondritic asteroids and those asteroids large enough to experience melting, differentiation, and core formation. The DaG 319 specimen shown above is a 5.7 g specimen, which has a weathering grade of W2, and has features reflecting low shock.


Files in this item

Thumbnail
This item appears in the following Collection(s)
  • Records of the Monnig Meteorite Gallery [2247]
    The files are arranged alphabetically, usually according to the location of discovery of the meteorite. The files contain correspondence and research material on the meteorites in the collection.

Show simple item record