Dar Al Gani 319 (DaG 319) meteorite, Dar al Gani, Jufra District, Libyai

Regional Level Types
Dar Al Gani 319 (DaG 319) meteorite	Meteorite Fall Location
Dar al Gani	- not defined -
Jufra District	District
Libya	Country

Ureilite (polymict breccia, W2)
Find, 1997; 740 g, 3 pieces

The Dar al Gani 319 (DaG 319) is a unusually diverse polymict ureilite with a variety of lithic aggregates and clasts. [Polymict meteorites possess two or more distinct lithologies — usually, but not always, derived from separate regions of their original parent body.] Several of the lithic varieties found in DaG 319 are known from other ureilites, but others may represent foreign inclusions brought to this particular meteorite by collision and happenstance. Most ureilite clasts are olivine-pigeonite clasts similar to those found in most normal ureilites, while other augite-bearing clasts and Mg-rich olivine-rich clasts are similar in texture and composition to those found in only a small minority of ureilites. However, while most of the aggregates and clasts are derived from ureilites and other achondritic objects, a number of these tiny grains are of chondritic origins. Some of the more exotic enstatite-, phosphide-, and silicide-bearing clasts are reminiscence of the very reduced enstatite-rich mineral assemblages found in aubrites and enstatite chondrites. Other grains contain phases (phyllosilicates, carbonates, magnetite, pentlandite, pyrrhotite) which have experienced at least some hydrous activity in preterrestrial environments geochemically similar to those found in carbonaceous chondrites. Dark regions may be dark from carbon-bearing phases and/or minute grains of magnetite. Small, but ubiquitous grains of Fe-rich metal, frequently associated with sulfides, are also quite diverse. Small grains of ordinary kamacite and taenite are found, but some very unusual iron contains ~10 wt% silicon. In addition, terrestrial weathering has produced limonite and calcite veins which may further complicate the interpretation of the very small chondrules, fragments, and isolated grains.

After Hiroi and his various colleagues described the petrography and mineralogy of DaG 319 in several reports around 2000 [Cf. references below], subsequent work has tried to account for the origin of Dag 319's various complexities. Chronometric studies using different isotopes all suggest that the primary meteorite constituents were assembled very early in solar system history — less than 5 Ma after formation of the earliest CAI condensates. The suggestion has been made that Dag 319 may contain primitive ureilite 'building blocks' which were later incorporated into the less diverse and more equilibrated, more normal ureilites within our collections. Many meteoriticists would like to believe that the ureilites in our collection have been derived from a single parent body. This may yet prove to be the case, but the issue is not settled. The contradictory implications of cumulate olivine-pyroxene textures suggest a moderately large ureilite parent body (UPB) but the range and pattern of oxygen isotopes and the textures produced by carbon-abetted reduction seem to require the later mixing of separate, smaller nebular reservoirs involving several ureilite bodies (UPBs). The primary features of ureilites may be derived from a nebular epoch when the supposed ureilite parent body/bodies had not achieved the singular identities presupposed in many ureilite discussions.

As of mid-July 2015, no ureilite falls and only 6.5 % of the total ureilite population (26 of 400) have been classified as polymict ureilites. Indeed only 1 of the 38 ureilites with mass ≥ 1 kg is classified as polymict. So we can probably expect that polymict ureilites with moderate mass such as North Haig (964 g) and Dag 319 (740 g) will continue to be objects of research.

References

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