DAR AL GANI 084


Ureilite
Monomict/Unbrecciated/Main Group
Olivine–pigeonite

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Found 1995
27° 02.44' N., 16° 24.26' E.

Two paired stones of this ureilite were found on the Dar al Gani plateau in the Sahara Desert, which have a total weight of 277 g. The brecciated, highly-shocked DaG 084 exhibits mosaicism in its olivines and has experienced heavy terrestrial weathering consistent with grade W3. The meteorite belongs to Berkley's fayalite-rich subgroup I, having a Mg# in the range of Fo76–87. This ureilite is probably paired with the polymict ureilites DaG 164 (57 g) and DaG 165 (32 g), and possibly with numerous other monomict and polymict named masses found in close proximity. All of these individual stones might represent the breakup of a >7 kg polymict regolith fragment (Downes et al., 2010).

A Mn–Cr isotopic study was conducted by Shukolykov and Lugmair (2006) on the paired polymict ureilite DaG 165 and some others. Their results indicate that DaG 165 last equilibrated very early in Solar System history, ~4.562 b.y. ago, which is much earlier than Kenna. Three volatile-rich CI-like clasts present in the polymict ureilite DaG 164 pairing have been studied by Patzek et al. (2016, 2017, 2018, 2019). They found that these fine-grained hydrous clasts are highly enriched in D (δD up to +1000‰) and plot along an extension of the CCAM line on an O-isotopic diagram (see top diagram below). The heavier bulk oxygen composition of these clasts is derived from the incorporation of 16O-poor ices from the outer Solar System. A meteorite sample with a mineralogy and isotopic composition similar to these clasts has not yet been recovered.

In contrast, CI-like (C1) clasts from CR chondrites plot in the CR field and likely represent endogenous material, while CM-like clasts from HEDs plot in the CM field and represent exogenous CM-impactor material (Patzek et al., 2019). In further studies, Patzek et al. (2020) analyzed O and Cr isotopes as well as δD signatures for CI-like clasts in a sampling of polymict ureilites plus Ivuna, CR chondrites (Renazzo, Al Rais), HEDS (NWA 7542, Saricicek), and C2-ung chondrites (Bells, Essebi, Tagish Lake), and again demonstrated that the C1 clasts in polymict ureilites and CR chondrites derive from one or more unique CC parent bodies, while the clasts in the HED meteorites are consistent with an origin from a CI host body (see bottom two diagrams below).

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Diagram credit: Patzek et al., 81st MetSoc, #6254 (2018)

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Diagram credit: Patzek et al., 82nd MetSoc, #6027 (2019)

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Diagram credit: Patzek et al., GCA, vol. 272, pp. 177–197 (2020)
'Hydrogen isotopic composition of CI- and CM-like clasts from meteorite
breccias—sampling unknown sources of carbonaceous chondrite materials'
(https://doi.org/10.1016/j.gca.2019.12.017)

In an attempt to identify possible common ejection events among the ureilites, Beard and Swindle (2017) conducted a comparative study of 39 different samples utilizing three parameters: CRE age, Fo content in olivine (Mg#), and Δ17O value. They resolved ten potential clusters, several of which show concordance in their CRE age and Mg# but not in Δ17O value (heterogeneous), and three that are concordant in all three parameters (homogeneous). One of the homogeneous clusters reflects an ejection event that occurred 20.1 (±1.2) m.y. ago and comprises DaG 084, DaG 319, Goalpara, and Haverö; however, the Δ17O values for DaG 084 and DaG 319 have not yet been determined. The CRE age of this cluster is consistent with the average of all CRE age results obtained to date of 19.7 (±2.8) m.y. (Riebe et al., 2017).

Current theories of ureilite formation are presented on the Kenna and Almahata Sitta pages. The photo above shows the cut face of this 15.6 g DaG 084 specimen. The photo below shows the outer surface where remnant fusion crust has been affected by desert varnish, while light-colored desert soil still adheres to the part of the stone that laid beneath the surface.

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