Geology Reference
In-Depth Information
Figure 5.4.
Ureilite AlH A78019 is the first low shock-stage ureilite discovered and retains sharp extinction in olivine (upper image)
and almost undeformed euhedral graphite (lower image), which demonstrated that graphite was a primary mineral in ureilites.
The images are 2.5 mm across (upper) and 1.25 mm across (lower).
of the parent asteroid coupled with modern analytical
techniques does support a restite model for ureilite gen-
esis. The highly siderophile element ratios in ureilites can
be understood as arising from two components. One is
residual metal remaining after extraction of partial melts
in the Fe-Ni-S system, while the other may be a total melt
of the Fe-Ni-S, a portion of which was trapped in the
silicate host, as found by
Rankenburg et al.
[2008]. These
authors also considered that the second component could
be chondritic material injected during disruption of the
ureilite parent asteroid, but this seems less likely consid-
ering that the analyzed ureilites are not breccias. This
study relied heavily on ANSMET ureilites; 16 of 22 mete-
orites analyzed were from the US collection.
