Geology Reference
In-Depth Information
L impact melt
8550.621 g
Found December 20, 1991
19.1 × 14.3 × 14.5 cm
Weathering = B
likely been formed during impact. These rare samples offer a glimpse at
the pressure and temperature conditions and temporal relations among
the most common chondritic materials known. Collectively, Ar-Ar ages
of H, L, and LL chondrites suggest the occurrence of multiple large
impact events on the ordinary chondrite parent bodies.
,50
1cm
PAT91501
PAT91501
1mm
4.60
1. 50
4.55
PAT 91501
1. 20
4.50
4.45
0.90
4.40
0.60
4.35
4.30
0.30
[k] =935 ppm,[Ca] =1.6%
4.25
4.20
0.00
1cm
0.0
0.2
0.4
39
Ar cumulative fraction
0.6
0.8
1. 0
Plate 8
MiNERALogy
SigNiFiCANCE
PAT 91501 shows an equigranular (~0.4 mm grain size)
aggregate of anhedral to subhedral olivine (Fa
24
) and
low-Ca pyroxene (Fs
20
), with minor plagioclase (An
12
)
and accessory nickel-iron and troilite. Plagioclase laths
are larger than olivine and pyroxene (up to 3 mm long)
and poikilitically enclose these minerals.
PAT 91501 is unique among impact-melted ordinary
chondrites for the distinct vesicle-metal-sulfide nodules it
contains. While the silicate melt texture suggests incom-
plete melting, the cm-sized vesicles are obvious on the
exterior of this large meteorite and common throughout
the mass. High-resolution X-ray computed tomography
reveals that the vesicles are often associated with metal-
sulfide nodules that have a distinctive alignment of the
dense metal and lighter sulfide (left, [31]). This orienta-
tion can be used to infer the gravitational field on the
asteroid at the time of impact melting, which may have
occurred at 4.47 ga (right, [31]). The associated vesicles
likely formed by volatilization of sulfur, and the
compound vesicle-metal-sulfide particles may have been
neutrally buoyant within the silicate melt.
References [31-33]
