Geology Reference
In-Depth Information
H chondrite impact melt
28.163 g
Found December 21, 2002
3.9 × 2.5 × 2.5 cm
Weathering = C
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.
1000
LAO 02240
DaG 896: 0.003 °C/s
LAP 04751
10
-2
10
-1
10
0
10
1
10
2
10
3
10
4
10
5
LAP 03922
Rose city
LAP 04462
LAP 031125
LAP 031173
100
LAP 031308
Orvinio
Yanzhuang
melt pockets
Yanzhuang
melt vein
10
Lunar
spherules
1
10
6
0.1
0.01
0.1 1 10
Maximum diameter of metal globules [mm]
100
(a)
(b)
5 mm
5 mm
Unmelted
host
chondrite
Quiescent melt
Mobilized melt
Opaque vein
Plate 3
MiNERALogy
SigNiFiCANCE
LAP 02240 consists of ~10% coarse-grained relict phases
and ~90% fine-grained olivine and pyroxene (1-10
microns). The mineral compositions are homogenous;
olivine is Fa
18
and orthopyroxene is Fs
16
.
LAP 02240 impact melts were rapidly cooled as indicated
by the homogeneous compositions of glass and opaque
veins (upper right, [14]). impact melt from LAP 02240
has yielded an Ar-Ar age of 3.9 ga. it is one of perhaps a
dozen Antarctic H chondrite impact melts that have an
irregular distribution of ages <1.3 ga and 3.4 to 4.5 ga.
These ages help to unravel the impact and geologic
history (bottom, [15]) of ordinary chondrites, including
some very recent impacts that are <500 Ma.
References [10-15]
