Geology Reference
In-Depth Information
L6 chondrite
124.8 g
Found November 28, 1978
3.0 × 2.5 × 2.0 cm
Weathering = C
Many ordinary chondrites exhibit melt veins that have formed by shock
processes. The veins can be composed mainly of silicates like the host, or
of sulfide and metal veins. Such samples offer information about the
impact processes and conditions experienced on small asteroid-sized
bodies, which in turn offers information about the dynamics of
cratering.
ALHA78-
-001
-003
-039
ALH78003:~17GPa
2400
Y701384:~20GPa
2200
Tw o liquids
Mp
Cp
Sp: Spinel
OI: Olivine
Gt: Garnet (majorite)
Px: Orthopyroxene
(enstatite)
Cx: Clynopyroxene
(diopside)
2000
5mm
Liquidus
1800
Mw
β
Gt
OI
α
+
β
Solid + Sulfide liquid
1600
β
+
γ
γ
Cx
Px
αα
+
γ
α
: Olivine
β
: Wadsleyite
γ
: Ringwoodite
1400
Sp
Mw: Magnesiowustite
Mp: Mg-perovskite
Cp: Ca-perovskite
Solidus
1200
Ringwoodite (
γ
)
1000
+Wadsleyite (
β
)
Olivine (
α
)
0
5
10
15
Pressure (GPa)
20
25
30
5mm
Plate 7
MiNERALogy
SigNiFiCANCE
ALH A78003 contains olivine (Fa
24
)
,
low-Ca pyroxene
(Fs
20
), plagioclase, troilite, and iron nickel metal.
Like many L6 chondrites, ALH A78003 is cross-cut by a
series of shock melt veins formed during impact on the
parent asteroid. These shock veins consist of micro-
melted silicates and, in this case, much of the vein is filled
with troilite. Veins in ALH A78003 contain high-pressure
polymorphs of olivine and pyroxene, such as ringwoodite
and wadsleyite (left, [29]), of the type found in the mantle
of the Earth. These high pressure phases help constrain
the shock pressures experienced by the sample on its par-
ent body (right, [29]).
References [29, 30]
