Geology Reference
In-Depth Information
Lherzolitic shergottite
482.5 g
Found December 29, 1977
9.5 × 7.5 × 5.25 cm
Weathering = A
olivine, orthopyroxene, chromite, and plagioclase (maskelynite). A distinc-
tive characteristic of lherzolitic shergottites is the abundant evidence for
shock, including maskelynite, mosaicised olivine, and pockets of melted
rock in the interior. Lherzolitic shergottites may represent the residue from
melting of the martian mantle during production of basaltic rocks. They
also are among the most heavily shocked of all the martian meteorites.
Thus, they hold information about the interior and differentiation history
of Mars as well as constraints on its impact history.
Evolved melt
(parent of olivine-phyric and basaltic shergottites??)
Pyroxene oikocrysts
with few small olivine
Augite rim
RBT04261
/04262
Evolved
intercumulus
melt
LEW88516
Y- 763605
Three Y00s
NWA1950
GRV99027
ALH77005
Accumulation
Pyroxene oikocrysts
with abundant large olivine
Plate 72
MiNERALogy
SigNiFiCANCE
ALH A77005 is a cumulate achondrite comprising olivine
(~Fo
74
), low- and high-Ca pyroxene, maskelynite (An
54
-
An
45
), and minor amounts of chromite, ilmenite, troilite,
and whitlockite.
ALH A77005 was the first recognized lherzolitic shergottite
and provides unique information about melting and the
martian mantle over and above what we can learn from
nakhlites, basaltic shergottites, and chassignites. The
trapped melt inclusions (right, [731]) provide information
about possible parental liquids. Shock minerals and
chemical characteristics indicate that this meteorite (and
LEW 88516, another lherzolitic shergottite from Antarctica)
have been severely shocked. The two distinct lithologies,
poikilitic and nonpoikilitic, offer important constraints on
the detailed magmatic history of the lherzolitic shergottites
(left, [770]). Combined with RBT 04261/262, these samples
may represent the bottommost and topmost, respectively,
units of a martian magmatic complex.
References [723-763]
