Hi,
Presumably then a similar story is true
for Martian meteorites? Any trace of chondritic material in Martians?
Mark
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Randy Korotev
Sent: 01 September 2006 23:28
To: meteorite-list@meteoritecentral.com
Subject: [meteorite-list]
Meteorites on the moon
Regarding meteorites on the Moon...
There is a great deal of "meteoritic matter" on the Moon, but very
few meteorites. The two miniscule fragments that Martin Altmann mentioned
are the best known ones from the Apollo collection, but I'm aware of 2
others even smaller.
Virtually all meteoroids that strike the Moon either melt or vaporize on
impact. If they melt, they mix with the melted silicates of the lunar
target rocks. So either way, they become unidentifiable as
meteorites. Lunar impact-melt rocks and breccias do contain blebs of
meteoritic metal - metal the melted during the impact but as a liquid was
immiscible with the molten silicates.
All lunar soils and breccias contain meteoritic material. In any handful
of lunar soil, 1-4% of the mass is "extralunar" stuff. Except
for blebs of metal, most of which were melted and resolidified,
"meteorites" are virtually absent, however. In the lunar soil,
most of the meteoritic material arrives as micrometeorites. By one estimate,
approximately 80 grams per square kilometer of micrometeoroids accrete to the
Moon (and Earth's atmosphere) each year.
We know the meteoritic material (melted and mixed, recondensed from vapor)
exists in lunar regolith (soil) and breccias because both are loaded with
"siderophile" (iron-loving) elements like iridium, gold, and platinum
in ratios characteristic of chondrites. In contrast, the unbrecciated
igneous rocks of the lunar crust - the basalts and anorthosites - have almost
immeasurably low concentrations of these elements, as do igneous rocks on
Earth.
So, every one of the lunar meteorite that is a breccia (which is nearly all of
them) contains "regular" meteoritic material. Those lunar
meteorites that are regolith breccias (like NWA 3136 that Adam Hupe mentioned)
tend to contain the most. Those that are impact-melt breccias tend to
contain the least, judged on the basis of concentrations or, say,
iridium.
Here's a quote from a paper I've submitted on PCA 02007, a lunar meteorite
regolith breccia with a high proportion of chondritic material:
"The mean Ir concentration of PCA 02007 is equivalent to a component of
2.7% ordinary chondrite or 2.8% CM chondrite. This means that 14% of the Fe and
9% of the Mg and Cr in PCA 02007 derive from extralunar sources (Figs. 8, 9).
Day et al. (2006) report an actual meteorite fragment in their thin section of
PCA 02007."
To my knowledge, the chondrite fragment in a lunar meteorite reported by Day et
al. is a first.
Randy Korotev
