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Re: Moonquakes

Subject: Re: Moonquakes
From: "George"
Date: Fri, 17 Mar 2006 00:43:56 GMT
Newsgroups: sci.astro, alt.sci.planetary, sci.geo.earthquakes
"John Curtis" <john@xxxxxxxxx> wrote in message 
news:1142552857.107615.175030@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> George wrote:
>>
>> Umm, are you suggesting that water is necessary for the formation of
>> olivine, and if so, why?
>>
> Water begins to condense at sunspot temperature @ 3200K and
> serves as a reactant in subsequent condensations of minerals.
> Water combines with silicon to form silicic acid Si(OH)4, which
> is usually written as H4SiO4.  Iron and magnesium combine
> with the SiO4 portion of silicic acid to form olivine. John Curtis

That may be true, but how does that relate to the presence of olivine on 
the moon and elsewhere?  Many lines of evidence point to the absense of 
hydrogen on the moon.  On earth, olivine forms from magma that is rich in 
magnesia and low in silica, forming such rocks as gabbro, norite, 
peridotite and basalt, and yes, most of these usually form in the presence 
of some water - under terrestrial conditions.  Considering the apparent 
absence of water of formation involved in the formation of lunar minerals, 
I think it is evident you have to approach it from a different perspective. 
For instance, just because Si02 mawas likely present when the mare basalts 
was formed doesn't mean that water was involved.  The reason is simply that 
the silica may have already existed within the moon, originating, for 
instance, during the moon's original formation.

If the earth impact theory of lunar formation is correct, much of the SiO2 
could have originally formed during the creation of the solar system, and 
accreted to the original bodies that later collided, forming the earth-moon 
system. There is a recently published paper (I don't have a link, but you 
can problem find it on the internet) that discusses the origin of the mare 
basalts, and suggests that those flood basalts formed as a result of a huge 
asteroid impact on the far side of the moon.  It is also possible that a 
lot of the original olivine on the moon existed in the parent bodies prior 
to impact, and was incorporated into the moon during its formation, having 
re-melted at that time.  Remember, the mare basalts are younger than the 
moon itself, having formed I think about 3.8 billion years ago.  So these 
basalts would have formed from a partial melt of earlier material, 
something possibly resembling the peridotite or dunite we see in Earth's 
mantle.  At any rate, if water was present on the moon, it could never have 
been substantial, or else we would see it's signature in the form of 
hydrated minerals like amphibole, sheet silicates and possibly even 
sulphates.  AFAIK, to date, none of these minerals have been detected on 
the moon.

George 



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