[meteorite-list] Titanium content

[Randy Korotev]

The rocks in question are all extrusive volcanic rocks - 
basalts.  The Ti variation reflects that the lunar mantle is 
heterogeneous.  The source regions where different episodes of 
melting occurred had to have varied considerably in ilmenite 
abundance.  The mantle of the Moon is not well mixed.  Plate 
tectonics did not happen on the Moon.  Although the terrestrial 
mantle is not homogenous, it's probably more homogenous than the Moon's mantle.

There is evidence for "mantle overturn" on the Moon. The dense 
mineral ilmenite crystallized from the magma ocean only after the 
less dense olivine had already crystallized and settled.  This led to 
a gravitational instability where the ilmenite plunged through the 
olivine (inverse diapir).  So, depending where melting occurs, both 
laterally and vertically, some magmas have more ilmenite than others.



At 06:57 08-05-07 Tuesday, you wrote:
>   Yes, Randy is correct about titanium content varying
>around the Moon.
>   What are the petrological reasons why this varies?
>   In southeast Pennsylvania, we have high titanium
>diabase intrusions (The "York Haven" intrusion) and
>low titanium diabase intrusions in highly folded and
>complex rocks which date from the precambrian. The
>lunar variation does not have the same cause, I am
>sure. But what are some of the ideas that account for
>the lunar variation?
>
>Francis Graham