Shale to Slate

DAVEW
Would any creationist care to propose a mechanism that would cause shale to metamorphose into slate in a mere few thousand years?
http://www.lumcloon.net/oldmaterial/rocks/sedimentary/sedimentary.html

(scroll down to the "shale" entry: "When shale gets buried deep in the earth for millions of years, the heat and pressure of the earth can change it into a metamorphic rock called slate.")


JOE G MEERT
The question is really more complex than the shale to slate transition.
There was an outcrop (since bulldozed) where the shale to slate transition was observable over less than 100 feet (Lehigh Gap Pa.). One could argue that the conditions necessary to create slate from shale occurred during a narrow time frame during compression (or burial).
What you really want to ask about are the transitions seen in shale to gneiss progression and the mechanism for regional metamorphism of the crust (especially those that involve either prograde or retrograde mineral growth).
What's most intriguing about regional metamorphism are the geochronologic/thermobarometric studies from medium/high-grade rocks which clearly (and unambiguously) show that it is a lengthy process (when compared to the 6-10K advocated by ye-creationists). Nevertheless, regional metamorphism is one of those subjects that are hard to find in creationist literature. The other subject typically avoided by ye-creationists is the subject of paleosols.