"I am going to strongly disagree with the idea that the cooling
of batholiths and volcanic intrusions are not evidence that the
flood was much longer ago than 4000 years."
In this post, I want to present the opinion of a neo-
catastrophist rather than defend a specific model of earth
history. It is my view that the long timescales commonly
associated with batholiths are dependent on debateable
assumptions.
GM: "As I have mentioned several times, during the time I left
publishing, I played at programming all sorts of physics problems
on my computer. It was a lot of fun. I wrote a program for
calculating how rapidly an object would cool in a conductive
situation. I just ran the program placing a 3 meter thick/ 18
meter long dike 50 meters below the surface. I ran the program
in 50 year increments and even after 20,000 years, the heat wave
had not reached the surface and the temperature profile of the
model was not at equilibrium. Hot things, even small hot things
take a long time to lose their heat when surrounded by rock.
this is because thermal conductivities are very, very small for
earth materials."
To a large extent, you are getting out of this program what you
put in. You are considering only conduction - and you are
absolutely right, heat energy takes a very long time to
dissipate. But who says the real world is like this?
GM: "Large batholiths can take 100,000 to 1,000,000 years to cool
down. Often the batholiths have cooked the rocks around them,
then erosion, took off the entire top of the batholith and
sediments above it, and new uncooked sediments were deposited on
top. Such is the situation at a geologic feature off New Jersey
known as the Great Stone Dome. The sediments above it are
uncooked and the sediments immediately in contact with it were
cooked. A long interval separated the intrusion from the
overlying sediments."
The first sentence is again model-dependent. If you rely only
on conduction to cool the hot body - it takes ages! What is the
link with reality?
Sure there are uncovered batholiths with new uncooked sediments
layed down over them. We have a good example in Yorkshire.
There is much more to be said: if the erosion went down to the
granite, then there is plenty of opportunity for water to get at
it to cool it. The Yorkshire granite seems to have been still
hot when uncovered - as there is plenty of mineralisation in the
overlying sediments which seem to be associated with the granite.
I'm confident that in this case, timescales need not be long.
But I fully accept that every case must be considered on its
merits.
GM: "Similar examples abound in the south atlantic offshore
Georgia. I am very familiar with these examples because I used
to be Area Geophysicist for the Atlantic Offshore for Atlantic
Richfield. Off Georgia, the Cretaceous sediments lie on top of
a major unconformity. Beneath the COST GE-1 Well which was
drilled to 13,000 feet, lies Devonian metamorphosed shales. This
means that the rock had been heated. Above the unconformity, the
Cretaceous rocks show no sign of ever having been cooked..."
The issue of regional metamorphism is distinct from the cooling
of batholiths. It needs to be addressed, but I don't want to
spread my net too wide in this response.
GM: "Not only do earth materials make it hard for heat to escape,
they make it hard for heat to get into the earth under some
circumstances. Glacial moraines with cores of relict glacial
ice have been found in large numbers around the world. Flint
notes, ...
These glacial ices have been preserved by the low thermal
conductivities of dirt."
Point taken. I do not wish to express any dissent.
GM: "Thermal arguments are great for showing a huge age to the
earth. The Deccan volcanic field is up to 10,000 feet thick.
If the flood was 4000 years ago it should still be hot."
There are lots of assumptions in here. The Deccan volcanics are
made up of separate flows. Each cooled sufficiently to form at
least a stable surface for the next flow. The mechanisms of
cooling need to be clarified before cooling times can be
assigned.
I wrote:
> If conductive cooling is dominant, it may take thousands of
> years, depending on the size of the intrusion. But most
> volcanic systems today have some convective cooling (because
> they are near the surface). The timescales then depend
> entirely on which characteristics are built into the model.
GM: "Convection only can occur within the lacolith (molten part
of the magma chamber) If that chamber is buried deeply, all the
heat must escape via conduction. So convection is only partly
applicable."
Note that my comments were related to volcanic systems, which I
will address first. Magmatic convection occurs within the magma
chamber - but I am much more interested in the convection that
occurs outside the chamber. I cited the oceanic ridge systems:
buried several kilometres down, but with enormous water
convection cells cooling them. The amount of water moving
through the oceanic crust is enormous. Conductive heat loss is
negligible compared with convective loss.
But Glenn says "If that chamber is buried deeply, all the heat
must escape via conduction." How deep do you want to go? We
expected the deeper parts of the crust to be dry - but all
probing so far reveals the presence of water! You cannot rule
out convection! And since convection is far more efficient than
conduction, all statements about cooling times linked to
conductive heat losses must be regarded as giving extreme upper
limits.
I have to limit this post - time is gone. I will briefly throw
in a few other issues that seem relevant to me. The model of
batholith formation in vogue has numerous problems. Large magma
bodies moving upwards through the crust of the earth have the
problem of "What creates the space into which they move?" I do
not consider the suggested answers convincing: stoping is, in my
view, a late stage, minor characteristic of batholith formation.
There is a growing feeling that batholiths are aggregations of
much smaller intrusions of magma, where the space is created
tectonically. With this model, there is much more scope for
water cooling.
There is an even more minority view: that the main batholith
forming process is not magma moving upwards in the crust, but is
linked to mineral alteration by rising gases and fluids. My
interest at present is not to take sides on this one, but merely
to promote debate. If this model is valid, the times for cooling
are likely to be much shorter.
The main message of this post is that many geological statements
about timescales are presupposition dependent. There is a need
for more genuine testing of these presuppositions than has taken
place in the past.
I said last week that I would reply to Glenn. I'm now in the
position of being out of the country for a week - so as it will
take some time to respond to Glenn's reply, please accept my
apologies now.
Best wishes,