THE COOLING OF THICK IGNEOUS BODIES ON A YOUNG EARTH

Andrew A. Snelling, Ph.D.


Presented at the Fourth International Conference on Creationism,
Pittsburgh, PA, August 3-8, 1998.

Creation Science Fellowship, Inc.

ABSTRACT

Not only is the presence of water deep in the Earth's crust crucial
in producing granitic magmas, but water is also included within such
melts. Once a pluton is emplaced (probably rapidly by dikes) and
crystallization begun, the magma's water content significantly aids
cooling. Meteoric water also penetrates into the pluton via joints
and fractures that develop in the cooled outer rind of the pluton,
setting up hydrothermal circulation. The permeability of the cooling
pluton is maintained as the cooling/cracking front penetrates
inwards, while vapor pressures ensure the fracturing of the
surrounding country rocks. Thus convective cooling rapidly
dissipates heat over a time-scale compatible with a young Earth.

INTRODUCTION

One of the persistent scientific objections to the Earth being young
(6,000-7,000 years old rather than 4.55 billion years), and the
Flood being a year-long, global event, has been the apparent
evidence that large plutons of granitic and other igneous intrusive
rocks found today at the Earth's surface necessarily required
millions of years to cool from magmas. The purpose of this work is
to examine critically this oft-quoted assumption.

Deep in the Earth's lower crust the temperatures are sometimes high
enough to melt the rocks locally, particularly if there are applied
high pressures due to tectonic forces and/or elevated temperatures.
The latter can result from the proximal presence of basaltic magmas
ascended from the upper mantle. Most geologists now agree that large
blobs of granitic magmas are thus generated at 700-900C, and
owing to the fact that these blobs are lighter than the
surrounding rocks, they are supposed to have risen like
balloon-shaped diapirs into the cooler upper crust. There they
crystallize into the familiar granitic rocks. When exposed at the
Earth's surface due to erosion these plutons cover large areas,
sometimes hundreds of square kilometers. Indeed, it is estimated
that up to 86 per cent of the intrusive rocks within the upper
continental crust are of granitic composition [109].

Young [114] has insisted that an immense granitic batholith like
that of southern California required a period of about one million
years in order to crystallize completely, an estimate repeated by
Hayward [43] and Strahler [100], the latter in a widely-quoted
anti-creationist book. Others quote on the order of 10 million years
for the complete process of magma generation, injection and cooling.
Pitcher [81, p. 187] says:

My guess is that a granitic magma pulse generated in a collisional
orogen may, in a complicated way involving changing rheologies of
both melt and crust, take 5-10 Ma to generate, arrive, crystallize
and cool to the ambient crustal temperature.
Of course, to this must be added the time to unroof the batholith.
However, most recent estimates of these time-spans are inflated, as
they are based not solely on presumed cooling rates, but primarily
on radiometric dating determinations and other uniformitarian
assumptions.

WATER IN GRANITIC MELTS

Recent research in experimental igneous petrology has shown that the
temperatures required for melting of rocks to form granitic magmas
are significantly lowered by increasing water activity up to
saturation, and the amount of temperature lowering increases with
increasing pressure [28]. A corollary to this is that water
solubility in granitic magmas increases with pressure, and therefore
depth, so that whereas at 1kbar pressure (3-4km depth) the water
solubility is 3.7wt% [45], at 30kbar pressure (100km depth) the
water solubility is approximately 24wt% [47]. Indeed, the amount of
water available is one of three crucial factors in the control of
granitic magma formation, the others being parent rock composition
and temperature [51, p.13]. Three sources are believed to provide
the needed water adjacent country rocks, subducted hydrated
oceanic crust, and hydrous minerals present in the melting rock
itself. These three processes may act either simultaneously or
independently of each other. While the adjacent country rocks are of
local importance, the other two sources are regarded as supplying
large quantities of water.

Water is generally recognized as the most important magmatic
volatile component, both for its abundance and for its effects on
physical and chemical properties of melts. Indeed, the dramatic
effects of the changes of water contents of melts on phase relations
is due to the variation of physical properties of melts with
changing water content (for example, viscosity, density,
diffusivity, solubility of other elements). Therefore, the role of
water in melting processes (collecting and segregation of melts),
migration of melts, and crystallization of magmas is fundamental.
Experimental investigations have demonstrated that pressure is the
most important parameter controlling water solubility in granite
petrogenesis, although the influence of temperature and melt
composition is also of importance [51, p. 58]. However,
water-saturated conditions commonly do not prevail in ascending
granitic magmas. Usually they are water-undersaturated, and their
viscosity and density thus ensures that they ascend to higher
crustal levels where crystallization and cooling of granitic plutons
takes place. Thus if there has been a relatively fast pressure
release due to rapid ascent and emplacement of the granitic magma,
even if initially water-undersaturated at depth, fast
crystallization will occur, and, once water saturation is reached,
excess water may be released.

ASCENT OF GRANITIC MAGMAS

There has always been a problem with the accepted wisdom of slow
magma ascent in balloon-shaped diapirs the so-called space
problem. How does a balloon-shaped diapir with a diameter of several
kilometers or more find room to rise through the Earth's crust from
20-40km (or more) depths and then the space to crystallize there
(even at 2-5km depth) in spite of the continual confining pressures?
As Petford et al., [80, p. 845] point out,
The established idea that granitoid magmas ascend through the
continental crust as diapirs is being increasingly questioned by
igneous and structural geologists.

Clemens and Mawer [20] maintain that the idea of long distance
diapir transport of granitic magmas is not viable on thermal and
mechanical grounds, so they favor the growth of plutons by dike
injection propagating along fractures. Pitcher [81, p. 186] comments:

... what is particularly radical is their calculation that a
sizeable pluton may be filled in about 900 years. This is really
speedy!

However, Petford et al.'s calculations show that a crystal-free
granitoid melt at 900C, with a water content of 1.5wt%, a viscosity
of 8 x 105Pa s, a density of about 2,600kg/m3 and a density contrast
between magma and crust of 200kg/m3, can be transported vertically
through the crust a distance of 3Okm along a 6m wide dike in just 41
days [80]. This equates to a mean ascent rate of about 1cm/sec. At
this rate they calculated that the Cordillera Blanca batholith of
north-west Peru, with an estimated volume of 6,000km3, could have
been filled from a 10km long dike in only 350 years. Magma transport
has to be at least this fast through such a dike or else the
granitic magma would freeze due to cooling within the conduit as
it ascended. Yet because of the radiometric dating constraints on
the fault movements believed responsible for the dike intrusion of
the granitic magma, Petford et al., couldn't accept this 350 year
rapid filling of this batholith, but concluded that the intrusion of
the batholith must have been very intermittent, the magma being
supplied in brief, catastrophic pulses, while the conduit supposedly
remained in place for 3 million years

Epidote is found in some granitic rocks and therefore can have a
magmatic origin, its stability in granitic magmas being restricted
to pressures of >6kbar (21 km depth). Brandon et al.'s experimental
work [6] has shown that epidote dissolves rapidly in granitic melts
at pressures of <6kbar, such that at 700-800C (temperatures
appropriate for granitic magmas) epidote crystals (0.2-0.7mm) would
dissolve within three-200 years. Therefore, if magma transport from
sources in the lower crust were slow (>1,000 years), epidote would
not be preserved in upper-crustal batholiths. However, granitic
rocks of the Front Range (Colorado) and the White Creek batholith
(British Columbia) contain epidote crystals, and Brandon et al.found
that the 0.5mm wide epidote crystals in the Front Range granitic
rocks would dissolve at 800C in less than 50 years. They concluded
[6, p. 1846]:

Preservation of 0.5mm crystals therefore requires a transport rate
from a pressure of 600 to 200 MPa [6 to 2kbar] of greater than
70Orn year-1

This equates to a maximum ascent rate of 14km per year, which is
similar to magma transport rates for dikes based on numerical
modeling [20, 78, 79, 80], and close to measured ascent rates for
upper crustal magmas [17, 84, 88]. By contrast, the modeling of
magma transport by ascending diapirs has yielded slow ascent rates
of 0.3-50m per year, meaning ascent times of 10,000-100,000 years
(62, 110]. In fact, in his widely-quoted anti-creationist book,
which is replete with outdated uniformitarian claims, Strahler [100]
has alleged 150,000 years. In reality, however, the preservation of
epidote crystals in some granitic rocks which crystallized at
shallow crustal levels not only implies magma transport had to be
rapid (very much less than 1,000 years), but that the transport had
to be via dikes rather than diapirs.

The mechanical behavior of partially molten granite has been
investigated experimentally at temperatures of 800-1100C, 25OMPa
and confining pressure, different strain rates and under
fluid-absent conditions [85]. Over that temperature range, strength
decreased progressively from 500MPa to less than 1MPa. The
comparative viscosity of the melt alone was estimated at 950 and
1000C from the distance it could be made to penetrate into a porous
sand under a known pressure gradient. Rutter and Neumann [85]
concluded:-

Shear-enhanced compaction is inferred to drive melt into a network
of melt-filled veins, whereupon porous flow through the
high-permeability vein network allows rapid drainage of melt to
higher crustal levels.

Furthermore, it was suggested that the overall kinetics are faster
than just gravity-driven porous flow, because transport distances to
the veins are small and melt pressure gradients, although small, are
hundreds to thousands of times higher than those arising in
large-scale porous flow. And once the melt accumulates in veins, the
effective permeability due to channel flow in the fractures is
several orders of magnitude higher than for intergranular flow.
Even more recent experiments have determined the viscosity of
Himalayan leucogranite between 800 and 1100C, 300 and 800MPa, for
meltwater contents of 3.98 and 6.66wt% [87]. The melt viscosity was
found to be independent of pressure, and so the experimentally
determined phase equilibria constrain the viscosity of this granite
to around 104,5 Pa s during its emplacement. It was concluded that
These viscosities and the widths of dikes belonging to the feeder
system [20-50m] are consistent with the theoretical relationship
relating these two parameters and show that the precursor magma of
the leucogranite was at near liquidus conditions when emplaced
within host rocks with preintrusion temperatures around 350C.
Calculated terminal ascent rates for the magma in the dikes are
around 1m/s. Magma chamber assembly time is, on this basis,
estimated to be less than 100 years (for a volume of 15Okm3). In
addition, the dynamical regime of the magma flow in the dikes was
essentially laminar, thus allowing preservation of any chemical
heterogeneity acquired in the source.

The investigators also noted that repeated injections of magmas over
protracted periods will increase the temperatures of the host rocks,
and whereas the first injected magmas will traverse cold crust
through dikes, later ones will encounter a hotter medium, so that
the lower viscosity contrast may then be more favorable to diapiric
ascent.

CONDUCTIVE VERSUS CONVECTIVE COOLING

Until relatively recently, both intrusives and extrusives were
believed to cool primarily by conduction (see Figure 1). In the last
20 years or so, however, the role of convective cooling (Figure 1)
has become increasingly appreciated [68, 104]. In addition, a
variety of empirical studies [7, 40, 41] have proved that thick
igneous bodies do in fact cool primarily by circulating water.
Cooling models which assume exclusive conductive cooling have been
superseded by those which recognize convective cooling in the host
rock [19], followed by those which allow for the convective cooling
of the outer parts of the plutons also [72], and finally those which
allow for constant permeabilities of both host rock and plutons (14,
76, 105].

The most recent generation of models [42], for cooling plutons, has
been based on the computer program HYDROTHERM [49]. Unlike earlier
models, this program takes into account the multiphase flow of
water, and the heat it carries, at temperatures in the range
0-1200C and pressures in the range of 0.05-1,000 MPa. Based on a
small pluton (2 x 1 km, at 2 km depth), the model indicates that the
cooling time is 5,000 years (at a system permeability of 10md).
Increasing the permeability to 33md shortens the time to only 3,500
years. Unfortunately, however, the program HYDROTHERM has not been
applied to plutons of batholitic dimensions. For this reason, our
study, described below, must rely on simpler models. Such an
approach is justified by the fact that re-analysis of the data used
in simpler models, by HYDROTHERM, does not lead to substantially
different conclusions [42] regarding inferred cooling time, as
predicted by simpler models.

To begin our study, we must point out that it is at least
theoretically possible that some intrusive igneous lithologies had
supernatural origins during Creation Week some initial rocks had
to be supernaturally created with an appearance of a formational
history and therefore age. And, of those magmas intruded during the
Flood, a large fraction of their latent heat of crystallization may
date back to Creation and the pre-Flood era. This follows from the
fact that 20%-60% of the crystals in a granitic magma may already be
crystallized at the time of intrusion [104]. Since the latent heat
of a crystallizing magma is 65cal/g and the specific heat is only
0.3cal/g/C [112], it follows that an intrusion with 50%
pre-crystallization has already, in effect, experienced a built-in
cooling of over 100C.

Furthermore, there is evidence accumulating that many granitic
bodies, including the large batholiths, may be essentially
rootless and not as thick (deep) as the areal extents they cover
have seemingly suggested. The subsurface shapes of intrusive igneous
masses have been until recently only indirectly known. Mafic bodies
appear to have simple dike-like forms extending to great depths,
whereas the granitic types are elongate to equant in plan view and
extend only to a fraction of their diameters in depth. From a
combination of seismic, gravity and heat flow data, Hamilton and
Myers [38] suggested that batholithic masses in particular may be
only a few kilometers thick. More recently, a seismic reflection
study of the internal structure of the English Lake District
batholith showed the presence at depth of interpreted granitic sills
500-1000m thick separated by country rock, which suggested to Evans
et al. [30] that the batholith is made up of a series of horizontal
sheets with flat tops and floors, or an overall laccolithic
structure. Similar sill-like geometries occur in sections of the
Sierra Nevada batholith [21] and the High Himalaya [86], while the
Harney Peak Granite pluton of the Black Hills (South Dakota) has now
been mapped as a multiple intrusion that consists of perhaps a few
dozen large sills (which are probably no more than 100m thick,
extend laterally for only a few kilometers, and have gentle dips in
accord with a domal pattern) and thousands of smaller sills, dikes
and irregularly-shaped intrusions [74]. Hutton [48] has reviewed
granite emplacement mechanisms in three principal tectonic settings
and concluded that the plutons have been constructed by multiple
granite sheeting parallel to shear zone walls and deformation
fabrics. A detailed fractal analysis of the geometries of small to
medium laccoliths and plutons [66] indicates that they exhibit
scale-invariant tabular-sheet geometries, which also implies that
larger intrusions (and notably batholiths) are composed of composite
sheets of smaller intrusions. This conclusion has been corroborated
by a theoretical analysis [66] which suggests an upper limit of
2.5km for the thickness of any single sheet of magma. Finally a
variety of geophysical evidences, recently summarized [66],
constrain batholiths to total thicknesses of less than 12km. The
implications of all these findings is that many granitic plutons and
batholiths consist of relatively thin sills and laccoliths, and
hence the time-scale of the apparent crystallization and cooling
problem is significantly diminished.

The convective overturn caused by settling crystals, in the magma
chamber, is a significant factor in the dissipation of its heat.
This allows a 10-meter diameter sill to cool in one year [12] and,
at the other extreme, for a 10km thick lava ocean to theoretically
cool in 10,000 years [65] by this process alone. In the case of a
2.15km cuboid pluton which cools by conduction through the country
rock (but whose magma can experience convective overturn), its
temperature will drop from 850C to 650C in 3000 years [94] by this
factor alone. If, however, the cooling is exclusively conductive
both outside and inside the magma chamber, the time increases to
20,000 years.

Plutons with considerable amounts of magmatic water cool much faster
than do those which don't. Spera [97] has developed a parameterized
model for cooling plutons which accounts for heat transfer by
conduction and convection within the magma chamber and into the
surrounding country rocks. According to his model's central equation
linking the crucial parameters, the thermal history of a pluton is
most sensitively dependent upon the depth of pluton emplacement, the
heat-transfer characteristics of the local environment (for example,
emplacement into hydrous or anhydrous country rock), the size of the
pluton, and the bulk composition of the melt.

From the essential results of his study, Spera concluded that
emplacement depths and the scale of hydrothermal circulatory systems
are first-order parameters in determining the cooling times of large
plutons. Figure 2 shows the remarkable role water plays in
determining the cooling time.

For a granodioritic pluton 10km wide emplaced at 7km depth, the
cooling time from liquidus to solidus temperatures decreases almost
ten-fold as the water content increases from 0.5wt% to 4wt%, other
factors remaining constant. However, Spera also found that if the
temperature of the magma chamber country rock contact decreases
from 700C to 500C, which depends on the geothermal gradient, the
emplacement depth and the hydrothermal fluid/magma volume ratio, the
cooling time decreases by eighteen-fold (with only 2wt% water
content). Additionally, conduction cooling times were estimated to
vary with the square of the radius R, whereas in convective cooling
the solidification time varies approximately according to R1,3.
Spera [97, p. 299] concluded:

Hydrothermal fluid circulation within a permeable or fractured
country rock accounts for most heat loss when magma is emplaced
into water-bearing country rock ... Large hydrothermal systems
tend to occur in the upper parts of the crust where meteoric water
is more plentiful.

ROCK PERMEABILITY: THE RATE-DETERMINING FACTOR OF COOLING

All of the factors endogenous to the magma itself pale into
insignificance, in terms of cooling rate of igneous, once either
meteoric or connate water can enter near or into a hot igneous body
at an appreciable rate. This is so whether the convection is a heat
engine driven by the cooling body itself [14], or is a result of
extraneous forced convection [3] (discussed below). The rate of
convective cooling itself scales closely with the rate of water
circulated through a temperature anomaly [14], and the volume of
water involved in cooling a pluton is less than the volume of the
igneous body itself [14].

Equation (1) gives the rate of water flux, and is a summary of
Equation (A1) in Cathles [14]. The flux rate [Q in Equation (1)] is
closely proportional to the rate of heat removal from the pluton,
since it is the water that carries away virtually all of the heat in
a pluton whenever convective cooling dominates over conductive
cooling.
Q=[KA (Q=[KA (DT)/[V](1)

Q scales with size of intrusion because large intrusions generate
proportionately more powerful convective heat engines [13]. The K
refers to permeability of both host rock and igneous body (in
millidarcies). The other term, A, encompasses the respective
products of other variables (the gravitational constant, the
coefficient of thermal expansion of water, and water density changes
with depth), whereas V refers to the viscosity of the hydrothermal
water. DT refers to the elimination of three-quarters of the
temperature anomaly between the original temperature of the
intrusion and that of the country rock. For instance, if the magma
had been intruded at 800C and the country rock's temperature had
been originally 200C, there would be 600C of temperature to
eliminate. Thus in the formula DT would equal 450C. Based on
differing geologic conditions, all of the variables in Equation (1),
with the exception of permeability K, can change by only about a
factor of 2 or so.

The situation is entirely different for permeability K. The
permeability K of earth materials varies by several orders of
magnitude [4] in crystalline rocks. It is thus obvious that the
value of Q, and hence the time needed to cool the pluton, is, for
all practical purposes, governed by K.

This is borne out by Figure 3 (which is modified after Figure 6 of
Cathles [14]). It indicates the time to cool off a pluton of
specified transverse dimension as a function of the permeability of
the pluton and host rock. (Actually, the cooling in Figure 3 starts
with solidus temperatures and ends at 25% of the difference between
ambient temperatures and solidus temperature. The remainder of the
cooling to ambient crustal temperatures is not covered by Figure 3,
but is accounted for later.)

The effects of changing permeability K, on cooling time, is striking
(see Figure 3). An infinitely-long batholith that is 11km wide,
16.5km thick, and is buried 20km below the surface of the ground,
when at zero rock permeability (that is, conductive cooling only)
needs a few million years to cool. But with the intensity of
convective cooling that is allowed by a permeability K of 10
millidarcies (easily exceeded see below), the time to cool this
batholith falls to a mere 3000 years.

To put this cooling batholith in geothermal perspective, let us
consider this: It implies an average geothermal output of 25W/m2
sustained for the 3000 years. This pessimistically assumes that the
geothermal circulation extends no further than the batholith itself,
but thus allows for the presence of parallel batholiths nearby (as
is usually the case in orogenic belts), which must undergo their own
convective cooling. The quoted heat output is half that of the
present-day Grimsvotn geothermal region of Iceland (50W/m2,
sustained over 100km2 and for 400 years [2]).

We now perform a sensitivity analysis for the
batholithic-emplacement parameters assumed for Figure 3. Varying the
geometry of the pluton (that is, its width-thickness ratio), and its
depth of burial relative to its size, from the values arbitrarily
chosen for Figure 3, is relatively unimportant [13]. For instance,
if the burial depth was doubled, the time to cool would be much less
than doubled. Conversely, if it were halved, time to cool would
decline by much less than a factor of two. This owes to the fact
that the convective cell becomes somewhat more efficient when at
greater depth (and vice-versa for shallower depth), and this partly
cancels out the increasing (or decreasing) distance which the hot
hydrothermal fluid has to travel before reaching the surface and
dissipating its heat.

This discussion does not imply that all of the large batholiths had
cooled by the time they were uplifted after the Flood. Since most
(virtually all?) large batholiths show satellite intrusions and/or
pegmatites, this indicates that their centers could have been still
liquid at the time they had been uplifted and/or unroofed. And in
many areas of the world, geothermal activity from still-hot igneous
bodies continues to the present, itself challenging an old Earth
(see below).

THE EXTENT OF PERMEABILITY AND HYDROTHERMAL ACTIVITY

Since the plutons' cooling rates are essentially limited by rock and
crustal permeability, as well as the depth of hydrothermal action,
we must go beyond theory and examine how these agents are, in turn,
limited under realistic geologic conditions. We also need to
understand how these factors came into play during and after the
Flood.

By way of introduction, Darcy's Law allows for the same level of
permeability in a rock to be governed by apertures of
widely-divergent sizes, and this has been confirmed by actual
observations [32]. For instance [71], it is clear that a
permeability K of 10md, needed to cool the batholith within 3000
years (see Figure 3), can result from 10-micron microcracks spaced
every 0.7cm, 0.2mm hairline cracks separated from each other at
outcrop scale (100 meters), or even 1mm joints spaced 10km apart.
Strictly speaking, Darcy's Law applies to permeable rather than
fractured media. However, both theoretical and experimental
evidences [108] indicate that fractured domains closely approximate
the behavior of equivalent-porous domains when large distances and
travel times are involved, when the network of fractures is
continuous, and when the heat source which drives the movement of
water is large in comparison to the geometry of the fractures and
the intervals which separate them. These conditions are largely
fulfilled by cooling plutons. Moreover, reasonably similar values
are obtained for cooling models which allow for a mass flux going
through widely-separated fractures of high permeability (and
separated by large intervals of low rock-permeability) when
contrasted with models which simply compute an equivalent average
permeability for the same domain [31, 32]. Nevertheless, a
residual-cooling model, described below, considers the consequences
of the convective cooling which results from hydrothermal water
flowing through widely-separated (but interconnected) fractures
which cut through large thicknesses of otherwise-impermeable rock.
Darcy's Law is based on the assumption that apertures are perfectly
planar, and of constant size. Concerns that deviations from these
assumptions would cause a severe reduction in actual permeability in
the rock have proved unfounded. To begin with, many if not most
joints and cracks are reasonably close to planar [57]. Moreover,
studies on sinuous apertures [7] demonstrate that their permeability
is reduced by only about 10-30% over that of perfectly planar ones.
And while on the subject of theory versus actual geology, it should
be noted that convective circulation of the type of interest to us
is very difficult to destabilize [67].

But how permeable are rocks in actuality? Studies which infer the
permeabilities of rocks on a microscopic or hand-sample scale
greatly underestimate the permeability of the crust from which they
came [4, 71]. This indicates that apertures in rocks tend to occur
frequently, but at irregular intervals. Thus, the limiting factor
now becomes the largest permeability existing over a significant
fraction of a given crustal region. This should seldom if ever pose
a problem, for joints are virtually universal in granitic terrains
[89], as are microfractures [1]. In fact, the considerable
difficulty of locating granites with low permeability, suitable for
long-term storage of radioactive wastes [37], attests to this fact.
And, even when located, such bodies often turn out to be dissected
by previously-unrecognized joints [37].

Among existing granites, the largest K in an area is 1-100md [4]
(not including joints), and these values underestimate the
permeability it had when hydrothermal solutions circulated through
it [60]. The latter results from the clogging of apertures during
cooling, as is manifested by secondary mineralizations in fractures
[60, 82] in the rock. There is evidence that presently-impermeable
granites were once very permeable, even with micro-sized apertures.
When examined under cathodoluminiscence, seemingly-intact granitic
fabrics betray evidence of a former extensive network of microcracks
[99].

Thus far, we have discussed long-inert granites. By contrast, the
permeability of a granite in the actual process of cooling remains
unknown. The most recent models [49] assume that an
initially-impermeable granite does not become appreciably permeable
until it cools below about 360C, at which time its ductile behavior
gives way to brittle behavior, and thus jointing becomes possible.
Even if this is correct, it need not imply that plutons are
virtually impermeable, in a creationist-diluvialist context, when
their fabrics are still ductile. Owing to the ubiquity of repeated
tectonic stresses as a result of the Flood and its aftermath,
combined with the high viscosity of even hot granitic rock, joints
will still open up and probably remain open for significant
intervals of time before they are "healed" by the flowing of the
still-ductile granitic fabric.

These rates of repeated creation of joints (under catastrophic
tectonism) and the opposing rates of "healing" in still-ductile rock
need to be quantified. An analysis of some of these factors [33],
albeit in an actualistic context, suggests the following
conclusions: For a sialic pluton at a geothermal gradient of 125C,
and subject to a strain rate of 10-12, the brittle-ductile
transition occurs at about 3900. Under identical conditions, but in
the case of a more mafic granitic rock (e.g., diorite), the same
transition occurs at about 490C.

Crustal strain rates of 10-13 have been measured after moderate
earthquakes, and long-term strain rates on the order of 10-14 are
considered plausible [33]. It is unclear how much greater the strain
rates were during Flood-related tectonism. Assuming that the
conditions discussed above, for a sialic pluton [33, Figure 1,
left], can be validly extrapolated to considerably higher strain
rates, the ductile-brittle transition then occurs at approximately
500C at a strain rate of 10-10, and even, at least theoretically,
at approximately 600C under a strain rate of 10-8. However, at such
high strain rates, the heating and remelting of crustal material
increasingly becomes a factor. More research is needed to understand
and quantify these effects.

Both theoretical and experimental evidence [25] indicate that, not
only can ostensibly-ductile hot granite behave as a brittle material
under sufficiental impulsive tectonic stresses, but so can granitic
magma itself. Moreover, even without the presence of repeated
tectonic stresses, and as discussed in the ensuing paragraphs, there
are a variety of evidences against a simple ductile/brittle boundary
at or about 360C.

How deep can meteoric water operate? Uniformitarian beliefs had such
water limited to only the upper few to several kilometers of the
crust, and to crustal temperatures of only a few hundred degrees.
Deep boreholes, spaced many thousands of kilometers apart [52, 53],
have surprised everyone by revealing that free water exists to at
least 12km depth. They also have contradicted the notion that
crustal permeability greatly decreases, if not disappears, at such
depths because the overpressure was supposed to crush pores and
cracks shut [52]. To those who make much of the testable
predictions claimed for uniformitarian geology, here is yet another
example of a set of predictions proved false. Furthermore, seismic
data suggest that fractures can exist, at least transiently, down to
15 or 20km [71].

As for temperatures, we now have isotopic evidence that meteoric
waters interacted with gabbros, implying temperatures of 500-900C
[87]. This also means that such waters can reach the melting zone
itself for mafic magmas [87], to say nothing of the cooler sialic
magmas which give rise to granites.

FORCED CONVECTION AND THE REMOVAL OF RESIDUAL PLUTONIC HEAT

We now consider what takes place when the convective cell that cools
the pluton has eliminated 75% of the temperature anomaly (see Figure
3), and starts to die down. All this time, tectonically and
hydrostatically-driven groundwater movement (occurring during and
after the Flood) has been taking place, but, until now, has been
shunted away by the powerful convection around the pluton. Now, with
the heat engine petering out [13], the pluton becomes subject to
forced convection from the extraneous groundwater migrations.
The limiting factor in the remaining cooling rate now becomes the
thinnest distance between parallel water-cooling surfaces within the
pluton itself. Thus, in order for the remaining heat of the pluton
to be dissipated in 2000 years, the joints allowing free access of
water to the pluton need not be spaced any closer than 180 meters in
a slab-shaped block [3]. Under comparable conditions, a 160-m
diameter granitic spheroid cools in 2000 years [68]. These
computations, however, do not take actual temperature into account.
Allowing a joint-dissected pluton to have previously cooled from
850C (assumed temperature of intrusion) to 650C, only 2000 more
years are needed to cool conductively the pluton to an ambient
crustal temperature of 300C if each dimension of the cuboid pluton
is on the order of 400-500m [94]. This latter computation does not
take into account the constant hydrothermal bathing of the cube's
walls.

WHAT IF THE APERTURES CLOG UP?

These rough calculations account for the complete closing of
microcracks, and thus pessimistically assume zero permeability (and
thus exclusive conductive cooling) of the jointed slabs, spheroids,
and cubes themselves. Under such restrictions, the convective water
cooling is restricted to the jointed surfaces.

However, several factors counteract the sealing of microcracks. One
is size. As microcracks approach macroscopic size (1mm in aperture),
they become exponentially more resistant to clogging [93]. The
common occurrence of partially-filled veins in rock [55] indicates
that the sealing of cracks often does not go to completion. Also, if
the water table fluctuates drastically in an area (as from
tectonics), this acts to help keep crustal fractures open [2].

Tectonic action counteracts clogging by increasing fluid pressure
and causing the flushing-out of streamlines, as is manifested by the
increase of geothermal activity after even small earthquakes [111].
It is also recognized that, where there are high tectonic strain
rates, permeabilities at least 10 times greater than we have adopted
for our model (Figure 3) may be sustained at depth in spite of
competing processes such as silica deposition [49]. Obviously, such
strain rates must have been the norm during and after the Flood, as
a consequence of rapid mountain-building, crustal readjustments,
etc.

Finally, when cracks do get filled up, they are easily replaced by
new ones, especially under catastrophic conditions. Indeed, the
rocks which occur in tectonic environments show evidence [82] of
repeated generations of mineral-filled fissures and extension
cracks, and so permeability of the host rock becomes quickly
restored. For instance, a new 0.5cm-wide fracture spaced every 1km
apart will create, or re-create, a crustal permeability K of
approximately 10 darcies [98]. This is three orders of magnitude
greater than that needed for a batholith to cool in 3000 years (see
Figure 3). Furthermore, as new joints develop, they allow access of
water to hot surfaces. The ensuing cooling generates a new
generation of microcracks from the thermoelastic gradients produced
by the percolating water [115]. Thus, in a sense, both macro- and
micro-cracks are self-regenerating, much like the hairs of the
fabled Medusa.

BOUNDARY CONDITIONS: MAGMA AND INFILTRATING WATERS (EXTRUSIVES)

Thick lava flows, being surficial, generally cannot develop
convection cells as can plutons (see Figure 3). They remain,
however, quite vulnerable to cracking and water infiltration. Lister
[57] has demonstrated an intense positive feedback process which
exists between meteoric water and lava flows (see Figure 4). Upon
contact with water, the lava surface cools rapidly, creating a thin,
solid crust. In doing so, a very steep temperature gradient between
the recently water-cooled surface (100C) and the magma just below
the surface (1000C) has been formed, causing severe thermoelastic
tension. This soon leads to cracking of the hardened lava crust,
allowing water access to the hot interior. So, at once, the lava is
cooled to a greater depth, and a new zone of thermoelastic stress is
created.

The cycle repeats itself, and the extreme temperature gradient is
displaced downwards. All the while, the water-cooled crust is
growing thicker, the cracks with their concomitant entry of water
keep propagating, and the cooling front is advancing downward.
Eventually, the fractures in the lava solidify completely [83],
allowing access to deeply-penetrating water. This completes the
cooling of the thick lava flow.

Based on calculations [57], the feedback-generated cooling front can
move 5-170 meters in a year. At the slowest rate, this suffices for
cooling the thickest layers of lavas on Earth in a few thousand
years. Empirical observations on the cooling of a lava lake [40,
41], have demonstrated the movement of a cooling front of over 2
meters a year, and further evidence for the importance of this
process comes from the heat-production rates of an Icelandic
geothermal system [2]. It is also recognized that this feedback
process explains the occurrence of columnar jointing in basalts
[83], and the fact that entablatures in ancient lavas follow
downward-growing joints [23].

BOUNDARY CONDITIONS: MAGMA AND CIRCULATING WATER (INTRUSIVES)

We now focus on processes which make plutons themselves accessible
to hydrothermal waters. Consider crustal permeability first. The
magma injected into host rock itself exerts pressure upon the host
rock, facilitating its fracture [55], and all the more so whenever
the intrusion is emplaced rapidly [24]. Also, the heat from the
pluton [32] itself induces fracturing in the country rock as the
fluid pressure in the pores of the host rock increase from the heat
[54]. Upon entry of the pluton's heat into these new cracks, the
process repeats itself [54].

Plutons are commonly surrounded by rim monoclines or anticlines. In
the past, this has been mistaken as evidence for regional tectonic
action. Now it is realized [35] that these regional structures are
caused by the fact that, as the plutons cooled, they first weakened
the wall rock by giving off heat and fluids. Subsequently, the
plutons foundered as they cooled, causing the adjacent and
superjacent wall rock to buckle downward. Obviously, such a process
could only help open up the country rock, and then the pluton
itself, to circulating ground water.

Although plutons also rapidly become permeable, let us
pessimistically suppose that, unlike the situation discussed in
describing Figure 3, we have permeable crust and a
perpetually-impermeable pluton. As before, we have a convective
cell, but water cannot enter the pluton itself. So the heat must
leave the pluton itself solely by conduction, and a cooling time of
3000 years (to within 25% of ambient crustal temperatures) suffices
for an infinitely-long impermeable pluton which is 0.6km wide, 0.9km
thick, and 11km deep [14]. For thicker plutons, the limiting factor
becomes the spacing of joints. These would have to split the cooling
pluton into slabs no larger than 0.6 x 0.9km, which, as discussed
above, is easily met.

Many mineral/metal deposits appear to have been formed by fluids of
magmatic-hydrothermal origin associated with granitic and other
plutons. Indeed, a granitic magma has enough energy to drive roughly
its mass in meteoric fluid circulation [14, 70]. Meteoric fluids
would thus seem to dominate the magmatic fluid component of even up
to 10wt% or so for some granitic magmas [8], but several factors can
act to focus the magmatic fluids in parts of the hydrothermal
system. Magmatic fluids are released only while the intrusion is
crystallizing, and fractionation of the magmatic fluids to the upper
part of the magma chamber can focus their release in a small region
of the crust compared with the full extent of the hydrothermal
system, so magmatic fluids can locally dominate over meteoric fluids
and should not be ignored for the part they can play in cooling
plutons [39].

Following the emplacement of a granitic magma in the upper crust,
crystallization occurs due to the irreversible loss of heat to the
surrounding country rocks [11]. Heat passes out of the magma chamber
at the margins of the body, and the solidus moves towards the
interior of the chamber, defining an inwardly progressing boundary
(see Figure 5). As crystallization proceeds, water increases in
concentration in the residual melt. When the saturation water
concentration is lowered to the actual water concentration in the
melt, first boiling occurs and water (as steam) is expelled from
solution in the melt, which is driven towards higher
crystallinities. Bubbles of water vapor then nucleate and grow,
causing second (or resurgent) boiling within the zone of
crystallization just underneath the solidus boundary and the already
crystallized magma (see Figure 5). As the concentration and size of
these vapor bubbles increase, vapor saturation is quickly reached,
but initially the vapor bubbles are trapped by the immobile
crystallized magma crust [10]. The vapor pressure thus increases and
the aqueous fluid can then only be removed from the sites of bubble
nucleation through the establishment of a three-dimensional critical
percolation network, with advection of aqueous fluids through it or
by means of fluid flow through a cracking front in the crystallized
magma and out into the country rocks. Once such fracturing of the
pluton has occurred (and the cracking front will go deeper and
deeper into the pluton as the solidus boundary moves progressively
inwards towards the core of the magma chamber), not only is magmatic
water released from the pluton carrying heat out into the country
rocks, but cooler meteoric water in the country rocks is able to
penetrate into the pluton and to establish hydrothermal circulation.

There is now petrographic evidence, in the form of complex quartz
growth histories [26], which is consistent with the above-discussed
sequence of events. Abrupt zone boundaries in quartz crystals
indicate fluctuations in melt composition and/or temperature during
the crystallization interval [26]. In fact, the acceptance of
erratic temperature fluctuations in the melt is not favored [26],
precisely because of the belief that large plutons "should" cool at
slow, continuous rates!

In conclusion, therefore, a long-impermeable pluton is, for our
purposes, as unrealistic as it is pessimistic. Pressure build-up
within the magma [24] will cause the solidified rind of the pluton
to crack in short order, resulting in a permeable pluton (see Figure
3). The more water dissolved in the magma, the greater will be the
pressure exerted at the magma/rock interface [55]. If the magma
moves in surges, there will be a cyclic cooling and heating of the
pluton's solidified rind, and the resulting thermal stress will
exacerbate its cracking [1]. As the pluton cools, the cracking front
moves progressively deeper into the pluton as the magma/rock
boundary recedes inward.

However, this release of magmatic water from a pluton will tend to
be focused towards the top or apical region of the magma chamber.
The vapor bubbles which nucleate on the magma chamber side-walls
will tend to rise as they grow, combining with adjacent vapor
bubbles and migrating upwards as a plume towards the top of the
magma chamber [10]. Because the density of water vapor is reduced as
it rises, the buoyancy of the plume is further enhanced, so that
this process of bubble-laden plume flow may be a driving force for
convection within some magma chambers. Furthermore, the rate of
plume flow can be calculated [64], and in the case of a typical
granitic magma chamber with 6wt% water at saturation emplaced at
7-8km depth, a bubble-laden plume would rise to the top of the
pluton in less than a year [10].

A relevant example that graphically illustrates the rapid release of
magmatic fluids through fractures concentrated at the apex of a
granitic magma chamber is the typical development of a porphyry
copper

( molybdenum gold) ore deposit system (Figure 6), which is now
well understood [8]. A stock-like body of granodioritic magma is
emplaced at shallow depth in a subvolcanic environment, and when
water saturation is reached and second boiling occurs the vapor
pressure becomes concentrated at the apex or carapace, while the
concurrent crystallization process also expands the crystallizing
rock mass. The net result is large-scale, brittle fracture of the
already crystallized pluton above, so that an intense stockwork of
fractures develops into which hydrothermal fluids can flow to
deposit their metallic loads (see Figure 6). The myriad of fractures
is extended upward and outward by continued hydraulic action
(hydrofracturing), even into the wallrocks and sometimes the
overlying volcanics that were earlier extruded from the same magma
chamber a chimney-like fracture system that channels ore-bearing
fluids and heat away from the underlying cooling magma chamber.
Breccia pipes [69] also demonstrate that initially-impermeable rinds
often fail catastrophically, particularly as a result of the rapid
build-up of vapor pressure at the tops of magma chambers. We can
only under- estimate the significance of these intense fracture
systems and breccia pipes in the tops of plutons and overlying
rocks, as subsequent erosion and the unroofing process must tend to
remove them (except in the case of surviving porphyry copper
deposits). There is every reason to suppose that this fracturing of
the tops of plutons and overlying roof-rocks is ubiquitous, but such
fracturing will invariably assist subsequent deep weathering and
their rapid erosion and removal to expose the plutons beneath. The
same holds for many extrusive equivalents of plutons. The vents
responsible for extrusion of comagmatic lavas/volcanics and release
of steam and heat from the cooling plutons below have been
subsequently eroded away. At other times, however, extrusive
equivalents of plutons have only belatedly been recognized to be in
genetic association with each other. Such has been the case, for
example, for many tuff-batholith associations in the western USA
[56].

Petrographic evidence [99] contradicts the view that plutons remain
impermeable for significant periods of time. To the contrary:
cracking begins as soon as the quartz is brittle enough, and before
the granitic magma has even fully crystallized [99], and continues
during its subsequent cooling [99].

Finally, the observed rates of geothermal output in modern
hydrothermal systems [2] are explicable only if meteoric water has
free access to both hot rock and intrusives. Note also that the
previously-discussed water-induced feedback cooling mechanism of
thick lava flows [57] must apply to plutons, if only because
lithostatic pressure has relatively little effect on the process
[57].

RAPID COOLING OF IGNEOUS BODIES: GEOLOGIC NON-PROBLEMS

We must now account for the implications of rapid cooling. Consider
igneous mineralogy, and the belief that relatively large crystals in
extrusives mean long cooling times. To begin with, this premise is,
on its own terms, inconsistent with the ubiquitous distribution of
very tiny crystals in many very thick lava flows [65], which are
precisely the ones supposed to take the longest to cool.
Ironic to Young's argument [114] about the slowly-cooling Palisades
Sill, it also consists of relatively small crystals, and shows
evidence of emplacement in 3-4 pulses [91], each of which could have
cooled relatively rapidly [40]. Of course, the Palisades Sill need
not have cooled (or even congealed) within one year (except at its
surface) before becoming overlain by fossiliferous rock. In fact, a
still-flowing lava soon develops a crust strong enough [113] to
support a walking person (approximately 770N [9]), and so could also
support a modest overburden of sediment almost immediately. And,
based on analogy with the Kilauea lava [40], a crust of hardened
lava a few meters thick can form in a few months, thus being capable
of supporting a significant overburden of fossiliferous sediment
within that time-frame. Consistent with all of these suggestions,
the Palisades Sill shows evidence of cooling in both top-down and
bottom-up directions [91], as well as evidence for it (and its
probable extrusive equivalent) having been deposited subaqueously
[91], which, of course, would have greatly accelerated the
development of a crust thick enough to support an appreciably-thick
superjacent layer of fossiliferous sediments.

It is now recognized that relatively large crystals found in
extrusives are not evidence for protracted periods of cooling, if
only because these phenocrysts could have formed long before the
emplacement of the magma [65]. But even in situ crystals can grow
rapidly [107]. lronically, we now realize that it is the rate of
nucleation in the magma, rather than the rate of its cooling, which
determines the eventual size of its crystals [106].

Contrary to old uniformitarian beliefs, phaneritic textures in
granites are not evidence for millions of years of slow cooling.
Macroscopic igneous minerals can crystallize and grow to requisite
size, in a sialic melt, well within a few thousand years [101, 102].
So, for that matter, can phaneritic crystals in a mafic melt [5,
27]. It is extraneous geologic factors, not potential rate of
mineral growth, which constrain the actual size of crystals attained
in igneous bodies [65].

Perhaps the most vivid and relevant example is that of granitic
pegmatites, regarded as dike-like offshoots of granite plutons
because of their spatial associations and identical major
mineralogies and bulk compositions [59]. At the point of aqueous
vapor saturation of a granitic melt, crystal fractionation can
sometimes occur, so that volatiles are concentrated in a mobile
vapor (hydrothermal)-residual melt phase which readily migrates
(usually upwards) into open fractures within the wallrocks
immediately adjacent to the granitic pluton, but sometimes within
the granite itself [50]. It is widely assumed and stated in most
textbooks that the giant crystal sizes (sometimes meters long) in
pegmatites require very long periods of undisturbed crystal growth,
that is, that pegmatite magmas cool slowly. However, London [58]
noted that constant crystal growth rates of approximately 10-6cm/s
could produce quartz and feldspar crystals of pegmatitic dimensions
in a few years. Furthermore, in a model of the cooling history of
the large Harding pegmatite dike, New Mexico, Chakoumakos and
Lumpkin [18] applied conservative boundary conditions (for example,
heat loss by conduction only, which is unrealistic) with a
magma-wallrock temperature difference of 300C at emplacement and
calculated that the center of the pegmatite dike would have cooled
below its equilibrium solidus in about 1-2 years.

What about entablatures and colonnades? It is now recognized that
these basaltic textures do not give unambiguous estimates for
cooling rates [23]. Entablatures form when lavas cool at 1-10C per
hour [60], and colonnades do so at tenfold slower cooling rates. But
both estimates are compatible with much higher cooling rates [60],
so long as the relative cooling rates of these features differ by at
least an order of magnitude.

CONVECTIVE COOLING OF PLUTONS: PETROGRAPHIC SIGNATURES

We now examine some of the pitfalls of attempting to minimize the
significance of hydrothermal cooling. There is considerable evidence
for hydrothermal action (for example, hydrothermal ore deposits,
widespread hydrothermal alteration), but absence of evidence for
such a process associated with most plutons is not evidence that
hydrothermal convective cooling has not occurred. As noted earlier,
a major result of hydrothermal action will be intense fracturing in
the rocks overlying plutons and the upper zones of plutons
themselves, but this has also facilitated erosion and thus removal
of the evidence.

Consider secondary hydrous minerals (epidote, chlorite, serpentine,
and various clay minerals). Gabbros betray isotopic evidences for
hydrothermal alteration, but are astonishingly free [104] of such
hydrothermal minerals. This is because groundwater alteration has
occurred at excessive temperatures for these low PT assemblages.
Likewise, if certain granites were cooled by hydrothermal fluids at
temperatures higher than commonly supposed, there would be no
secondary minerals to show this.

However, even this reasoning generously allows for waters cooling
the pluton to have experienced free access to its fabric. In
actuality, if the fluids flowed mostly through larger cracks or
joints, then only the walls of large granitic blocks would show
alteration. In fact, such is typical of granites [73]. Cathles [16]
warns against geologists consciously or unconsciously attempting to
infer the volume of hydrothermal fluids having circulated through a
pluton based on the degree of its alteration. One pluton whose
petrographic fabric shows little alteration may have passed a
thousand-fold greater volume of hydrothermal fluids than did a
second pluton whose fabric shows more alteration than the first
[71]!

Now consider contact metamorphic aureoles. Their size doesn't give
unequivocal evidence for the importance or unimportance of
hydrothermal cooling, in spite of models which predict [77] that
large aureoles are associated with primarily conductive cooling and
small ones result from extensive hydrothermal cooling at high
crustal permeabilities. The size of the aureole actually shows the
maximum distance reached by a certain high temperature [77]
emanating from the cooling pluton. If, as predicted, microcracks
tend to clog as convective cooling proceeds, there may come a time
when there is a temporary impermeable cap [14] above the pluton. The
contact metamorphic aureole would enlarge as the hydrothermal fluids
pool and temporarily flow greater distances from the pluton.
Furthermore, tectonic effects can perturb, and temporarily expand,
circulation streamlines.

RAPID CONVECTIVE COOLING OF PLUTONS: ISOTOPIC SIGNATURES
An exciting line of evidences for extensive former hydrothermal
activity around plutons is provided by the isotopic fractionating of
18O/16O and 2H/1H, and high permeabilities also favor the formation
of such signatures [76]. Compared with ocean water, meteoric water
tends to be isotopically lighter, by several parts per million, and
magmatic water tends to be heavier. Therefore, whenever ground water
interacts with plutons, these rocks should be slightly depleted in
18O relative to 16O and, to a less reliable extent, be likewise
slightly depleted in deuterium(2H) relative to protium (1H). Large
assemblages of plutons, exposed over vast areas (such as the
Canadian Cordilleras [61]) show this.

It is the contrast between isotopic signatures of pluton and host
rock that is the most informative. However, the absence of such
isotopic signatures need not mean that hydrothermal cooling was
unimportant in the history of the pluton, for the following reasons
(any of which would have blurred or eliminated the isotopic contrast
between pluton and host rock). The magma itself may have been
anomalously light isotopically, ground water may have mixed with the
magma itself (especially under catastrophic conditions [44]), the
isotopic signature may have been obscured or erased by subsequent
geologic effects [104], etc.

Let us now consider a different hydrological cycle prior to the
Flood. Paucity of rainfall facilitates the evaporation of water in
landlocked bodies of water, making their isotopes heavier [103].
Whenever these waters (and/or their connate water equivalents) had
interacted with the cooling plutons, there would be little or no
isotopic contrast between them and the magmatic water. Of course, we
cannot know the isotopic composition of the connate waters which
existed when God had created the Earth and which were the first to
cool the plutons.

Under such conditions, the first isotopically-light water came into
existence only after extensive Flood rainfall had taken place. Upon
percolating to great depths and displacing the older,
isotopically-heavy connate water, hydrothermal-cooling isotopic
signatures were created. Earlier-cooled plutons carry no such
signatures despite also having experienced extensive hydrothermal
cooling.

CONCLUSIONS

With this work, yet another objection to the young-Earth creationist
position has hopefully been answered. Millions of years are not
necessary for the cooling of large igneous bodies. Moreover, the
geologic role of hydrothermal cooling has already been extended to
account for the rapid origin of thick metamorphic lithologies [95,
96]. We now have evidence [34] that regional metamorphism is, thus
not unexpectedly, associated with hydrothermal circulation systems
which extend 10-100km from the metamorphic belt itself. Moreover,
the metamorphic fabric itself can give access to circulating fluids
as a result of the microcracking that is now recognized to be a
consequence of metamorphic reactions [22]. Gabbros themselves can be
metamorphosed to the point of acquiring metamorphic hornblende (for
example, the so-called amphibolite facies of metamorphism) in a time
period as short as a few thousand years down to a few centuries
[63].

A number of uniformitarian authors [14, 29, 92] have pointed out the
discrepancy which exists between the large measured permeabilities
routinely measured within the Earth's crustal rocks (implying
hydrothermal systems having lifetimes of only thousands of years),
and the (supposed) need for various geothermal processes to have
persisted for millions of years. For this reason, claims have been
made about hydrothermal action being episodic and recurring [15, 75,
92]. The progressive elimination and rejuvenation of rock
permeability, over countless cycles, has also been invoked [14].
While, as discussed above, there indeed is much evidence for the
previous searing of cracks, the pointed fact is the continued
existence of high crustal permeability (primarily cracks and
fractures at all scales) in spite of such evidences. Ironically,
therefore, hydrothermal cooling not only negates the cooling of
plutons as a valid argument for an old Earth, but, in and of itself,
is more compatible with a young Earth.

FUTURE RESEARCH

It has been noticed that rapid drops in groundwater levels are
sometimes correlated with magmatic activity [2]. This needs to be
explored in the light of the Flood and its aftermath. The computer
model HYDROTHERM [49], thus far applied only to small plutons [42],
needs to be employed in order to perform a more sophisticated study
of cooling batholiths. Moreover, the composite nature of these large
igneous bodies must be better understood and then taken into account
in modeling their cooling. The multiphase flow of water simulated by
HYDROTHERM also indicates that, as water approaches its critical
point (at which time the distinction between liquid water and steam
disappears), superconvection" or runaway convection" potentially
occurs [49]. In other words, convective heat transfer becomes
suddenly enhanced by a factor of 100 or more. For this to have a
chance to take place, a permeability of about 100md (which is an
order of magnitude larger than we have adopted for the cooling
batholith: Figure 3) is required [49], along with a narrow window of
temperatures. Present evidence [49] suggests that "superconvection"
may occur during cooling of small plutons, but probably not of
batholiths. Nevertheless, this question must be thoroughly
addressed.

More research is needed on the catastrophic extrusion of ancient
voluminous lava flows, particularly that which follows up on the
following tantalizing lines of evidence: The presence of large
vesicles [36] in basalts (suggestive of suddenly-trapped volatiles),
and textural evidence of very small changes in temperature over
considerable distances traveled by extruded lava [46]. The latter is
true of the Columbia River Basalts (northwest USA), and is
consistent with their "extraordinarily rapid emplacement" over an
area with a transverse distance of 500km [46].

A major follow-up to this work needs to be a study of economic
mineral deposits in the light of the rapid cooling of large igneous
bodies. An analogy from the eastern Pacific Ocean provides a
fascinating example: massive sulfide deposits of a few tons each
have formed, from hydrothermal activity, in less than one year [90].

ACKNOWLEDGMENTS

Helpful comments and three recent technical references were brought
to our attention by STEVEN A. AUSTIN of the Institute for Creation
Research. Other information was provided by several uniformitarian
specialists. Additionally, we need to stress that all the work on
this paper was our own, including the sourcing of all relevant
research papers. However, even though we did not use it, we
recognize the "Catastrophe Reference Database" (CATASTROREF)
produced by Steven Austin (version 1.2, January 1997) as a very
useful source of information on this and many other topics.

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