Answers Research Journal 1 (2008): 11�25.
www.answersingenesis.org/contents/379/Catastrophic-Granite-Formation.pdf
Catastrophic Granite Formation:
Rapid Melting of Source Rocks,
and Rapid Magma Intrusion and Cooling
Andrew A. Snelling, Director of Research, Answers in Genesis, P.O. Box 510, Hebron, KY 41048
Abstract
The timescale for the generation of granitic magmas and their subsequent intrusion, crystallization,
and cooling as plutons is no longer incompatible with the biblical time frames of the global, year-long
Flood cataclysm and of 6,000�7,000 years for earth history. Though partial melting in the lower crust is the
main rate-limiting step, it is now conjectured to only take years to decades, so partial melting to produce
a large reservoir of granitic magmas could have occurred in the pre-Flood era as a consequence of
accelerated nuclear decay early in the Creation Week. Rapid segregation, ascent, and emplacement
now understood to only take days via dikes would have been aided by the tectonic “squeezing� and
“pumping� during the catastrophic plate tectonics driving the global Genesis Flood cataclysm. Now that it
has also been established that granitic plutons are mostly tabular sheets, crystallization and cooling would
be even more easily facilitated by hydrothermal convective circulation with meteoric waters in the host
rocks. The growth of large crystals from magmas within hours has now been experimentally determined,
while the co-formation in the same biotite flakes of adjacent uranium and polonium radiohalos, the latter
from short-lived parent polonium isotopes, requires that crystallization and cooling of the granitic plutons
only took about 6�10 days. Thus the sum total of time, from partial melting in the lower crust to crystallization
and cooling of granitic plutons emplaced in the upper crust, no longer conflicts with the biblical time frame
for earth history, nor is it an impediment to accounting for most of the fossil-bearing geologic record during
the global year-long Flood catastrophe.
Keywords: granites, magma, partial melting, melt segregation, magma ascent, dikes, magma
emplacement, emplacement rates, crystallization and cooling rates, convective cooling, hydrothermal
fluids, polonium radiohalos
and each with its own name, make up the Sierra
Introduction
Nevada batholith. The batholith stretches in a belt
The major, almost exclusive, rock type in some
approximately 600 km (373 miles) long northwest-
areas on the earth’s surface, such as in the Yosemite
southeast and more than 165 km (102 miles) wide. It
National Park, is granite. Huge masses of many
adjoining granite bodies outcrop
on a grand scale throughout that
area (ï¬g. 1), as they also do along
the length of the Sierra Nevada
and the Peninsular Ranges of
central and southern California
respectively.
The Sierra Nevada batholith
is the collective name given
to all the granite bodies that
outcrop in, and form much of,
the magniï¬cent Sierra Nevada
range. Each recognizably
distinctive granite mass, the
boundary of which can be traced
on the ground, is marked as a
separate geologic unit called
a pluton on a geologic map.
Hundreds of such granite Fig. 1. Panoramic view of the Yosemite valley with the Half Dome rising above
plutons, ranging in size from the cliffs to the right, as seen from Glacier Point. The entire landscape in this
1 km2 to more than 1,000 km2, panoramic view is composed of granites.
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12 A. A. Snelling
is uncertain how deep the granite plutons are, that is, However, this long-accepted timescale for
how thick they are. Evidence suggests that many may these processes is now being challenged, even by
only be several kilometers (or less) thick. conventional geologists (Clemens 2005; Petford et
The Sierra Nevada batholith, and the Peninsular al 2000). The essential role of rock deformation
Ranges batholith just south of it, are part of a is now recognized. Previously accepted granite
discontinuous belt of batholiths that circle the Paciï¬c formation models required unrealistic deformation
Ocean basin. For example, granite batholiths are and flow behaviors of rocks and magmas, or they
found all through the coastal ranges along the west did not satisfactorily explain available structural
coast of South America and extend northward from or geophysical data. Thus it is now claimed that
the Sierra Nevada through Idaho and Montana, mechanical considerations suggest granite formation
western Canada, and into Alaska. The granite is a “rapid, dynamic process� operating at timescales
plutons making up the Sierra Nevada batholith have of less than 100,000 years, or even only thousands of
intruded into and displaced earlier sedimentary and years.
volcanic strata sequences, some of which had been
transformed by heat, pressure, and earth movements Magma Principles
into metamorphic rocks. These strata sequences First, however, it will be helpful to explain what
have been variously designated as Upper Proterozoic magma is and why it is thought to exist underground.
(uppermost Precambrian) to Paleozoic and Paleozoic The molten material which flows from volcanoes
to Mesozoic. (In the biblical framework for earth is known as lava and cools to form volcanic rocks.
history, that makes them Flood strata.) After the So lavas must be molten rocks; that is, they were
granite plutons intruded underground into these originally rocks that melted deep inside the earth
strata sequences, erosion (at the end of the Flood and underneath volcanoes. When deep inside the earth,
since) removed all the rocks above the granites to these molten rock materials are called magmas
expose them at today’s ground surface. Again, it is because they are slightly different in composition and
uncertain as to just what thickness of overlying rocks physical properties due to the steam and gases they
have been eroded away, but it is likely only 1�3 km. have dissolved in them that erupt separately from the
Because we don’t observe granites forming today, lavas through volcanoes.
debate has raged for centuries as to how granites form. Before volcanic eruptions there are warning
While there is now much consensus, some details “rumbles� inside volcanoes. These are earthquakes
of the processes involved are still being elucidated. generated by the magmas moving up into the
Nevertheless, the conventional wisdom has been volcanoes. Such earthquakes have allowed geologists
adamant until recently that granites take millions of to reconstruct how magmas ï¬rst “pondâ€? below
years to form, which is thus an oft-repeated scientiï¬c volcanoes in reservoirs known as magma chambers
objection to the recent year-long global Genesis Flood before their ï¬nal passage upward through volcanoes
on a 6,000�7,000 year-old earth as clearly taught in to erupt as lavas. If the magma cools when it “ponds�
the Scriptures (Strahler 1987; Young 1977). in the magma chamber, rather than rising further
Several steps are required to form granites. The to erupt at the earth’s surface, then it crystallizes as
process starts with partial melting of continental an intrusion. Subsequent erosion of all the overlying
sedimentary and metamorphic rocks 20�40 km rock layers eventually exposes such intrusions at the
(12�25 miles) down in the earth’s crust (a process earth’s surface.
called generation) (Brown 1994). This must be followed This scenario has been conï¬rmed by copper mining
by the collection of the melt (called segregation), operations that have excavated into granite intrusions
then transportation of the now less dense, buoyant that must have formed under volcanoes. The remnants
magma upwards (ascent), and ï¬nally the intrusion of such volcanoes overlie the granite intrusions, and
of the magma to form a body in the upper crust their volcanic rocks are the same compositions as the
(emplacement). There, as little as 2â€?5 km (1â€?3 miles) granite intrusions (the former magma chambers) (ï¬g.
below the earth’s surface, the granite mass fully 2). Similarly, seismic surveys across the mountains
crystallizes and cools. Subsequent erosion exposes somewhat central to many ocean basins have detected
it at the earth’s surface. When reviewing this list of the magma chambers under the rift zones where
sequential processes, it is not difï¬cult to understand lavas have erupted onto the ocean floor. Because the
why it has been hitherto envisaged that granite magma is less dense than the surrounding rocks, the
formation, especially the huge masses of granites passage of the seismic (sound) waves when recorded
outcropping in the Yosemite area, must surely have and compiled actually produces images (or three-
taken millions of years (Pitcher 1993). Of course, such dimensional pictures) of the magma chambers.
estimates are claimed to be supported by radioisotope Laboratory experiments have produced very small
dating. quantities of magmas by the melting of appropriate
13
Catastrophic Granite Formation
the atoms inside the magma, the resistance of their
arrangement or bonding to the stress that would cause
0
0
flow. Viscosity is the internal friction or “stickiness� of
breccia pipe
a magma. A more viscous magma is very sticky and
1
flows very slowly. A magma (or lava) that flows easily
and thus quickly has a low viscosity.
0.5
2
dike
Rheology is the study of the flow of magmas and
Pressure (kb)
Depth (km)
of the ways in which magmas (and rocks) respond
3 dike
to applied pressures or stress. If a body of material
1.0
4
returns instantaneously to its initial undeformed
dike
state once the stress applied to it wanes, it is said to
5
be elastic. Magmas are not elastic, just viscous and
1.5
S2 S1
plastic, because once deformed by applied stress they
6 S1 S2
do not recover their original shapes, but instead flow.
1000°C
7 H 2O
The viscosity of a magma is dependent on its
S3
2.0
saturated
S3
temperature and composition. It should be fairly
carapace
8
obvious that the hotter a magma, the more quickly it
2 1 0 1 2
will flow, because the heat gives its atoms more energy
Distance (km)
so their bonding is less resistant to applied stress. A
Fig. 2. Schematic cross-section through a small granite
hotter magma is thus less viscous. However, there are
pluton at the stage of waning magmatic activity in
two compositional factors that affect magma viscosity
the development of a porphyry copper ore deposit. The
chaotic line pattern represents the extensive fracture the most—silica content and water content.
system in the apex above the cooling water-saturated When igneous rocks are analyzed, their content
granite magma. Note that the granite has intruded into of silicon atoms is expressed as a compositional
the volcanic rocks that earlier erupted from the volcano
percentage of silica, which is silicon dioxide (SiO2) or
its magma supplied.
the glassy mineral called quartz (similar to window
glass). Granites have a silica composition of around
rocks. Such experiments are not easy to perform
70%, whereas basalts contain around 50% silica.
because of the difï¬culties of simulating the high
Thus granitic magmas are far more viscous than
temperatures and pressures inside the earth. The
basaltic magmas. The latter are also hotter. This is
required laboratory apparatus thus only contains a
why basalt lavas tend to flow freely, compared with
very small vessel in which magmas can be produced.
rhyolite (granitic) lavas that are very viscous.
Yet many such experiments have enabled geologists to
The water content of magmas varies, but in general
study and understand the compositions and behavior
granitic magmas have far more water dissolved in
of magmas.
them than basaltic magmas. Indeed, the amount of
water dissolved in granitic magmas increases with
Magma Processes
pressure and therefore depth, from 3.7 wt % water
Measurements on extruded magma (lava),
content at 3�4 km depth (Holtz, Behrens, Dingwell,
together with evaluations of the temperatures
and Johannes 1995) to 24 wt % water at 100 km depth
at which constituent minerals form and coexist,
(Huang and Wyllie 1975). The effect of more water
and experimental determinations of rock melting
in a granitic magma is to reduce its viscosity. It is
relationships, indicate that magmas near the
this greater water content and viscosity of granitic
earth’s surface are generally at temperatures from
(rhyolitic) magma that make its volcanic eruption so
700°C to 1,200°C (1,300�2,200°F). We know from
explosive. The viscous granitic magma forms a better/
direct measurements in many deep drillholes
stronger “cork� (as it were) on the volcano, and with so
that rock temperatures inside the earth’s crust
much water as steam, the volcano’s top explodes. By
increase progressively with depth. This is known
comparison a basalt eruption is usually less explosive
as the geothermal gradient. From these measured
because the magma contains much less steam and
geothermal gradients it is thus estimated that the
the lava is much less viscous.
temperatures needed to melt rocks and form magmas
must occur at depths of greater than 30 km, at and
near the bottom of the crust of continents, and in the Magma Generation by Partial Melting
Typical geothermal gradients of 20°C/km do not
upper mantle below.
generate the greater than 800°C temperatures at
Being molten rock materials, magmas are very
35 km depth in the crust needed to melt common
dense liquids which have varying abilities to flow.
crustal rocks (Thompson 1999). However, there are
Viscosity describes the ability of the magma to
at least three other factors, besides temperature, that
flow. This depends on the degree of immobility of
14 A. A. Snelling
are important in melt generation: (1) water content of 2001) and is a function of melt composition, water
magma, (2) pressure, and (3) the influence of mantle- content, and the temperature (Dingwell, Bagdassarov,
derived basaltic magmas. The temperatures required Bussod, and Webb 1993). It has been demonstrated
for melting are signiï¬cantly lowered by increasing that the temperature and melt’s water content are
water activity up to saturation, and the amount of interdependent (Scalliet, Holtz, and Pichavant
temperature lowering increases with increasing 1998), yet the viscosities and densities of granitic
pressure (Ebadi and Johannes 1991). Indeed, water melts actually vary over quite limited ranges for
solubility in granitic melts increases with pressure, melt compositions varying between tonalite (65 wt %
the most important controlling factor (Johannes and SiO2, 950°C) and leucogranite (75 wt % SiO2, 750°C)
Holtz 1996), so that whereas at 1 kbar (generally (ï¬g. 3) (Clemens and Petford 1999). An important
equivalent to 3�4 km depth) the water solubility is implication is that the segregation and subsequent
3.7 wt % (Holtz et al. 1995), at 30 kbar (up to 100 km ascent processes, which are moderated by the physical
depth, though very much less in tectonic zones) it is properties of the melts, thus occur at broadly similar
approximately 24 wt % (Huang and Wyllie 1975). This rates, regardless of the tectonic setting and the
water is supplied by the adjacent rocks, subducted pressures and temperatures to which the source rock
oceanic crust, and hydrous minerals present in the has been subjected over time. Furthermore, granitic
melting rock itself. magmas are only 10�1,000 times more viscous than
Nevertheless, local melting of deep crustal rocks basaltic magmas (Baker 1996; Clements and Petford
is even more efï¬cient where the lower crust is 1999; Scalliet, Holtz, Pichavant, and Schmidt 1996),
being heated by basaltic magmas generated just which readily flow.
below in the upper (hotter) mantle (Bergantz 1989). Most ï¬eld evidence points to deformation
Partial melting of crustal rocks preheated in this (essentially “squeezing�) as the dominant mechanism
way is likely to be rapid, with models predicting a that segregates melt flow in the lower crust (Brown
melt layer two-thirds the thickness of the basaltic and Rushmer 1997; Vigneresse, Barbey, and Cuney
intrusions forming in 200 years at a temperature of 1996). Rock deformation experiments indicate that
950°C (Huppert and Sparks 1988; Thompson 1999). when 10�40% of a rock is a granitic melt, the pore
Experiments on natural rock systems have also pressures in a rock are equivalent to the conï¬ning
shown the added importance of mineral reactions pressure, so the residual grains move relative to one
involving the breakdown of micas and amphiboles to another resulting in macroscopic deformation due to
rapidly produce granitic melts (Brown and Rushmer melt-enhanced mechanical flow (Brown and Rushmer
1997; Thompson 1999). One such experiment found 1997; Rutter and Neumann 1995). These experiments
that a quartzo-feldspathic source rock undergoing also imply that deformation-enhanced segregation
water-saturated melting at 800°C could produce can in principle occur at any stage during partial
20�30 vol. % of homogeneous melt in less than 1�10
10
years (Acosta-Vigil et al. 2006).
A crucial consequence of fluid-absent melting is Leucogranite (SiO2, 75 wt%), 750°C
reaction-induced expansion of the rock that results in Tonalite (SiO2, 65 wt%), 950°C
8
log10 [Viscosity (Pa s)]
local fracturing and a reduction in rock strength due
to the increased pore fluid (melt) pressures (Brown 6
and Rushmer 1997; Clemens and Mawer 1992).
Stress gradients can also develop in the vicinity
of an intruding basaltic heat source and promote 4
local fractures. These processes, in conjunction
with regional tectonic strain, are important in 2
providing enhanced fracture permeabilities in the
melt H2O range melt H2O range
region of partial melting, which aid subsequent melt
0
segregation (Petford et al. 2000). 0 1 2 3 4 5 6 7 8 9 10
Water (wt%)
Fig. 3. Melt viscosity as a function of melt water (wt%)
Melt Segregation
content for typical tonalite and leucogranite liquid
The small-scale movement of magma (melt plus
compositions (after Clemens and Petford 1999) at a
suspended crystals) within the source region is called
ï¬xed pressure of 800 MPa. The horizontal line shows
segregation. The granitic melt’s ability to segregate
the range of water contents typical for natural melts.
mechanically from its matrix is strongly dependent on The estimated log10 values of the median viscosities
its physical properties, of which viscosity and density (in Pa s) of the liquids at their “ideal� water contents of
are the most important. Indeed, the viscosity is the 4 wt% (tonalite) and 6 wt% (leucogranite) are 3.8 and
crucial rate-determining variable (Woodmorappe 4.9 respectively.
15
Catastrophic Granite Formation
Life cycle of a vein fed by porous flow
Porous flow of melt into Rapid draining of Vein refills by
vein. Local compaction melt. Vein closes. porous flow.
4
in surrounding matrix.
Dike propagation
of granitic melt.
Zone of partial melt
3
Veins coalesce.
1 2 3
Critical dike
width exceeded.
1
Positive ï¿? Vmelting
2
(fluid-absent).
Porous flow and local
Formation of
compaction. Grain size
extensional fractures.
important.
Mafic Intrusion
T
Fig. 4. Schematic representation of a possible sequence of events (1�4) resulting from fluid-absent melting reactions
in a protolith above a maï¬c (intrusive) heat source in the lower crust. Veins ï¬ll by porous flow, with some local
compaction (inset).
melting. Furthermore, the deformation-assisted equilibrated between the two phases. Similarly, based
melt segregation is so efï¬cient in moving melt from on comparable evidence in a Quebec granite, Canada,
its source to local sites of dilation (“squeezing�) over the inferred time for the extraction of the melt from its
timescales of only a month up to 1,000 years. Thus the residuum was only 23 years (Sawyer 1991).
melts may not attain chemical or isotopic equilibrium
with their surrounding source rocks before ï¬nal Magma Ascent
extraction and ascent (Davies and Tommasini 2000; Gravity is the essential driving force for large-scale
Sawyer 1991). vertical transport of melts (ascent) in the continental
According to the best theoretical models, melted crust (Petford et al. 2000). However, the traditional
rock in the lower crust segregates via porous flow idea of buoyant granitic magma ascending through
into fractures within the source rock (usually the continental crust as slow-rising, hot diapirs or by
metamorphic) above a maï¬c intrusion (the heat stoping (that is, large-scale veining) (Weinberg and
source), the fractures inflating to form veins (Petford Podladchikov 1994) has been largely replaced by
1995). Local compaction of the surrounding matrix more viable models. These models involve the very
then allows the veins to enlarge as they ï¬ll further rapid ascent of granitic magmas in narrow conduits,
with melt, and the fluid-ï¬lled veins coalesce to form a either as self-propagating dikes (Clemens and Mawer
dike (ï¬g. 4). At a certain critical melt-fraction percent 1992; Clemens, Petford, and Mawer 1997), along
of the source rock, a threshold is reached where the preexisting faults (Petford, Kerr, and Lister 1993), or
critical dike width is achieved. Once that critical dike as an interconnected network of active shear zones
width is exceeded, “rapid (catastrophic) removal of and dilational structures (Collins and Sawyer 1996;
the melt from the source� occurs. The veins collapse D’Lemos, Brown, and Strachan 1993). The advantage
abruptly, only to be then reï¬lled by continuously of dike/conduit ascent models is that they overcome the
applied heat to the source rock. Thus the process is severe thermal and mechanical problems associated
repeated, the granitic melt being extracted and then with transporting very large volumes of granite
ascending through dikes to the upper crust in rapid magmas through the upper brittle continental crust
and catastrophic pulses. (Marsh 1982), as well as explain the persistence of
These rapid timescales for melt extraction are near-surface granite intrusions and associated silicic
well-supported by geochemical evidence in some volcanism. Yet to be resolved is whether granite
granites. For example, some Himalayan leucogranites plutons are fed predominantly by a few large conduits
are strongly undersaturated with respect to the or by dike swarms (Brown and Solar 1999; Weinberg
element zirconium (Harris, Vance, and Ayres 2000) 1999).
because the granitic melt was extracted so rapidly The most striking aspect of the ascent of granitic
from the residual matrix (in less than 150 years) that melts in dikes is the extreme difference in the magma
there was insufï¬cient time for zirconium to be re- ascent rate compared to diapiric rise, the dike ascent
16 A. A. Snelling
rate being up to a million times faster depending on emplacement-generated wall-rock structures, and
the magma’s viscosity and the conduit width (Clemens, density effects between the spreading flow and its
Petford, and Mawer 1997; Petford, Kerr, and Lister surroundings (Hogan and Gilbert 1995; Hutton
1993). The narrow dike widths (1�50 m) and rapid 1988). The mechanisms by which the host rocks
ascent velocities predicted by fluid dynamical models make way for this incoming magma have challenged
are supported by ï¬eld and experimental studies geologists for most of the past century and have been
(Brandon, Chacko, and Creaser 1996; Scalliet, Pecher, known as the “space problem� (Pitcher 1993). This
Rochette, and Champenois 1994). For example, for problem is particularly acute where the volumes of
epidote crystals to have been preserved as found in magmas forming batholiths (groups of hundreds of
the granites of the Front Range (Colorado) and of the individual granite plutons intruded side-by-side over
White Creek batholith (British Columbia) required large areas, such as the Sierra Nevada of California)
an ascent rate of between 0.7 and 14 km per year. are 100,000 km3 or greater and are considered to have
Therefore the processes of melt segregation at more been emplaced in a single event.
than 21 km depth in the crust and then magma ascent New ideas that have alleviated this problem are
and emplacement in the upper crust all had to occur (1) the recognition of the important role played by
within just a few years (Brandon, Chacko, and Creaser tectonic activity in making space in the crust for the
1996). Such a rapid ascent rate is similar to magma incoming magma (Hutton 1988), (2) more realistic
transport rates in dikes calculated from numerical interpretations of the geometry of granitic intrusions
modeling (Clemens and Mawer 1992; Petford, Kerr, at depth, and (3) the recognition that emplacement
and Lister 1993; Petford 1995, 1996), and close to is an episodic process involving discrete pulses of
measured ascent rates for upper crustal magmas magma. Physical models (Benn, Odonne, and de
(Chadwick, Archuleta, and Swanson 1988; Rutherford Saint Blanquat 1998; Cruden 1998; Fernández and
and Hill 1993; Scandone and Malone 1985). Indeed, Castro 1999; Roman-Berdiel, Gapais, and Brun
Petford, Kerr, and Lister (1993) calculated that a 1997) indicate that space for incoming magmas can
granite melt could be transported 30 km up through be generated through a combination of lateral fault
the crust along a 6 m wide dike in just 41 days at a opening, roof lifting. and lowering of the growing
mean ascent rate of about 1 cm/s. At that rate the magma intrusion floor. For example, space is created
Cordillera Blanca batholith in northwest Peru, with by uplift of the strata above the intrusion, even at the
an estimated volume of 6,000 km3, could have been earth’s surface, and their erosion.
ï¬lled from a 10 km long dike in only 350 years. The three-dimensional (3D) shapes of crystallized
It is obvious that magma transport needed to have plutons provide important information on how the
occurred at such fast rates through such narrow dikes granitic magmas were emplaced. The majority of
or else the granite magmas would “freeze� due to plutons so far investigated using detailed geophysical
cooling within the conduits as they ascended.Instead, (gravity, magnetic susceptibility, and seismic) surveys
there is little geological, geophysical, or geochemical appear to be flat-lying sheets to open funnel-shaped
evidence to mark the passage of such large volumes structures with central or marginal feeder zones
of granite magma up through the crust (Clemens and (Améglio and Vigneresse 1999; Améglio, Vigneresse,
Mawer, 1992; Clemens, Petford, and Mawer 1997). and Bouchez 1997; Evans et al. 1994; Petford and
Because of the rapid ascent rates, chemical and Clemens 2000), consistent with an increasing number
thermal interaction between the dike magmas and the of ï¬eld studies (collecting fabric and structural data)
surrounding country rocks will be minimal. Clemens that ï¬nd plutons to be internally sheeted on the 0.1
(2005) calculates typical ascent rates of 3 mm/s to meter to kilometer scale (Améglio, Vigneresse, and
1 m/s, which, assuming there is continuous, efï¬cient Bouchez 1997; Grocott et al. 1999).
supply of magma to the base of the fracture system, Considerations of ï¬eld and geophysical data
translates to between ï¬ve hours and three months suggest that the growth of a laterally spreading and
for 20 km of ascent. Such rapid rates make granite vertically thickening intrusive flow obeys a simple
magma ascent effectively an instantaneous process, mathematical scaling or power-law relationship
bringing plutonic granite magmatism more in line (between thickness and length) typical of systems
with timescales characteristic of silicic volcanism and exhibiting scale-invariant (fractal) behavior and size
flood basalt magmatism (Petford et al. 2000). distributions (McCaffrey and Petford 1997; Petford
and Clemens 2000). This inherent preference for
scale-invariant tabular sheet geometries in granitic
Magma Emplacement
The ï¬nal stage of magma movements is horizontal plutons from a variety of tectonic settings (ï¬g. 5)
flow to form intrusive plutons in the upper continental (Petford et al. 2000) is best explained in mechanical
crust. This emplacement is controlled by a combination terms by the intruding magma flowing horizontally
of mechanical interactions, either preexisting or some distance initially before vertical thickening then
17
Catastrophic Granite Formation
Emplacement Rates
2
Average crustal thickness (35km)
The tabular 3D geometry of granite plutons
and their growth by vertical displacements of their
log [Mean thickness (km)]
roofs and floors enables limits to be placed on their
1
emplacement rates (ï¬g. 6) (Petford et al. 2000). If we
assume that a disk-shaped pluton grows according
1
a=
to the empirical power-law relation shown in ï¬g.
0
5, T = 0.6 (±0.15) L0.6±0.1, then its ï¬lling time can be
estimated when the volumetric ï¬lling rate is known.
-1 Taking conservative values for magma viscosities,
wall-rock/magma density differences and feeder
Laccoliths (a = 0.88)
Plutons (a = 0.60)
dike dimensions results in pluton ï¬lling times of
between less than 40 days and 1 million years for
-2
-1 0 1 2 3
plutons under 100 km across. If the median value for
log [Mean length (km)]
the volumetric ï¬lling rate is used, then at the fastest
Fig. 5. Mean (vertical) thickness versus mean (horizontal)
length for granitic plutons and laccoliths (after Petford magma delivery rates most plutons would have been
et al. 2000). Reduced major-axis regression deï¬nes a emplaced in much less than 1,000 years (Harris,
power-law curve for plutons with an exponent a of
Vance, and Ayres 2000; Petford et al. 2000). Even
0.6 ± 0.1. Laccoliths (shallow-level intrusions) are
a whole batholith of 1,000 km3 could be built in only
described by a power-law exponent of 0.88 ± 0.1
1,200 years, at the rate of growth of an intrusion in
(McCaffrey and Petford 1997). The line a = 1 deï¬nes the
today’s noncatastrophic geological regime (Clemens
critical divide between predominantly vertical inflation
2005).
(a > 1) and predominantly horizontal elongation (a < 1)
Thus the formation of granite intrusions in the
during intrusion growth. Signiï¬cantly different power-
law exponents rule out a simple genetic relationship middle to upper crust involves four discrete processes�
between both populations. Differences may be due to partial melting, melt segregation, magma ascent,
mechanical effects, with limits in thickness reflecting
and magma emplacement. According to conventional
floor depression (plutons) and roof lifting (laccoliths).
Log [T (km)]
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2
occurs, either by hydraulic lifting of the overburden 8
(particularly above shallow-level intrusions) or -1
s
7 3
sagging of the floor beneath. Plutons thus go from a
-1
m s
.01
3
1m
0
birth stage characterized by lateral spreading to an 6
inflation stage marked by vertical thickening.
-1
s
3
m
5 00
This intrusive tabular sheet model envisages 1
larger plutons growing from smaller ones according
Log [t (yr)]
4
to a power-law inflation growth curve, ultimately MGP
3
to form crustal-scale batholithic intrusions (Cruden DCP
1998; McCaffrey and Petford 1997). Evidence of this 2
DCP lobe
growth process has been revealed by combined ï¬eld,
BMP
1
petrological, geochemical, and geophysical (gravity)
studies of the 1,200 km long Coast batholith of Peru 0 DCP field estimate
(Atherton 1999). On a crustal scale this exposed
-1
batholith was formed by a thin (3�7 km thick) low- 0 0.5 1 1.5 2 2.5
density granite layer that coalesced from numerous Log [L (km)]
smaller plutons with aspect ratios of between 17:1 Fig. 6. Estimated ï¬lling times for tabular disk-shaped
and 20:1. Thus this batholith would only amount to plutons (after Petford et al. 2000). This thickness
5�10% of the crustal volume of this coastal sector (T) to width (L) ratio is given by the equation in the
of the Andes (Petford and Clemens 2000), which text for a range of permissible ï¬lling rates (Q). Heavy
horizontal lines are the thickness ranges estimated
greatly reduces the so-called space problem. Detailed
using that equation for the Mount Gwens pluton
studies of the Sierra Nevada batholith of California
(MGP), the Dinkey Creek pluton (DCP) and the Bald
(which includes the Yosemite area) reveal a similar
Mountain pluton (BMP) in the Sierra Nevada batholith,
picture, in which batholith construction occurred by
California. Vertical lines are the ranges of their possible
progressive intrusion of coalescing granitic plutons ï¬lling times, bracketed by their ï¬lling rates. The colored
2�2,000 km2 in area, supposedly over a period of 40 prism indicates the range of thicknesses estimated
million years (as determined by radioisotope dating) independently for the southwest lobe of the DCP using
(Bateman 1992). structural data (Bateman 1992).
18 A. A. Snelling
geologists (Petford et al. 2000), the rate-limiting step multiphase flow of water and the heat it carries in the
in this series of processes in granite magmatism is relevant ranges of temperatures and pressures, so that
the timescale of partial melting (Harris, Vance, and a small pluton (1km × 2 km, at 2 km depth) is estimated
Ayres 2000; Petford, Clemens, and Vigneresse 1997), to have taken 3,500�5,000 years to cool depending
but “the follow-on stages of segregation, ascent, and on the system permeability. But this modeling does
emplacement can be geologically extremely rapid� not take into account the relatively thin, tabular
perhaps even catastrophic.â€? However, as suggested structure of plutons that would signiï¬cantly reduce
by Woodmorappe (2001), the required timescale their cooling times. Similarly, convective overturn
for partial melting is not incompatible with the caused by settling crystals in the plutons would be
6,000â€?7,000 year biblical framework for earth another signiï¬cant factor in the dissipation of their
history because a very large reservoir of granitic heat (Snelling and Woodmorappe 1998).
melts could have been generated in the lower crust
in the 1,650 years between Creation and the Flood, Convective Cooling:
particularly due to residual heat from an episode of The Role of Hydrothermal Fluids
accelerated nuclear decay during the ï¬rst three days Granitic magmas invariably have huge amounts
of the Creation Week (Humphreys 2000; Vardiman, of water dissolved in them that are released as the
Snelling, and Chafï¬n 2005). This very large reservoir magma crystallizes and cools. As the magma is
of granitic melts would then have been mobilized and injected into the host strata, it exerts pressure on
progressively intruded into the upper crust during the them that facilitates fracturing of them (Knapp and
global, year-long Flood when the rates of these granite Norton 1981). Also, the heat from the pluton induces
magmatism processes would have been greatly fracturing as the fluid pressure in the pores of the host
accelerated with so many other geologic processes strata increases from the heat (Knapp and Knight
due to another episode of accelerated nuclear decay 1977), this process repeating itself as the pluton’s
(Humphreys, 2000; Vardiman, Snelling, and Chafï¬n heat enters these new cracks.
2005) and catastrophic plate tectonics (Austin et al. Following the emplacement of a granitic magma,
1994), the likely driving mechanism of the Flood crystallization occurs due to this irreversible heat loss
event. to the surrounding host strata (Candela 1992). As heat
passes out of the intrusion at its margins, the solidus
(the boundary between the fully crystallized granite
Crystallization and Cooling Rates
The so-called space problem may have been solved, and partially crystallized magma) progressively
but what of the heat problem, that is, the time needed moves inward towards the interior of the intrusion
to crystallize and cool the granite plutons after their (Candela 1991). As crystallization proceeds, the water
emplacement? As Clemens (2005) states, given that dissolved in the magma that isn’t incorporated in the
it has now been established that the world’s granitic crystallizing minerals stays in the residual melt, so its
plutons are mostly tabular in shape and typically only water concentration increases. When the saturation
a few kilometers thick, it is a simple matter to model water concentration is lowered to the actual water
the cooling of granitic plutons by conduction (Carslaw concentration in the residual melt, ï¬rst boiling occurs
and Jaeger 1980). So using typical values for physical and water (as superheated steam) is expelled from
properties of the magma and wall-rock temperatures, solution in the melt, which is consequently driven
thermal conductivities and heat capacities, Clemens towards higher crystallinities as the temperature
(2005) determined that a 3 km thick sheet of granitic continues to fall. Bubbles of water vapor then nucleate
magma would take around 30,000 years to completely and grow, causing second (or resurgent) boiling within
solidify from the initially liquid magma. the zone of crystallization just underneath the solidus
However, this calculation completely ignores, as boundary and the already crystallized granite (ï¬g. 7).
already pointed out by Snelling and Woodmorappe As the concentration and size of these vapor bubbles
(1998), the ï¬eld, experimental, and modeling evidence increase, vapor saturation is quickly reached, but
that the crystallization and cooling of granitic plutons initially these vapor bubbles are trapped behind the
occurred much more rapidly as a result of convection immobile crystallized granite margin of the pluton
due to the circulation of hydrothermal and meteoric (Candela 1991). The vapor pressure thus increases
fluids, evidence that has been known about for more until the aqueous fluid can only be removed from the
than 25 years (for example, Cathles 1977; Cheng and sites of bubble nucleation through the establishment
Minkowycz 1977; Hardee 1982; Norton, 1978; Norton of a three-dimensional critical percolation network,
and Knight 1977; Paramentier 1981; Spera 1982; with advection of aqueous fluids through it or by
Torrance and Sheu 1978). The most recent modeling means of fluid flow through a cracking front in
of plutons cooling by hydrothermal convection the already crystallized granite and out into the
(Hayba and Ingebritsen 1997) takes into account the surrounding host strata. Once such fracturing of the
19
Catastrophic Granite Formation
The emplacement depth and the scale of the
Crystallized
hydrothermal circulatory system are ï¬rst-order
Solidus
Magma 1% Crystallization
parameters in determining the cooling time of a
large granitic pluton (Spera 1982). Water also plays
a “remarkable role� in determining the cooling time.
For a granitic pluton 10 km wide emplaced at 7 km
depth, the cooling time of the magma to the solidus
decreases almost tenfold as the water content of the
magma increases from 0.5 wt % to 4 wt %. As the
Country
temperature of the pluton/host rock boundary drops
Melt with <1%
Rock
Crystals
through 200°C during crystallization, depending on
the hydrothermal fluid/magma volume ratio, with
Liquid + Solid
only a 2 wt % water content, the pluton cooling time
decreases eighteen-fold. As concluded by Spera (1982,
Liquid + Solid
p. 299):
+ Vapor
Hydrothermal fluid circulation within a permeable
Vapor Bubbles
or fractured country rock accounts for most heat loss
when magma is emplaced into water-bearing country
Cracking Crystallization
Front rock . . . . Large hydrothermal systems tend to occur
Interval
Fig. 7. Cross-section through the margin of a magma in the upper parts of the crust where meteoric water
chamber traversing (from left to right): country rock, is more plentiful.
cracked pluton, uncracked pluton, solidus, crystallization
Of course, granitic magmas rapidly emplaced
interval, and bulk melt (after Candela 1991).
during the Flood would have been intruded into
pluton has occurred (because the cracking front will sedimentary strata that were still wet from just
go deeper and deeper into the pluton as the solidus having been deposited only weeks or months earlier.
boundary moves progressively inward toward the Furthermore, complete cooling of such granitic plutons
core of the intrusion), not only is magmatic water did not have to all occur during the Flood year.
released from the pluton carrying heat out into the It is also a total misconception that the large
host strata, but the cooler meteoric water in the crystals found in granites required slow cooling rates
host strata is able to penetrate into the pluton and (Luth 1976, pp. 405�411; Wampler & Wallace 1998).
thus establish a convective hydrothermal circulation All the basic minerals found in granites have been
through the fracture networks in both the granite experimentally grown over laboratory timescales
pluton and the surrounding host strata. The more (Jahns and Burnham 1958; Mustart 1969; Swanson,
water is dissolved in the magma, the greater will Whitney, and Luth 1972; Winkler and Von Platen
be the pressure exerted at the magma/granite and 1958), so macroscopic igneous minerals can crystallize
granite/host strata interfaces and thus the greater and grow rapidly to requisite size from a granitic
the fracturing in both the granite pluton and the melt (Swanson 1977; Swanson and Fenn 1986). So,
surrounding host strata (Knapp and Norton 1981; asks Clemens (2005), how long did it take to form the
Zhao and Brown 1992). plagioclase feldspar crystals in a particular granite?
Thus by the time the magma has totally crystallized Linear crystal growth rates of quartz and feldspar
into the constituent minerals of the granite, the solidus have been experimentally measured and rates of
boundary and cracking front have both reached the 10-6.5 m/sec to 10-11.5 m/sec seem typical. This means
core of the pluton as well. It also means that a fracture that a 5 mm long crystal of plagioclase could have
network has been established through the total volume grown in as short a time as one hour, but probably
of the pluton and out into the surrounding host strata no more than 25 years (Clemens 2005). Actually, it
through which a vigorous flow of hydrothermal fluids is extraneous geologic factors, not potential rate of
has been established. These hydrothermal fluids thus mineral growth, which constrain the sizes of crystals
carry heat by convection out through this fracture attained in igneous bodies (Marsh 1989). Indeed, it
network away from the cooling pluton, ensuring the has been demonstrated that the rate of nucleation
temperature of the granitic rock mass continues to is the most important factor in determining growth
rapidly fall. The amount of water involved in this rates and eventual sizes of crystals (Lofgren 1980;
hydrothermal fluid convection system is considerable, Tsuchiyama 1983). Thus the huge crystals (meters
given that a granitic magma has enough energy due long) sometimes found in granitic pegmatites have
to inertial heat to drive roughly its mass in meteoric grown rapidly at rates of more than 10-6 cm/s from
fluid circulation (Cathles 1981; Norton and Cathles fluids saturated with the components of those
1979). minerals within a few years (London 1992).
20 A. A. Snelling
(Snelling 2005; Snelling and Armitage 2003). Such
Crystallization and Cooling Rates:
a timescale for crystallization and cooling of granite
The Evidence of Polonium Radiohalos
plutons is certainly compatible with the biblical
There is a feature in granites that severely restricts
timescales for the global Flood event and for earth
the timescale for their emplacement, crystallization,
history.
and cooling to just days or weeks at most—polonium
It might be argued that the uranium in the
radiohalos (Snelling 2005; Snelling and Armitage
zircon grains could continue to supply polonium
2003). Radiohalos are minute spherical (circular in
and radon isotopes to the polonium deposition sites
cross-section) zones of darkening due to radioisotope
via hydrothermal fluids for an extremely long time
decay in tiny central mineral inclusions within the
period after the temperature of the granites fell
host minerals (Gentry 1973; Snelling 2000). They are
below 150°C, so the polonium radiohalos would
generally proliï¬c in granites, particularly where biotite
not need to form in hours to days. Even though the
(black mica) flakes contain tiny zircon inclusions that
half-lives of the polonium isotopes are very short,
contain uranium. As the uranium in the zircon grains
a long steady-state decay of uranium would surely
radioactively decays through numerous daughter
build up slowly the uranium radiohalos, and the
elements to stable lead, the α-radiations from eight
hydrothermal fluids would steadily transport the
of the decay steps produce characteristic darkened
radon and polonium to slowly generate the polonium
rings to form uranium radiohalos around the zircon
radiohalos nearby.
radiocenters. Also present adjacent to these uranium
However, this presupposes that the hydrothermal
radiohalos in many biotite flakes are distinctive
fluids continued to flow for long periods of time after
radiohalos formed only from the three polonium
the granites cooled below 150°C. To the contrary,
radioisotopes in the uranium decay chain. Because
once the granites and hydrothermal fluids fall below
they have been parented only by polonium, they are
150°C most of the energy to drive the hydrothermal
known as polonium radiohalos.
fluid flow has already dissipated. The hydrothermal
The signiï¬cance of these polonium radiohalos in
fluids are expelled from the crystallizing granite and
granites is that they had to form exceedingly rapidly
start flowing just below 400°C (ï¬g. 8). So unless the
because the half-lives (decay rates) of these three
granite cooled rapidly from 400°C to below 150°C,
polonium radioisotopes are very short�3.1 minutes
most of the radon and polonium transported by the
(218Po), 164 microseconds (214Po), and 138 days (210Po).
hydrothermal fluids would have been flushed out of
Furthermore, each visible radiohalo requires the
the granites by the vigorous hydrothermal convective
decay of 500 million to one billion parent radioisotope
flows as they diminished. Simultaneously, much of
atoms to form them (Gentry 1973; Snelling 2000).
the energy to drive these fluid flows dissipates rapidly
The zircons at the centers of the adjacent uranium
as the granite temperature drops. Thus, below 150°C
radiohalos are the only nearby source of polonium
the hydrothermal fluids have slowed down to such an
(from decay of the same uranium that produces
extent that they cannot sustain protracted flow, and
the uranium radiohalos). The hydrothermal fluids
with the short half-lives of the radon and polonium
released by the crystallization and cooling of the
isotopes, they would decay before those atoms reached
granites flow between the sheets making up the
the polonium deposition sites. Furthermore, the
biotite flakes to transport the polonium from the
capacity of the hydrothermal fluids to carry dissolved
zircons to adjacent concentrating sites. These then
radon and polonium decreases dramatically as the
become the radiocenters which produce the polonium
temperature continues to drop.
radiohalos (Snelling 2005; Snelling and Armitage
Thus sufï¬cient radon and polonium had to be
2003). Furthermore, the radiohalos can only form
transported quickly to the polonium deposition sites
after the granites have cooled below 150°C (Laney
to form the polonium radiohalos, while there was
and Laughlin 1981), which is very late in the granite
still enough energy at and just below 150°C to drive
crystallization and cooling process. Yet uranium decay
the hydrothermal fluid flow rapidly enough to get
and hydrothermal transport of daughter polonium
the polonium isotopes to the deposition sites before
isotopes starts much earlier when the granites are
the polonium isotopes decayed. This is the time and
still crystallizing. Nevertheless, because of the very
temperature “window� depicted schematically in Fig.
short half-lives of these three polonium radioisotopes
8. The time “window� is especially brief in the case
that necessitate their rapid hydrothermal fluid
of the decay of the 218Po and 214Po isotopes (half-lives
transport to generate the polonium radiohalos within
of 3.1 minutes and 164 microseconds respectively)
hours to a few days, it is estimated that the granites
and the formation of their radiohalos. It would thus
also need to have crystallized and cooled within 6�10
be simply impossible for these polonium radiohalos
days, or else the required large quantities of polonium
to form slowly over millions of years at today’s
(from grossly accelerated decay of uranium) would
groundwater temperatures in cold granites. Heat is
decay before they could form the polonium radiohalos
21
Catastrophic Granite Formation
was catastrophically subducted
800 Intrusion of granite magma into pluton
under the overriding North
(with zircon grains already releasing Po)
American plate, the western
First mineral grains begin crystallizing
735
(plagioclase, biotite, orthoclase,quartz)
edge region of the latter was
700
Crystallization of
deformed, resulting in buckling
Biotite grains have crystallized Magma
of its sedimentary strata and
600 metamorphism at depth (ï¬g.
All mineral grains have crystallized
573
9). The Paciï¬c plate was also
and are stable
Resi
progressively heated as it was
500
dua
subducted, so that its upper
Temperature (°C)
l ma
side began to partially melt
and thus produce large volumes
gm
400 First release of hydrothermal fluids
a
of basalt magma. Rising into
385
so Rn and Po transport commences
the lower continental crust of
the deformed western edge of
Hy
300 ot
dr
he
the North American plate, the
rm
al
heat from these basalt magmas
flu
ids Time/Temperature “Window� for the
200
in turn caused voluminous
Formation of Polonium Radiohalos
Annealing temperature
partial melting of this lower
150 Polon
of radiohalos
continental crust, generating
ium ra
diohalo
s form
100
buoyant granitic magmas.
Hydrothermal convection too slow
75
These rapidly ascended via
dikes into the upper crust,
0
where they were emplaced
0 1 2 3 4 5 6 7 8 9 10
rapidly and progressively as the
Time (days)
hundreds of coalescing granitic
Fig. 8. Schematic, conceptual, temperature versus time cooling curve diagram
plutons that now form the
to show the timescale for granite crystallization and cooling, hydrothermal
Sierra Nevada batholith. The
fluid transport, and the formation of polonium radiohalos.
presence of polonium radiohalos
needed to dissolve the radon and polonium atoms, and in many of the Yosemite area granitic plutons (Gates
to drive the hydrothermal convection that moves the 2007; Snelling 2005) is conï¬rmation of their rapid
fluids which transport the radon and polonium atoms crystallization and cooling late in the closing phases
to supply the radiocenters to generate the polonium of the Flood year. Conventional radioisotope dating,
radiohalos. Furthermore, the required heat cannot which assigns ages of 80�120 million years to these
be sustained for the 100 million years or more while granites (Bateman 1992), appears to be grossly
sufï¬cient 238U decays at today’s rates to produce in error because of not taking into account the
the required polonium atoms to form the polonium acceleration of the nuclear decay (Vardiman, Snelling,
radiohalos. Thus the granites need to have crystallized and Chafï¬n 2005). Subsequent rapid erosion at the
and cooled rapidly (within 6�10 days) to still drive the close of the Flood, as the waters drained rapidly off
hydrothermal fluid flow rapidly enough to generate the continents, followed by further erosion early in
the polonium radiohalos within hours to a few days. the post-Flood era and during the post-Flood Ice
Age, have exposed and shaped the outcropping of
Formation of the Yosemite Area these granitic plutons in the Yosemite area as seen
Granitic Plutons today.
Finally, the formation of the hundreds of granitic
plutons of the Sierra Nevada batholith, some of Conclusions
which outcrop on a grand and massive scale in the Even the conventional long-ages geologic
Yosemite area, can thus be adequately explained community now regards the formation stages of
within the biblical framework for earth history. The granite plutons, after partial melting of source rocks
regional geologic context suggests that late in the to form granitic melts, that is, melt segregation, ascent
Flood year, after deposition of thick sequences of and emplacement, to be “geologically extremely rapid�
fossiliferous sedimentary strata, a subduction zone perhaps even catastrophic.� At today’s apparently
developed just to the west at the western edge of the slow rates of partial melting signiï¬cant granite
North American plate (Huber 1991). Because plate magmatism is not now occurring. However, a large
movements were then catastrophic during the Flood reservoir of granitic melts could have been generated
year (Austin et al. 1994), as the cool Paciï¬c plate in the lower crust during the 1,650 years between
22 A. A. Snelling
Creation and the Flood, particularly Metamorphism and
due to residual heat from an episode of crustal deformation
accelerated nuclear decay during the ï¬rst Intrusion of
granitic magma
three days of the Creation Week. This very
large reservoir of granitic melts would then Continental
have been mobilized and progressively Oceanic crust
crust
intruded into the upper crust during the Upper
global Flood cataclysm, when another mantle
episode of accelerated nuclear decay would Melting
have greatly accelerated many geologic Assimilation of
oceanic plate
processes, including granite magmatism, into mantle
driven by catastrophic plate tectonics.
Partial melting occurs, due to Fig. 9. Subduction of an oceanic plate (Paciï¬c plate) during
heating of the lower crust by basalt convergence with a continental plate (North American plate).
magmas intruded from the mantle, to Magma, formed by partial melting of the overriding continental
the elevated local water content, and to plate, rises into the continental plate to form volcanoes and granite
locally increased pressures as a result of plutons along a mountain chain (after Huber 1991).
tectonic activity. Once it occurs, continued
deformation (“squeezing�) segregates the melt so that need to have crystallized within 6�10 days.
it flows. Melt-ï¬lled veins then coalesce into dikes Quite clearly, timescales for the generation of
as “squeezing� continues episodically, effectively granitic magmas and their intrusion, crystallization,
“pumping� the granitic melt into the dikes and up the and cooling are no longer incompatible with the
dike-ï¬lled fractures into the upper crust. Thus, with a biblical time frame for earth history and its global
continuous supply of magma at the base of the fracture Flood cataclysm.
system in the lower crust, the magma could typically
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