Granite formation: catastrophic in its suddenness
by Tas Walker
‘In fact, just about everything that was taught as recently as ten years ago
about granitic magmatism has been turned on its head.’1
So concludes John Clemens in his overview paper about the origin of granite, published
in the UK in the Proceedings of the Geologists’ Association.
In his introduction to Clemens’s paper and the accompanying discussion, editorial
board member W.J. French explains that the origin of granite has been controversial
since before James Hutton (1726–1797). After summarizing the turbulent disputes
through the 1950s and up to the present, French boldly proclaimed that with Clemens’s
paper, ‘The granite controversy ends’!
Conflict with the Bible
Figure 1. Model for the origin of granite: (1) partial melting of source rock deep
inside the crust, (2) separation of magma from solid residue, (3) transport of magma
in dykes to upper crust, (4) accumulation of magma into tabular pluton, (5) crystallization
of pluton, and (6) cooling of pluton.
For more than a century geologists have accepted that granites formed slowly over
millions of years. Any suggestion that the biblical account with its 6,000-year
timeframe be taken seriously has been dismissed as nonsense.
Geologist Paul Blake, in the newsletter of the Australian Geological Society, argued
exactly that—that granite formation means that any geological model based
on ‘the Bible’s flood myth’ is absurd, and ‘all the available
evidence contradicts such ideas.’2
He illustrates his point using granite outcrops:
‘Field relationships [in this area of Australia] show that there are two entirely
separate granitoid intrusive events in the sequence, each of which require at least
3,500 years to cool. How does Dr Walker fit 7,000 years worth of granitoid cooling
into 60 days? Unless Dr Walker can find a way to emplace, cool and unroof granitoids
within a couple of days then his model does not stand up to scrutiny.’2
But, according to Clemens, slow-and-gradual ideas about granite formation are wrong:
‘The long-cherished picture of granitic diapirs [balloons of magma] slowly
pushing their way toward the upper crust and grinding to a halt by solidification
has been replaced by an altogether different picture of narrow feeder dykes punching
their way upward in months, pulsing with magma and feeding rapidly growing plutons.’1
Surprisingly, Clemens suggests that belief in an old earth has long led thinking
down the wrong path. He claims that the idea the earth is 4,600 million years old
had ‘a psychological effect of tempting one to consider geological processes
as slow and continuous. After all, there is all that time to fill.’ He concludes
that granites belong with increasing number of geological processes that were ‘catastrophic
in their suddenness’.
Clemens has researched igneous rock-forming processes most of his professional career.
He specialised in crystalline rocks, particularly granites, and applied field, geochemical,
isotopic and experimental approaches to understanding their origin.
The whole thrust is that granites form quickly, much faster than previously imagined,
something that creationists have previously reported.
One of the contributors invited to discuss Clemens’s paper, Wallace Pitcher,
took mild exception to the idea that Clemens’s views are new. Pitcher, who
had researched the granite problem for over 60 years, said he had ‘long abandoned
the idea of vertically extensive, deep-seated pyramidal batholiths, envisaging instead
dyke-interconnected magma chambers, themselves filled pulsively.’3 Note the word ‘pulsively’, suggesting
crustal dynamics were involved.
The whole thrust is that granites form quickly, much faster than previously imagined,
something that creationists have previously reported.4
Magma production
Granite magma is the result of melting or partial melting of a pre-existing source
rock (figure 1). The second step is that the melt must be separated from the solid
residue and collected into bodies. The evidence points to the process of melt segregation
being rapid.5
Clemens explains that metamorphic rocks of the granulite facies6 are considered to be the solid residue from the
process of partial melting and melt segregation. So, since the granitic magma was
produced rapidly, then the associated metamorphism was also rapid. The mineral transformations
that occur during metamorphism are the result of chemical reactions, and these need
abundant water to allow the free exchange of ions. With the appropriate physical
conditions chemical reactions proceed quickly.
Magma transport
Also, since the melts are produced deep within the crust, the magma must have travelled
tens of kilometres upward. How this occurs depends in part on the physical properties
of the melts, which can be quite complicated. Some of the findings have been surprising.
Viscosity calculations have shown that the flow properties of granitic magma remain
relatively unaffected by the presence of crystals.7
Furthermore, for magma to ascend to the surface it is found that the critical widths
of the dykes are quite small, of the order of 1–2 m only. In other words,
narrow dykes can be very efficient transporters of granitic magma in the crust.7
With the dyke model, the ascent rates of granitic magma could vary by less than
10% over a broad compositional range.7
The crystals that form in granitic magma can actually resorb during and after ascent.
This means that any remnants of the source rock (resistite) could be destroyed during
ascent causing the magma viscosity to lower. In fact, the ascent rate could increase
during ascent, meaning that the magmas would accelerate rather than slow down.7
Magma can be transported through pre-existing structures such as faults and joints.
However, pre-existing structures are not necessary because the buoyancy of the magma
in vertical cracks will cause the cracks to propagate. Any sudden failure of the
wall rock would lead to an upward migration of the crack tips and an upward flow
of the magma.
So how long does it take for magma to ascend 20 km in the crust? With typical magma
and crust properties it could be anywhere between five hours and three
months. Clements says:
‘Such rapid ascent rates are clearly negligible on the scale of geological
time. This would make granitic magma ascent effectively an instantaneous process
… ’8
What sort of time would it take to build a huge pluton? According to Clemens, a
dyke 3 m wide and 1 km long (in plan) could build a batholith of 1,000 km3
in 1,200 years.
While this is longer than the biblical timescale, remember that that Clemens is
working within the uniformitarian paradigm of a 4.6-billion-year-old earth. A period
of 1,200 years is probably the longest he could comfortably stretch the time. A
slightly modified combination of parameters (such as dyke dimensions, magma viscosity
and fluid content) would make the biblical timeframe even more plausible. ‘Huge
batholiths could be created quickly with relatively small dykes or pipes that tap
magma sources many kilometres to tens of kilometres below.’8
Clemens describes how the crystals in some granites are arranged in patterns resembling
textures in sedimentary rocks: graded-layering, cross-layering, scour and fill structures,
flame structures and swirls or enclaves of crystals.9 According to Clemens these ‘attest to the
fluid character of the magma’. But they do more than that. They point to the
fact that the magma was flowing when the crystals settled, and that the flow was
pulsing. These support the concept that the batholiths filled quickly during times
of tectonic disturbance.
Magma crystallization
Another idea that Clemens ‘turns on its head’ is that the large crystals
in granite grow slowly over long periods of time. This has long been used as an
argument against the reliability of the biblical timescale, but it has been refuted
before.10 Clemens too
notes that crystallization can be much faster than previously imagined possible:
‘Experimentally measured rates indicate that a 5 mm crystal of plagioclase
could have grown in as short a time as 1 hour, but probably no more than 25 years.’11
Pluton cooling is another geological process that has been said to take millions
of years, but geological understanding of pluton geometry no longer supports this.
Recent geological and geophysical observations have revealed that the world’s
granitic plutons are mostly tabular in shape and typically only a few kilometres
thick. This runs counter to the old idea of vertically extensive batholiths, but
this is now accepted as an observational fact.8
Photo by Mark Armitage
Figure 2. A polonium halo.
Given this tabular shape, it is a simple matter to model the cooling by conduction
of a 3 km sheet of granitic magma.8 Based on conduction alone (i.e. ignoring
the cooling effect of fluids) it would take only 30,000 years to completely solidify
from the initially liquid magma. But we know that fluids play a controlling role
in the cooling of granitic magma, and their behaviour would drastically reduce the
time.12
Rapid crystallization and cooling is also indicated by the presence of tiny spheres
of radiation damage within biotite crystals in granite. Halos produced by polonium
(figure 2) are abundant in granites, pointing to catastrophic geologic processes
on a young earth.13,14 Clemens did not mention this remarkable evidence,
but it further confirms the general thrust of his paper.
Pitcher agrees with Clemens’s conclusions about the shape of granitic plutons,
quipping that ‘the single towering body was an offence to reason.’15 He also pointed out that
a thin geometrical shape ‘is consistent with the remarkably low degree of
contact metamorphism against bodies of considerable outcrop area.’16
More and more consistent with the biblical timeframe
Clemens’s overview of the latest findings on the origin of granite demonstrates
that the geological evidence is leading to models that are consistent with the biblical
record.
But there are still important unanswered questions. Why do granite rocks form in
the first place? What initiates the melting of the source rocks? This is where the
biblical model of the Genesis Flood provides a simple but elegant explanation. The
enormous tectonic upheaval involved is sufficient cause—from beginning to
end. Global scale catastrophe created continental scale crustal movements that initiated
partial melting deep inside the earth, forcing the magma through the crust, and
emplacing it in huge magma chambers—all quickly. We do not see granitic magma
being produced and emplaced on these scales today.
In spite of the revolution in thinking about granite discussed in the Geologists’
proceedings, and the recognition of granitic catastrophism, the authors nowhere
suggest that the age of the earth should be questioned, even though they recognize
the harmful psychological effects of the long-age paradigm. This problem was not
recognized or explored. But, now that they have extended geologic catastrophism
from sedimentary rocks to igneous (and, by association, metamorphic) ones, where
do they propose inserting the billions of years of time?
‘Obvious truth is rarely as obvious as one thinks.’11
Related articles
Further reading
Related resources
References
- Clemens, J.D., Granites and granitic magmas: strange
phenomena and new perspectives on some old problems, Proceedings of the Geologists’
Association 116:9–16, 2005; p. 15. Return
to text.
- Blake, P., Granite cooling times and the Bible, The Australian
Geologist 111:10, 30 Jun. 1999. Return to text.
- Pitcher, W.S., Invited comment on Clemens’s ‘Granites
and granitic magmas’, Proceedings of the Geologists’ Association
116:21–23, 2005; p. 21. Return to text.
- Woodmorappe, J.,
The rapid formation of granitic rocks: more evidence, Journal of Creation
15(2):122–125, 2001. Return to text.
- Clemens, ref. 1, p. 11. Return to text.
- The granulite metamorphic facies is interpreted as forming
at pressures equivalent to some 10 to 40 km depth and temperatures greater than
about 750°C. Return to text.
- Clemens, ref. 1, p. 13. Return to text.
- Clemens, ref. 1, p. 14. Return to text.
- Clemens, ref. 1, pp. 9, 10. Return to text.
- Walker, T.B., Granite grain size: not a problem
for rapid cooling of plutons,
Journal of Creation 17(2):49–55, 2003.
Return to text.
- Clemens, ref. 1, p. 15. Return to text.
- Snelling, A.A. and Woodmorappe, J., The cooling of thick
igneous bodies on a young Earth; in: Walsh, R.E. (Ed.), Proceedings of the Fourth
International Conference on Creationism, Technical Volume, Creation Science
Fellowship, Pittsburgh, pp. 527–545, 1998. See Snelling, A. and Woodmorappe,
J., Rapid Rocks: granites … they didn’t need millions of years of cooling,
Creation 21(1):42–44, 1999, for a lay-level summary. Return to text.
- Snelling, A.A., Radiohalos in granites: evidence
for accelerated nuclear decay; in: Vardiman, L., Snelling, A.A., and Chaffin, E.F.,
Radioisotopes and the Age of the Earth, volume II, ICR and CRS, El Cajon
and Chino Valley, ch 3, pp. 101–207, 2005. Return to text.
- Snelling, A., Radiohalos: Startling evidence of catastrophic
geologic processes on a young earth,
Creation 28(2):46–50, 2006. Return
to text.
- Pitcher, ref. 3, p. 21. Return to text.
- Pitcher, ref. 3, p. 22. Return to text.
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