Do large crystals in granite prove very slow cooling?
First posted: 5 August 2002; republished: 13 March 2009 (GMT+10)
From Byron Bultsma, USA—he accuses Dr Tas Walker of ignorance of materials science, because he claims that large crystals are a disproof of slow cooling. However, as Dr Walker shows in his response below, there is a lot more to materials science in the area of the kinetics of crystal growth than Mr Bultsma realises.
Apparently your Tas Walker is not familiar with material science. In Geology and the young earth, Answering those ‘Bible-believing’ bibliosceptics, Tas says that granite plutons do not require long cooling times. This is rationalized by the claiming that circulating water cooled the granites rapidly. This ignores the fact that the microstructure of the rock is dependent on the cooling rate. If the magma were cooled rapidly the resulting structure would be finer grained, in a word, no longer a granite but a rhyolite. If there were a large variation in the cooling rates of plutonic rocks as described in Rapid Rocks: Granites … they didn’t need millions of years of cooling, then the structure would be differentiated. The regions near these fractures would exhibit finer grain sizes than regions more centrally located. But granites do not exhibit such a structure. The microstructure of any material is a function of the composition and thermo-chemical history. And the microstructure of the granites in question does not affirm the thermo-chemical history you attach to them. Rather it indicates a slow and steady cooling.
The Bible teaches that the world is ‘young’: ‘If the Bible taught that the world was millions of years old, we would believe that. However, the concept of millions of years of death and suffering contradicts the Word of God, and destroys the foundation of the Gospel of Christ.’
So, when it comes to the microstructure of granite, the issue is not that ‘Tas Walker is not familiar with material science.’ Rather the issue is: ‘Am I going to believe what the Bible says, or am I going to believe what the geology textbooks say?’ As you so rightly point out, there is a glaring discrepancy.
From the outset, it is sobering to realise no geologist has ever seen a granite pluton form. Everything that you and I were taught in our geology courses about pluton formation is circumstantial speculation interpreted within a preconceived framework. However, once we accept the biblical Flood as a reality, many new factors become significant. New solutions become apparent. Naturally, these need to be tested in the field and new ideas then emerge.
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There are many field clues that grain size is affected by factors other than slow cooling over millions of years. For example, there are often thin dykes (aplite dykes) associated with granite intrusions, and these have a coarse-grained texture. Such thin dykes would have cooled faster than a large pluton but they still have large crystals. Conversely, rhyolite bodies are often very large but have a fine-grained volcanic texture in the middle. If cooling rate were the only factor, the middle of such a large volume of magma would cool slowly and produce coarse-grained texture. Robert Gentry, in his book Creation’s Tiny Mystery, cites a case where a magma more than 500 m underground cooled to produce a fine-grained rhyolite.1
What other factors could affect grain size? Field evidence shows that granites are associated with folded sedimentary rocks and this suggests that crustal compression was important. Uniformitarians assume the processes of compression and emplacement took tens of millions of years. However, in the catastrophic Flood the processes may have only taken days. In this case dynamic forces would have been significant and produced great pressure changes in the magma. Pressure affects a material’s melting point. Specifics differ for individual materials depending on the P-V-T-density-entropy space.
Field evidence also shows that significant volumes of magmatic fluid (volatiles) were released when granite plutons were emplaced. Such fluids are frequently associated with economically significant deposits of gold and other minerals, and these are often located at the edges of plutons.
Since receiving your question I have consulted a number of reference books about crystallization.2,3 Although I have a reasonable general knowledge on materials science, I am not an expert. Crystallization is widely used in the chemical industry and of enormous economic importance. The size of crystals depends on two factors: the rate of crystal nucleation and the rate of crystal growth. Our present understanding of both these factors is still in its infancy. For large crystals, the rate of nucleation simply needs to be low, and the rate of growth high.
I suspect that rapid changes in magma chamber pressure during the Flood and rapid changes in magma fluid content (volatiles) were important factors. These would have greatly affected the rates of crystal nucleation and growth. Interestingly, I found two other clues in the reference books that point to rapid crystal growth.
First, when crystals grow rapidly they trap some of the surrounding liquid, forming fluid inclusions inside the crystal.4 In many industrial applications it is important to grow crystals sufficiently slowly so they do not have inclusions. Interestingly, mineral crystals in granite contain fluid inclusions, yet they are supposed to have grown slowly over millions of years.
Second, in industrial applications, special attention is needed to prevent crystals settling.5 If the crystals in granites formed slowly over millions of years, we would expect them to have settled into layers. The layers would reflect the relative density of the crystals and the order of crystallization. In fact there are igneous intrusions where such layering has occurred. Yet the crystals in granites are reasonably homogeneous throughout the pluton, suggesting they crystallized rapidly before they had time to settle.
Here are two specific field examples. The Tatoosh granodiorite pluton (i.e. large crystals) in Mt Rainier National Park of Washington State shows unequivocal field evidence of shallow emplacement and rapid cooling—directly opposite the conventional geologic teaching that plutons cooled slowly at great depth.6 Field evidence indicates the magma crystallized due to dehydration under a cover so thin that volatiles streamed up through the roof. In Nevada, field evidence indicates that a batholith (a huge pluton) cooled so rapidly that its upper crust was strengthened against extensional stress.7
One laboratory study found crystal growth starts at nucleation sites already present before the magma cools. This produces granitic textures much faster than previously thought.8 Another study determined crystal-growth rates of several millimetres per day within polyphase granitic systems showing that granitic texture can occur rapidly.9
Wampler and Wallace,10 in The Journal of Geoscience Education, say the idea that large crystals grow only if they have time to grow slowly should no longer be taught. In their article they discuss some of the many exceptions such as coarse-grained aplite dykes (mentioned above) and pegmatites, which have enormous crystals. They say that the idea that slow-cooling magma produces large crystals discourages students from thinking about the possible processes of formation.
So, rather than crystal size being a problem, the apparent contradiction leads to new insights into possible geological processes. I hope this encourages you to start ‘thinking’ along these lines. ‘The fear of the Lord is the beginning of wisdom’ (Proverbs 9:10).
- Gentry, R. Creation’s Tiny Mystery, 3rd Ed., Earth Science Associates, Knoxville, TN, pp. 130–131, 1992.
- Mersmann, A. (Ed.), Crystallization Technology Handbook, 2nd Ed., Marcel Dekker, New York, 2001.
- Mullin, J.W., Crystallization, 4th Ed., Butterworth Heinemann, Oxford, 2001.
- Mersmann, Ref. 2, p. 621.
- Mullin, Ref. 3, pp. 451–459.
- Fiske, R.S., Hopson, C.A. and Waters, A.C., Geology of Mount Rainier National Park Washington: United States Geological Survey Professional Paper 444, p. 93, 1963, cited in Catastroref, Institute of Creation Research.
- Sawyer, D.A., Fleck, R.J., Lanphere, M.A., Warren, R.G., Broxton, D.E. and Hudson, M.R., Episodic caldera volcanism in the Miocene southwestern Nevada Volcanic field: Revised stratigraphic framework, 40Ar/39Ar geochronology, and implications for magmatism and extension, Geological Society of America Bulletin 106:1301–1318, 1994, cited in Catastroref, Institute of Creation Research.
- Lofgren, G., Experimental studies on the dynamic crystallization of silicate melts: in; Hargraves, R.B. (Ed.), Physics of Magmatic Processes, Princeton University Press, Princeton, pp. 487–552, 1980, cited in Catastroref, Institute of Creation Research.
- Swanson, S.E., Relation of nucleation and crystal growth rate to the development of granitic textures, American Mineralogist 62:966–978, 1977, cited in Catastroref, Institute of Creation Research.
- Wambler, J.M. and Wallace, P., Misconceptions—a column about errors in geoscience textbooks: misconceptions of crystal growth and cooling rates in the formation of igneous rocks: the case of pegmatites and aplites, Journal of Geoscience Education 46:497–499, 1998, cited in Catastroref, Institute of Creation Research.