CPT Q. 072: How do you respond to those who claim that granite simply cannot form from a melt?

In your response to question 30, you stated: “The case is strong that melting of these subducted sediments generated the staggering volume of granitic magma that was emplaced along the western margin of North, Central, and South America during the Flood.”

You also claimed that the majority of creation scientists would agree with you on this matter, to which I must object. In fact, I know that three of the present forum authors, and many of our honorable panelists besides myself would disagree strongly in that granite cannot form from a melt. Ollier and Pain would also contend that the composition of the Sierra Nevada batholiths isn’t even remotely close to the sediments it was supposed to have been formed from – and they’re right: For example, where do the carbonates fit into this picture of granites forming from molten sediments?

There are many good, physical reasons for why granite cannot form from a melt, and the weight of the evidence would be on our side, as granite has never been formed in the lab, nor has it ever been observed to form in the best laboratory around: nature. The onus would be upon yourself and anyone who make such claims to explain and demonstrate how granite can form from a melt. I will go so far as to say that granite forming from a melt must defy physical laws. In order to get the large crystals of granite, the minerals must cool slowly – yet letting the minerals cool slowly means the mineral will separate out by density – and thus you would not get granite.

Response: You certainly seem passionate about this topic. But frankly, I find myself utterly bewildered by your outlook. It would be helpful if I could chat with you regarding these issues. It seems that you have not been keeping up with the creationist thinking on the formation of granite that has been published over the last 10-15 years. Let me point you, for example, to the 2003 article by Tas Walker entitled, “Granite grain size: not a problem for the rapid cooling of plutons,” TJ 17(2), 49-55 (online). Let me quote from one section that deals crystal growth rates and crystal size in granitic melts, based primarily on laboratory experiments.

The science of crystallization has been developing apace because crystallization is widely used in the chemical industry, metallurgy and ceramics and so is of enormous economic importance. Today many books are available on the scientific understanding of the process. ^{27, 28} 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. If the physical and chemical conditions are such that the rate of crystal nucleation is high and the rate of crystal growth is low, then the product will have abundant fine-grained crystals (Figure 6a). To produce large crystals, as occur in granite, the rate of nucleation needs to be low, and the rate of growth high (Figure 6b). Such a situation would be produced if the physical and chemical conditions changed rapidly, not providing time for nucleation to occur but allowing for crystal growth.

One laboratory study by Swanson determined that crystal-growth rates could reach several millimeters per day within polyphase granitic systems.²⁹ With such growth rates he concluded that granite could be produced rapidly. Swanson found that maximum growth rates of crystals are lower in systems which contain a H₂O-rich vapor phase and higher in systems that are undersaturated with H₂O. This means that a sudden loss of volatiles within a magma chamber would lead to rapid crystal growth. Swanson’s work demonstrates that long periods of time are not necessary to produce the coarse-grained granitic textures. Another factor is the degree of undercooling, that is, the extent to which the temperature of the melt is lower than the crystallization temperature. Under conditions of low undercooling, a relatively small number of large crystals could be grown in a few days. The degree of undercooling within a magma chamber would depend on magma chamber pressure and magma volatile content, both of which could be changed quickly by the tectonic processes associated with the Flood. It is worth noting that this work by Swanson has already been discussed in the context of rapid cooling of granite by Snelling and Woodmorappe.⁶

Another laboratory study³⁰ on silicate melts found crystal growth starts at nucleation sites already present before the magma cools. This produces granitic textures much faster than previously thought.

Crystallization theory and practice reveals other clues that point to granite crystals having grown rapidly. First, when crystals grow rapidly they trap some of the surrounding liquid, forming fluid inclusions inside them.³¹ In many industrial applications it is important to grow crystals sufficiently slowly so they do not have inclusions. But mineral crystals in granite contain fluid inclusions, indicating they grew quickly, not slowly over millions of years.

This article makes a number of relevant points. First of all, granitic rocks have indeed been produced from melts in the laboratory by many different investigators over the past 35 years, with no physical laws being violated in the process. Th article also emphasizes that grain size does not depend primarily on the cooling rate. Other factors such as the nucleatio rate, volatile content, and abrupt pressure changes can play a much larger role than the cooling rate. Crystal growth rates as high as several millimeters per day have been demonstrated in the laboratory. Under conditions of rapid intrusio of magma and rapid crystallization after intrusion, negligible settling of the crystals takes place. The article also alludes t the vast number of intrusive granitic bodies, in many cases, intruding into fossiliferous Flood sediments that are exposed and readily available for study at many sites around the world. In other words there are literally thousands of field examples of granite bodies that have intruded near-surface rocks as melt and solidified with a coarse-grained crystalline fabric in nature’s (or perhaps more appropriately God’s) laboratory.

The Tas Walker article cites a note by J. M. Wampler and P. Wallace in the Journal of Geoscience Education, vol. 46, pp. 497-499, 1998 entitled “Misconceptions—a column about errors in geoscience textbooks.” These authors state that the common textbook claim that, in igneous rocks, “large crystals form only if they have time to grow slowly,” without any further qualification, should be discontinued in view of the large number of exceptions, especially given the fact that coarse-grained igneous rocks frequently give evidence for rapid cooling. They claim this error causes students to misidentify hand specimens, infer the wrong crystallization sequences, and ignore the crucial role of volatiles in rock formation. They attribute the problem to writers of introductory geology textbooks and field guides, and recommend that, in future, writers explain how crystal size depends on many factors other than cooling rate—factors such as nucleation rate, viscosity, original composition of the melt, pressure variation and the amount of volatiles. So this idea that grain size is determined primarily by cooling rate is not only a misconception among some creationists, it is widespread in the uniformitarian community. In fact, defective uniformitarian reasoning is almost certainly how this misconception gained such a foothold in the first place.

Since you mention the granite of the Sierra Nevada, I am curious concerning your thinking as to when and under what circumstances this granite came into existence. Are you aware of careful field studies that have concluded that these granitic rocks from a structural standpoint represent a maze of overlapping horizontal sills, like pancakes, intruded into the surrounding country rock, with each intrusion identifiable from its own distinctive chemical and isotopic signature? Are you aware of the Cretaceous radioisotope ages obtained consistently by many different investigators for these granitic rocks? And are you aware of the work of the RATE team which showed that radioisotope dating, probably in more cases than not, does give generally reliable relative ages? The radioisotope dates for the Sierra Nevada granites suggest rather strongly that these rocks were intruded and crystallized during the Flood. This is in addition to the fact that the surrounding regional geology indicates the country rock into which these intrusive rocks were emplaced corresponds to an incredibly thick sequence of fossiliferous Paleozoic and Mesozoic sediments. On the issue of the fate of subducted carbonates, upon heating calcium carbonate and dolomite readily decompose to CaO, MgO, and CO₂, and CaO and MgO are both readily incorporated into the lattices of most silicate minerals.

In conclusion, I urge you to read the article by Walker carefully, to check out the papers and books he references, and, if is possible for you, to reconsider this issue of how granites, especially those intruded into Flood sediments, formed.