Robert Gentry and Instant Granites

YEC Robert Gentry claims that granites containing Polonium halos were formed instantaneously during the "creation week." According to Gentry, these granites could not have originated from high-temperature, intrusive magmas: "The simple evidence of the halos is that the basement rocks of the earth were formed solid." We will return to that idea later. The halos.com homepage states:

"Etched within Earth's foundation rocks--the granites--are beautiful microspheres of coloration produced by the radioactive decay of primordial polonium, which is known to have only a fleeting existence. A simple analogy shows, on one hand, how these polonium microspheres--or halos--contradict the evolutionary belief that granites formed as hot magma slowly cooled over millions of years. On the other hand, it demonstrates how these halos provide unambiguous evidence of an almost instantaneous creation of granites"

While I don't consider myself competent to evaluate the physics of Gentry's claim, I have checked out the field evidence courtesy of Lorence Collins and Richard Wakefield, and this evidence clearly and directly refutes Gentry's claims of "instant granites."

The pages I consulted can be found at:

The Tiny Mystery Homepage
Examining Radiohalos: A Creationist Critique
Equal Time for the Origin of Granite - A Miracle!

Additional Information:

Contact Metamorphism - Tulane University
Contact Metamorphism
Contact Metamorphism - Pictures
Cooling History of the Carion Pluton

Problems with Gentry's "Instant Granite" Hypothesis

1. Many of Gentry's biotite samples are not even from granites at all, they are from pegmatite dikes and cacite veins. These pegmatite veins are, as far as I know, almost universally regarded as hydrothermal deposits formed long after the the rocks in which they are enclosed.

The field relationships show very clearly that the pegmatite dikes from which Gentry collected many of his sample are not "primordial" at all. Describing the geologic context in which the pegmatite dikes are found, Collins writes:

"Figure 5 diagrammatically shows the geological relationships of part of the Shield and the location of Gentry’s Faraday samples. Let me emphasize that these relationships are not based primarily on some ill-defined 'uniformitarian principle' but on hard-won field observations over more than 100 years of work by hundreds of geologists. The pegmatite dikes in the area cut a gabbro (shown at the bottom right), which cuts different types of metasedimentary rocks. In the Madoc area south of Bancroft (middle block), the metasedimentary rocks can be shown to rest in a complex way on metavolcanics. The supergroup, in turn, rests unconformably on the metamorphosed Algonquin Batholith, which intrudes the deep- and shallow-water metasediments to the north (top block), which abuts (by a major fault) and partly rests on the metasedimentary column of the Southern Province, which rests unconformably on the "greenstone" metasediments and metavolcanics intruded by granites, which abuts the metasedimentary and gneissic belts to the north in the Superior Province. So, if Gentry’s claim of created granite is valid, then the entire sequence also must have been instantly created -'in just three brief minutes.' This is not science, but merely a monumental example of the Omphalos argument."

Figure 5 can be found at:

http://www.csun.edu/~vcgeo005/gentry/fig5.htm

Wakefield describes his attempts to inform Gentry about the evidence from the sedimentary rocks. I found this most amusing, and *highly* revealing:

"In his book Gentry talks of 'pristine sedimentary' created rocks which look as though they were intruded by granites. When Gentry phoned me (unfortunately, Gentry has never responded to my letters in any manner other than with phone calls) after I sent him a copy of this paper in preliminary form, I asked him about these sedimentary rocks. He claimed that metasedimentary rocks show no clear origin because of their recrystallization. Because his response was so patently false, I told him that many of these metasedimentary rocks show clear and unambiguous sedimentary features, like clastic grains, cobbles, ripple marks, mudcracks, bedding plains and, most important, stromatolites. He had no answer."

Unless one is willing to accept that God instantaneously created thick sections of ripple-marked, mudcracked, sedimentary sedimentary rocks containing stromatolites, then Gentry's interpretation simply cannot be correct.

2. Gentry plays fast and loose with physical "constants." Gentry postulates changes in decay rates at the creation, at the fall, and during the flood. The amazing thing, though, is that his argument *requires* the decay rates of Po isotopes to remain stable, so he ends up arguing that uranium and other radioactive nuclides underwent rapid decay at these 3 times, yet the Po decay rates remained the same!

Even worse, Gentry's assumption of accelerated decay rates during the "creation" and flood compromises the accurate identification of halos in the first place. Gentry is identifying the halos based on their diameter, yet the diameter of the halos is partly a function of decay rate! R.H. Brown points out:

"Halo identification is achieved through the measurement of the halo diameter. The size of the halo and the half-life of the isotope producing it are related. Assuming that the half-life of the parent isotope has remained constant throughout the formation of the halo, the initial energy of the alpha particles that produced the halos can be determined, and hence the parent radioactive isotope identified.

"In making this identification, Gentry assumes, as do other scientists, a constancy of radioactive decay rate for polonium. However, Gentry also wants to invoke periods of time that '... may have been accompanied by an increased, nonuniform radioactive decay rate' (p. 134). If there were periods of nonuniform decay rates, identification of any pleochroic halo from its ring diameter would be questionable at best!

"All available data indicate that halo ring diameter increases with increase in decay rate. Either the rates remain constant or they do not. Evidence from other sources suggests that the decay rates have remained constant for all radioactive isotopes. Several problems arise when one attempts to invoke increased decay rates while at the same time keeping the halo diameters constant! Such inconsistency cannot be considered as a satisfactory argument.

Gentry arbitrarily postulates wildly "variant" laws of physics. Decay rates are constant sometimes, they are accelerated sometimes, and only some decay rates are accelerated, while others are not.

3. I'm not sure why, but Gentry and many of his followers actually believe that *all* granites are primordial "creation rocks." I guess they don't want to argue that some granites were magically created by God during the creation week, while others exactly like them were created by slowly cooled intrusive magmas.

But again, the field evidence shows that this clearly not the case. There are *many* precambrian granitic bodies (dikes, sills, plutons) which intrude stromatolite-containing sedimentary rock, just as Gentry's examples do. Some phanerozoic granites intrude fossiliferous sedimentary rocks too, and even contain *fossiliferous* inclusions. These observations conclusively disprove the notion that all granites are "primordial." Did God instantly create the granites with inclusions of fossiliferous sedimentary rock? Collins' list several examples of this:

" the Donegal granites in northwest Ireland intrude and enclose inclusions of sedimentary rocks of Cambrian age, illustrating that the granites are younger than the Cambrian deposits, whose contacts with the granites have a high-temperature metamorphic aureole (Pitcher and Berger, 1972). The same kinds of metamorphic contact-relationships are found in the granites that intrude fossil-bearing sediments in Maine, Connecticut, and Rhode Island (Harrison et al., 1983).

"The Narragansett Pier granite in Rhode Island surrounds inclusions of Pennsylvanian metamorphosed sediments containing flora fossils, Annularia stellata (Brown et al., 1978). The flora fossils are now totally carbonized as graphite, indicating the high temperature of the granite body that metamorphosed the sedimentary inclusions. The fact that the granite contains inclusions of these fossil-bearing sediments makes the granite younger than these supposed "Flood" sediments.

"The Sierra Nevada granite intrusions in California also have intruded and metamorphosed supposed 'Flood sediments' in roof pendants containing Ordovician graptolite fossils (Frazier et al., 1986) and Pennsylvanian brachiopod fossils (Rinehart and Ross, 1964; Rinehart et al., 1959). In other places, the Sierran granites have intruded and metamorphosed "Flood sediments" containing Triassic ammonites (coiled cephalopods) (Smith, 1927).

"A granite in the Mojave desert in California near Cadiz intrudes Cambrian limestone containing stromatolite fossils. At the contact, this limestone is converted to marble with high-temperature metamorphic minerals, but remnants of the stromatolites can still be found (Richard Squires, oral communication, 1998). Thus, it is very clear from the above examples that some granite masses are the same age as or even younger than the 'Noachian Flood deposits.'"

 

Brown, A., Daniel, P., and Barghoorn, E. S., 1978, Pennsylvanian fossils from metasediments within the Narragansett Pier granite, Rhode Island: Geological Society of America Abstracts with Programs, v. 10, n. 2, p. 34-35.

Frazier, M., Stevens, C. H., Berry, W., Smith, B. M., and Varga, R., 1986, Relationship of the Sierran Coyote Creek pendant to the adjacent Inyo Mountains, east-central California: Geological Society of America Abstracts with Programs, v. 18, n. 2, p. 106.

Harrison, W., Flower, M., Sood, M., Tisue, M., and Edgar, D., 1983, Crystalline rocks of northeastern United States: ANL/ES- Argonne National Laboratory, v. 137, p. 414.

Pitcher, W. S., and Berger, A. R., 1972, The Geology Of Donegal: A Study Of Granite Emplacement And Unroofing: New York, Wiley Interscience, 435 p.

Rinehart, C. D., and Ross, D. C., 1964, Geology and mineral deposits of the Mount Morrison quadrangle, Sierra Nevada, California: U. S. Geological Survey Professional Paper 385, 106 p.

Smith, J. P., 1927, Upper Triassic marine invertebrate faunas of North America: U. S. Geological Survey Professional Paper 141, 262 p.

R.H. Brown mentions an example from the Ural Mountains, where sedimentary inclusions in granite include brachiopod shells:

Malakhova, N. R and L. N. Ovchinnikov. 1970. A find of fossils in granite of the central Urals. USSR Academy of Sciences, Doklady, Earth Science Section 188:33-35.

4. Maybe the most absurd part of the instant granite scenario is the presence of metamorphic aureoles and "baked" contacts in sedimentary rocks which have been intruded by granites. Why are they present? This makes perfect sense if the granitic bodies originated as magmas which cooled slowly, but Gentry doesn't think that granites originated from magma at all! As I said earlier, it is also common to find baked inclusions of the surrounding rock within the granite. I have an excellent picture of some large blocks of banded gneiss clasts in a granite like raisins in raisin bread. This is hardly expected if the granites originated as solid bodies, as Gentry claims. Another excellent quote from Collins:

"As further evidence of the high temperature origin of granite is the contact metamorphic aureole that occurs in sedimentary rocks where they are intruded by granite magma. The minerals found in sediments are generally stable near 25 degrees C and one atmosphere of pressure and result from weathering processes at the earth's surface. When these minerals are heated to temperatures approaching those of an adjacent hot granite magma, some will remain as the same mineral but will recrystallize and increase in size while others will form new minerals that are stable at high temperatures and pressures. For example, find-grained fossil-bearing limestones that consist of calcite (calcium carbonate), which are intruded by granite magma, commonly recrystallize as coarse-grained calcite marbles; in this process the fossils are destroyed as the tiny calcite crystals in the fossils grow in size. On the other hand, sedimentary shales, consisting mostly of aluminum-rich clay, are recrystallized to form other aluminum-rich minerals, some of which are stable at the highest temperatures closest to the granite contact; others are stable at intermediate temperatures at greater distances away; and still others are stable at lower temperatures at even farther distances from the contact (e.g., Pitcher and Berger, 1972; Holtta, 1995). Such aureoles (a few meters to a 1,000 meters or more) of high-temperature contact-metamorphism of sedimentary wall rocks are found world-wide around most granite bodies of large size and support the concept that these granite bodies were intruded as a very hot magma."

5. Collins lists additional evidence for the liquid/magmatic origin of granites:

"In the field, granite can be seen to intrude other rocks and in some places to exhibit flow banding, both of which are possible characteristics of moving liquids or plastic solids. In many places, however, fragments of older rock along the walls of a granite body are broken off and enclosed in the granite body when it was first formed. Finally, if a granite body has a liquid origin, it should have the capability of mixing with other liquids, such as basalt magma, and this clearly occurs, for example, in Maine (Wiebe, 1996) and in other parts of the world."

Wiebe, R. A., 1996, Mafic-silicic layered intrusions: the role of basaltic injections on magmatic processes and the evolution of silicic magma chambers: Transactions of the Royal Society of Edinburgh, Earth Sciences, v. 87, pts. 1 and 2, p. 233-242.

6. Radiometrically determined cooling histories. It is possible to determine the "cooling history" of igneous bodies by dating different minerals within the body. Because these minerals have different "closure temps," they can be used to determine when the melt passed certain temperatures. Results from such thermochronologic studies shows that granites do in fact originate from high-temp magmas that cool slowly over time.

Joe Meert at Indiana University describes evidence for the cooling history of the Carion Pluton in Madagascar. This is just one of many examples that can be found in the "cooling history" literature. Meert writes:

"Closure temperature of isotopic systems also provides a check of radiometric dates. In slowly-cooled igneous bodies such as granites, different minerals become closed systems at different temperatures (McDougall and Harrison, 1999). This is due, at least in part, to the fact that the minerals crystallize at different temperatures. The temperatures at which minerals close is easily verifiable through experimentation and this has been conducted numerous times including the famous experiments of Bowen. Therefore, if a body has indeed cooled slowly then the radiometric dates from that rock should demonstrate such a cooling trend.

"The Carion pluton in central Madagascar is approximately 20 kilometers in diameter and is the subject of an ongoing paleomagnetic study (Meert et al., in press). The rocks have been dated using both the U-Pb system and the 40Ar/39Ar system on a variety of minerals. The following table outlines the closure temperatures of the various minerals used in the Carion study along with their ages. Details regarding closure temperature studies can be found in McDougall and Harrison (1999).

Isotopic System /Closure Temperature/Age

Zircon U-Pb 850 +/- 50 C 532.1 +/- 5 Ma

Hornblende 40Ar/39Ar 500+/-50 C 512.7 +/-1.3Ma

Biotite 40Ar/39Ar 350+/-50 C 478.9 +/-1.0Ma

K-spar 40Ar/39Ar 200+/-25 C 435.0 +/-10Ma

K-spar 40Ar/39Ar 100+/-25 C 410 +/-10Ma

"**Note that the ages of the minerals yields a cooling-curve that is consistent with the experimentally-derived closure temperatures of the isotopic systems**. Had decay rates not been constant, then we might expect to see a gross discordance of mineral ages in this study. Instead, we see a very nice cooling curve for this magma. The story doesn't end there however! This study also included a look at the paleoposition of Madagscar at the time this rock cooled. This is done through the study of paleomagnetism. Madagascar was thought to be a part of a larger supercontinent called Gondwana during this time period. A reference curve for Gondwana has been developed that basically traces the paleoposition of Gondwana during the time interval from 550-475 Ma (Meert et al., in press). If Madagascar was indeed a part of this supercontinent, then the paleomagnetic directions for Madagascar should be indentical to the directions from other continents that make up Gondwana. Since magnetic minerals in the Carion rocks lock in their directions at temperatures between 550-450 C (in this study), then the age of magnetization is about 511 +/- 10 Ma. The position of Mdagascar should match up with other 510 Ma directions from Gondwana---and they do!.

"Here, as above, we have many independent verifications for the age of the Carion pluton that are internally self-consistent. This presents a serious problem for those who might advocate random decay rates for the different isotopic systems."

1. Torsvik et al., 1998, Late Cretaceous magmatism in Madagascar: paleomagnetic evidence for a stationary Marion hotspot, EPSL (64), 221-232.

2. Meert et al., 1998, Tectonic significance of the Fen Province, S. Norway: Constraints from geochronology and paleomagnetism, J. Geol., 106, 553-564.

3. Storey et al., 1995, Timing of hotspot related volcanism and breakup of Madagascar and India, Science, 267, 852-855.

4. Dahlgren, 1994, Late Proterozoic and Carboniferous ultramafic magmatism of carbonatitic affinity in southern Norway, Lithos, 31, 141-154.

5. Verschure et al., 1983, dating explosive volcanism perforating the Precambrian basement in southern Norway, Norg. Geol. Under., 380, 35-49.

6. Meert et al., in prep, Timing of Cretaceous magmatism in northern Madagascar: Additional paleomagnetic constraints.

7. McDougall, I. and Harrison, T.M., 1999, Geogchronology and thermochronology by the 40Ar/39Ar method, Oxford University Press, Oxford, 269 pp.

8. Meert, J.G. et al., in press, Paleomagnetism, geochronology and tectonic implications of the Cambrian-age Carion granite, central Madagascar, Tectonophysics.