PYROCLASTIC NATURE OF KIMBERLITES: REALITY AND ILLUSIONS.

Igor Kryvoshlyk.

Toronto, Canada. (416) 248-8514, e-mail: ikryvoa481@rogers.com

"All truth passes through three stages. First, it is ridiculed.

Second, it is violently opposed. Third, it is accepted as self-evident."

-- Arthur Schopenhauer

So far very few geologists [V.V.Kovalsky, 1963; I.N.Kryvoshlyk, 1976, 1998] did not accept a pyroclastic idea of emplacement of kimberlite rocks in its full size. Why? Because it is necessary to estimate, how realistic this idea is. There are some questions, which are ignored for many years, but they still demand proper answers.

First of all, how often have usual (rhyolitic/andesitic/basaltic) lapilli been observed within their own crater (Fig. 1)?

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Fig.1. Tephra from volcano B can be described as samples from volcano A [18]. The entire B-tephra is going OUT of B-crater (red arrows), while the same B-tephra is coming INTO the A-crater (green arrows). Ash-B can not make a deposit in its own B-crater, but in the A-crater and in a surrounded area only.

There are a lot of pyroclastic rocks around craters [8], but what is inside? For comparison, let’s imagine, how many pellets drop back down into the same rifle after shooting up into the air? Please, make an experiment.

Really pyroclastic lapilli have a very distinctive texture of their surface well known among volcanologists [5] as a “bread crust” (Fig. 1a & 1b). Does anybody have a sample of “kimberlitic lapilli” with such “bread crust”? And what about “ribbon bombs” (Fig. 2a & 2b)? How often these and another so distinctive pyroclasts (Fig. 3, 4, 5) can be observed within kimberlite pipes?

Fig.1a. “Bread crust” bomb [6]. Fig.1b. “Bread crust” bomb [6].

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Fig.2a. Ribbon bomb [6]. Fig.2b. Ribbon bomb [6].

Fig.3. Explosion bomb [6]. Fig.4. Rotation bomb [6].

Fig.5. Volcanic cow-pie bomb. Idaho. Fig.6. Spherical bomb with vesicular surface. Arizona

“By far the greater number of bombs is…very vesicular” [5]. Nobody ever described vesicular kimberlite bombs or lapilli, as well as pumice or scoria - well-known pyroclastic rocks variety (Fig. 6, 7, 8), however still unknown for kimberlites. But, please, don’t confuse this originally magmatic feature (Fig. 8, 15) with secondary porosity of some kimberlites which is a result of postmagmatic leaching mostly of pseudomorphs after olivine.

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Fig.7. Volcanic pumice can float, Fig.8. Porous scoria. The view is about kimberlite - does not two inches across. Courtesy of Lynn S. Fichter, James Madison University, Harrisonburg, Virginia

Fig. 9. Sharply angular and porous shard Fig. 10. “Tuffisitic kimberlite” withof real volcanic ash under electron micro solid well rounded ash size particlesscope. Mt. Erebus, Antarctica. [10]. Red (PL) which are similar to drops of

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1 mm

arrows join the same size particles. liquid inside another liquid (like oil in water, Fig. 12). Tuzo kimberlite. PPL [16].

Let’s compare so-called “kimberlitic ash” which has to be a main component of tuffisitic kimberlite (Fig. 10) with the real volcanic ash (Fig. 9). Does anybody really see similarities (except their size) between sharply angular and porous ash shards from Erebus and very well rounded solid particles of TK from Tuzo kimberlite (Fig. 10)? The texture of the kimberlite “tuff” (Fig. 10) is clearly identical to the texture of the rocks like Chilean orbicular macrocrystalline granite (Fig. 11) which is definitely NOT a pyroclastic rock.

Fig. 11. Example of liquid immiscibility. Fig. 12. The vegetable oil (yellow) andOrbicular granite on the Pacific coast in water are immiscible liquids. Curriculum northern Chile. Homeschool Conservation – Liquid Layers.69 by Aurora Lipper.Park "Santuario de la Naturaleza”. GrahamWilson. February 2009.

The simplest experiment which illustrates a natural phenomenon of liquid immiscibility is system water – oil (Fig. 12).

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From the point of view of the resistance against mechanical disintegration, massive kimberlites look like solid magmatic but altered and weathered paleotypal rocks. On the contrary, many of pyroclastic rocks look like typical alluvium (Fig. 13, 14), perhaps, because both of them have similar sedimentary origin?

Fig.13. Tephra deposit 130 km from the Fig. 14. Sedimentary alluviumsource. Crater Lake, Oregon. [11]. The Pele’s tears are the important element of tephra (Fig. 16). As lava drops fall through the air, they are aerodynamically shaped with comet-like tails. Frankly speaking, during my 40-years career in kimberlite geology I never saw and never heard about such shape of kimberlitic autoliths like a separated piece of rock with comet-like tails.

Fig.15. Highly vesicular basalt tephra Fig. 16. Pele’s tears. Mauna Ulu,

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clasts. Thin section [9, sample 197]. Hawaii. [Photo by J.D.Griggs, 1984].

Finally, let’s remember the existence of so-called “blind” kimberlite pipes. Not the pipes covered by latest sediments, but diatremes, which never had an exit to the earths’ surface like 5034 North Lobe. How could they be filled up by “pyroclastic” material, which has virtually never been in the air? It is obvious nonsense. Also, the existence of this type of diatremes eliminates an idea about the growth of pipes starting from the earth surface towards the depth.

For the better understanding of the inner structure of volcanoes / kimberlite pipes it is important to bear in the mind the proper sequence of events, because not first (tephra?), but the latest / final magmatic material filled up the crater / diatreme. This material is represented by lava flows only [8], not by pyroclactics (Fig. 17).

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Fig. 17. Cross-section of the 3D model of the typical volcano. Kimberlite pipe can be classified as a main volcanic vent. Orange – magma, brown – pyroclastic rocks [12]. Clear absence of pyroclastic in the main vent.

Suggestion of the underground (???) volcanic explosions inside the solid rocks looks especially unrealistic (Fig. 20). The term “tuffisites” was proposed by Cloos for fragmented country rock in pipes located in Swabia, synonym – “intrusive tuff” [13]. However, it is well known that “intrusive” means “macrocrystalline abyssal rock” and “tuff” means “consolidated volcanic ash”. Therefore, their combination in the phrase “abyssal ash” does not make any sense.

There are other good examples of poor petrography in volcanology. “Accretionary lapilli” are wide spread terms for specific kind of tephra.

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„Accretionary lapilli are pellets that formed by the accretion of fine ash around condensing water droplets or solid particles, particularly in steam-rich eruptive columns. Commonly, they exhibit (Fig. 18, 19) a concentric internal structure [22, 23].

Fig. 18. Close-up of a lapilli-bearing dike Fig. 19. Accretionary lapilli from the basal penetrating the basal breccia near Fuentes suevite breccia near Corbatón in the RubielosCalientes. Note that many lapilli have the de la Cérida impact basin [23].typical onion skin structure around a stony core [22].

Reviewing the attached photos (Fig. 18, 19), it is hard to identify this “typical onion skin structure“. Some kind of concentricity is clearly present, but rather like trivial contact alteration. Contact – between two chemically different melts generated by the liquid immiscibility of the original magma.

It believes that it is hard to expect the presence of droplets of liquid water in the ash cloud. The temperature of ash particles in the eruptive column above the crater was definately higher than 100 degree, thus, water could not be present as liquid.

Finely, the rocks on Figs. 18-19 have a matrix-support texture. For how long time these „lapilli“ were hanged in the air motionlessly before the matrix was created? Is this possible?

What kind of material created this matrix? If this was the same ash, so why part of the ash became „organized“ into lapilli, when other part of the same ash was left intact? There are only two extreme products of this process:

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lapilly and matrix. Where are the intermediate formations between lapilli and matrix?

Current texture (Figs. 18, 19) remind rather liquid immiscibility (Fig. 12) than a volcanic product.

Petrology = Petrography + Thermodynamics. Without them it’s not a science, it’s just a science fiction. Mechanism of volcanic explosions requires having an open compressible space like the earth’s atmosphere. Magmatic melt itself is not a compressible substance as well as all other liquids. Small first portion of volatile-rich magma does not make big difference because without having an open space with lower pressure volcanic gases will stay inside the original system.

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Fig.20. Example of wrong interpretation of poor petrography [14]. Tuffisites injected in the solid Riphean sandstones (???).

The same quality has a “theory of phreatomagmatism” which authors are trying to prove that interaction between magma and water has to trigger the water boiling and explosive eruption. They suggest that a vapor film, which is produced between magma and water, can cause the fragmentation of magma. This idea is widely used for explanation of the microglobular texture of some kimberlite rocks called tuffisitic kimberlites or volcaniclastic kimberlites. Has anybody observed this type of fragmentation in action in the nature or at least in the thermodynamically correct experiment?

Latest experiment [19] should not be taken into consideration. Discussion of these results with the author of experiment revealed some serious errors. Thermodynamically important to copy during experiment physical conditions which were in nature. Thus, injection of water into magma can create different products compare with those which could be observed if magma was injected into water. That is why, perhaps, authors of experiment [19] did not create a necessary conditions for generation of the spinifex texture which should appear in ultrabasic portion of experimental system.

They are trying to prove that the phreatomagmatic mechanism had created all kimberlitic and other diatremes. However, it’s hard to believe that each diatreme was provided (?) with “individual” lake of water. About 90% of Canadian kimberlites have occurred under the lakes. And who was that lucky “sniper” who hundred of times had shot the magma columns exactly in the center of each lake from a distance of 150-200 km? And what if there is no water around?

What kind of explosions authors of phreatomagmatism have expected? Which substance has to explode? What kind of detonator was in use? Who has synchronized explosive with detonator? Why contemporary volcanoes do not explode according to this “theory” and do not create diatremes instead of banal volcanoes?

Fig. 21 shows clear absence of explosions on the contact of very hot (>1,000C) basaltic lava and ocean water. There are a lot of proves that the kimberlite magma has had a very low temperature, much lower than basaltic

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magma had [<200C, 15, 17] and thus it could not create an intensive water boiling which is so necessary for phreatic eruption. So, is the “phreatomagmatism” a real natural phenomenon or just an illusion?

Above mentioned fragmentation is most likely nothing else than a product of liquid immiscibility, and a microglobular texture (Fig. 10) is a natural emulsion which was created by two immiscible liquids, in case of kimberlites – picrite in the immiscible carbonatite [4]. Only liquid immiscibility could produce superfine fragmentation of magma because it starts on the molecular level.

Why there are no any traces of contact metamorphism between kimberlites which belong to allegedly different magma batches within the same diatreme? Perhaps, because there was only ONE kimberlite magma eruption in each diatreme following by spatial differentiation between immiscible liquids? Relatively heavier picrite material sank into deeper parts of diatreme forming massive HK kimberlite when lighter carbonatite has concentrated at the upper parts of the diatreme forming fragmented TK kimberlite which was an emulsion of immiscible liquids which components did not have a time for the final spatial separation.

As a matter of fact, there are no intrusive contacts between petrographycally different kimberlites within any diatreme. All such “contacts” have a very gradual smooth accumulative nature. They can be stretched for tens centimeters to first meters with frequent alternation of the same petrographycal types of kimberlites. That is why the sequence HK – HKt – TKt – TK is a classic type of the contacts which is rarely broken.

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Fig.21. Kilauea, Hawaii. Lava flows into the ocean. There is a lot of steam, but no explosions. Photo from web site of Hedonisia Hawaii Eco-Hostel.

Let’s compare (Figs.22-23) “regular” Hawaiian volcano against theoretical phreatic one [20].

Fig.22. Hawaiian eruption: 1: ash plume, Fig.23. Phreatic eruption: 1: water 2: lava fountain, 3: crater, 4: lava lake, vapor cloud, 2: volcanic bomb,5: fumaroles, 6: lava flow, 7: layers of 3: magma conduit, 4: layers of lava

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lava and ash, 8: stratum, 9: sill, 10: and ash, 5: stratum, 6: water table,magma conduit, 11: magma chamber, 7: explosion, 8: magma chamber12: dike [20]. [20].

Hawaiian volcano looks unnaturally “dry” in the centre of Pacific Ocean. Is Pacific Ocean not big enough to produce at least one phreatic volcano?

Once again, which substance explosion was observed (?) at point 7? When magma will approach a water table, water will be partially vaporized and partially will go away from magma. Without explosion. Thermodynamically it is an open system. After the first touch of magma, water table will be completely dried up and there is no more water around to serve for the second explosion. Thus, phreatomagmatic system might (?) work as a one-time event. However, statistically [21] for the year 1994, the main number of volcanic activity lasted 10 – 100 days. Can phreatic volcano stay active for the so long time?Each natural phenomenon must be reproduced multiple times at different conditions. For example, the phenomenon of liquid immiscibility can be observed easily every day in the cup of soup as an oil-water system. About ten years ago the phenomenon of liquid immiscibility was discovered in the bilious system of humans [24]. But how often and where we can observe a phreatic phenomenon? Finally, let’s get back to kimberlites. More than a century ago, A. Du Toit (1906) noted that grooves or striae (after mechanical abrasion of the pipe walls by intruded kimberlite) could be inclined or even horizontal [1]. This would be absolutely impossible if kimberlite magma had just one - vertical direction of its movement. How do you combine this fact with a pyroclastic idea?

All questions have one answer: NO. But, nevertheless, against the logic and natural facts you still call kimberlites –”pyroclastic” rocks. Why?

REFERENCES:

1. C.R.Clement, J.W.Harris, D.N.Robinson, J.B.Hawthorne. The De Beers kimberlite pipe – a historic South African diamond mine. Mineral Deposits of Southern Africa. 1986. 2193-2214.

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2. V.V.Kovalsky. Kimberlite rocks of Yakutia and the main principles of their petrogenetic classification. Academy of Sciences of USSR, Moscow, 1963.

3. I.N.Kryvoshlyk. The peculiarity of morphology and some questions of genesis of the autolithes in kimberlite breccias. “Geology and Geophysics”, # 7, Novosibirsk, 1976.

4. I.N.Kryvoshlyk. Brief review of the theory of liquid immiscibility of kimberlite magma. Seventh International Kimberlite Conference. Cape Town, April 1998. Extended abstracts. 473-474.

5. G.A.Macdonald. Volcanoes. Prentice-Hall. 1972.6. Glendale Community College. Earth Science Image Archive.7. Scanning Service Konsult Inc. Patricia Sheahan. Periodical Newsletter.

University of British Columbia.8. Volcano. The Canadian Encyclopedia.

http://www.thecanadianencyclopedia.com9. http://www.ga.gov.au/odp/publications/197_IR/chap_03/c3_f13.htm

#133330310. New Mexico Bureau of Geology and Mineral Resources. Secondary

Electron Images.11. http://www.flickr.com/photo/johnn/259216887/ 12. www.britannica.com/ebc/art-54103/In-a-typical... 13. J.A.Jackson. Glossary of Geology. 1997.14. K.E. Yakobson, A.P. Kazak, E.V. Tolmacheva. Injective tuffisites in the

north of the Siberian Platform. Proceedings of the 23d Geological Conference. Komi, Syktyvkar, 1999, 177-178.

15. Myk. Zinchuk. 2008. MINERALOGICAL COLLECTION. N 58 (1–2). P. 80–87.

16. Hetman, C.M., Scott Smith, B.H., Paul, J.L., Winter, F., 2004. Geology of the Gahcho Kue Kimberlite pipes, NWT, Canada: root to diatreme magmatic transition zones. Lithos 76, 51 – 74.

17. W. Dan Housel. 2006. Diamonds. In: Industrial Minerals & Rocks, 7th

Edition.18. Moss, S.W. 2009. Volcanology of the A154N kimberlite at Diavik: implications for eruption dynamics. The University of British Columbia. 19. Kurszlaukis, S., Büttner, R., Zimanowski, B. and Lorenz, V. 1998. On the first experimental phreatomagmatic explosion of a kimberlite melt. Journal of Volcanology and Geothermal Research. Volume 80, Issues 3- 4, February 1998, Pages 323-326.20. Volcanism of Canada. From Wikipedia, the free encyclopedia.21. Simkin T., Siebert L. Volcanoes of the World. Geoscience Press,

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Tuscon, Arizona, 1994.22. Allaby, A., Allaby, M. 1999; A Dictionary of Earth Sciences. Oxford: Oxford University Press. Online version.23. Accretionary lapilli from the Azuara and Rubielos de la Cérida impact structures (Spain). www.impact-structures.com/Archiv/wkarchiv15.html24. I.N.Kryvoshlyk, O.A.Khoma. Liquid immiscibility in human bile. Optical method of diagnostics of gallstone disease. www.docstoc.com/docs/.../Liquid-immiscibility-in-human-bile

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