GEOCHEMISTRY INTRODUCTION

Written By Aubrey Whymark 2013-2017
BORING! Well at least that's what I thought when I first studied it at university. It was hard to get my head around and then it suddenly clicked. The nice thing about geochemistry is that geology is not an exact science, whereas geochemistry, whilst maybe not perfectly exact, is getting there. When it comes to tektites, a lot of geochemical work has been done and if you care to spend the time trying to understand the data then it tells you a hell of a lot. Many times I've heard people say things about tektites or possible source craters, but even with only cursory review, the geochemistry will tell you if you're pointing in the right direction. If you ever want to shut down an argument then use geochemistry (not with the wife though 'yeah, whatever, I'm not really interested').

For me, the most fascinating use of geochemistry has been in decisively telling us where tektites are from, that they are wholly terrestrial, drawing isochemical contours that point to the crater source and telling you about the source rock composition, source rock age and even the age of the source material that went into making up the source rock, and even further back, when that material differentiated from the mantle! The amount of information geochemistry provides is truly astounding and in many cases it is incontrovertible. So, if you ever have a theory on tektites then always paw through any geochemical papers first! 

Introduction

Geochemistry

To the lay person tektites can simply be described as glass, very similar to any man-made window glass (see Table 5.1). A typical window glass comprises 70 to 74 percent silica (SiO2). Because of the low weight percentage of alkalis (sodium and potassium oxides) and increased percentage of aluminium oxide in tektite glass, tektite glass has an even closer resemblance high grade borosilicate glasses used for manufacturing ovenware or aluminosilicate glasses also used for high temperature applications.
Geochemistry in its simplest form looks at major elements. Trace elements and ratios thereof, provide an interesting insight to events. Isotope ratios provide an even deeper insight into age, source rock chemistry and even provide information on the impactor. In order to interpret elemental ratios and isotopic ratios we need to know what the different elements or isotopes do in differentiation, sedimentation and during the impact event. Some may be concentrated or lost entirely. Understanding when this happens is key. This is why different isotope systems can be used to date different events.
 
In order to understand tektites one must understand the material from which they are made and the properties of that material. Tektites are made of glass. The behaviour of glass during atmospheric entry differs markedly from that of iron meteorites or stony meteorites. Consequently, the final morphologies of tektites will differ considerably from meteorites, although some comparisons may be drawn.

Most people are familiar with the properties of glass. Tektite glass is high grade, similar to Pyrex glass, but essentially has the same properties as any man-made glass. Glass is tough, but brittle when solid. Glass is also sensitive to rapid temperature changes. If one part of a glass body is a significantly different temperature to another part then the relative expansion or contraction of the glass will create internal stresses resulting in cracks or explosive fragmentation of the glass.

When attempting to understand tektites it helps to consider what would happen to a familiar wine glass or glass window in the same situation. What would happen to the glass if re-entering the atmosphere at high velocity – would it melt and fold, ablate or crack and explode? On the ground what would happen if the object was transported in a river – how would it look afterwards?
ABOVE: Typical compositional ranges of some man-made glasses. Note that the silica content is similar to that of tektites, but other compounds differ in quantity. All data in wt%. Different glass recipes for the similar glass types can vary considerably. Sourced from various glass making company websites.

References used in the subsequent geochemistry pages:

Tektite Glass

Aggrey K., Tonzola C., Schnabel C., Herzog G. F., Wasson J. T. 1998. Beryllium-10 in Muong Nong-type tektites. 61st Annual Meeting of the Meteoritical Society: Abstract #5142.

Albarède F. 2003. Geochemistry: An Introduction. Cambridge University Press.

Alden A. 2011. Potassium-Argon Dating Methods.
http://geology.about.com/od/geotime_dating/a/K_argon_dating.htm

Beran A., Koeberl C. 1997. Water in tektites and impact glasses by fourier-transformed infrared spectrometry. Meteoritics & Planetary Science. 32: 211-216.

Bigazzi G., De Michele V. 1996. New fission-track age determinations on impact glasses. Meteoritics & Planetary Science. 31: 234-236.

Bjørlykke K.(ed.). 2010. Petroleum Geoscience: From Sedimentary Environments to rock Physics. Springer-Verlag. Berlin Heidelberg.

Blum J. D., Chamberlain C. P. 1992. Oxygen isotope constraints on the origin of impact glasses from the Cretaceous-Tertiary boundary. Science. 257 (5073): 1104-1107.

Blum J. D., Papanastassiou D. A., Koeberl C., Wasserburg G. J. 1991. Nd and Sr isotopic study of Muong Nong and splash-form Australasian tektites. Abstracts of the Lunar and Planetary Science Conference. 22nd: 113-114.

Blum J. D., Papanastassiou D. A., Wasserburg G. J., Koeberl C. 1992. Neodymium and Strontium isotopic study of Australasian tektites: new constraints on the provenance and age of the target materials. Geochimica et Cosmochimica Acta. 56 (1): 483-492.

Bottomley R. J., York D., Grieve R. A. F. 1990. 40Argon-39Argon dating of impact craters. Abstracts of the Lunar and Planetary Science Conference. 20th: 421-431.

Chao E. C. T. 1963. The petrographic and chemical composition of tektites. In: O'Keefe J. A (ed.) Tektites. University of Chicago Press, Chicago. 51-94.

Chamberlain C. P., Blum J. D., Koeberl C. 1993. Oxygen isotopes as tracers of tektite source rocks: an example from the Ivory Coast tektites and Lake Bosumtwi Crater. Abstracts of the Lunar and Planetary Science Conference. 24th (Part 1: A-F): 267-268.

Chapman D. R., Scheiber L. C. 1969. Chemical investigation of Australasian tektites. Journal of Geophysical Research. 74 (27): 6737-6776.

Cordani U. G., Mizusaki A. M., Kawashita K., Thomaz-Filho, A. 2004. Rb-Sr systematic of Holocene politic sediments and their bearing on whole-rock dating. Geol. Mag. 141 (2): 233-244.

Cuttitta F., Clarke R. S., Carron M. K., Annell C. S. 1967. Martha's Vineyard and selected Georgia tektites: new chemical data. Journal of Geophysical Research. 72 (4): 1343-1349. Also in: Astrogeologic Studies: Annual Progress Report, '65-'66, Part C, Cosmic Chemistry and Petrology.

Deloule E., Chaussidon M., Glass B. P., Koeberl C. 2001. U-Pb isotopic study of relict zircon inclusions recovered from Muong Nong-type tektites. Geochimica et Cosmochimica Acta. 65 (11): 1833-1838.

Dicken A. P. 2005. Radiogenic Isotope Geology. 2nd Edition. Cambridge University Press.

Engelhardt W. von, Berthold C., Wenzel T., Dehner T. 2005. Chemistry, small-scale inhomogeneity, and formation of moldavites as condensates from sand vaporized by the Ries impact. Geochimica et Cosmochimica Acta. 69 (23): 5611-5626.

Englert P., Pal D. K., Tuniz C., Moniot R. K., Savin W., Kruse T. H., Herzog G. F. 1984. Manganese-53 and beryllium-10 contents of tektites. Abstracts of the Lunar and Planetary Science Conference. 15th: 250-251.

Fleischer R. L., Naeser C. W., Price P. B., Walker R. M., Maurette M. 1965. Cosmic ray exposure ages of tektites by the fission-track technique. Journal of Geophysical Research. 70 (6): 1491-1496.

Fleischer R. L., Price P. B. 1964. Fission track evidence for the simultaneous origin of tektites and other natural glasses. Geochimica et Cosmochimica Acta. 28 (6): 755-756.

Fleischer R. L., Price P. B. 1964. Glass dating by fission fragment tracks. Journal of Geophysical Research. 69 (2): 331-339.

Fleischer R. L., Price P. B. 1964. Tektite ages by fission-track dating. Geological Society of America. Special Paper. 76: 60. (Abstracts for 1963 meeting, New York).

Fleischer R. L., Price P. B., Woods R. T. 1969. A second tektite fall in Australia. Earth and Planetary Science Letters. 7: 51-52. Also in Barnes, V. E. and Barnes M. A. (Eds.) 1973. Benchmark Papers in Geology: Tektites. Dowden, Hutchinson & Ross, Inc.

Friedman I. 1958. The water, deuterium, gas and uranium content of tektites. Geochimica et Cosmochimica Acta. 14 (4): 316-322.

Gentner W., Glass B. P., Storzer D., Wagner G. A. 1970. Fission track ages and ages of deposition of deep-sea microtektites. Science. 168 (3929): 359-361.

Gentner W., Storzer D., Wagner G. A. 1969b. New fission track ages of tektites and related glasses. Geochimica et Cosmochimica Acta. 33 (9): 1075-1081. Also in Barnes, V. E. and Barnes M. A. (Eds.) 1973. Benchmark Papers in Geology: Tektites. Dowden, Hutchinson & Ross, Inc.

Gilchrist J., Thorpe A. N., Senftle F. E. 1969. Infrared analysis of water in tektites and other glasses. Journal of Geophysical Research. 74 (6): 1475-1483.

Izett G. A., Obradovich J. D. 1992a. Laser-fusion 40Ar/39Ar ages of Australasian tektites. Abstracts of the Lunar and Planetary Science Conference. 23rd: 593-594.

Izett G. A., Obradovich J. D. 1992b. Laser-fusion 40Ar-39Ar ages of Australasian tektite cores and flanges. EOS: Transactions of the American Geophysical Union. 73: 328. (Abstract for poster).

Izett G. A., Obradovich J. D. 1994. Ar-40/Ar-39 age constraints for the Jaramillo Normal Subchron and the Matuyama-Brunhes geomagnetic boundary. Journal of Geophysical Research. 99 (B2): 2925-2934.

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Kadik A. A., Lukanin O. A., Zharkova E. V., Feldman V. I. 2003. Measurements of oxygen intrinsic fugacity and water content in tektitic glasses: The problem of oxygen and hydrogen regime during tektite formation. Electronic Scientific Information Journal "Herald of the Department of Earth Sciences RAS". 1 (21). Informational Bulletin of the Annual Seminar of Experimental Mineralogy, Petrology and Geochemistry.

Kashkarov L. L., Genaeva L. I., Lavrukhina A. K., Izokh E. P. 1985. Fission track ages of Viet-Nam tektites. Meteoritics. 20: 679-680. (Abstract).

Koeberl C. 1986. Geochemistry of tektites and impact glasses. Annual Review of Earth and Planetary Sciences. 14: 323-350.

Koeberl C. 1990. The geochemistry of tektites: an overview. Tectonophysics. Special Issue. Proceedings of the Workshop on Cryptoexplosions and Catastrophes in the Geological Record, with a special focus on the Vredefort Structure. 171 (1/4): 405-422.

Koeberl C., Beran A. 1988. Water content of tektites and impact glasses and related chemical studies. Proceedings of the Lunar and Planetary Science Conference (1987). 18th: 403-408.

Koeberl C., Kluger F., Kiesl W. 1985. Rare earth element patterns in some impact glasses and tektites and potential parent materials. Chemie der Erde. 44: 107-121.

Koeberl C., Shirey S. B. 1993. Osmium isotopes in Ivory Coast tektites: confirmation of a meteoritic component and rhenium depletion. Abstracts of the Lunar and Planetary Science Conference. 24th: 809-810.

Koeberl C., Shirey S. B. 1993. Detection of a meteoritic component in Ivory Coast tektites with Rhenium-Osmium Isotopes. Science. 261 (5121): 595-598.

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Lovering J. F., Morgan J. W. 1964. Rhenium and Osmium Abundances in Tektites. Geochimica et Cosmochimica Acta. 28 (6): 761-768. Also in Barnes, V. E. and Barnes M. A. (Eds.) 1973. Benchmark Papers in Geology: Tektites. Dowden, Hutchinson & Ross, Inc.

Ma P., Aggrey K., Tonzola C., Schnabel C., de Nicola P., Herzog G. F., Wasson J. T., Glass B. P., Brown L., Tera F., Middleton R., Klein J. 2004. Beryllium-10 in Australasian tektites: constraints on the location of the source crater. Geochimica et Cosmochimica Acta. 68: 3883-3896.

Ma P., Tonzola C., DeNicola P., Herzog G. F., Glass B. P. 2001. 10Be in Muong Nong-type Australasian tektites: constraints on the location of the source crater. Abstracts of the Lunar and Planetary Science Conference. 32nd: Abstract #1351.

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Middleton R., Klein J., Kutschera W., Paul M., Margaritz H. 1987. 26Al: Measurement and application [and discussion]. Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences. 323 (1569): 121-143.

Middleton R., Klein J., Kutschera W., Paul M., Margaritz H. 1987. 26Al: Measurement and application [and discussion]. Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences. 323 (1569): 121-143.

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Raisbeck G. M., Yiou F., Klein J., Middleton R. 1983. 26Al/10Be in an australite tektite; further evidence for a terrestrial origin. EOS: Transactions of the American Geophysical Union. 64 (18): 284. (Abstract).

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In it's simplest form tektite glass is very comparable many man-made glasses. We can use the properties of man-made glasses as analogues to help us understand other tektite features, such as brittle failure / cracking or colour.