Wolf v. Engelhardt

Shock induced planar deformation structures in quartz from the Ries crater, Germany

Crystalline rocks from breccias of the Ries basin, Germany, contain highly deformed quartz. Various planar deformation structures could be observed and classified into five different types: (1) Decorated planar elements, (2) Non-decorated planar elements, (3) Homogeneous lamellae, (4) Filled lamellae, (5) Planar fractures. All these structures are parallel to crystallographic planes: {10¯13}, {10¯12}, {10¯11}, {0001},{11¯21}, {11¯22}, {21¯31}, {51¯61}, {10¯10}. The most typical and most abundant planar structures are decorated and nondecorated planar elements parallel to {10¯13} and {10¯12}. Planar fractures are parallel to {0001} and {10¯11} and form at lower stress levels, probably earlier than the planar elements.Quartz containing planar elements, especially of the non-decorated type, has lower density, index of refraction and birefringence than normal quartz. This “quartz” is apparently a mixture of an amorphous phase and crystalline quartz, the amount of which can be calculated using average density or refractive index.Comparison of planar quartz structures found in tectonites and those produced artificially under static or dynamic high pressure conditions demonstrates that Ries quartz closely resembles deformed quartz recovered from shock wave experiments. The planar structures found in Ries quartz have been formed by shock wave actions with peak pressures in the 100–400 kbar range.Planar elements are explained to be traces of gliding processes during shock loading visible due to the fact that a high pressure phase (stishovite and/or a stishovite-like glass phase) has been produced along the glide planes. Upon pressure release most of the high pressure phase was transformed into an SiO2-glass (diaplectic glass).In comparison with experimental data the amount of residual crystalline quartz as well as type and orientation of planar structures in the quartz grains are clues to estimate the peak pressures responsible for these deformations. Shock waves with peak pressures exceeding about 400 kbar completely transform quartz into diaplectic SiO2-glass.

Origin of moldavites

Abstract Moldavites are supposed to be products of the Ries impact; but neither has the source material been identified in the Ries area nor is the mode of moldavite glass formation sufficiently clear. It is the purpose of this investigation to elucidate both problems by means of new chemical data. Fifty-nine moldavites from 20 localities in Bohemia and Moravia and 30 samples of Middle Miocene sediments from the Ries were analyzed for major oxides (X-ray fluorescence), 30 trace elements (neutron activation), water content (infrared spectroscopy) and 18 O 16 O - ratios . Microprobe analysis shows that moldavites are composed of thin laminae of optically and chemically somewhat different glasses, bent and curled in three dimensions, indicating the confluence of primary melt units under conditions of laminar flow. The moldavites cannot be derived from crystalline basement rocks and Mesozoic sediments involved in the Ries impact. The only lithology from which moldavites could have been formed is Middle Miocene sands, which formed a thin veneer in the Ries area at the time of the impact. Moldavites and these Middle Miocene sands are compositionally similar but not identical, which indicates that moldavite formation from sands involved chemical fractionation. Enrichments and depletions of individual elements in moldavites can not be explained by fractional vaporization. This was confirmed also by melting experiments with sand samples. Moreover, the negligible water content in moldavites and the scarcity of vesicles excludes the formation of moldavite melt by simple fusion of sands. For individual elements the distribution ratios q (concentration in moldavites: concentration in sands) and ionic radii R are significantly correlated: q = 2.21R − 1.18. It is inferred that at the encounter of the impactor with the ground surficial sands were transformed by high pressures and temperatures into a plasma-like vapor. In the expanding and ascending vapor droplets of a liquid phase condensed, consisting of a framework of interconnected (Si, Al)O4-tetrahedra which selectively incorporated cations to compensate its negative charge. The uptake of cations was controlled by the ionic radius because ions fit better into the interstices of the liquid framework the larger they are. The primary melt droplets separated from residual vapor and coalesced to moldavite bodies. The lower δO content of moldavites (11.5) as compared to dry sands (16) is explained by an admixture meteoric water (δO = −10) which filled the pore space.

Shock produced rock glasses from the Ries crater

In the suevite breccia of the Ries impact crater, Germany, glasses occur as bombs, and small particles in the groundmass. These glasses were formed from melt produced by shock fusion of crystalline basement rocks. Ejection from the crater resulted in the formation of aerodynamically shaped bombs, a few homogeneous spherules and a large mass of small glass particles which were deposited in the suevite breccia. Bombs and small particles included within chilled bottom and top layers of suevite deposits have been preserved in vitreous state, whereas glasses within the interior of the suevite devitrified, due to slower cooling rates.This paper summarizes the results of petrographical and chemical investigations of suevite glasses and their devitrification products. Conclusions are derived on origin and history of bombs and glass particles.Vitreous bombs and glass particles consist of schlieren-rich glass, mineral fragments (mainly quartz), rock fragments and vesicles. Wet chemical, trace element and microprobe analyses reveal that a primary melt was formed by shock fusion of a basement complex, consisting of about 80% biotite granite and 20% amphibolite. The, originally, more than 1800° C hot melt then incorporated shocked and desintegrated rocks of outer zones of the impact. Partial fusion of the rock debris resulted in a polyphase mixture consisting of melts, different in composition, accumulations of refractory mineral fragments and vesicles.Devitrified bombs and glass particles which are found in the interior of suevite deposits show alterations of texture and composition, due to microcrystallite growth and action of hydrothermal and weathering solutions. Incipient devitrification is indicated by brown staining of the glasses, originating, probably, by exsolution of minute magnetite particles. By optical microscopy and X-ray analysis, plagioclase and pyroxenes have been identified as main devitrification products. Shapes and textures of microcrystallites indicate fast crystal growth in a viscous and supercooled medium. Hot fluids permeating the suevite deposited microcrystalline quartz in vesicles and cracks. Later, montmorillonite was precipitated by solutions corroding the glass. Action of solutions on glasses which were weakened in coherence by devitrification resulted in oxidation of iron, leaching of iron and magnesium, and enrichment in alkalis.

Chemical composition of Ries glass bombs

Abstract Thirty-two chemical analyses of glass bombs, taken from various suevitelocalities within and outside the Ries crater, Germany are presented. Two main glass types, (I: non recrystallized, III: highly recrystallized), and one intermediate (II: slightly recrystallized) can be distinguished. All glass bombs originate from the same melt. The textural differences between the types I, II and III are due to locally different cooling rates of the suevite. The melt was formed in the impact crater by shock melting of a limited mass of magmatic or metamorphic rocks of uniform granitic composition. Minor chemical differences between the glasses are mainly caused by later oxidation and leaching processes which were controlled by the degree of recrystallization. Some textural features are discussed by which products of incomplete shock melting (like the Ries glasses) can be distinguished from rocks formed by differential anatexis or magmatic dissolution.

Diaplektische Gläser in den Breccien des Ries von Nördlingen als Anzeichen für Stoßwellenmetamorphose

Two kinds of glasses are to be found in the breccias of the Ries basin both which have been generated by shock wave action on the rocks of the crystalline basement: a) Normal glasses, containing flow structures and vesicles; they are formed by shock waves of high energy which after unloading, leave behind material, the temperature of which is above the melting point. b) Diaplectic glasses without vesicles and flow structures, preserving the grain boundaries, cleavages and twin lamellae of the primary minerals; they are formed by shock waves of lower energy which destroy the crystal lattice but after unloading, leave behind material, the temperature of which is below the melting point. — Measurements have been taken of the density and index of refraction of diaplectic quartz- and plagioclase-glasses. The values obtained proved to be higher than those of the normal glasses and lower than those of the crystalline phases. Diaplectic glasses are distinguishable from normal glasses by their physical properties. They represent intermediate stages of structural order between the crystalline and normal glass phases.ZusammenfassungIn den Breccien des Ries kommen wie in anderen vermutlichen und sicheren Meteoritenkratern zwei Arten von Gläsern vor, die beide durch die Einwirkung von Stoßwellen auf die Gesteine des kristallinen Untergrundes entstanden sind:a)Normale Mineral- und Gesteinsgläser: Sie zeigen Fließstrukturen und Blasen und sind durch Stoßwellen entstanden, deren Energie so hoch war, daß nach der Druckentlastung eine flüssige Schmelze zurückblieb, die zum Glas erstarrte.b)Diapiektische Mineralgläser: Sie bilden als Pseudomorphosen Korngrenzen, Spaltrisse und Zwillingsgrenzen der primären Minerale ab und zeigen weder Fließ-strukturen noch Blasen; sie sind durch Stoßwellen entstanden, deren Energie wohl zur Zerstörung des Kristallgitters, nicht aber dazu ausreichte, um das Material so stark zu erwärmen, daß es nach der Entlastung als Schmelze zurückblieb. — Es werden Werte der Dichte und der Lichtbrechung diaplektischer Quarz- und Andesingläser mitgeteilt. Sie sind höher als die Werte der normalen Gläser und niedriger als die der kristallinen Phasen. Diapiektische Gläser sind daher von normalen Gläsern physikalisch unterschieden und stellen Zwischenzustände der Ordnung zwischen kristallinen Phasen und normalen Gläsern dar.

Stable isotope composition of impact glasses from the Nordlinger Ries impact crater, Germany

Abstract The Ries impact, which today is represented by a 24-km-diameter complex crater, occurred at 15 Ma. It is estimated that a projectile of about 1 km diameter formed a transient crater of 6 to 7 km radius and 2.8 km depth. Impact melt glasses investigated are found within the suevite, the breccia that forms the uppermost layers of the ejecta blanket around the crater. The glasses are considered to represent quenched melts produced as a result of the impact. The oxygen isotope compositions of several glasses sampled from widely spaced localities are very homogeneous with δ 18 O values in the range of 6.7 to 7.4‰ and δ 17 O of 3.3 to 3.7‰. With increasing devitrification and alteration the δ 18 O values increase up to 15.8‰, δ 17 O up to 8.1‰. Water content also increases with devitrification from fresh glasses with about 1.3 wt.% to 3.8 wt.% in devitrified glass. δD values decrease with increasing water content from about −87 to −127‰. Whole-rock oxygen isotope compositions of the sedimentary cover sequence range from 17 to 27‰, and crystalline basement rocks range from 8.8 to 13.5‰ for granites and gneisses, whereas amphibolites have δ 18 O values of 5.2 and 6.1‰. Models suggesting that the glass in the suevite represents a mixed melt derived from all the rocks present in the suevite in proportion of their occurrence (Engelhardt, 1997) do not agree with the oxygen isotope composition of the glass. The simplest explanation for the homogeneous chemical and oxygen isotope composition is that the glass represents quenched melts from a few closely spaced lithologies only. High Fe and Ni contents in the glass, Cr/Ni and Cr/Co ratios, and relatively low δ 18 O values indicate involvement of amphibolites during melting. The balance of the melt was made up of spatially associated granites or gneisses as indicated by the major element and rare-earth element geochemistry. The best agreement between major element and oxygen isotope composition of the glass and model melts is obtained by mixtures of amphibolite and granite in proportions similar to their average occurrence in the fallout suevite.

Riesgläser und moldavite

Abstract From analyses of glasses from the Ries basin, Bavaria, Germany (4 new analyses) and of moldavites from Bohemia and Moravia mean chemical composition and standard deviations have been calculated. The Ries glasses have been formed by melting of rocks of the crystalline basement. There are no indications for the melting of the 500 m thick sedimentary rocks covering the crystalline basement. Although this basement contains different rock types—granites, diorites, gneisses, amphibolites etc.—the variability of glass composition from different sites is rather low. The melting, therefore, occurred presumably within a limited volume of the basement made up of a paragneiss of rather constant composition. The very different composition of the moldavites can neither be related to the crystalline material which produced the Ries glasses, nor can the differences be explained by normal differential vaporization of the molten glasses during the flight from the Ries to the moldavite sites. Although Ries glasses and moldavites have the same K/Ar-age the common origin of both glasses from the same melt seems to be improbable. In comparison with Ries glasses standard deviations are higher for most oxides of moldavites. Average chemical composition and character of chemical variability of moldavites are difficult to reconcile with a terrestrial origin.

Shock deformation of quartz influenced by grain size and shock direction: Observations on quartz-plagioclase rocks from the basement of the Ries Crater, Germany

Planar elements in quartz, produced by shock induced plastic deformation, have been investigated in four quartz-plagioclase veins contained in an amphibolite from the crystalline basement of the Ries Crater from the drill hole ‘Nördlingen 1973’.The crystallographic orientation of planar elements in quartz grains is similar in all four rocks ({10¯13} predominant, {0001} less frequent, {10¯12} and others still rarer), indicating an average shock pressure in the range between 150 and 200 kbar.The spatial density of planar elements as measured by the number of systems per shocked grain, the number of individual elements per shocked grain, or as ratio shocked: unshocked grains increases with increasing grain size. This grain size effect is supposed to be primarily a consequence of the heterogeneity of the stress field which produced a random distribution of local stress maxima and locally restricted areas of plastic quartz deformation in the rock. The probability that planar elements develop within one individual grain increases, therefore, with increasing grain size.In one leucosome in which the quartz grains were randomly oriented planar elements parallel to {10¯13} cluster in a stereographic projection within one belt. It is supposed that the pole of this belt indicates the direction in which the shock front passed through the rock.

Der Eukrit von Stannern

Die Beobachtungen beim Fall des Meteoriten von Stannern am 22. Mai 1808 werden zusammenfassend dargestellt. Der Eukrit von Stannern besitzt eine Porositat von 15 % und besteht nach mikroskopischen Beobachtungen aus ophitischen und brecciosen Partien, welche 33 Vol.-% Bytownit (An84),11 Vol.-% Hypersthen (Fs55), 49 Vol.-% Pigeonit (Fs55En35Wo10), etwa 5 Vol.-% Quarz und geringere Mengen von Ilmenit, Troilit und Chromit enthalten. Alle these Mineralien werden naher beschrieben. Eine neue chemische Analyse wird mitgeteilt, die mit dem mikroskopischen Befund gut ubereinstimmt. Aus einer Schmelze bildeten sick zuerst Bytownit und Hypersthen in nahezu eutektischem Mengenverhaltnis. Danach wurde der Hypersthen unter gleiehzeitiger starker mechanischer Beanspruchung des ganzen Gesteins (Breccienbildung) zum grosten Teil in Pigeonit umgewandelt und es kam zusatzlicher Pigeonit zur Abscheidung. Nach Abschlus der Breccienbildung entstanden als letzte Bildungen Quarz, Ilmenit und Troilit. In den letzten Phasen der Bildung spielten moglicherweise fluchtige Bestandteile eine Rolle, die heute nicht mehr im Meteoriten vorliegen. Die chemische Zusammensetzung des Eukrits von Stannern und die der ubrigen Careichen Achondrite wird mit der der Chondrite und irdischen Basalte verglichen und es werden mogliche genetische Zusammenhange diskutiert. Jedenfalls konnen Eukrite und Howardite nur auf nicht zu kleinen planetarisehen Korpern entstanden sein, wo Kristallisationsdifferentiation und lanusame Abkiihlung moglich waren. Die in der Atmosphare gebildete Schmelzrinde der Steine von Stannern enthalt viele Blasen, die durch des Sieden der Silikatschmelze erzeugt wurden. Aus dem Dampf schlug sick bei der Abkuhlung in den Blasen und auf der Ausenseite der Steine Wollastonit ab. Im Glas entstanden geringe Mengen Enstatit oder Klinoenstatit.

Normative composition and classification of lunar igneous rocks and glasses, II Lunar glasses

Abstract Rittman norms of lunar glasses were calculated for 1499 major element analyses from the literature and unpublished data obtained in our laboratory. The norm values, grouped according to increasing clinopyroxene content, were plotted into quartz-plagioclase-orthopyroxene and olibine-plagioclase-orthopyroxene triangles, respectively. The plots indicate that lunar glasses, like lunar rocks, form a compositional continuum which starts from glasses very high in plagioclase and continues, with increasing clinopyroxene, to plagioclase-poorer and orthopyroxene- and olivine-richer glasses. According to apparent clusters in the plots and taking into account the rock groups defined in Part I of this paper, the continuum was divided into eleven glass groups: GI 1 (anorthite), GI 2 (anorthositic), GII 1 (noritic and gabbronoritic), GII 2 (troctolitic), GIIIA (K-rich noritic), GIIIB (noritic), GIV (mafitic tholeiitic), GV (Ti-rich tholeiitic), GVI 1 (Ti-poor olivine gabbronoritic), GVI 2 (olivine gabbronoritic), GVI 3 (Ti-rich olivine gabbronoritic). Chemical and normative correspondence between rock (R) and glass (G) groups could be achieved by a refinement of our rock classification given in Part I of this paper: RI was divided into RI 1 (>95%plag) , and RI 2 (90–95% plag); RII into RII 1 (75–90% plag) and RII 2 (50–75% plag); RIIIB into RIIIB 1 (40–55% plag) and RIIIB 2 (55–75% plag). This refined rock classification comprises 10 groups. Reasonable chemical and normative correspondence exists between the following pairs: RI 1 /GI 1 , RI 2 /GI 2 , RII 1 /GII 1 , RIIIA/GIIIA, RIIIB 1 /GIIIB, RIV/GIV, and RVB/GV. No equivalent glasses exist for rocks RII 2 , RIIIB 2 and RVA. No equivalent rocks are known for glasses GII 2 , GVI 1 (Apollo 15 green glasses), GVI 2 , and GVI 3 (Apollo 17 orange glasses). Figures are given for the frequencies of rock and glass groups at the Apollo and Luna landing sites. The abundance of chemically corresponding rocks and glasses at each site is similar in most cases, suggesting genetic relationships. It is suggested that GI, GII, GIII, GIV and GV glasses were formed by impact fusion of chemically corresponding rocks. GVI 1 , GVI 2 and GVI 3 glasses are probably of volcanic origin. Frequency distributions of major element concentrations in glass and rock groups show that glass groups contain an excess of Na-poor, some also of K-poor samples, in comparison with corresponding rock groups. It is suggested that this difference is due to alkali volatilization caused by impact fusion at high temperatures. Average data are given on colours and refractive indices of the glasses.