Alfred Kracher

Origin of Iron Meteorite Groups IAB and IIICD

Abstract Several low-Ni iron meteorites previously assigned to group IAB are reclassified IIICD on the basis of lower Ge, Ga, W and Ir concentrations and higher As concentrations; the low-Ni extreme of IIICD is now 62 mg/g, that of IAB is 64 mg/g. The resulting fractionation patterns in the two groups are quite similar. It has long been established that, in contrast to the magmatic iron meteorite groups, IAB and IIICD did not form by fractional crystallization of a metallic magma. Other models have been proposed, but all have serious flaws. A new model is proposed involving the formation of each iron in small pools of impact melt on a parent body consisting of material similar to the chondritic inclusions found in some IAB and IIICD irons, but initially unequilibrated. These impact melts ranged in temperatures from ~ 1190 K to ~ 1350 K. The degree of equilibration between melt and unmelted solids ranged from minimal at the lowest temperature to moderate at the highest temperature. The lowest temperature melts were near the cotectic in the Fe-Ni-S system with Ni contents of ~ 12 atom %. Upon cooling, these precipitated metal having ~ 600 mg/g Ni by equilibrium crystallization. The Ni-rich melt resulted from the melting of Ni-rich sulfides and metal in the unequilibrated chondritic parent. Low-Ni irons formed in high temperature melts near the composition of the FeS-Fe eutectic or somewhat more metal rich. We suggest that the decreasing Ge, Ga and refractory abundances with increasing Ni concentration reflect the trapping of these elements in oxide phases in the unequilibrated chondritic material, and that very little entered the Ni-rich melt parental to the Oktibbeha County iron. The remaining elements tended to have element/Ni ratios in the melts that were more or less independent of temperature. The remarkable correlation between I-Xe age of the chondritic inclusions and Ni content of the host metal is explained by a detailed evolution of (mega)regolith in which these groups originated. The most Ni-rich melts could only be generated from an unequilibrated chondrite parent; as the continuing deposition of impact energy produced increasingly higher grades of metamorphism, the maximum Ni content of the impact melts (and their subsequently precipitated metal) gradually decreased.

Chemical and crystallographic study of cronstedtite in the matrix of the Cochabamba (CM2) carbonaceous chondrite

The principal mineral component in the matrix of the Cochabamba carbonaceous chondrite is a phyllosilicate, which is identified as cronstedtite mainly on the basis of its chemical composition. Its approximate idealized formula is given by M6 Fe 0.7 3+ Al0.5Si2.7O10 (OH)8 with M=Fe2+, Fe3+, and Mg in somewhat variable amounts. TEM studies reveal the presence of three polytypes, and show a high degree of stacking disorder parallel to (001) with the displacement vector ±b/3 or ±2b\(\bar 3\). Crumpled amorphous masses in the matrix may contain structural building blocks of phyllosilicates. They, rather than the anhydrous minerals, seem to be the most likely progenitors of cronstedtite. Some constraints on its origin are reviewed. In addition to cronstedtite, observations on some other matrix phases are also reported.

Basalts in the Lancé Carbonaceous Chondrite

Abstract We describe three lithic fragments from the Lancé carbonaceous chondrite which apparently are of igneous origin and of basaltic parentage. They consist of large enstatite grains (pheno-crysts ?) which poikilitically include some olivine and abundant Fe-Ni metal and Fe sulfide blebs. These enstatites are set into a matrix of partly ophitic and partly porphyritic plagioclase (~ an71) and interstitial clinopyroxene and clinopyroxene plus plagioclase intergrowths. Mineral compositions are highly variable and reflect a complex genesis. Olivine compositions range from fo5 to fo60 and sometimes exhibit compositional zoning. Enstatites are mostly of en 98 com-position with some Fe-enrichment towards grain surfaces and cracks. Plagioclases have about an71 but mostly are altered to nonstoichiometric high-alkali compositions (with original Al/Si ratios corresponding to ~ an 70) or are partly replaced by K-free nepheline. Generally two clinopyroxenes are present within the plagiophyric portions of the fragments: One low Fe/Mg augite (~ en53 wo44) rich in Ti, Al, Cr, and Mn (Fe/Mn ≦ 2) and a ferrosalite (~ en15 wo47) poor in Ti, Cr, and Mn (Fe/Mn ~ 100). One fragment also contains spinel (hercynite) which apparently is xenocrystic in nature. Our investigation indicates: (1) The fragments are of igneous origin. (2) The original melt was of basaltic composition, crystallizing the primary mineral association ol + en + plag + low-Fe augite. (3) During crystallization the melt suffered strong reduction which led to segregation of Fe-Ni droplets from the melt and which continuously lowered the Fe/Mn ratio of successively crystallizing silicates from nearly chondritic (~ 100) to 0.6. (4) Probably after incorporation into the Lancé breccia the fragments suffered to different degrees metasomatic alterations which were caused by the addition of Na, K, and Fe to the system. The origin of the pre-Lancé basaltic melt cannot yet be established.

The upper mantle beneath Kapfenstein and the Transdanubian volcanic region, E Austria and W Hungary: A comparison

SummaryA representative suite of ultramafic xenoliths from Kapfenstein, Austria, has been investigated petrographically. Textures and mineral chemistries are compared with published data on Hungarian xenoliths and discussed within the framework of the hypothesis of a mantle diapir beneath the Transdanubian Volcanic Region (TVR) of E Austria and W Hungary. We succeeded in recognizing important differences which seem to support the TVR mantle diapir concept. Below the external part of the TVR (Kapfenstein) the upper mantle seems to be essentially untectonized and lithologically rather monotonous (e.g., Type II clinopyroxenites are absent). In contrast, both deformed (equigranular) and undeformed (protogranular) peridotite xenoliths occur in the internal part (Balaton area) where Type II clinopyroxenite xenoliths as well as Type I/Type II composite rocks are present. It is remarkable that at Gérce (Hungary), situated approximately mid-way between the internal and external regions, almost exclusively porphyroclastic xenoliths occur.The undeformed xenoliths from Kapfenstein are largely unfractionated. A small proportion exhibits depletions in basaltic component or some mild influence of mantle metasomatism. Several mineral chemical parameters, such asmg-number of olivine, Al2O3 content of spinel and clinopyroxene, apparent pyroxene equilibration temperature, etc., show a narrow distribution with a pronounced maximum in the undeformed Kapfenstein xenoliths. By contrast, the deformed xenoliths from the internal TVR show a much broader range of values with no distinct maximum, attesting to a more complex chemical and physical evolution. Thus a direct relationship between deformation and chemistry seems to be confirmed. The deformed rocks can be extreme in two ways: they can either be strongly depleted or strongly enriched as documented by the high contents of clinopyroxene in equigranular xenoliths from Szigliget. Tectonization apparently opens the way for mass transport in either direction.ZusammenfassungEine repräsentative Suite von ultramafischen Xenolithen von Kapfenstein, Steiermark, wurde petrologisch untersucht. Die Gefüge und Mineralchemismen werden mit publizierten Daten von ungarischen Vorkommen verglichen und im Rahmen der Mantel-Diapir-Hypothese für die Transdanubische Vulkanische Region (TVR) diskutiert. Der Vergleich ergab wesentliche Unterschiede, welche das TVR-Mantel-Diapir-Konzept unterstützen. Der Mantel unterhalb des äußeren Teiles der TVR (Kapfenstein) ist praktisch untektonisiert und lithologisch monoton (z.B. fehlen Typ II Klinopyroxenite). Im Gegensatz dazu finden sich im inneren Teil (Balaton-Region) sowohl deformierte (equigranulare) als auch nicht-deformierte (protogranulare) Xenolithe zusammen mit Typ II Klinopyroxeniten. Auch zusammengesetzte Xenolithe, bestehend aus Typ I und Typ II Gesteinen sind vorhanden. Bemerkenswert ist, daß bei Gérce (Ungarn), eine Lokalität, welche sich zwischen dem inneren und äußeren Teil der TVR befindet, fast ausschließlich nur porphyroklastische Xenolithe vorkommen.Die undeformierten Xenolithe von Kapfenstein sind größtenteils unfraktioniert. Einige wenige zeigen Verarmungen oder geringfügige metasomatische Anreicherungen. Histogramme mineralchemischer Parameter zeigen sehr deutlich die Unterschiede zwischen den undeformierten Kapfenstein Xenolithen und den deformierten der inneren TVR. Die Kapfenstein Xenolithe zeigen typischerweise regelmäßige Verteilungen mit einem deutlichen Maximum. Die Xenolithe der inneren TVR hingegen zeigen eine flache Verteilung und weisen damit auf eine wesentlich komplexere chemische Entwicklung hin. Unsere Daten scheinen einen direkten Zusammenhang zwischen Deformation und chemischer Veränderung aufzuzeigen. Die deformierten Gesteine können in dieser Hinsicht zwei Extreme annehmen: Sie können entweder stark verarmt oder stark angereichert sein. Letzeres wird z.B. beeindruckend durch die hohen Gehalte an Klinopyroxen der equigranularen Xenolithe von Szigliget dokumentiert. Tektonisierung scheint die Wege für Massen-Transporte in beiden Richtungen zu öffnen.

Pyroxene chemistry and evolution of alkali basaltic rocks from Burgenland and Styria, Austria

SummaryThe mineral chemistry of several Pliocene alkali basaltic rocks from Burgenland and Styria (Eastern Austria) have been investigated in order to determine the evolution path of the basalt magmas prior to eruption. With their wide range of substitutions, clinopyroxenes provide the best records of the evolution history of rocks. Pyroxene phenocrysts of the investigated basalts show both concentric and sector zoning. The investigation of sector zoned crystals shows, that not only Ti, Al and Fe contents are different in different sectors but there can be significant differences also in their Cr content. This fact apparently suggests that the distribution of Cr between clinopyroxene and melt could be influenced by crystallization kinetics.The depth of crystallization and differentiation of the basalts can be estimated from Ti and Al contents of clinopyroxene phenocrysts. From a combination of data on clinopyroxene composition, compatible trace element contents and mg-values of the rocks, it is concluded, that the alkali basalts of Pauliberg and Steinberg underwent slight olivine and clinopyroxene fractionation in shallow magma chambers prior to eruption, while the nephelinite of Stradnerkogel evolved mainly through clinopyroxene fractionation under high pressure conditions, probably in the upper mantle.ZusammenfassungEinige pliozäne alkalibasaltische Gesteine aus dem Burgenland und der Steiermark wurden mineral-chemisch untersucht, um Aufschluß über ihre Evolution vor der Eruption zu erhalten. Klinopyroxene mit ihren vielfältigen Subtitutionsmöglichkeiten erlauben am besten eine Abschätzung der Evolution der Basalte. Pyroxen-Einsprenglinge der Basalte zeigen sowohl konzentrischen als auch sektoralen Zonarbau. Die von uns untersuchten Einsprenglinge zeigen in den verschiedenen Sektoren nicht nur unterschiedliche Gehalte an Ti, Al und Fe, sondern vielfach auch unterschiedliche Cr-Gehalte. Dies macht es wahrscheinlich, daß die Verteilung von Cr zwischen Klinopyroxen und Schmelze von der Kristallisations-Kinetik beeinflußt wird.Die Tiefe in der die Basalte kristallisierten und differenzierten kann von den Ti- und Al-Gehalten der Klinopyroxen- Einsprenglinge abgeschätzt werden. Die Zusammensetzung der Klinopyroxene im Verein mit den Gehalten an kompatiblen Spurenelementen und denmg-Werten der Gesteine erlauben den Schluß, daß die Alkalibasalte von Pauliberg und Steinberg vor ihrer Eruption eine geringfügige Olivinund Klinopyroxen-Fraktionierung in einer seichten Magmakammer erlebten. Der Nephelinit vorn Stradnerkogel hingegen erfuhr hauptsächlich eine Klinopyroxen Fraktionierung unter Hochdruck-Bedingungen, möglicherweise im oberen Erdmantel.

Stories and Theories: A Scientific Challenge to Theology

Stories about the divine are meant to help our imagination cope with what is ultimately not fully imaginable. In the process we make use of metaphors that rely on quantitative relationships to express the qualitative difference between the reality accessible to us and the transcendent reality of God. For example, because we have no notion of what it would mean to «be outside of time», eternity tends to be explained in terms of infinite temporality. With the increasingly bizarre and unimaginable worldview of contemporary physics, it is perhaps no longer clear what the difference is between the unknown and the unknowable, or even whether it is possible to articulate a meaningful difference. Science appears to have outrun theology in creating stories that engage our imagination. How to overcome the difficulties this raises, particularly with respect to a widening gulf between academic analysis and popular belief, is at present not clear. A «flight from metaphor» into formalized theory, although apparently valid in science, leads to a dead end in theology. A rethinking of many traditional concepts, such as immanence and transcendence, seems to be indicated.

Are We Special? Humanity and Extraterrestrial Life

The discovery of ubiquitous planets around other stars, some of them Earth-like, has brought renewed attention to the question of whether humans are the only intelligent species in the galaxy or one of many. So far we have no indication that other intelligent beings (ETI) exist. Even if they do, huge astronomical distances together with the finite speed of light makes it much more likely that, if we encounter them at all, it will be by long-distance contact rather than meeting in person. Our hope that such a signal might be received is based on the expectation that at least some ETI will develop human-like technology. Whether extraterrestrial evolution should be expected to converge on this kind of techno-intelligence or diverge in ways we cannot now imagine is an open question. Not only may we never receive a signal, we may also never know why. This uncertainty also cautions us against theological speculations about the nature of aliens. Astrotheology is ultimately about us humans; about aliens we can only learn, if at all, through their own free self-disclosure.

Respect for Life in the Age of Science

The Scientific Revolution of the sixteenth and seventeenth century replaced a holistic view of nature with one that became increasingly reductionist. This has made it difficult to find a rational basis for apprehending the objects of moral reasoning, like humans or other organisms in general, as more than the sum of their elementary parts. But the previous world view, here labeled substantialism, cannot be recreated against the evidence of modern science. Substantialism has been replaced by atomism and its ontological consequences. Splitting the world into atomistic science and substantialist philosophy can only be attained by an intolerable ontological relativism. Trying to derive moral principles from a forced amalgamation of the two world views is self-defeating and can have destructive consequences. Theory change in science can suggest patterns whereby solutions that we want to retain can be reconstructed “from the ground up” with a new ontology. However, we should not expect to reconstruct a static theory of moral certitudes in a world that is dynamic and evolutionary.

Phenomenology and Theology—Reflections on the Study of Religion

The academic study of religious belief and practice is frequently taken to debunk the content of religion. This attitude impedes the science-theology dialogue and causes believers to react defensively toward studies of religion. I argue that a large, although not unrestricted, domain exists in which phenomenology of religion is neutral with respect to content, that is, compatible with either belief or unbelief. Theology can constructively interact with secular studies of religion, in some cases even explicitly hostile ones. Three themes emerge that elaborate on this interaction: (1) the claim that a scientific study of religion is capable of refuting belief is a logical mistake; (2) religious practice, and to some extent belief, can benefit from secular scrutiny; (3) the entirety of religious expressions is richer than the content that can be captured by analytical study of the phenomenon.