Engineering topics

Bischoff, A.

Publications and source records attributed to Bischoff, A..

13 records

NASA NTRS2020

Characteristics of a New Carbonaceous Chondrite, Metal-Rich-Lithology Found in the Carbonaceous Chondrite Breccia Aguas Zarcas

The Aguas Zarcas meteorite fell in Costa Rica on 23 April 2019 at 21:07 local time, with a total mass of about 27 kg. Hundreds of fusion-crusted stones ranging from 0.1 to 1868 g were recovered (The Meteoritical Bulletin). The meteorite was classified as a CM chondrite, but some lithlogies show a different texture to that of CM. In this study, we investigated the petrography, mineral-ogy, chemistry, and isotopic composition of an unusual “Metal-rich-lithology” from this fresh fall.

Kerraouch, I.↗

NASA NTRS2019

A Re-Investigation of a Chondritic Xenolith in the Murchsion (CM2) Chondrite: Formation by Fluid-Assisted Percolation During Metamorphism

The CM chondrites are generally complex impact breccias, in which lithic clasts and mineral fragments showing various degrees of aqueous alteration and possibly originating from different parent bodies are mixed together. The occurrence of CM-like clasts in other chondritic and achondritic meteorite breccias is also well-documented, however, reports on the occurrence of foreign clasts in CM chondrites are rare. In this study, we reinvestigated the white clast in the Murchison CM chondrite and demonstrate that the clast is not related to R chondrites as earlier suggested. In addition to the classification we discuss the origin and the history of its formation by studying several aspects like mineralogy, bulk chemistry, Rare Earth Elements (REE), oxygen isotopes, and the soluble organic compounds.

Kerraouch, I.↗

NASA NTRS2018

Mineralogical Study of a White Clast from Murchison (CM2): Comparison with R-Chondrites

R-chondrites share some properties with ordinary chondrites (OC) and carbonaceous chondrites (CC). The proportions of the textural types of chondrule from R chondrites and their FeO/(FeO+MgO) ratios are similar to those of OC, but the high matrix abundance in R chondrites more closely resembles that of CC (matrix abundances: OC ~12 vol% vs. CC 34->60 vol%;). In this study, we characteristize the mineralogy of a white clast from Murchison (CM2), which was earlier considered to be a R-chondrite. First, all the petrographic and mineralogical characteristics will be described and compared with those of R-chondrites. Finally, all data will be considered in order to test, whether this clast is a real R-chondrite or a unique recrystallized chondrite?

Kerraouch, I.↗

NASA NTRS2008

Sm-Nd and Rb-Sr Isotopic Studies of Meteorite Kalahari 009: An Old VLT Mare Basalt

Lunar meteorite Kalahari 009 is a fragmental basaltic breccia contain ing various very-low-Ti (VLT) mare basalt clasts embedded in a fine-g rained matrix of similar composition. This meteorite and lunar meteorite Kalahari 008, an anorthositic breccia, were suggested to be paired mainly due to the presence of similar fayalitic olivines in fragment s found in both meteorites. Thus, Kalahari 009 probably represents a VLT basalt that came from a locality near a mare-highland boundary r egion of the Moon, as compared to the typical VLT mare basalt samples collected at Mare Crisium during the Luna-24 mission. The concordant Sm-Nd and Ar-Ar ages of such a VLT basalt (24170) suggest that the extrusion of VLT basalts at Mare Crisium occurred 3.30 +/- 0.05 Ga ag o. Previous age results for Kalahari 009 range from approximately 4.2 Ga by its Lu-Hf isochron age to 1.70?0.04 Ga of its Ar-Ar plateau ag e. However, recent in-situ U-Pb dating of phosphates in Kalahari 009 defined an old crystallization age of 4.35+/- 0.15 Ga. The authors su ggested that Kalahari 009 represents a cryptomaria basalt. In this r eport, we present Sm-Nd and Rb-Sr isotopic results for Kalahari 009, discuss the relationship of its age and isotopic characteristics to t hose of other L-24 VLT mare basalts and other probable cryptomaria ba salts represented by Apollo 14 aluminous mare basalts, and discuss it s petrogenesis.

Shih, C.-Y.↗

NASA NTRS1994

Constraints on chondrule agglomeration from fine-grained chondrule rims

Fine-grained rims around chondrules, Ca,Al-rich inclusions, and other coarse-grained components occur in most types of unequilibrated chondrites, most prominently in carbonaceous chondrites of the CM group. Based on mineralogical and petrographic investigations, it was suggested that rim structures in unequilibrated ordinary chondrites could have formed in the solar nebula by accretion of dust on the surfaces of the chondrules. Dust mantles in CM chondrites seem to have formed by accretion of dust on the surfaces of chondrules and other components during their passage through dust-rich regions in the solar nebula. Concentric mantles with compositionally different layers prove the existence of various distinct dust reservoirs in the vicinity of the accreting parent body. Despite mineralogical and chemical differences, fine-grained rims from other chondrite groups principally show striking similarities to dust mantle textures in CM chondrite. This implies that the formation of dust mantles was a cosmically significant event like the chondrule formation itself. Dust mantles seem to have formed chronologically between chondrule-producing transient heating events and the agglomeration of chondritic parent bodies. For this reason the investigation of dust mantle structures may help to answer the question of how a dusty solar nebula was transformed into a planetary system.

Metzler, K.↗

NASA NTRS1994

Origin of dark clasts in the Acfer 059/El Djouf 001 CR2 chondrite

The ten specimens of the paired Acfer 059/El Djouf 001 CR2 chondrite contain abundant lithic fragments which we refer to as dark clasts. Petrological and mineralogical studies reveal that they are not related to the CR2 host meteorite but are similar to dark clasts in other CR2 chondrites. Dark clasts consist of chondrule and mineral fragments, phyllosilicate fragments and clusters, magnetite, sulfides and accessory phases, embedded into a very fine-grained, phyllosilicate-rich matrix. Magnetite has morphologies known from CI chondrites: spherules, framboids and platelets. Average abundances of major elements in the dark clasts are mostly in the range of both CR and CV chondrites, but strong depletions in Na and S are apparent. Oxygen isotopic compositions of two dark clasts suggest relationships to type 3 carbonaceous chondrites and dark inclusions in Allende. The dark clasts are clearly different in texture and mineralogical compositions from the host matrix of Acfer 059/El Djouf 001. Therefore, these dark clasts are xenoliths and are quite unlike the Acfer 059/El Djouf 001 CR2 host meteorite. We suggest that dark clasts accreted at the same time with all other components during the formation of Acfer 059/El Djouf 001 whole rock.

Endreb, M.↗

NASA NTRS1993

Alkali-granitoids as fragments within the ordinary chondrite Adzhi-Bogdo: Evidence for highly fractionated, alkali-granitic liquids on asteroids

Adzhi-Bogdo is an ordinary chondrite regolith breccia (LL3-6) that fell October 30, 1949 in Gobi Altay, Mongolia. The rock consists of submm- to cm-sized fragments embedded in a fine-grained elastic matrix. The breccia contains various types of clasts, some of which must be of foreign heritage. Based on chemical compositions of olivine some components have to be classified as L-type. Components of the breccia include chondrules, impact melts (some are K-rich, similar to those found in other LL-chondrites, highly recrystalized rock fragments ('granulites'), pyroxene-rich fragments with achondritic textures, and alkali-granitoidal fragments that mainly consist of K-feldspar and quartz or tridymite. Probably, this is the first report on granitoids from asteroids. It can be ruled out that these fragments represent huge rock assemblages of the parent body like granites do on Earth. Therefore, to avoid misunderstandings, these rocks will be designated as granitoids. In one thin section four granitoids were observed. The main phases within these clasts are K-feldspar and SiO2-phases. Minor phases include albite, Cl-apatite, whitlockite, ilmenite, zircon, Ca-poor pyroxene, and an unidentified Na,Ti-bearing silicate. Based on chemical composition and on optical properties quartz appears to be the SiO2-phase in two fragments, whereas tridymite seems to occur in the other two. The calculated formula of the unknown Na,Ti-rich silicate is very close to (Na,Ca)2.7(Fe,Mg)6(Ti)1.3(Si)7(O)24. Quartz and K-feldspar can reach sizes of up to 700 microns. Thus, the fragments can be described as coarse-grained (by chondritic standards). This is especially the case considering that quartz and K-feldspar are very rare minerals in ordinary chondrites. Representative analyses of minerals from some granitoidal clasts are given. Based on the mineral compositions and the modal abundances the bulk compositions were calculated. Besides these granitoidal rocks, pyroxene-rich fragments occur that show exsolution textures that are similar to those found in eucrites.

Bischoff, A.↗

NASA NTRS1988

Shock effects in meteorites

The impacts that can occur between objects on intersecting solar system orbits can generate shock-induced deformations and transformations, creating new mineral phases or melting old ones. These shock-metamorphic effects affect not only the petrography but the chemical and isotopic properties and the ages of primordial meteoritic materials. A fuller understanding of shock metamorphism and breccia formation in meteorites will be essential not only in the study of early accretion, differentiation, and regolith-evolution processes, but in the characterization of the primordial composition of the accreted material itself.

Stoeffler, D.↗

NASA NTRS1984

Al-rich objects in ordinary chondrites - Related origin of carbonaceous and ordinary chondrites and their constituents

A description is given of 169 Al-rich objects (arbitrarily defined as having 10 wt pct or more of Al2O3) from 24 ordinary chondrites of types 3 and 4, five regolith breccias containing unequilibrated material, the unique meteorite Kakangari, and a few ordinary chondrites of types 5 and 6. On the basis of shape and texture, the Al-rich objects are divided into chondrules (round, with igneous textures), irregularly shaped inclusions (similar to type F and spinel-rich complex Ca-Al-rich inclusions), and fragments (probably fragments of Al-rich chondrules and inclusions). For descriptive purposes, the Al-rich chondrules are further subdivided into compositional subgroups, although they are entirely transitional.

Bischoff, A.↗

NASA NTRS1984

Ion microprobe magnesium isotope analysis of plagioclase and hibonite from ordinary chondrites

Ion and electron microprobes were used to examine Mg-26 excesses from Al-26 decay in four Al-rich objects from the type 3 ordinary hibonite clast in the Dhajala chondrite. The initial Al-26/Al-27 ratio was actually significantly lower than Al-rich inclusions in carbonaceous chondrites. Also, no Mg-26 excesses were found in three plagioclase-bearing chondrules that were also examined. The Mg-26 excesses in the hibonite chondrites indicated a common origin for chondrites with the excesses. The implied Al-26 content in a proposed parent body could not, however, be confirmed as a widespread heat source in the early solar system.

Hinton, R. W.↗

NASA NTRS1984

Bulk compositions of Al-rich chondrules in ordinary and carbonaceous chondrites: Variations and similarities

An extended study of ordinary chondrites revealed that chondrules exist which are transitional in composition between Al-rich and Mg-Fe-rich types in contrast to the finding of Wlotzka, who inferred a gap in compositions between the Ca-Al-rich and Mg-Fe-rich chondrules. Transitional chondrule bulk compositions are plotted. They show that no compositional gap exists between the Mg-Fe-rich and Al-rich chondrules. Chondrules with Na2O-contents 3.0 wt.% are indicated. Variable CaO/Na2O-ratios for chondrule bulk compositions exist, similar to what was described for the subgroups of Al-rich chondrules. Al-rich and transitional chondrules similar to those described above were found also in carbonaceous chrondrites. Thirty-nine chondrules from the carbonaceous chondrites Leoville, Allende, Vigarano and Colony were investigated. Their bulk compositions in terms of Al2O3 vs. CaO were plotted.

Bischoff, A.↗

NASA NTRS1983

Lithification opf gas-rich chondrite regolith breccias by grain boundary and localized shock melting

The fine-grained matrices (less than 150 microns) of 14 gas-rich ordinary chondrile regolith breccias were studied in an attempt to decipher the nature of the lithification process that converted loose regolith material into consolidated breccias. It is found that there is a continuouos gradation in matrix textures from nearly completely clastic (class A) to highly cemented (class C) breccias in which the remining clasts are completely surrounded by interstitial, shock-melted material. It is concluded that this interstitial material is formed by shock melting in the porous regolith. In general, the abundances of solar-wind-implanted He-4 and Ne-20 are inversely correlated with the abundance of intenstitial, shock-melted, feldspathic material. Chondrites with the highest abundance of interstitial, melted material (class C) experienced the highest shock pressures and temperatures and suffered the most extensive degassing. It is this interstitial, feldspathic melt that lithifies and cements the breccias together; those breccias with very little interstitial melt (class A) are the most porous and least consolidated.

Bischoff, A.↗

NASA NTRS1983

Ca-Al-rich chondrules and inclusions in ordinary chondrites

Ca-Al-rich objects, hitherto mostly found in carbonaceous chondrites, are shown to be widespread, albeit rare, constituents of type 3 ordinary chondrites. Widespread occurrence and textural similarities of Ca-Al-rich chondrules to common, Mg-Fe-rich chondrules suggest that they formed by related processes. It is suggested in this article that Ca-Al-rich chondrules were formed by total melting and crystallization of heterogeneous, submillimeter- to submillimeter-sized dustballs made up of mixtures of high-temperature, Ca-Al-rich and lower-temperature, Na-K-rich components.

Bischoff, A.↗