Acfer 182 and paired samples, an iron-rich carbonaceous chondrite: Similarities with ALH85085 and relationship to CR chondrites

Abstract-Fine-grained, heavily-hydrated lithic clasts in the metal-rich (CB) chondrites Queen Alexandra Range (QUE) 94411 and Hammadah al Hamra 237 and CH chondrites, such as Patuxent Range (PAT) 91546 and Allan Hills (ALH) 85085, are mineralogically similar suggesting genetic relationship between these meteorites. These clasts contain no anhydrous silicates and consist of framboidal and platelet magnetite, prismatic sulfides (pentlandite and pyrrhotite), and Fe-Mn-Mg-bearing Ca-carbonates set in a phyllosilicate-rich matrix. Two types of phyllosilicates were identified: serpentine, with basal spacing of~O.73 nm, and saponite, with basal spacings of about 1.1-1.2 nm. Chondrules and FeNi-metal grains in CB and CH chondrites are believed to have formed at high temperature (> 1300 K) by condensation in a solar nebula region that experienced complete vaporization. The absence of aqueous alteration of chondrules and metal grains in CB and CH chondrites indicates that the clasts experienced hydration in an asteroidal setting prior to incorporation into the CH and CB parent bodies. The hydrated clasts were either incorporated during regolith gardening or accreted together with chondrules and FeNi-metal grains after these high-temperature components had been transported from their hot formation region to a much colder region of the solar nebula.

Section: Mineralogy and Petrographymentioning

confidence: 86%

Heavily‐hydrated lithic clasts in CH chondrites and the related, metal‐rich chondrites Queen Alexandra Range 94411 and Hammadah al Hamra 237

Greshake

Krot

Meibom

et al. 2002

“…Although no such grains have ever been observed in CAIs from Ningqiang, several Sc 2 O 3 -rich (>25 wt%) and/ or ZrO 2 -rich (>50 wt%) phases were reported in a spectacular blue inclusion that consists of Y-, Zr-rich perovskite and grossite from Acfer 182 (CR) (Bischoff et al 1993). Alternatively, the Sc-fassaite in NQJ3-5-7 could be a relict, and the Sc-fassaite rims on perovskite in other ultrarefractory CAIs are possible sources.…”

Section: Sc-rich Fassaitementioning

confidence: 99%

Fassaites in compact type A Ca‐Al‐rich inclusions in the Ningqiang carbonaceous chondrite: Evidence for partial melting in the nebula

Lin

Kimura

Wang

2003

Abstract-Fassaite is a major component of Ca-Al-rich inclusions (CAIs) of Types B and C that crystallized from liquids. In contrast, this mineral is rarely reported in Type A inclusions and has been much less studied. In this paper, we report highly Ti-, Al-enriched fassaite that occurs as rims on perovskite in two compact Type A inclusions from the Ningqiang meteorite. In addition, one of the inclusions contains an euhedral grain of Sc-fassaite (16.4 wt% Sc 2 O 3 ) isolated in melilite. The occurrence and mineral chemistry of the fassaite rims can be explained by a reaction of pre-existing perovskite with CAI melts. Hence, such rims may serve as an indicator for partial melting of Type A inclusions. The Sc-fassaite is probably a relict grain. A third spherical CAI contains several euhedral grains of V-fassaite (4.8-5.4 wt% V 2 O 3 ) enclosed in a melilite fragment. The high V content of fassaite cannot be related to any Fremdlinge, magnetite, or metallic Fe-Ni, because these phases are absent in the inclusion. In the same CAI, other fassaites intergrow with spinel and minor perovskite, filling voids inside of the melilite and space adjacent to the Wark-Lovering rim. The fassaite intergrown with spinel is almost V-free. The coexistence of two types of fassaite suggests that this CAI has not been completely melted.

“…However, the origin of phyllosilicates in ALHA 77307 (Brearley, 1990, which are locally present in regions of amorphous materials, is not clear. pointed out that it is not possible to determine unequivocally whether these phases formed by extraterrestrial processes or during weathering in the Antarctic ice.…”

Section: Co and CV Chondritesmentioning

confidence: 99%

“…There are only very few reported occurrences of hydrous minerals in CO chondrites (e.g., Kerridge, 1964;Christophe Michel-Levy, 1969;Kurat, 1975;Ikeda, 1983;Keller and Buseck, 1990a,b;Brearley, 1990; and in most cases, parent body aqueous alteration is suggested for their origin.…”

Section: Co and CV Chondritesmentioning

confidence: 99%

Aqueous alteration of carbonaceous chondrites: Evidence for preaccretionary alteration—A review

Bischoff

1998

Self Cite

129

113

Abstract-In most groups of carbonaceous chondrites, minerals occur that are formed due to aqueous alteration in the nebula and/or within meteorite parent bodies. For determining the evolution of materials in the early solar system, it is of significant importance to clearly identify evidence for either nebular or planetary aqueous alteration. Therefore, results fi-om the study of chondrites have fundamental implications for ideas concerning nebular dynamics, gas-solid interactions in the nebula, and accretionary processes.Considering the topic of this review, it is important to define nebular and parent body processes. The solar nebula activity should include condensation processes of high-and low-temperature components as well as processes of chemical fractionation and grain-size sorting, mixing of solids and gas, and interactions between early formed solids with the remaining gas; but it should exclude processes that occurred in small uncompacted protoplanetary objects that may have been totally destroyed again before accretion of the final meteorite parent bodies. Therefore, the term "preaccretionary" instead of "nebula" is used in this paper to include all these processes that may have occurred in small precursor planetesimals.Currently, there is no doubt that parent body aqueous alteration is a fundamental process in the evolution of several groups of carbonaceous chondrites. However, due to textural and mineralogical observations and chemical analyses, strong arguments have been found also indicating preaccretionary aqueous alteration of distinct components in carbonaceous chondrites. In this paper, evidence for preaccretionary aqueous alteration in carbonaceous chondrites and their components taken from previous studies is discussed in detail.The strongest evidence for preaccretionary alteration comes from studies of CM chondrites. The survival of highly unequilibrated mineral assemblages in accretionary rims, and sharp contacts between chondrule glass and surrounding phyllosilicates, are only two important arguments for preaccretionary alteration features among many others discussed in the paper. Similar observations were also made in CR, CH and related chondrites. Due to the small abundance of water-bearing phases in CO and CV chondrites, the origin of phyllosilicates in these groups is less clear. A preaccretionary origin of hydrous phases in Ca-Al-rich inclusions (CAIs) has also been suggested by several scientists. In CI chondrites, no strong indications for such processes have been found, mainly due to heavy brecciation and severe parent body alteration.