A new metal‐rich chondrite grouplet

Abstract

Abstract-A new grouplet of primitive, metal-rich chondrites, here called the CB (C, carbonaceous; B, bencubbinite) chondrites, has been recognized. It includes Bencubbin, Weatherford, Hammadah a1 Hamra (HH) 237 and Queen Alexandra Range (QUE) 94411, paired with QUE 94627. Their mineral compositions, as well as their oxygen and nitrogen isotopic compositions, indicate that they are closely related to the CR and CH chondrites, all of which are members of the more inclusive CR clan. CB chondrites have much greater metal/silicate ratios than any other chondrite group, widely increasing the range of metal/silicate fractionation recorded in solar nebular processes. They also have the greatest moderately volatile lithophile element depletions of any chondritic materials. Metal has compositional trends and zoning patterns that suggest a primitive condensation origin, in contrast with metal from other chondrite groups. CB chondrites, as well as other CR clan chondrites, have much heavier nitrogen (higher 15N/14N) than that in other chondrite groups. The primitive characteristics of the CB chondrites suggest that they contain one of the best records of early nebular processes.Another chondrite, Grosvenor Mountains 9555 1, is petrographically similar to the CB chondrites, but its mineral and oxygen and nitrogen isotope compositions indicate that it formed from a different nebular reservoir.

Osmium isotope systematics of ureilites

“…6). The ureilites plot along an extension of the CV field on the CCAM line, partly overlapping with oxygen data for the CR chondrites (Weisberg et al, 2001). The CCAM line may be explained as a mixing line between 16 Orich condensates from the unaltered primary nebular gas having approximately -45‰ for both δ 17 O and δ 18 O, and material from the inner part of the accretion disk enriched in 17 O and 18 O by the photolysis of CO (Clayton, 2002).…”

“…A basic tool for distinguishing between different meteorite classes is a categorization based upon their oxygen isotope composition (Clayton, 2003). Although ureilites do not have a 1:1 match with any known chondrite parent body (Clayton and Mayeda, 1996), they plot along an extension of the CV field on the CCAM line, partly overlapping with oxygen isotope data for the CR chondrites (Weisberg et al, 2001). Recently, it has been shown that there are significant differences in the 187 Re/ 188 Os and 187 Os/ 188 Os of carbonaceous chondrites compared with ordinary and enstatite chondrites (Walker et al, 2002).…”

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

“…These properties include (1) a broad compositional range of FeNi-metal, which is characterized by an approximately solar CofNi ratio; (2) large depletions in moderately volatile elements, such as Mn, Na, K, Ga, Ge, and S; (3) bulk oxygen isotopic compositions plotting on or near the CR-mixing line on a three-isotope diagram; and (4) large positive anomalies in ol5N (Herzog et al, 2000;Weisberg et al, 1993Weisberg et al, , 1995Weisberg et al, ,2001Rubin et al, 2001;Krot et al, unpubl. data).…”

“…data). Based on these observations, QUE 94411, HH 237, Bencubbin, Weatherford, and Gujba have recently been placed together in a new metal-rich chondritic grouplet called CB (carbonaceous Bencubbin-like) chondrites (Weisberg et al, 2001). Due to their strong similarities to CR and CH chondrites they are considered as a part ofthe CR carbonaceous chondrite clan (Weisberg et al, 1995(Weisberg et al, ,2001.…”

Smithsonian Institution

“…In addition to the 13 well-defined groups, ~14 chondritic grouplets or unique meteorites (Meibom and Clark, 1999;Brown et al, 2000;Weisberg et al, 2001) have been recognized. Thus, the full range of chondritic meteorites probably requires at least 27 distinct parent bodies.…”