Maralinga, a metamorphosed carbonaceous chondrite found in Australia

Abstract

Abstract-The Maralinga meteorite was found near the village of Maralinga, South Australia (30 018'S, 131°16'E) in 1974, but was not recognized as a meteorite until 1989. One weathered individual was recovered with a total mass of 3.38 kg. The bulk composition and petrography of Maralinga indicate that it is a metamorphosed (petrographic type 4) carbonaceous chondrite with major similarities to the Vigarano-subtype. However, recent trace element data from the literature suggest that Maralinga should be included with the CK (Karoonda-type) carbonaceous chondrites. We classify Maralinga as an anomalous CK4 chondrite because of its abundant chondrules and refractory inclusions relative to other known members of the CK group. Maralinga contains homogeneous silicates, including Ni-bearing olivines (Fa,.), high-Ca clinopyroxene, and rare orthopyroxene. Plagioclase is chemically heterogeneous and falls into two distinct compositional groups one of -An,oand an -An. o group. Highly oxidizing conditions during metamorphism of Maralinga are indicated by the abundance of magnetite and the paucity of Fe-Ni metal.

A weathering index for CK and R chondrites

“…Keller et al (1992) reported rust stains surrounding some magnetite aggregates in CK4-an Maralinga, but our observations indicate that sulfides are the primary source of oxidized iron. The rust stains around Maralinga magnetite may be due to decomposition of associated sulfide.…”

The Kobe CK carbonaceous chondrite: petrography, mineralogy and metamorphism

“…All these features are common to most CK chondrites (e.g., Geiger and Bischoff, 1989;1995;Kallemeyn et al, 1991;Keller et al, 1992;Rubin, 1992;Nakamura et al, 1993;Noguchi, 1993). The thin sections of Kobe show a higher modal abundance of chondrules ( 32 vol%) than typical CK4 5 chondrites (10 15 vol%; Kallemeyn et al, 1991).…”

“…However, there are considerable differences in chondrule abundance among the reported CK chondrites. For example, the Maralinga CK4 chondrite has a much higher abundance of chondrules ( 50 vol%) (Keller et al, 1992). Thus, there may be some range in chondrule abundance in CK chondrites.…”

“…These two kinds of lamellae are distinct in orientation. Magnetite with spinel and ilmenite lamellae is common in CK chondrites (Keller et al, 1992;Geiger and Bischoff, 1995;Nakamura et al, 1993). Closer examination of the magnetite grains reveals that, in addition to the micrometer wide lamellae, submicrometer (< 0.2 μ m) wide lamellae occur at high density (Fig.…”

Rare earth element abundances in the CK chondrites including the Kobe meteorite.

“…Y-82191 (CK6) exhibits anomalously high REE abundances (about 3 times CI), which appears to be parallel the higher abundances of Ca, Sr, Ba and K and lower abundances of Mg and Fe. The Maralinga (CK4) chondrite is considered to be an anomalous CK due to the fact that it contains much more abundant chondrules and CAIs compared with other CK (Keller et al, 1992). As shown in Fig.…”