Carbonaceous xenoliths in the Krymka LL3.1 chondrite: Mysteries and established facts

NWA 10214 is an LL3‐6 breccia containing ~8 vol% clasts including LL5, LL6, and shocked‐darkened LL fragments as well as matrix‐rich Clast 6 (a new kind of chondrite). This clast is a dark‐colored, subrounded, 6.1 × 7.0 mm inclusion, consisting of 60 vol% fine‐grained matrix, 32 vol% coarse silicate grains, and 8 vol% coarse opaque grains. The large chondrules and chondrule fragments are mainly Type IB; one small chondrule is Type IIA. Also present are one 450 × 600 μm spinel‐pyroxene‐olivine CAI and one 85 × 110 μm AOI. Clast 6 possesses a unique set of properties. (1) It resembles carbonaceous chondrites in having relatively abundant matrix, CAIs, and AOIs; the clast's matrix composition is close to that in CV3 Vigarano. (2) It resembles type‐3 OC in its olivine and low‐Ca pyroxene compositional distributions, and in the Fe/Mn ratio of ferroan olivine grains. Its mean chondrule size is within 1σ of that of H chondrites. The O‐isotopic compositions of the chondrules are in the ordinary‐ and R‐chondrite ranges. (3) It resembles type‐3 enstatite chondrites in the minor element concentrations in low‐Ca pyroxene grains and in having a high low‐Ca pyroxene/olivine ratio in chondrules. Clast 6 is a new variety of type‐3 OC, somewhat more reduced than H chondrites or chondritic clasts in the Netschaevo IIE iron; the clast formed in a nebular region where aerodynamic radial drift processes deposited a high abundance of matrix material and CAIs. A chunk of this chondrite was ejected from its parent asteroid and later impacted the LL body at low relative velocity.

Section: Introductionmentioning

confidence: 99%

NWA 10214—An LL3 chondrite breccia with an assortment of metamorphosed, shocked, and unique chondrite clasts

Rubin

Breen

Isa

et al. 2016

“…); ordinary chondrites (Semenko et al. , ; Nakashima et al. ); carbonaceous chondrites (Olsen et al.…”

Section: Introductionmentioning

confidence: 99%

“…Clasts of lithologies that are foreign to the host rock occur in all classes of meteorites, for example, in ureilites (Prinz et al 1987;Brearley and Prinz 1992;Bischoff et al 2010); HED achondrites (Reid et al 1990;Brearley and Papike 1993;Zolensky et al 1996); ordinary chondrites (Semenko et al 2001(Semenko et al , 2005Nakashima et al 2003); carbonaceous chondrites (Olsen et al 1988;Bischoff et al 1993;Endress et al 1994;Greshake et al 2002;Jogo et al 2011); and in ungrouped meteorites, such as the Kaidun microbreccia (Zolensky et al 1991;Zolensky and Ivanov 2003).…”

Section: Introductionmentioning

confidence: 99%

Clasts in theCM2 carbonaceous chondrite Lonewolf Nunataks 94101: Evidence for aqueous alteration prior to complex mixing

Lindgren

Lee

Sofe

et al. 2013

Abstract-Clasts in the CM2 carbonaceous chondrite Lonewolf Nunataks (LON) 94101 have been characterized using scanning and transmission electron microscopy and electron microprobe analysis to determine their degrees of aqueous alteration, and the timing of alteration relative to incorporation of clasts into the host. The provenance of the clasts, and the mechanism by which they were incorporated and mixed with their host material are also considered. Results show that at least five distinct types of clasts occur in LON 94101, of which four have been aqueously altered to various degrees and one is largely anhydrous. The fact that they have had different alteration histories implies that the main part of aqueous activity occurred prior to the mixing and assimilation of the clasts with their host. Further, the presence of such a variety of clasts suggests complex mixing in a dynamic environment involving material from various sources. Two of the clasts, one containing approximately 46 vol% carbonate and the other featuring crystals of pyrrhotite up to approximately 1 mm in size, are examples of unusual lithologies and indicate concentration of chemical elements in discrete areas of the parent body(ies), possibly by flow of aqueous solutions.

“…Although they used very different analytical techniques, both groups concluded that mysterite belongs to an unknown kind of carbonaceous material (Higuchi et al 1977;Grossman et al 1980). The inclusion is made of a fine-grained mixture of silicates and FeS (here identified as troilite, e.g., Semenenko et al 2005) and, in addition, coarse grains of pyroxene, olivine, and rare metal particles.…”

Section: Introductionmentioning

confidence: 99%

“…It was inferred that its graphite was formed from organic compounds as a result of metamorphism. In addition to graphite crystals, there are also C-rich areas of unknown material and organic compounds (Semenenko et al 2005). The spatial concentration of certain ion species (such as H − , C − , CH − , C 2 − , and C 2 H − ; Semenenko et al 2005), measured with time-of-flight secondary ion mass spectrometry, are visible in black areas in scanning electron microscopy (SEM) images.…”

Section: Introductionmentioning

confidence: 99%

TEM studies and the shock history of a “mysterite” inclusion from the Krymka LL chondrite

Weber

Semenenko²,

Stephan

et al. 2006

Self Cite

TEM studies and the shock history of a "mysterite" inclusion from the Krymka LL chondrite Abstract-The microstructure and composition of the matrix of one carbonaceous inclusion (K1) in the Krymka LL3.1 chondrite were studied using transmission electron microscopy (TEM). K1 has previously shown an enigmatic nature and similarities with volatile-rich, fine-grained, dark inclusions of Krymka called "mysterite."In the present study, four minerals were identified by TEM. Olivine, pyroxene, and pyrrhotite typically have grain sizes of one micrometer; graphite occurs as flakes of a similar size. Olivine shows a moderately high dislocation density most probably caused by shock. Pyroxene shows coexisting ortho-and clinoenstatite lamellae that probably originated from shear stress after a shock event or from the rapid cooling of the protoenstatite stability field. However, we demonstrate that in this case, a shock trigger is more likely. Pyrrhotite in the studied sample occurs as a 4C monoclinic superstructure. The graphite flakes in the fragment are well crystallized, as can be seen by discrete spots in the diffraction pattern. In graphite, the degree of crystallization increases with the metamorphic grade. Based on the microstructure of this mineral we conclude that after a first moderate shock event, the residual temperature between 300 °C and 500 °C led to thermal metamorphism. A second shock event, possibly at excavation from the parent body, is responsible for the shock features observed in olivine, pyroxene, and graphite.