Ca,Al-rich inclusions, amoeboid olivine aggregates, and Al-rich chondrules from the unique carbonaceous chondrite Acfer 094: I. mineralogy and petrology

Abstract-Here we report the petrography, mineralogy, and bulk compositions of Ca,Al-rich inclusions (CAIs), amoeboid olivine aggregate (AOA), and Al-rich chondrules (ARCs) in Sayh al Uhaymir (SaU) 290 CH chondrite. Eighty-two CAIs (0.1% of the section surface area) were found. They are hiboniterich (9%), grossite-rich (18%), melilite ± spinel-rich (48%), fassaite ± spinel-rich (15%), and fassaiteanorthite-rich (10%) refractory inclusions. Most CAIs are rounded in shape and small in size (average = 40 µm). They are more refractory than those of other groups of chondrites. CAIs in SaU 290 might have experienced higher peak heating temperatures, which could be due to the formation region closer to the center of protoplanetary disk or have formed earlier than those of other groups of chondrites. In SaU 290, refractory inclusions with a layered texture could have formed by gas-solid condensation from the solar nebula and those with an igneous texture could have crystallized from melt droplets or experienced subsequent melting of pre-existing condensates from the solar nebula. One refractory inclusion represents an evaporation product of pre-existing refractory solid on the basis of its layered texture and melting temperature of constituting minerals. Only one AOA is observed (75 µm across). It consists of olivine, Al-diopside, anorthite, and minor spinel with a layered texture. CAIs and AOA show no significant low-temperature aqueous alteration. ARCs in SaU 290 consist of diopside, forsterite, anorthite, Al-enstatite, spinel, and mesostasis or glass. They can be divided into diopsiderich, Al-enstatite-rich, glass-rich, and anorthite-rich chondrules. Bulk compositions of most ARCs are consistent with a mixture origin of CAIs and ferromagnesian chondrules. Anorthite and Al-enstatite do not coexist in a given ARC, implying a kinetic effect on their formation.

Section: High-temperature Nebular Processes Recorded By Cais In Sau 290mentioning

confidence: 99%

Section: High-temperature Nebular Processes Recorded By Cais In Sau 290mentioning

confidence: 99%

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Refractory inclusions and aluminum‐rich chondrules in Sayh al Uhaymir 290 CH chondrite: Petrography and mineralogy

Zhang¹,

Hsu²

2009

“…In contrast, hibonite-rich inclusions are the intensely studied objects in CM2 chondrites (e.g., Macdougall 1979;MacPherson et al 1983;Ireland 1990;Simon et al 1998), whereas grossitebearing inclusions appear more abundant in CR clan chondrites (e.g., Kimura et al 1993;Weber and Bischoff 1997;Aléon et al 2002;Krot et al 2002). Fine-grained anorthite-spinel-rich inclusions (ASI) were reported in the Ningqiang carbonaceous chondrite (Lin and Kimura 1998), with their counterparts in CR chondrites (Weber and Bischoff 1997;Aléon et al 2002), reduced CV chondrites (Krot et al 2004a), Yamato-81020 (CO3) (Itoh et al 2004) and the unique Acfer 094 carbonaceous chondrite (Krot et al 2004b). In addition, fine-grained spinel-pyroxene and melilite-spinelrich (fluffy type A) inclusions have been widely reported from CV chondrites.…”

Section: Introductionmentioning

confidence: 99%

Petrographic comparison of refractory inclusions from different chemical groups of chondrites

Lin

Kimura

Miao

et al. 2006

Abstract-Twenty-four refractory inclusions (40-230 μm, with average of 86 ± 40 μm) were found by X-ray mapping of 18 ordinary chondrites. All inclusions are heavily altered, consisting of finegrained feldspathoids, spinel, and Ca-pyroxene with minor ilmenite. The presence of feldspathoids and lack of melilite are due to alteration that took place under oxidizing conditions as indicated by FeO-ZnO-rich spinel and ilmenite. The pre-altered mineral assemblages are dominated by two types: one rich in melilite, referred to as type A-like, and the other rich in spinel, referred to as spinelpyroxene inclusions. This study and previous data show similar type and size distributions of refractory inclusions in ordinary and enstatite chondrites. A survey of refractory inclusions was also conducted on Allende and Murchison in order to make unbiased comparison with their counterparts in other chondrites. The predominant inclusions are type A and spinel-pyroxene, with average sizes of 170 ± 130 μm (except for two mm-sized inclusions) in Allende and 150 ± 100 μm in Murchison. The relatively larger sizes are partially due to common conglomerating of smaller nodules in both chondrites. The survey reveals closely similar type and size distributions of refractory inclusions in various chondrites, consistent with our previous data of other carbonaceous chondrites. The petrographic observations suggest that refractory inclusions in various groups of chondrites had primarily formed under similar processes and conditions, and were transported to different chondrite-accreting regions. Heterogeneous abundance and distinct alteration assemblages of refractory inclusions from various chondrites could be contributed to transporting processes and secondary reactions under different conditions.

“…The most attractive model is that ARCs formed from precursors consisting of a heterogeneous mixture of ferromagnesian chondrules and refractory materials via processes that produced normal chondrules (Krot et al 2002(Krot et al , 2004, i.e., a flash heating event followed by rapid cooling and crystallization. ARCs in Ningqiang reveal several pieces of evidence that support this argument.…”

Section: Petrogenesis Of Arcs In Ningqiang: Implications For Genetic mentioning

confidence: 99%

Petrology and mineralogy of the Ningqiang carbonaceous chondrite

Wang

Hsu

2009

Ningqiang are composed mainly of olivine, plagioclase, spinel, and pyroxenes. In ARCs, spinel and plagioclase are enriched in moderately volatile elements (Cr, Mn, and Na), and low-Ca pyroxenes are enriched in refractory elements (Al and Ti). The petrology and mineralogy of ARCs in Ningqiang indicate that they were formed from hybrid precursors of ferromagnesian chondrules mixed with refractory materials during chondrule formation processes. We found 294 CAIs (55.0% type A, 39.5% spinel-pyroxene-rich, 4.4% hibonite-rich, and several type C and anorthite-spinelrich inclusions) and 73 AOAs in 15 Ningqiang sections (equivalent to 20 cm 2 surface area). This is the first report of hibonite-rich inclusions in Ningqiang. They are texturally similar to those in CM, CH, and CB chondrites, and exhibit three textural forms: aggregates of euhedral hibonite single crystals, fine-grained aggregates of subhedral hibonite with minor spinel, and hibonite ± Al,Ti-diopside ± spinel spherules. Evidence of secondary alteration is ubiquitous in Ningqiang. Opaque assemblages, formed by secondary alteration of pre-existing alloys on the parent body, are widespread in chondrules and matrix. On the other hand, nepheline and sodalite, existing in all chondritic components, formed by alkali-halogen metasomatism in the solar nebula.