Cristobalite‐ and tridymite‐bearing clasts in Parnallee (LL3) and Farmington (L5)

Bridges, J. C.; Franchi, I. A.; Hutchison, Robert; Morse, A. D.; Long, J. V. P.; Pillinger, C. T.

doi:10.1111/j.1945-5100.1995.tb01169.x

Cited by 40 publications

(44 citation statements)

References 40 publications

(39 reference statements)

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“…We believe the most straightforward explanation is that this occurred through crystal-melt fractionation in a planetary setting, although Brigham et al proposed a nebular setting for olivine-gas fractionation. In addition to the bulk major element compositions, the evidence for a planetary origin (in clasts with similar mineral assemblages to the Bo Xian chondrules) is the presence of bulk low rare earth element abundances greater than high rare earth element abundances with a positive Eu anomaly in one sample (Bridges et al, 1995). Such trace element abundances are compatible with crystal-melt fractionation but not volatilisation.…”

Section: Chondrule Textures and Chemical Fractionationmentioning

confidence: 93%

“…The other two chondrules (BX71, BX122) have 2 and 10 vol% cristobalite, respectively. Previous x-ray diffraction (XRD) analyses of pyroxene-silica clasts in ordinary chondrites have shown that cristobalite is the most likely identity of the silica polymorph (Bridges et al, 1995).…”

Section: Chemically Fractionated Chondrulesmentioning

confidence: 99%

“…These chondrules are cristobalite-rich (Krot and Wasson, 1994), Al-rich (Bischoff and Keil, 1984), feldspathoid-and CI-bearing , and chromite-bearing (Ramdohr, 1967). Such compositional fractionations in clasts and chondrules have resulted both from igneous fractionation (Bridges et a/., 1995) and volatility controls (Bischoff and Keil, 1984).…”

Section: Introduction: the Bo Xian Meteorite And Aims Of This Studymentioning

confidence: 99%

“…It has been demonstrated that the main phase of isotopic exchange in the unequilibrated ordinary chondrite (UOC) parent bodies is largely controlled by the structural properties of the mineral phases, framework silicates, and glass allowing higher rates of diffusion of '60-poor gases than olivine and pyroxene (Bridges et al, 1995(Bridges et al, , 1998(Bridges et al, , 1999a). Here we aim to explore further the mineralogical controls by examining the 0-isotopic compositions of chondrules with varying mineral assemblages and textures.…”

Section: Introduction: the Bo Xian Meteorite And Aims Of This Studymentioning

confidence: 99%

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Bo Xian (LL3.9): Oxygen‐isotopic and mineralogical characterisation of separated chondrules

Li¹,

Bridges²,

Hutchison³

et al. 2000

Meteorit & Planetary Scien

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Abstract-We report the results of a mineralogical and 0-isotopic study of 362 chondrules disaggregated from the Bo Xian chondrite. The range of mineral compositions (Fa = 0.8-31.2%0, mean = 23.5%, mode = 27-28%) are consistent with a reclassification of this meteorite from LL4 to LL3.9. Chondrule diameters range from 0.20 to 3.40 mm (mean = 0.74 mm) in the disaggregated population. A lower mean diameter (0.64 mm) calculated from thin-section measurements partly reflects the high proportion of chondrule fragments. The chondrule size distribution, which is approximately log-normal, is consistent with sizesorting mechanisms. This sorting could be linked to the fragmentation of many chondrules on the parent body. However, in detail, the variation in diameter of different chondrule types and a hiatus in the size distribution at 0.6 mm indicate that there may have been complex controls perhaps partly being determined by the chondrule formation mechanism. Seven percent of the sectioned chondrules (1 02) contain chemically fractionated mineral assemblages:This significant degree of chemical heterogeneity probably resulted from both igneous and volatility controls.Oxygen-isotopic compositions were determined on mineral separates and 16 of the sectioned chondrules. Three separate isotopic exchange events have been identified. The dominant one is a low-temperature hydrous gas-solid exchange event between 160-rich solid and 160-poor gas reservoirs that lay along a slope 1.0 line on three-isotope plots. Partial equilibration with the gas by feldspar and cristobalite, which exchanged more rapidly than olivine or pyroxene, led to formation of a slope 0.77 mixing line for Bo Xian and other LL chondrites. Mineralogy is the dominant control on the extent of this exchange; no relationship between isotopic composition and chondrule texture or size was identified. The feldspar separate and cristobalite-rich chondrules have the most 160-poor compositions. Subsequently, thermal metamorphism in the parent body led to partial isotopic equilibration between the different mineral phases. A third exchange event, predating the other two events, is probably shown by one of the Al-rich chondrules. This has an 160-rich composition, lying below the terrestrial fractionation line. Another Al-rich chondrule has a normal ordinary chondrite isotopic composition. It is not clear whether the isotopic fractionation recorded in some Al-rich chondrules can be achieved by the dominant gas-solid exchange. Instead, the precursor 0 to the mineral phases may have become 160-rich during an earlier phase of mass-independent fractionation. cristobalite-bearing and Al-rich.

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Section: Chondrule Textures and Chemical Fractionationmentioning

confidence: 93%

Section: Chemically Fractionated Chondrulesmentioning

confidence: 99%

Section: Introduction: the Bo Xian Meteorite And Aims Of This Studymentioning

confidence: 99%

Section: Introduction: the Bo Xian Meteorite And Aims Of This Studymentioning

confidence: 99%

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Bo Xian (LL3.9): Oxygen‐isotopic and mineralogical characterisation of separated chondrules

Li¹,

Bridges²,

Hutchison³

et al. 2000

Meteorit & Planetary Scien

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“…Moreover, sputtering ofsolids by energetic particles ejected by the YSO might have contributed a small proportion of refractory elements to the condensates. Cristobalite-and tridymite-bearing clasts that have been observed in a few ordinary chondrites (Bridges et al, 1995) are a compositional match for this hypothetical component. The clasts are < 16mm in size and composed of a silica polymorph + enstatite ± Capyroxene ± Ca-plagioclase.…”

Section: Origin Of the Silicon-and Magnesium-rich Component-fractionamentioning

confidence: 82%

Major element fractionation in chondrites by distillation in the accretion disk of a T Tauri Sun?

Hutchison

2002

Meteorit & Planetary Scien

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Abstract-Redistribution or loss ofbatches of condensate from a cooling protosolar nebula is generally thought to have led to the formation ofthe chemical groups of chondrites. This demands a nebula hot enough for silicate vaporization over 1-3 AU, the region where chondrites formed. Alternatively, heating of a protosolar accretion disk may have been confined to an annular zone at its inner edge, -0.06 AU from the protosun. Most infalling matter was accreted by the protosun, but a proportion was heated and carried outwards by an x-wind. Shu et at. (1996, 1997) proposed that larger objects such as chondrules and calcium-aluminum-rich inclusions (CAIs) were returned to the disk at asteroidal distances by sedimentation from the x-wind. Fine dust and gas were lost to space. The model implies that solids were not lost from the cold disk. The chemical compositions ofthe chondrite groups were produced by mixing different proportions ofCAIs and chondrules with disk solids ofCI composition. Heating at the inner edge of the disk was accompanied by particle irradiation, which synthesized nuclides including 26AI.The x-wind model can produce CAIs, not chondrules, and allows survival ofpresolar grains >0.06 AU from the protosun. Normalization to Al and CI indicates that non-carbonaceous chondrites may be disk material that gained a Si-and Mg-enriched fraction. Carbonaceous chondrites are different; they appear to be CI that lost lithophile elements more volatile than Ca. Five carbonaceous chondrite groups also lost Ni and Fe but the CH group gained siderophiles. Elemental loss from CI is incompatible with the x-wind model. Silicon and CI normalization confirms that the CM, CO, CK and CV groups may be CI that gained refractories as CAIs. The Si-, Mg-rich fraction may have formed by selective vaporization followed by precipitation on grains in the x-wind. This fractional distillation mechanism can account for lithophile element abundances in non-carbonaceous chondrite groups, but an additional process is required for the loss of Ca and Mn in the EL group and for fractionated siderophile abundances in the H, Land LL groups. Heated and recycled fractions were not homogenized across the disk so the chondrite groups were established in a single cycle of enhanced protosolar activity in <10 4 years, the time for a millimeter-sized particle to drift into the Sun from 2 to 3 AU, due to gas-drag.

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Oxygen Isotopes and Sampling of the Solar System

et al. 2020

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Cristobalite‐ and tridymite‐bearing clasts in Parnallee (LL3) and Farmington (L5)

Cited by 40 publications

References 40 publications

Bo Xian (LL3.9): Oxygen‐isotopic and mineralogical characterisation of separated chondrules

Bo Xian (LL3.9): Oxygen‐isotopic and mineralogical characterisation of separated chondrules

Major element fractionation in chondrites by distillation in the accretion disk of a T Tauri Sun?

Oxygen Isotopes and Sampling of the Solar System

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