We have found two refractory inclusions in the CO3.00 carbonaceous chondrite Dominion Range (DOM) 08006 that appear to be primary condensates from the early solar nebula. One, inclusion 56-1, ...contains the first four phases predicted to form by equilibrium gas-solid condensation: corundum; hibonite; grossite; and perovskite. The other, 31-2, contains nine predicted condensate phases: hibonite; grossite; perovskite; melilite; spinel; FeNi metal; diopside; forsterite; and enstatite. Except for melilite/spinel, the phases occur in the predicted sequence from core to rim of the inclusion, which has an irregular shape inconsistent with a molten stage. This inclusion preserves the most complete record of condensation in the early solar nebula that has yet been found. The physical evidence reported here supports equilibrium condensation calculations that predict the observed sequence as well as the assumptions upon which they are based, such as total pressure (∼10−3 atm), bulk system composition (solar), and COH proportions. All phases in both inclusions and the associated ferromagnesian silicates are 16O-rich, with Δ17O between −25 and −20‰, implying that this is the original composition of the vast majority of primary condensates and that 16O-poor compositions observed in many isotopically heterogeneous inclusions are largely due to subsequent isotopic exchange. While the nebula was well-mixed with respect to oxygen isotopic composition, clearly resolved anomalies in Ca and Ti isotopic compositions indicate that some isotopic heterogeneity existed early and was preserved during condensation. Inclusion 31-2 did not incorporate live 26Al and has nucleosynthetic anomalies in the heavy Ca and Ti isotopes (i.e., δ48Ca = 4.3 ± 1.9‰; δ50Ti = 8.8 ± 2.0‰). In contrast, inclusion 56-1 has radiogenic 26Mg excesses yielding a (26Al/27Al)0 ratio of (1.0 ± 0.1) × 10−5 and negative nucleosynthetic isotopic anomalies in Ca (δ48Ca = −10.3 ± 4.2‰) and Ti (δ50Ti = −4.3 ± 2.9‰). Thus, it represents a deviation from the mutual exclusivity relationship between 26Al incorporation and large nucleosynthetic anomalies. The reservoirs in which these inclusions formed had similar O-isotopic and different Al-, Ca– and Ti-isotopic compositions, suggesting that while the CAI-forming region was well-mixed with respect to oxygen isotopic composition, clearly resolved anomalies in Ca and Ti isotopic compositions indicate that some isotopic heterogeneity existed and was preserved during condensation.
•Mg isotopes show multiple populations of refractory inclusions.•Formation of the Solar System's first solids was punctuated and recurrent.•Episodic formation of refractory solids may be generic to ...the star-forming process.•Refractory inclusions formed through thermal processing of presolar material.•Refractory solids preserve isotope signatures from the proto-Solar molecular cloud.
Refractory inclusions Ca-Al-rich Inclusions (CAIs) and Amoeboid Olivine Aggregates (AOAs) in primitive meteorites are the oldest Solar System solids. They formed in the hot inner protoplanetary disk and, as such, provide insights into the earliest disk dynamics and physicochemical processing of the dust and gas that accreted to form the Sun and its planetary system. Using the short-lived 26Al to 26Mg decay system, we show that bulk refractory inclusions in CV (Vigarano-type) and CR (Renazzo-type) carbonaceous chondrites captured at least two distinct 26Al-rich (26Al/27Al ratios of ∼5 × 10−5) populations of refractory inclusions characterized by different initial 26Mg/24Mg isotope compositions (μ26Mg*0). Another 26Al-poor CAI records an even larger μ26Mg*0 deficit. This suggests that formation of refractory inclusions was punctuated and recurrent, possibly associated with episodic outbursts from the accreting proto-Sun lasting as short as <8000 yr. Our results support a model in which refractory inclusions formed close to the hot proto-Sun and were subsequently redistributed to the outer disk, beyond the orbit of Jupiter, plausibly via stellar outflows with progressively decreasing transport efficiency. We show that the magnesium isotope signatures in refractory inclusions mirrors the presolar grain record, demonstrating a mutual exclusivity between 26Al enrichments and large nucleosynthetic Mg isotope effects. This suggests that refractory inclusions formed by incomplete thermal processing of presolar dust, thereby inheriting a diluted signature of their isotope systematics. As such, they record snapshots in the progressive sublimation of isotopically anomalous presolar carriers through selective thermal processing of young dust components from the proto-Solar molecular cloud. We infer that 26Al-rich refractory inclusions incorporated 26Al-rich dust which formed <5 Myr prior to our Sun, whereas 26Al-poor inclusions (such as FUN- and PLAC-type CAIs) incorporated >10 Myr old dust.
Mineralogical observations, chemical and oxygen–isotope compositions, absolute
207Pb–
206Pb ages and short-lived isotope systematics (
7Be–
7Li,
10Be–
10B,
26Al–
26Mg,
36Cl–
36S,
41Ca–
41K,
53Mn–
...53Cr,
60Fe–
60Ni,
182Hf–
182W) of refractory inclusions Ca,Al-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs), chondrules and matrices from primitive (unmetamorphosed) chondrites are reviewed in an attempt to test (i) the
x-wind model
vs. the shock-wave model of the origin of chondritic components and (ii) irradiation
vs. stellar origin of short-lived radionuclides. The data reviewed are consistent with an external, stellar origin for most short-lived radionuclides (
7Be,
10Be, and
36Cl are important exceptions) and a shock-wave model for chondrule formation, and provide a sound basis for early Solar System chronology. They are inconsistent with the
x-wind model for the origin of chondritic components and a local, irradiation origin of
26Al,
41Ca, and
53Mn.
10Be is heterogeneously distributed among CAIs, indicating its formation by local irradiation and precluding its use for the early solar system chronology.
41Ca–
41K, and
60Fe–
60Ni systematics are important for understanding the astrophysical setting of Solar System formation and origin of short-lived radionuclides, but so far have limited implications for the chronology of chondritic components. The chronological significance of oxygen–isotope compositions of chondritic components is limited. The following general picture of formation of chondritic components is inferred. CAIs and AOAs were the first solids formed in the solar nebula ∼4567–4568
Myr ago, possibly within a period of <0.1
Myr, when the Sun was an infalling (class 0) and evolved (class I) protostar. They formed during multiple transient heating events in nebular region(s) with high ambient temperature (at or above condensation temperature of forsterite), either throughout the inner protoplanetary disk (1–4
AU) or in a localized region near the proto-Sun (<0.1
AU), and were subsequently dispersed throughout the disk. Most CAIs and AOAs formed in the presence of an
16O-rich (Δ
17O
∼
−24
±
2‰) nebular gas. The
26Al-poor (
26Al/
27Al)
0
<
1
×
10
−5,
16O-rich (Δ
17O
∼
−24
±
2‰) CAIs – FUN (fractionation and unidentified nuclear effects) CAIs in CV chondrites, platy hibonite crystals (PLACs) in CM chondrites, pyroxene–hibonite spherules in CM and CO chondrites, and the majority of grossite- and hibonite-rich CAIs in CH chondrites—may have formed prior to injection and/or homogenization of
26Al in the early Solar System. A small number of igneous CAIs in ordinary, enstatite and carbonaceous chondrites, and virtually all CAIs in CB chondrites are
16O-depleted (Δ
17O
>
−10‰) and have (
26Al/
27Al)
0 similar to those in chondrules (<1
×
10
−5). These CAIs probably experienced melting during chondrule formation. Chondrules and most of the fine-grained matrix materials in primitive chondrites formed 1–4
Myr after CAIs, when the Sun was a classical (class II) and weak-lined T Tauri star (class III). These chondritic components formed during multiple transient heating events in regions with low ambient temperature (<1000
K) throughout the inner protoplanetary disk in the presence of
16O-poor (Δ
17O
>
−5‰) nebular gas. The majority of chondrules within a chondrite group may have formed over a much shorter period of time (<0.5–1
Myr). Mineralogical and isotopic observations indicate that CAIs were present in the regions where chondrules formed and accreted (1–4
AU), indicating that CAIs were present in the disk as free-floating objects for at least 4
Myr. Many CAIs, however, were largely unaffected by chondrule melting, suggesting that chondrule-forming events experienced by a nebular region could have been small in scale and limited in number. Chondrules and metal grains in CB chondrites formed during a single-stage, highly-energetic event ∼4563
Myr ago, possibly from a gas-melt plume produced by collision between planetary embryos.
Chronology of the Solar System's Oldest Solids Connelly, James N; Amelin, Yuri; Krot, Alexander N ...
Astrophysical journal/The Astrophysical journal,
03/2008, Letnik:
675, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Determining the origins of our solar system and, by proxy, other planetary systems, depends on knowing accurately and precisely the timing and tempo of the transformation of the disk of gas and dust ...to the solids that formed the planets. Relative ages based on the short-lived nuclide super(26)Al indicate that high-temperature calcium-aluminum inclusions (CAIs) formed before lower temperature chondrules but these ages are heavily dependant on a model of homogeneous distribution of super(26)Al within the protoplanetary disk. The competing X-wind model argues for heterogeneous distribution of super(26)Al due to its formation by intra-solar system irradiation such that this system would have no chronological significance. We report a super(207)Pb- super(206)Pb isochron age of 4565.45 plus or minus 0.45 Myr for chondrules from the CV chondrite Allende, an age that is 1.66 plus or minus 0.48 Myr younger than the accepted Pb-Pb age for CAIs from this chondrite group. This age offset is in excellent agreement with the relative ages determined using the super(26)Al- super(26)Mg system, an observation that supports a supernova origin for super(26)Al and, importantly, the chronological significance of the super(26)Al- super(26)Mg system in general. This is consistent with an early and brief CAI-forming event followed by recurrent chondrule formation throughout the life span of the protoplanetary disk. The paucity of old chondrules in chondrite meteorites may reflect their early incorporation into the parent bodies of differentiated meteorites after CAIs were effectively removed from the innermost regions of the protoplanetary disk. Lastly, the agreement between the absolute and relative chronology of CAIs and chondrules requires a solar system age younger than similar to 4567.5 Myr.
Primitive chondritic meteorites contain material (presolar grains), at the level of a few parts per million, that predates the formation of our Solar System. Astronomical observations and the ...chemical composition of the Sun both suggest that silicates must have been the dominant solids in the protoplanetary disk from which the planets of the Solar System formed, but no presolar silicates have been identified in chondrites. Here we report the in situ discovery of presolar silicate grains 0.1-1 µm in size in the matrices of two primitive carbonaceous chondrites. These grains are highly enriched in 17O (δ17OSMOW > 100-400‰), but have solar silicon isotopic compositions within analytical uncertainties, suggesting an origin in an oxygen-rich red giant or an asymptotic giant branch star. The estimated abundance of these presolar silicates (3-30 parts per million) is higher than reported for other types of presolar grains in meteorites, consistent with their ubiquity in the early Solar System, but is about two orders of magnitude lower than their abundance in anhydrous interplanetary dust particles. This result is best explained by the destruction of silicates during high-temperature processing in the solar nebula.
The I-Xe system was studied in a ferromagnetic sample separated from the Orgueil CI carbonaceous chondrite with a hand-held magnet and in two magnetite samples, one chemically separated before and ...the other one after neutron irradiation. This work was done in order to investigate the effects of chemical separation by LiCl and NaOH on the I-Xe system in magnetite. Our test demonstrated that the chemical separation of magnetite before irradiation using either LiCl or NaOH, or both, does not contaminate the sample with iodine and thus cannot lead to erroneous I-Xe ages due to introduction of uncorrelated 128∗Xe.
The I-Xe ages of two Orgueil magnetite samples are mutually consistent within experimental uncertainties and, when normalized to an absolute time scale with the reevaluated Shallowater aubrite standard, place the onset of aqueous alteration on the CI parent body at 4564.3 ± 0.3 Ma, 2.9 ± 0.3 Ma after formation of the CV Ca-AI-rich inclusions (CAIs). The I-Xe age of the ferromagnetic Orgueil separate is 3.4 Ma younger, corresponding to a closure of the I-Xe system at 4560.9 ± 0.2 Ma. These and previously published I-Xe data for Orgueil (Hohenberg et al., 2000) indicate that aqueous alteration on the CI parent body lasted for at least 5 Ma.
Although the two magnetite samples gave indistinguishable I-Xe ages, their temperature release profiles differed. One of the two Orgueil magnetites released less radiogenic Xe than the other, 80% of it corresponding to the low-temperature peak of the release profile, compared to only 6% in case of the second Orgueil magnetite sample. This could be due to the difference in iodine trapping efficiencies for magnetite grains of different morphologies. Alternatively, the magnetite grains with the lower radiogenic Xe concentrations may have formed at a later stage of alteration when iodine in an aqueous solution was depleted.
The lead-lead isochron age of chondrules in the CR chondrite Acfer 059 is 4564.7 +/- 0.6 million years ago (Ma), whereas the lead isotopic age of calcium-aluminum-rich inclusions (CAIs) in the CV ...chondrite Efremovka is 4567.2 +/- 0.6 Ma. This gives an interval of 2.5 +/- 1.2 million years (My) between formation of the CV CAIs and the CR chondrules and indicates that CAI- and chondrule-forming events lasted for at least 1.3 My. This time interval is consistent with a 2- to 3-My age difference between CR CAIs and chondrules inferred from the differences in their initial 26Al/27Al ratios and supports the chronological significance of the 26Al-26Mg systematics.
Hutcheonite (IMA 2013-029), Ca3Ti2(SiAl2)O12, is a new garnet mineral that occurs with monticellite, grossular, and wadalite in secondary alteration areas along some cracks between primary melilite, ...spinel, and Ti,Al-diopside in a Type B1 Fractionation and Unidentified Nuclear effects (FUN) Ca-Al-rich inclusion (CAI) Egg-3 from the Allende CV (Vigarano type) carbonaceous chondrite. The mean chemical composition of type hutcheonite by electron probe microanalysis is (wt%) CaO 34.6, TiO2 25.3, SiO2 20.9, Al2O3 15.7, MgO 2.1, FeO 0.7, V2O3 0.5, total 99.8, giving rise to an empirical formula of Ca2.99(Ti4+1.53Mg0.25Al0.17Fe2+0.05V3+0.03) (Si1.68Al1.32)O12. The end-member formula is Ca3Ti2(SiAl2)O12. Hutcheonite has the Ia3d garnet structure with a = 11.843 Å, V = 1661.06 Å3, and Z = 8, as revealed by electron backscatter diffraction. The calculated density using the measured composition is 3.86 g/cm3. Hutcheonite is a new secondary phase in Allende, apparently formed by iron-alkali-halogen metasomatic alteration of the primary CAI phases like melilite, perovskite, and Ti,Al-diopside on the CV chondrite parent asteroid. Formation of the secondary Ti-rich minerals like hutcheonite during the metasomatic alteration of the Allende CAIs suggests some mobility of Ti during the alteration. The mineral name is in honor of Ian D. Hutcheon, a cosmochemist at Lawrence Livermore National Laboratory, California, U.S.A.
We report high-precision measurements of nitrogen and carbon isotopic compositions of a carbon-bearing titanium-nitride (osbornite) in a calcium-aluminum-rich inclusion (CAI) from the CH/CB-like ...carbonaceous chondrite Isheyevo. The mineralogy and petrography of the CAI and thermodynamic calculations indicate that the osbornite formed by gas-solid condensation in a high-temperature ( x2000 K) region of the solar nebula. Because isotopic fractionation at high temperature is small, the measured nitrogen super(15)N/ super(14)N = (2.356 c 0.018) x 10 super(-3) and carbon super(13)C/ super(12)C = 0.01125 c 0.00008; 1 isotopic compositions of the Isheyevo osbornite are representative of the solar nebula and, hence, of the Sun. This conclusion is supported by the observations that (1) the measured super(13)C/ super(12)C ratio is indistinguishable from the spectroscopic determination of the super(13)C/ super(12)C ratio of the solar photosphere and (2) the measured super(15)N/ super(14)N ratio of osbornite is in excellent agreement with the Galileo spacecraft measurement of the nitrogen isotopic composition of the Jovian atmosphere, the second largest reservoir of nitrogen in the solar system. The inferred super(15)N/ super(14)N ratio of the solar nebula is also similar to the nitrogen isotopic composition of the vast majority of chondritic nanodiamonds, suggesting their solar nebula origin.
Dmisteinbergite, CaAl2Si2O8 with P63/mcm structure, was identified in a rounded coarse-grained igneous Type B2 Ca-,Al-rich inclusion (CAI) STP-1 from the Allende CV3 carbonaceous chondrite. STP-1 ...belongs to a very rare type of refractory inclusions, Fractionation and Unknown Nuclear effects (FUN) CAIs, which experienced melt evaporation and crystallization at low total gas pressure (P < 10-6 bar) in a high-temperature (>1200 °C) region, possibly near the proto-Sun and were subsequently radially transported away from region, possibly by a disk wind. The Allende dmisteinbergite occurs as irregular single crystals (100-600 µm in size) in contact with gehlenitic melilite and Al,Ti-diopside, poikilitically enclosing euhedral spinel, and rare anorthite. It is colorless and transparent. The mean chemical composition, determined by electron microprobe analysis, is (wt%) SiO2 42.6, Al2O3 36.9, CaO 20.2, MgO 0.05, sum 99.75, giving rise to an empirical formula of Ca1.01Al1.96Si2.02O8. Its electron backscatter diffraction patterns are a good match to that of synthetic CaAl2Si2O8 with the P63/mcm structure and the unit cell a = 5.10 Å, c = 14.72 Å, and Z = 2. Dmisteinbergite could have crystallized from a silicate melt at high temperature (approximately 1200-1400 °C) via rapid cooling. Dmisteinbergite in Allende, the first find in a meteorite, is a new member of refractory silicates, among the first solid materials formed in the solar nebula.
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