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Gary R Huss - One of the best experts on this subject based on the ideXlab platform.
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Aluminum 26 in calcium Aluminum rich inclusions and chondrules from unequilibrated ordinary chondrites
Meteoritics & Planetary Science, 2001Co-Authors: G J Wasserburg, Glenn J Macpherson, Gary R Huss, S S Russell, Gopalan SrinivasanAbstract:In order to investigate the distribution of ^(26)A1 in chondrites, we measured Aluminum-magnesium systematics in four calcium-Aluminum-rich inclusions (CAIs) and eleven Aluminum-rich chondrules from unequilibrated ordinary chondrites (UOCs). All four CAIs were found to contain radiogenic ^(26)Mg (^(26)Mg^*) from the decay of ^(26)A1. The inferred initial ^(26)Al/^(27)Al ratios for these objects ((^(26)Al/^(27)Al)_0 ≅ 5 × 10^(−5)) are indistinguishable from the (^(26)Al/^(27)Al)_0 ratios found in most CAIs from carbonaceous chondrites. These observations, together with the similarities in mineralogy and oxygen isotopic compositions of the two sets of CAIs, imply that CAIs in UOCs and carbonaceous chondrites formed by similar processes from similar (or the same) isotopic reservoirs, or perhaps in a single location in the solar system. We also found ^(26)Mg^* in two of eleven Aluminum-rich chondrules. The (^(26)Al/^(27)Al)_0 ratio inferred for both of these chondrules is ∼1 × 10^(−5), clearly distinct from most CAIs but consistent with the values found in chondrules from type 3.0–3.1 UOCs and for Aluminum-rich chondrules from lightly metamorphosed carbonaceous chondrites (∼0.5 × 10^(−5) to ∼2 × 10^(−5)). The consistency of the (^(26)Al/^(27)Al)_0 ratios for CAIs and chondrules in primitive chondrites, independent of meteorite class, implies broad-scale nebular homogeneity with respect to ^(26)Al and indicates that the differences in initial ratios can be interpreted in terms of formation time. A timeline based on ^(26)Al indicates that chondrules began to form 1 to 2 Ma after most CAIs formed, that accretion of meteorite parent bodies was essentially complete by 4 Ma after CAIs, and that metamorphism was essentially over in type 4 chondrite parent bodies by 5 to 6 Ma after CAIs formed. Type 6 chondrites apparently did not cool until more than 7 Ma after CAIs formed. This timeline is consistent with ^(26)Al as a principal heat source for melting and metamorphism.
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Aluminum‐26 in calcium‐Aluminum‐rich inclusions and chondrules from unequilibrated ordinary chondrites
Meteoritics & Planetary Science, 2001Co-Authors: Gary R Huss, G J Wasserburg, Glenn J Macpherson, S S Russell, Gopalan SrinivasanAbstract:In order to investigate the distribution of ^(26)A1 in chondrites, we measured Aluminum-magnesium systematics in four calcium-Aluminum-rich inclusions (CAIs) and eleven Aluminum-rich chondrules from unequilibrated ordinary chondrites (UOCs). All four CAIs were found to contain radiogenic ^(26)Mg (^(26)Mg^*) from the decay of ^(26)A1. The inferred initial ^(26)Al/^(27)Al ratios for these objects ((^(26)Al/^(27)Al)_0 ≅ 5 × 10^(−5)) are indistinguishable from the (^(26)Al/^(27)Al)_0 ratios found in most CAIs from carbonaceous chondrites. These observations, together with the similarities in mineralogy and oxygen isotopic compositions of the two sets of CAIs, imply that CAIs in UOCs and carbonaceous chondrites formed by similar processes from similar (or the same) isotopic reservoirs, or perhaps in a single location in the solar system. We also found ^(26)Mg^* in two of eleven Aluminum-rich chondrules. The (^(26)Al/^(27)Al)_0 ratio inferred for both of these chondrules is ∼1 × 10^(−5), clearly distinct from most CAIs but consistent with the values found in chondrules from type 3.0–3.1 UOCs and for Aluminum-rich chondrules from lightly metamorphosed carbonaceous chondrites (∼0.5 × 10^(−5) to ∼2 × 10^(−5)). The consistency of the (^(26)Al/^(27)Al)_0 ratios for CAIs and chondrules in primitive chondrites, independent of meteorite class, implies broad-scale nebular homogeneity with respect to ^(26)Al and indicates that the differences in initial ratios can be interpreted in terms of formation time. A timeline based on ^(26)Al indicates that chondrules began to form 1 to 2 Ma after most CAIs formed, that accretion of meteorite parent bodies was essentially complete by 4 Ma after CAIs, and that metamorphism was essentially over in type 4 chondrite parent bodies by 5 to 6 Ma after CAIs formed. Type 6 chondrites apparently did not cool until more than 7 Ma after CAIs formed. This timeline is consistent with ^(26)Al as a principal heat source for melting and metamorphism.
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trace element abundances and the origin of Aluminum 26 bearing chondrules in unequilibrated ordinary chondrites
Meteoritics and Planetary Science Supplement, 1997Co-Authors: Gary R Huss, G J Wasserburg, S S Russell, Glenn J MacphersonAbstract:Calcium-Aluminum-rich inclusions (CAis) typically contain radiogenic ^(26)Mg (^(26)Mg^*) from the decay of ^(26)Al, with (^(26)Al/^(27)Al); up to 5 x 10^(-5) [e.g., 1]. Some Al-rich chondrules from unequilibrated ordinary chondrites contain detectable ^(26)Mg^*, but (^(26)Al/^(27)Al); is lower [e.g., 2].
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Mg and Ti isotopes in presolar Al_2O_3
Meteoritics, 1994Co-Authors: Gary R Huss, Albert J. Fahey, G J WasserburgAbstract:Previously, we reported O isotopic compositions and initial ^(26)Al/^(27) Al ratios for two presolar Al_2O_3 grains, Orgueil B and Bishunpur B39 [1-3]. In Orgueil B, ^(17)O/^(16)O is about twice the solar value but ^(18)O/^(16)O is normal. In B39, ^(17)O/^(16)O is ~7x higher than solar and ^(18)O/^(16)O is 0.6x the solar value. Spectroscopic observations of red giant stars show similar O compositions [4], which result when material that has experienced partial H burning is mixed into the stellar envelope by the first dredge-up [3,5]. The ^(17)O/^(16)O ratios indicate that Orgueil B originated around a star of ~1.5 M_☉, while B39 formed around either a ~2 Me or 4-7 M_☉ [3,5]. Both grains formed with ^(26)Al/^(27)Al ratios of ~10^(-3). Aluminum-26 is produced in the H shell after core H burning has ceased and first dredge-up has occurred. It is spread through the envelope by the third dredge-up, which occurs in low- and intermediate-mass stars as a series of mixing events driven by thermal pulses in the He shell. In intermediate-mass stars (3-8 M_☉), ^(26)Al can also be brought to the surface by the second dredge-up, which occurs at the end of core He burning.
Gopalan Srinivasan - One of the best experts on this subject based on the ideXlab platform.
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Aluminum 26 in calcium Aluminum rich inclusions and chondrules from unequilibrated ordinary chondrites
Meteoritics & Planetary Science, 2001Co-Authors: G J Wasserburg, Glenn J Macpherson, Gary R Huss, S S Russell, Gopalan SrinivasanAbstract:In order to investigate the distribution of ^(26)A1 in chondrites, we measured Aluminum-magnesium systematics in four calcium-Aluminum-rich inclusions (CAIs) and eleven Aluminum-rich chondrules from unequilibrated ordinary chondrites (UOCs). All four CAIs were found to contain radiogenic ^(26)Mg (^(26)Mg^*) from the decay of ^(26)A1. The inferred initial ^(26)Al/^(27)Al ratios for these objects ((^(26)Al/^(27)Al)_0 ≅ 5 × 10^(−5)) are indistinguishable from the (^(26)Al/^(27)Al)_0 ratios found in most CAIs from carbonaceous chondrites. These observations, together with the similarities in mineralogy and oxygen isotopic compositions of the two sets of CAIs, imply that CAIs in UOCs and carbonaceous chondrites formed by similar processes from similar (or the same) isotopic reservoirs, or perhaps in a single location in the solar system. We also found ^(26)Mg^* in two of eleven Aluminum-rich chondrules. The (^(26)Al/^(27)Al)_0 ratio inferred for both of these chondrules is ∼1 × 10^(−5), clearly distinct from most CAIs but consistent with the values found in chondrules from type 3.0–3.1 UOCs and for Aluminum-rich chondrules from lightly metamorphosed carbonaceous chondrites (∼0.5 × 10^(−5) to ∼2 × 10^(−5)). The consistency of the (^(26)Al/^(27)Al)_0 ratios for CAIs and chondrules in primitive chondrites, independent of meteorite class, implies broad-scale nebular homogeneity with respect to ^(26)Al and indicates that the differences in initial ratios can be interpreted in terms of formation time. A timeline based on ^(26)Al indicates that chondrules began to form 1 to 2 Ma after most CAIs formed, that accretion of meteorite parent bodies was essentially complete by 4 Ma after CAIs, and that metamorphism was essentially over in type 4 chondrite parent bodies by 5 to 6 Ma after CAIs formed. Type 6 chondrites apparently did not cool until more than 7 Ma after CAIs formed. This timeline is consistent with ^(26)Al as a principal heat source for melting and metamorphism.
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Aluminum‐26 in calcium‐Aluminum‐rich inclusions and chondrules from unequilibrated ordinary chondrites
Meteoritics & Planetary Science, 2001Co-Authors: Gary R Huss, G J Wasserburg, Glenn J Macpherson, S S Russell, Gopalan SrinivasanAbstract:In order to investigate the distribution of ^(26)A1 in chondrites, we measured Aluminum-magnesium systematics in four calcium-Aluminum-rich inclusions (CAIs) and eleven Aluminum-rich chondrules from unequilibrated ordinary chondrites (UOCs). All four CAIs were found to contain radiogenic ^(26)Mg (^(26)Mg^*) from the decay of ^(26)A1. The inferred initial ^(26)Al/^(27)Al ratios for these objects ((^(26)Al/^(27)Al)_0 ≅ 5 × 10^(−5)) are indistinguishable from the (^(26)Al/^(27)Al)_0 ratios found in most CAIs from carbonaceous chondrites. These observations, together with the similarities in mineralogy and oxygen isotopic compositions of the two sets of CAIs, imply that CAIs in UOCs and carbonaceous chondrites formed by similar processes from similar (or the same) isotopic reservoirs, or perhaps in a single location in the solar system. We also found ^(26)Mg^* in two of eleven Aluminum-rich chondrules. The (^(26)Al/^(27)Al)_0 ratio inferred for both of these chondrules is ∼1 × 10^(−5), clearly distinct from most CAIs but consistent with the values found in chondrules from type 3.0–3.1 UOCs and for Aluminum-rich chondrules from lightly metamorphosed carbonaceous chondrites (∼0.5 × 10^(−5) to ∼2 × 10^(−5)). The consistency of the (^(26)Al/^(27)Al)_0 ratios for CAIs and chondrules in primitive chondrites, independent of meteorite class, implies broad-scale nebular homogeneity with respect to ^(26)Al and indicates that the differences in initial ratios can be interpreted in terms of formation time. A timeline based on ^(26)Al indicates that chondrules began to form 1 to 2 Ma after most CAIs formed, that accretion of meteorite parent bodies was essentially complete by 4 Ma after CAIs, and that metamorphism was essentially over in type 4 chondrite parent bodies by 5 to 6 Ma after CAIs formed. Type 6 chondrites apparently did not cool until more than 7 Ma after CAIs formed. This timeline is consistent with ^(26)Al as a principal heat source for melting and metamorphism.
Glenn J Macpherson - One of the best experts on this subject based on the ideXlab platform.
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Aluminum 26 in calcium Aluminum rich inclusions and chondrules from unequilibrated ordinary chondrites
Meteoritics & Planetary Science, 2001Co-Authors: G J Wasserburg, Glenn J Macpherson, Gary R Huss, S S Russell, Gopalan SrinivasanAbstract:In order to investigate the distribution of ^(26)A1 in chondrites, we measured Aluminum-magnesium systematics in four calcium-Aluminum-rich inclusions (CAIs) and eleven Aluminum-rich chondrules from unequilibrated ordinary chondrites (UOCs). All four CAIs were found to contain radiogenic ^(26)Mg (^(26)Mg^*) from the decay of ^(26)A1. The inferred initial ^(26)Al/^(27)Al ratios for these objects ((^(26)Al/^(27)Al)_0 ≅ 5 × 10^(−5)) are indistinguishable from the (^(26)Al/^(27)Al)_0 ratios found in most CAIs from carbonaceous chondrites. These observations, together with the similarities in mineralogy and oxygen isotopic compositions of the two sets of CAIs, imply that CAIs in UOCs and carbonaceous chondrites formed by similar processes from similar (or the same) isotopic reservoirs, or perhaps in a single location in the solar system. We also found ^(26)Mg^* in two of eleven Aluminum-rich chondrules. The (^(26)Al/^(27)Al)_0 ratio inferred for both of these chondrules is ∼1 × 10^(−5), clearly distinct from most CAIs but consistent with the values found in chondrules from type 3.0–3.1 UOCs and for Aluminum-rich chondrules from lightly metamorphosed carbonaceous chondrites (∼0.5 × 10^(−5) to ∼2 × 10^(−5)). The consistency of the (^(26)Al/^(27)Al)_0 ratios for CAIs and chondrules in primitive chondrites, independent of meteorite class, implies broad-scale nebular homogeneity with respect to ^(26)Al and indicates that the differences in initial ratios can be interpreted in terms of formation time. A timeline based on ^(26)Al indicates that chondrules began to form 1 to 2 Ma after most CAIs formed, that accretion of meteorite parent bodies was essentially complete by 4 Ma after CAIs, and that metamorphism was essentially over in type 4 chondrite parent bodies by 5 to 6 Ma after CAIs formed. Type 6 chondrites apparently did not cool until more than 7 Ma after CAIs formed. This timeline is consistent with ^(26)Al as a principal heat source for melting and metamorphism.
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Aluminum‐26 in calcium‐Aluminum‐rich inclusions and chondrules from unequilibrated ordinary chondrites
Meteoritics & Planetary Science, 2001Co-Authors: Gary R Huss, G J Wasserburg, Glenn J Macpherson, S S Russell, Gopalan SrinivasanAbstract:In order to investigate the distribution of ^(26)A1 in chondrites, we measured Aluminum-magnesium systematics in four calcium-Aluminum-rich inclusions (CAIs) and eleven Aluminum-rich chondrules from unequilibrated ordinary chondrites (UOCs). All four CAIs were found to contain radiogenic ^(26)Mg (^(26)Mg^*) from the decay of ^(26)A1. The inferred initial ^(26)Al/^(27)Al ratios for these objects ((^(26)Al/^(27)Al)_0 ≅ 5 × 10^(−5)) are indistinguishable from the (^(26)Al/^(27)Al)_0 ratios found in most CAIs from carbonaceous chondrites. These observations, together with the similarities in mineralogy and oxygen isotopic compositions of the two sets of CAIs, imply that CAIs in UOCs and carbonaceous chondrites formed by similar processes from similar (or the same) isotopic reservoirs, or perhaps in a single location in the solar system. We also found ^(26)Mg^* in two of eleven Aluminum-rich chondrules. The (^(26)Al/^(27)Al)_0 ratio inferred for both of these chondrules is ∼1 × 10^(−5), clearly distinct from most CAIs but consistent with the values found in chondrules from type 3.0–3.1 UOCs and for Aluminum-rich chondrules from lightly metamorphosed carbonaceous chondrites (∼0.5 × 10^(−5) to ∼2 × 10^(−5)). The consistency of the (^(26)Al/^(27)Al)_0 ratios for CAIs and chondrules in primitive chondrites, independent of meteorite class, implies broad-scale nebular homogeneity with respect to ^(26)Al and indicates that the differences in initial ratios can be interpreted in terms of formation time. A timeline based on ^(26)Al indicates that chondrules began to form 1 to 2 Ma after most CAIs formed, that accretion of meteorite parent bodies was essentially complete by 4 Ma after CAIs, and that metamorphism was essentially over in type 4 chondrite parent bodies by 5 to 6 Ma after CAIs formed. Type 6 chondrites apparently did not cool until more than 7 Ma after CAIs formed. This timeline is consistent with ^(26)Al as a principal heat source for melting and metamorphism.
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trace element abundances and the origin of Aluminum 26 bearing chondrules in unequilibrated ordinary chondrites
Meteoritics and Planetary Science Supplement, 1997Co-Authors: Gary R Huss, G J Wasserburg, S S Russell, Glenn J MacphersonAbstract:Calcium-Aluminum-rich inclusions (CAis) typically contain radiogenic ^(26)Mg (^(26)Mg^*) from the decay of ^(26)Al, with (^(26)Al/^(27)Al); up to 5 x 10^(-5) [e.g., 1]. Some Al-rich chondrules from unequilibrated ordinary chondrites contain detectable ^(26)Mg^*, but (^(26)Al/^(27)Al); is lower [e.g., 2].
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the distribution of Aluminum 26 in the early solar system a reappraisal
Meteoritics, 1995Co-Authors: Glenn J Macpherson, A M Davis, Ernst ZinnerAbstract:— A compilation of over 1500 Mg-isotopic analyses of Al-rich material from primitive solar system matter (meteorites) shows clearly that 26Al existed live in the early Solar System. Excesses of 26Mg observed in refractory inclusions are not the result of mixing of “fossil” interstellar 26Mg with normal solar system Mg. Some material was present that contained little or no 26Al, but it was a minor component of solar system matter in the region where CV3 and CO3 carbonaceous chondrites accreted and probably was a minor component in the accretion regions of CM chondrites as well. Data for other chondrite groups are too scanty to make similar statements. The implied long individual nebular histories of CAIs and the apparent gap of one or more million years between the start of CAI formation and the start of chondrule formation require the action of some nebular mechanism that prevented the CAIs from drifting into the Sun. Deciding whether 26Al was or was not the agent of heating that caused melting in the achondrite parent bodies hinges less on its widespread abundance in the nebula than it does on the timing of planetesimal accretion relative to the formation of the CAIs.
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The distribution of Aluminum‐26 in the early Solar System—A reappraisal
Meteoritics, 1995Co-Authors: Glenn J Macpherson, A M Davis, Ernst ZinnerAbstract:— A compilation of over 1500 Mg-isotopic analyses of Al-rich material from primitive solar system matter (meteorites) shows clearly that 26Al existed live in the early Solar System. Excesses of 26Mg observed in refractory inclusions are not the result of mixing of “fossil” interstellar 26Mg with normal solar system Mg. Some material was present that contained little or no 26Al, but it was a minor component of solar system matter in the region where CV3 and CO3 carbonaceous chondrites accreted and probably was a minor component in the accretion regions of CM chondrites as well. Data for other chondrite groups are too scanty to make similar statements. The implied long individual nebular histories of CAIs and the apparent gap of one or more million years between the start of CAI formation and the start of chondrule formation require the action of some nebular mechanism that prevented the CAIs from drifting into the Sun. Deciding whether 26Al was or was not the agent of heating that caused melting in the achondrite parent bodies hinges less on its widespread abundance in the nebula than it does on the timing of planetesimal accretion relative to the formation of the CAIs.
Yuichi Morishita - One of the best experts on this subject based on the ideXlab platform.
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the relative formation ages of ferromagnesian chondrules inferred from their initial Aluminum 26 Aluminum 27 ratios
Meteoritics & Planetary Science, 2002Co-Authors: S Mostefaoui, N T Kita, Shigeko Togashi, Shogo Tachibana, Hiroko Nagahara, Yuichi MorishitaAbstract:We performed a systematic high precision SIMS 26Al-26Mg isotopic study for 11 ferromagnesian chondrules from the highly unequilibrated ordinary chondrite Bishunpur (LL3.1). The chondrules are porphyritic and contain various amounts of olivine and pyroxene and interstitial plagioclase and/or glass. The chemical compositions of the chondrules vary from FeO-poor to FeO-rich. Eight chondrules show resolvable 26Mg-excesses with a maximum δ26Mg of ~1% in two chondrules. The initial 26Al/27Al ratios inferred for these chondrules range between (2.28 ± 0.73) x 10^(-5) to (0.45 ± 0.21) x 10^(-5). Assuming a homogeneous distribution of Al isotopes in the early solar system, this range corresponds to ages relative to CAIs between 0.7 ± 0.2 My and 2.4^(-0.4/+0.7) My. The inferred total span of the chondrule formation ages is at least 1 My, which is too long to form chondrules by the X-wind. The initial 26Al/27Al ratios of the chondrules are found to correlate with the proportion of olivine to pyroxene suggesting that olivine-rich chondrules formed earlier than pyroxene-rich chondrules. Though we do not have a completely satisfactory explanation of this correlation we tentatively interpret it as a result of evaporative loss of Si from earlier generations of chondrules followed by addition of Si to the precursors of later generation chondrules.
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The relative formation ages of ferromagnesian chondrules inferred from their initial Aluminum‐26/Aluminum‐27 ratios
Meteoritics & Planetary Science, 2002Co-Authors: S Mostefaoui, N T Kita, Shigeko Togashi, Shogo Tachibana, Hiroko Nagahara, Yuichi MorishitaAbstract:We performed a systematic high precision SIMS 26Al-26Mg isotopic study for 11 ferromagnesian chondrules from the highly unequilibrated ordinary chondrite Bishunpur (LL3.1). The chondrules are porphyritic and contain various amounts of olivine and pyroxene and interstitial plagioclase and/or glass. The chemical compositions of the chondrules vary from FeO-poor to FeO-rich. Eight chondrules show resolvable 26Mg-excesses with a maximum δ26Mg of ~1% in two chondrules. The initial 26Al/27Al ratios inferred for these chondrules range between (2.28 ± 0.73) x 10^(-5) to (0.45 ± 0.21) x 10^(-5). Assuming a homogeneous distribution of Al isotopes in the early solar system, this range corresponds to ages relative to CAIs between 0.7 ± 0.2 My and 2.4^(-0.4/+0.7) My. The inferred total span of the chondrule formation ages is at least 1 My, which is too long to form chondrules by the X-wind. The initial 26Al/27Al ratios of the chondrules are found to correlate with the proportion of olivine to pyroxene suggesting that olivine-rich chondrules formed earlier than pyroxene-rich chondrules. Though we do not have a completely satisfactory explanation of this correlation we tentatively interpret it as a result of evaporative loss of Si from earlier generations of chondrules followed by addition of Si to the precursors of later generation chondrules.
S S Russell - One of the best experts on this subject based on the ideXlab platform.
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Aluminum 26 in calcium Aluminum rich inclusions and chondrules from unequilibrated ordinary chondrites
Meteoritics & Planetary Science, 2001Co-Authors: G J Wasserburg, Glenn J Macpherson, Gary R Huss, S S Russell, Gopalan SrinivasanAbstract:In order to investigate the distribution of ^(26)A1 in chondrites, we measured Aluminum-magnesium systematics in four calcium-Aluminum-rich inclusions (CAIs) and eleven Aluminum-rich chondrules from unequilibrated ordinary chondrites (UOCs). All four CAIs were found to contain radiogenic ^(26)Mg (^(26)Mg^*) from the decay of ^(26)A1. The inferred initial ^(26)Al/^(27)Al ratios for these objects ((^(26)Al/^(27)Al)_0 ≅ 5 × 10^(−5)) are indistinguishable from the (^(26)Al/^(27)Al)_0 ratios found in most CAIs from carbonaceous chondrites. These observations, together with the similarities in mineralogy and oxygen isotopic compositions of the two sets of CAIs, imply that CAIs in UOCs and carbonaceous chondrites formed by similar processes from similar (or the same) isotopic reservoirs, or perhaps in a single location in the solar system. We also found ^(26)Mg^* in two of eleven Aluminum-rich chondrules. The (^(26)Al/^(27)Al)_0 ratio inferred for both of these chondrules is ∼1 × 10^(−5), clearly distinct from most CAIs but consistent with the values found in chondrules from type 3.0–3.1 UOCs and for Aluminum-rich chondrules from lightly metamorphosed carbonaceous chondrites (∼0.5 × 10^(−5) to ∼2 × 10^(−5)). The consistency of the (^(26)Al/^(27)Al)_0 ratios for CAIs and chondrules in primitive chondrites, independent of meteorite class, implies broad-scale nebular homogeneity with respect to ^(26)Al and indicates that the differences in initial ratios can be interpreted in terms of formation time. A timeline based on ^(26)Al indicates that chondrules began to form 1 to 2 Ma after most CAIs formed, that accretion of meteorite parent bodies was essentially complete by 4 Ma after CAIs, and that metamorphism was essentially over in type 4 chondrite parent bodies by 5 to 6 Ma after CAIs formed. Type 6 chondrites apparently did not cool until more than 7 Ma after CAIs formed. This timeline is consistent with ^(26)Al as a principal heat source for melting and metamorphism.
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Aluminum‐26 in calcium‐Aluminum‐rich inclusions and chondrules from unequilibrated ordinary chondrites
Meteoritics & Planetary Science, 2001Co-Authors: Gary R Huss, G J Wasserburg, Glenn J Macpherson, S S Russell, Gopalan SrinivasanAbstract:In order to investigate the distribution of ^(26)A1 in chondrites, we measured Aluminum-magnesium systematics in four calcium-Aluminum-rich inclusions (CAIs) and eleven Aluminum-rich chondrules from unequilibrated ordinary chondrites (UOCs). All four CAIs were found to contain radiogenic ^(26)Mg (^(26)Mg^*) from the decay of ^(26)A1. The inferred initial ^(26)Al/^(27)Al ratios for these objects ((^(26)Al/^(27)Al)_0 ≅ 5 × 10^(−5)) are indistinguishable from the (^(26)Al/^(27)Al)_0 ratios found in most CAIs from carbonaceous chondrites. These observations, together with the similarities in mineralogy and oxygen isotopic compositions of the two sets of CAIs, imply that CAIs in UOCs and carbonaceous chondrites formed by similar processes from similar (or the same) isotopic reservoirs, or perhaps in a single location in the solar system. We also found ^(26)Mg^* in two of eleven Aluminum-rich chondrules. The (^(26)Al/^(27)Al)_0 ratio inferred for both of these chondrules is ∼1 × 10^(−5), clearly distinct from most CAIs but consistent with the values found in chondrules from type 3.0–3.1 UOCs and for Aluminum-rich chondrules from lightly metamorphosed carbonaceous chondrites (∼0.5 × 10^(−5) to ∼2 × 10^(−5)). The consistency of the (^(26)Al/^(27)Al)_0 ratios for CAIs and chondrules in primitive chondrites, independent of meteorite class, implies broad-scale nebular homogeneity with respect to ^(26)Al and indicates that the differences in initial ratios can be interpreted in terms of formation time. A timeline based on ^(26)Al indicates that chondrules began to form 1 to 2 Ma after most CAIs formed, that accretion of meteorite parent bodies was essentially complete by 4 Ma after CAIs, and that metamorphism was essentially over in type 4 chondrite parent bodies by 5 to 6 Ma after CAIs formed. Type 6 chondrites apparently did not cool until more than 7 Ma after CAIs formed. This timeline is consistent with ^(26)Al as a principal heat source for melting and metamorphism.
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trace element abundances and the origin of Aluminum 26 bearing chondrules in unequilibrated ordinary chondrites
Meteoritics and Planetary Science Supplement, 1997Co-Authors: Gary R Huss, G J Wasserburg, S S Russell, Glenn J MacphersonAbstract:Calcium-Aluminum-rich inclusions (CAis) typically contain radiogenic ^(26)Mg (^(26)Mg^*) from the decay of ^(26)Al, with (^(26)Al/^(27)Al); up to 5 x 10^(-5) [e.g., 1]. Some Al-rich chondrules from unequilibrated ordinary chondrites contain detectable ^(26)Mg^*, but (^(26)Al/^(27)Al); is lower [e.g., 2].
