Hf-W thermochronometry: Closure temperature and constraints on the accretion and cooling history of the H chondrite parent body
We obtained Hf-W metal-silicate isochrons for several H chondrites of petrologic types 4, 5, and 6 to constrain the accretion and high-temperature thermal history of the H chondrite parent body. The silicate fractions have 180Hf/184W ratios up to ∼ 51 and 182W/184W ratios up to ∼ 33 ε units higher t...
| Main Authors: | , , , , , , |
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| Format: | Journal article |
| Language: | English |
| Published: |
2008
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| _version_ | 1797067085576142848 |
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| author | Kleine, T Touboul, M Van Orman, J Bourdon, B Maden, C Mezger, K Halliday, A |
| author_facet | Kleine, T Touboul, M Van Orman, J Bourdon, B Maden, C Mezger, K Halliday, A |
| author_sort | Kleine, T |
| collection | OXFORD |
| description | We obtained Hf-W metal-silicate isochrons for several H chondrites of petrologic types 4, 5, and 6 to constrain the accretion and high-temperature thermal history of the H chondrite parent body. The silicate fractions have 180Hf/184W ratios up to ∼ 51 and 182W/184W ratios up to ∼ 33 ε units higher than the whole-rock. These high 180Hf/184W and radiogenic W isotope ratios result in highly precise Hf-W ages. The Hf-W ages of the H chondrites become younger with increasing metamorphic grade and range from ΔtCAI = 1.7 ± 0.7 Ma for the H4 chondrite Ste. Marguerite to ΔtCAI = 9.6 ± 1.0 Ma for the H6 chondrites Kernouvé and Estacado. Closure temperatures for the Hf-W system in H chondrites were estimated from numerical simulations of W diffusion in high-Ca pyroxene, the major host of radiogenic 182W in H chondrites, and range from 800 ± 50 °C for H4 chondrites to 875 ± 75 °C for H6 chondrites. Owing to these high closure temperatures, the Hf-W system closed early and dates processes associated with the earliest evolution of the H chondrite parent body. Consequently, the high-temperature interval of ∼ 8 Ma as defined by the Hf-W ages is much shorter than intervals obtained from Rb-Sr and Pb-Pb dating. For H4 chondrites, heating on the parent body probably was insufficient to cause W diffusion in high-Ca pyroxene, such that the Hf-W age of ΔtCAI = 1.7 ± 0.7 Ma for Ste. Marguerite was not reset and most likely dates chondrule formation. This is consistent with Al-Mg ages of ∼ 2 Ma for L and LL chondrules and indicates that chondrules from all ordinary chondrites formed contemporaneously. The Hf-W ages for H5 and H6 chondrites of ΔtCAI = 5.9 ± 0.9 Ma and ΔtCAI = 9.6 ± 1.0 Ma correspond closely to the time of the thermal peak within the H chondrite parent body. Combined with previously published chronological data the Hf-W ages reveal an inverse correlation of cooling rate and metamorphic grade: shortly after their thermal peak H6 chondrites cooled at ∼ 10 °C/Ma, H5 chondrites at ∼ 30 °C/Ma and H4 chondrites at ∼ 55 °C/Ma. These Hf-W age constraints are most consistent with an onion-shell structure of the H chondrite parent body that was heated internally by energy released from 26Al decay. Parent body accretion started after chondrule formation at 1.7 ± 0.7 Ma and probably ended before 5.9 ± 0.9 Ma, when parts of the H chondrite parent body already had cooled from their thermal peak. The well-preserved cooling curves for the H chondrites studied here indicate that these samples derive from a part of the H chondrite parent body that remained largely unaffected by impact disruption and reassembly but such processes might have been important in other areas. The H chondrite parent body has a 180Hf/184W ratio of 0.63 ± 0.20, distinctly lower than the 180Hf/184W = 1.21 ± 0.06 of carbonaceous chondrite parent bodies. This difference reflects Hf-W fractionation within the first ∼ 2 Ma of the solar system, presumably related to processes in the solar nebula. © 2008 Elsevier B.V. All rights reserved. |
| first_indexed | 2024-03-06T21:51:16Z |
| format | Journal article |
| id | oxford-uuid:4b58c785-41b0-4b8d-8922-ad593b613111 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-06T21:51:16Z |
| publishDate | 2008 |
| record_format | dspace |
| spelling | oxford-uuid:4b58c785-41b0-4b8d-8922-ad593b6131112022-03-26T15:43:04ZHf-W thermochronometry: Closure temperature and constraints on the accretion and cooling history of the H chondrite parent bodyJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:4b58c785-41b0-4b8d-8922-ad593b613111EnglishSymplectic Elements at Oxford2008Kleine, TTouboul, MVan Orman, JBourdon, BMaden, CMezger, KHalliday, AWe obtained Hf-W metal-silicate isochrons for several H chondrites of petrologic types 4, 5, and 6 to constrain the accretion and high-temperature thermal history of the H chondrite parent body. The silicate fractions have 180Hf/184W ratios up to ∼ 51 and 182W/184W ratios up to ∼ 33 ε units higher than the whole-rock. These high 180Hf/184W and radiogenic W isotope ratios result in highly precise Hf-W ages. The Hf-W ages of the H chondrites become younger with increasing metamorphic grade and range from ΔtCAI = 1.7 ± 0.7 Ma for the H4 chondrite Ste. Marguerite to ΔtCAI = 9.6 ± 1.0 Ma for the H6 chondrites Kernouvé and Estacado. Closure temperatures for the Hf-W system in H chondrites were estimated from numerical simulations of W diffusion in high-Ca pyroxene, the major host of radiogenic 182W in H chondrites, and range from 800 ± 50 °C for H4 chondrites to 875 ± 75 °C for H6 chondrites. Owing to these high closure temperatures, the Hf-W system closed early and dates processes associated with the earliest evolution of the H chondrite parent body. Consequently, the high-temperature interval of ∼ 8 Ma as defined by the Hf-W ages is much shorter than intervals obtained from Rb-Sr and Pb-Pb dating. For H4 chondrites, heating on the parent body probably was insufficient to cause W diffusion in high-Ca pyroxene, such that the Hf-W age of ΔtCAI = 1.7 ± 0.7 Ma for Ste. Marguerite was not reset and most likely dates chondrule formation. This is consistent with Al-Mg ages of ∼ 2 Ma for L and LL chondrules and indicates that chondrules from all ordinary chondrites formed contemporaneously. The Hf-W ages for H5 and H6 chondrites of ΔtCAI = 5.9 ± 0.9 Ma and ΔtCAI = 9.6 ± 1.0 Ma correspond closely to the time of the thermal peak within the H chondrite parent body. Combined with previously published chronological data the Hf-W ages reveal an inverse correlation of cooling rate and metamorphic grade: shortly after their thermal peak H6 chondrites cooled at ∼ 10 °C/Ma, H5 chondrites at ∼ 30 °C/Ma and H4 chondrites at ∼ 55 °C/Ma. These Hf-W age constraints are most consistent with an onion-shell structure of the H chondrite parent body that was heated internally by energy released from 26Al decay. Parent body accretion started after chondrule formation at 1.7 ± 0.7 Ma and probably ended before 5.9 ± 0.9 Ma, when parts of the H chondrite parent body already had cooled from their thermal peak. The well-preserved cooling curves for the H chondrites studied here indicate that these samples derive from a part of the H chondrite parent body that remained largely unaffected by impact disruption and reassembly but such processes might have been important in other areas. The H chondrite parent body has a 180Hf/184W ratio of 0.63 ± 0.20, distinctly lower than the 180Hf/184W = 1.21 ± 0.06 of carbonaceous chondrite parent bodies. This difference reflects Hf-W fractionation within the first ∼ 2 Ma of the solar system, presumably related to processes in the solar nebula. © 2008 Elsevier B.V. All rights reserved. |
| spellingShingle | Kleine, T Touboul, M Van Orman, J Bourdon, B Maden, C Mezger, K Halliday, A Hf-W thermochronometry: Closure temperature and constraints on the accretion and cooling history of the H chondrite parent body |
| title | Hf-W thermochronometry: Closure temperature and constraints on the accretion and cooling history of the H chondrite parent body |
| title_full | Hf-W thermochronometry: Closure temperature and constraints on the accretion and cooling history of the H chondrite parent body |
| title_fullStr | Hf-W thermochronometry: Closure temperature and constraints on the accretion and cooling history of the H chondrite parent body |
| title_full_unstemmed | Hf-W thermochronometry: Closure temperature and constraints on the accretion and cooling history of the H chondrite parent body |
| title_short | Hf-W thermochronometry: Closure temperature and constraints on the accretion and cooling history of the H chondrite parent body |
| title_sort | hf w thermochronometry closure temperature and constraints on the accretion and cooling history of the h chondrite parent body |
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