Pre-bombardment crystallization ages of basaltic clasts from Antarctic howardites EET87503 and EET87513
Igneous clasts of basaltic eucrites are found in both howardites and polymict eucrites. We have studied the Rb-Sr and Sm-Nd isotopic systematics of a number of such clasts, of metamorphic grades 1-6, using the classification of Takeda and Graham. Here, we report Rb-Sr, (147)Sm-(143)Nd, and (145)Sm-(...
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ftnasantrs:oai:casi.ntrs.nasa.gov:19940031665 2023-05-15T13:42:51+02:00 Pre-bombardment crystallization ages of basaltic clasts from Antarctic howardites EET87503 and EET87513 Shih, C.-Y. Bansal, B. M. Nyquist, L. E. Wiesmann, H. Unclassified, Unlimited, Publicly available JAN 1, 1994 application/pdf http://hdl.handle.net/2060/19940031665 unknown Document ID: 19940031665 Accession ID: 94N36172 http://hdl.handle.net/2060/19940031665 No Copyright CASI ASTROPHYSICS Lunar and Planetary Inst., The Twenty-Fifth Lunar and Planetary Science Conference. Part 2: H-O; p 1015-1016 1994 ftnasantrs 2015-03-15T03:42:58Z Igneous clasts of basaltic eucrites are found in both howardites and polymict eucrites. We have studied the Rb-Sr and Sm-Nd isotopic systematics of a number of such clasts, of metamorphic grades 1-6, using the classification of Takeda and Graham. Here, we report Rb-Sr, (147)Sm-(143)Nd, and (145)Sm-(142)Nd studies of clast, 53 from Antarctic howardite EET87503. Although there is no evidence of disturbance of trace element systematics by Antarctic weathering, the Rb-Sr and conventional Sm-Nd isotopic systematics are severely disturbed, which we ascribe to thermal metamorphism. The Ar-Ar age spectrum shows ages ranging from approximately 3.85-3.55 Ga in an unusual 'down stairstep'. The (146)Sm-(142)Nd systematics, however, show the presence of live (146)Sm(t(sub 1/2) = 103 Ma), with (146)Sm/(144)Sm = 0.0061 +/- 0.0007 at the time of crystallization. This result is very similar to that previously obtained for basaltic clast, 18 from howardite EET87513 (paired with EET87503), which has concordant Rb-Sr and Sm-Nd ages of approximately 4.5 Ga. Thus, the two clasts are nearly the same age, and we conclude further than the EET87503,53 clast crystallized within 33 +/- 19 Ma of the LEW86010 angrite by comparing initial (146)Sm/(144)Sm to that of the angrite. We suggest that disturbances in the isotopic systematics of EET87503,53 are consanguineous with pyroxene homogenization. Other/Unknown Material Antarc* Antarctic NASA Technical Reports Server (NTRS) Antarctic |
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Open Polar |
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NASA Technical Reports Server (NTRS) |
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topic |
ASTROPHYSICS |
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ASTROPHYSICS Shih, C.-Y. Bansal, B. M. Nyquist, L. E. Wiesmann, H. Pre-bombardment crystallization ages of basaltic clasts from Antarctic howardites EET87503 and EET87513 |
topic_facet |
ASTROPHYSICS |
description |
Igneous clasts of basaltic eucrites are found in both howardites and polymict eucrites. We have studied the Rb-Sr and Sm-Nd isotopic systematics of a number of such clasts, of metamorphic grades 1-6, using the classification of Takeda and Graham. Here, we report Rb-Sr, (147)Sm-(143)Nd, and (145)Sm-(142)Nd studies of clast, 53 from Antarctic howardite EET87503. Although there is no evidence of disturbance of trace element systematics by Antarctic weathering, the Rb-Sr and conventional Sm-Nd isotopic systematics are severely disturbed, which we ascribe to thermal metamorphism. The Ar-Ar age spectrum shows ages ranging from approximately 3.85-3.55 Ga in an unusual 'down stairstep'. The (146)Sm-(142)Nd systematics, however, show the presence of live (146)Sm(t(sub 1/2) = 103 Ma), with (146)Sm/(144)Sm = 0.0061 +/- 0.0007 at the time of crystallization. This result is very similar to that previously obtained for basaltic clast, 18 from howardite EET87513 (paired with EET87503), which has concordant Rb-Sr and Sm-Nd ages of approximately 4.5 Ga. Thus, the two clasts are nearly the same age, and we conclude further than the EET87503,53 clast crystallized within 33 +/- 19 Ma of the LEW86010 angrite by comparing initial (146)Sm/(144)Sm to that of the angrite. We suggest that disturbances in the isotopic systematics of EET87503,53 are consanguineous with pyroxene homogenization. |
format |
Other/Unknown Material |
author |
Shih, C.-Y. Bansal, B. M. Nyquist, L. E. Wiesmann, H. |
author_facet |
Shih, C.-Y. Bansal, B. M. Nyquist, L. E. Wiesmann, H. |
author_sort |
Shih, C.-Y. |
title |
Pre-bombardment crystallization ages of basaltic clasts from Antarctic howardites EET87503 and EET87513 |
title_short |
Pre-bombardment crystallization ages of basaltic clasts from Antarctic howardites EET87503 and EET87513 |
title_full |
Pre-bombardment crystallization ages of basaltic clasts from Antarctic howardites EET87503 and EET87513 |
title_fullStr |
Pre-bombardment crystallization ages of basaltic clasts from Antarctic howardites EET87503 and EET87513 |
title_full_unstemmed |
Pre-bombardment crystallization ages of basaltic clasts from Antarctic howardites EET87503 and EET87513 |
title_sort |
pre-bombardment crystallization ages of basaltic clasts from antarctic howardites eet87503 and eet87513 |
publishDate |
1994 |
url |
http://hdl.handle.net/2060/19940031665 |
op_coverage |
Unclassified, Unlimited, Publicly available |
geographic |
Antarctic |
geographic_facet |
Antarctic |
genre |
Antarc* Antarctic |
genre_facet |
Antarc* Antarctic |
op_source |
CASI |
op_relation |
Document ID: 19940031665 Accession ID: 94N36172 http://hdl.handle.net/2060/19940031665 |
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No Copyright |
_version_ |
1766173631241519104 |