Lunar Crustal History from Isotopic Studies of Lunar Anorthosites
Anorthosites occur ubiquitously within the lunar crust at depths of approx.3-30 km in apparent confirmation of the Lunar Magma Ocean (LMO) hypothesis. [1]. We will present recent chronological studies of anorthosites [2] that are relevant both to the LMO hypothesis and also to the lunar cataclysm hy...
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ftnasantrs:oai:casi.ntrs.nasa.gov:20100010840 2023-05-15T13:43:16+02:00 Lunar Crustal History from Isotopic Studies of Lunar Anorthosites Bogard, D. D. Shih, C.-Y. Nyquist, Laurence E. Yamaguchi, A. Unclassified, Unlimited, Publicly available May 31, 2010 application/pdf http://hdl.handle.net/2060/20100010840 unknown Document ID: 20100010840 http://hdl.handle.net/2060/20100010840 Copyright, Distribution as joint owner in the copyright CASI Geophysics JSC-CN-19836 JSC-CN-20775 GLUC-2010.1.1.A.4 Global Lunar Conference of the International Astronautical Federation; 31 May - 3 Jun. 2010; Beijing; China 2010 ftnasantrs 2019-07-21T01:16:23Z Anorthosites occur ubiquitously within the lunar crust at depths of approx.3-30 km in apparent confirmation of the Lunar Magma Ocean (LMO) hypothesis. [1]. We will present recent chronological studies of anorthosites [2] that are relevant both to the LMO hypothesis and also to the lunar cataclysm hypothesis. Old (approx.4.4 Ga) Sm-Nd ages have been determined for some Apollo 16 anorthosites, and primitive initial Sr-87/Sr-86 ratios have been measured for several, but well-defined Rb-Sr ages concordant with the Sm-Nd ages have not been determined until now. Lunar anorthosite 67075, a Feldspathic Fragmental Breccia (FFB) collected near the rim of North Ray Crater, has concordant Sm-Nd and Rb-Sr ages of 4.47+/-0.07 Ga and 4.49+/-0.07 Ga, respectively. Initial Nd-143/Nd-144 determined from the Sm-Nd isochron corresponds to E(sub Nd,CHUR) = 0.3+/-0.5 compared to a Chondritic Uniform Reservoir, or E(sub Nd,HEDPB) = -0.6+/-0.5 compared to the initial Nd-143/Nd-144 of the HED Parent Body [3]. Lunar anorthosites tend to have E(sub Nd) > 0 when compared to CHUR, apparently inconsistent with derivation from a single lunar magma ocean. Although E(sub Nd) < 0 for some anorthosites, if lunar initial Nd-143/Nd-144 is taken equal to HEDR for the HED parent body [3], enough variability remains among the anorthosite data alone to suggest that lunar anorthosites do not derive from a single source, i.e., they are not all products of the LMO. An anorthositic clast from desert meteorite Dhofar 908 has an Ar-39-Ar-40 age of 4.42+/-0.04 Ga, the same as the 4.36-4.41+/-0.035 Ga Ar-39-Ar-40 age of anorthositic clast Y-86032,116 in Antarctic meteorite Yamato- 86032 [3,4]. Conclusions: (i) Lunar anorthosites come from diverse sources. Orbital geochemical studies confirm variability in lunar crustal composition [1, 5]. We suggest that the variability extends to anorthosites alone as shown by the Sm-Nd data (Fig. 2) and the existence of magnesian anorthosites (MAN, [6]) and "An93 anorthosites" [3,4]. (ii) Anorthositic clasts in lunar meteorites retain "high" Ar-Ar ages compared to Apollo anorthosites. This is perhaps a hint that "cataclysmic" impacts were on average less energetic in the mostly farside source regions of these meteorites than on the lunar nearside. Other/Unknown Material Antarc* Antarctic NASA Technical Reports Server (NTRS) Antarctic Yamato ENVELOPE(35.583,35.583,-71.417,-71.417) |
institution |
Open Polar |
collection |
NASA Technical Reports Server (NTRS) |
op_collection_id |
ftnasantrs |
language |
unknown |
topic |
Geophysics |
spellingShingle |
Geophysics Bogard, D. D. Shih, C.-Y. Nyquist, Laurence E. Yamaguchi, A. Lunar Crustal History from Isotopic Studies of Lunar Anorthosites |
topic_facet |
Geophysics |
description |
Anorthosites occur ubiquitously within the lunar crust at depths of approx.3-30 km in apparent confirmation of the Lunar Magma Ocean (LMO) hypothesis. [1]. We will present recent chronological studies of anorthosites [2] that are relevant both to the LMO hypothesis and also to the lunar cataclysm hypothesis. Old (approx.4.4 Ga) Sm-Nd ages have been determined for some Apollo 16 anorthosites, and primitive initial Sr-87/Sr-86 ratios have been measured for several, but well-defined Rb-Sr ages concordant with the Sm-Nd ages have not been determined until now. Lunar anorthosite 67075, a Feldspathic Fragmental Breccia (FFB) collected near the rim of North Ray Crater, has concordant Sm-Nd and Rb-Sr ages of 4.47+/-0.07 Ga and 4.49+/-0.07 Ga, respectively. Initial Nd-143/Nd-144 determined from the Sm-Nd isochron corresponds to E(sub Nd,CHUR) = 0.3+/-0.5 compared to a Chondritic Uniform Reservoir, or E(sub Nd,HEDPB) = -0.6+/-0.5 compared to the initial Nd-143/Nd-144 of the HED Parent Body [3]. Lunar anorthosites tend to have E(sub Nd) > 0 when compared to CHUR, apparently inconsistent with derivation from a single lunar magma ocean. Although E(sub Nd) < 0 for some anorthosites, if lunar initial Nd-143/Nd-144 is taken equal to HEDR for the HED parent body [3], enough variability remains among the anorthosite data alone to suggest that lunar anorthosites do not derive from a single source, i.e., they are not all products of the LMO. An anorthositic clast from desert meteorite Dhofar 908 has an Ar-39-Ar-40 age of 4.42+/-0.04 Ga, the same as the 4.36-4.41+/-0.035 Ga Ar-39-Ar-40 age of anorthositic clast Y-86032,116 in Antarctic meteorite Yamato- 86032 [3,4]. Conclusions: (i) Lunar anorthosites come from diverse sources. Orbital geochemical studies confirm variability in lunar crustal composition [1, 5]. We suggest that the variability extends to anorthosites alone as shown by the Sm-Nd data (Fig. 2) and the existence of magnesian anorthosites (MAN, [6]) and "An93 anorthosites" [3,4]. (ii) Anorthositic clasts in lunar meteorites retain "high" Ar-Ar ages compared to Apollo anorthosites. This is perhaps a hint that "cataclysmic" impacts were on average less energetic in the mostly farside source regions of these meteorites than on the lunar nearside. |
format |
Other/Unknown Material |
author |
Bogard, D. D. Shih, C.-Y. Nyquist, Laurence E. Yamaguchi, A. |
author_facet |
Bogard, D. D. Shih, C.-Y. Nyquist, Laurence E. Yamaguchi, A. |
author_sort |
Bogard, D. D. |
title |
Lunar Crustal History from Isotopic Studies of Lunar Anorthosites |
title_short |
Lunar Crustal History from Isotopic Studies of Lunar Anorthosites |
title_full |
Lunar Crustal History from Isotopic Studies of Lunar Anorthosites |
title_fullStr |
Lunar Crustal History from Isotopic Studies of Lunar Anorthosites |
title_full_unstemmed |
Lunar Crustal History from Isotopic Studies of Lunar Anorthosites |
title_sort |
lunar crustal history from isotopic studies of lunar anorthosites |
publishDate |
2010 |
url |
http://hdl.handle.net/2060/20100010840 |
op_coverage |
Unclassified, Unlimited, Publicly available |
long_lat |
ENVELOPE(35.583,35.583,-71.417,-71.417) |
geographic |
Antarctic Yamato |
geographic_facet |
Antarctic Yamato |
genre |
Antarc* Antarctic |
genre_facet |
Antarc* Antarctic |
op_source |
CASI |
op_relation |
Document ID: 20100010840 http://hdl.handle.net/2060/20100010840 |
op_rights |
Copyright, Distribution as joint owner in the copyright |
_version_ |
1766186565604737024 |