Geochemical comparison of four cores from the Manson impact structure

Korotev, R. L.; Rockow, K. M.; Jolliff, Bradley L.; Haskin, L. A.; McCarville, P.; Crossey, L. J.

doi:10.1130/0-8137-2302-7.275

Cited by 4 publications

(3 citation statements)

References 11 publications

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“…That assumption is supported by studies of intracrater melt sheets from small terrestrial craters. Melt breccias taken from within the Manicouagan and the Manson impact craters, for example, are impressively homogeneous (Phinney and Floran eta/., 1978;Korotev et a/., 1996b). McCormick et a/.…”

Section: Compositional Differences Among Mafic Impact-melt Brecciasmentioning

confidence: 84%

The case for an Imbrium origin of the Apollo thorium‐rich impact‐melt breccias

Haskin¹,

Korotev²,

Rockow³

et al. 1998

Meteorit & Planetary Scien

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125

113

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Abstract-Mafic, Th-rich impact-melt breccias, most of which are identified with the composition known as low-K Fra Mauro (LKFM), are the most common rock type in the nonmare regoliths of the Apollo lunar landing sites. The origin of mafic impact-melt breccias bears on many lunar problems: the nature of the late meteoroid bombardment (cataclysm); the spatial distribution of KREEP, both near the surface and at depth; the ages of the major basins; and the composition of the early crust of the nearside lunar highlands. Thus, it is crucial that the origin of mafic impact-melt breccias be accurately understood. Because of both intra-and intersite differences in compositions of mafic impact-melt breccia samples, apparent differences in crystallization age, and differences in siderophile-element ratios, previous studies have argued that either (1) most mafic impact-melt breccias are the products of several large craters local to the site at which they were found but that some are of basin origin or that (2) they are all from the Imbrium (Apollos 14 and 15), Nectaris (Apollo 16), and Serenitatis (Apollo 17) basins. Here, we reconsider the hypothesis that virtually all of the Th-rich, mafic impact-melt breccias from the Apollo missions are products of the Imbrium impact.Ejecta deposit modeling based on modem crater scaling indicates that the Imbrium event produced ejecta deposits that average hundreds of meters thick or more at all Apollo highland sites, which is thicker than some previous estimates. Substantial amounts of Imbrium ejecta should have been sampled at every Apollo highland site. We suggest that the mafic impact-melt breccias may be the principal form of those ejecta. The Imbrium projectile impacted into Th-rich material that we regard as part of a unique, mafic, lunar geochemical province we call the High-Th Oval Region. Based on the surface distribution of Th, only basins within the High-Th Oval Region excavated Th-rich material; the Th concentrations of the highlands as observed by the Apollo orbiting y-ray experiments are consistent with the estimates from ejecta modeling. Of the younger basin-forming impacts, only Imbrium was large enough to produce the copious amount of melt required by the ubiquitous presence of mafic impact-melt breccias in the Apollo-sampled regolith. The HighTh Oval Region still may have been molten or hot at shallow depths -4 Ga ago when the Imbrium projectile struck. We reason that compositional heterogeneity of ejected melt breccia is to be expected under these circumstances. We argue that siderophile-element "fingerprints" of mafic impact-melt breccias are not inconsistent with production of all common types by a single projectile. We suggest that the narrow range of ages of 3.74.0 Ga for all successfully dated mafic impact-melt breccias may reflect a single event whose age is difficult to measure precisely, rather than a number of discrete impact events closely spaced in time, such that reported age variations among mafic impact-melt breccias reflect the ability to measure 40Ar...

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Section: Compositional Differences Among Mafic Impact-melt Brecciasmentioning

confidence: 84%

The case for an Imbrium origin of the Apollo thorium‐rich impact‐melt breccias

Haskin¹,

Korotev²,

Rockow³

et al. 1998

Meteorit & Planetary Scien

Self Cite

125

113

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“…Preliminary reports of the work reported in this chapter were given in abstract form by Koeberl et al (1993), , and Kracher et al (1994). Petrographical and geochemical studies on the new drill core samples by other research groups were reported in abstract form by Bell et al (1993a, b), Izett et al (1993b), Reagan et al (1993), and Korotev et al (1994), and in final form by Bell et al (this volume), Korotev et al (this volume), Reagan et al (this volume), and Short and Gold (this volume).…”

Section: Introductionmentioning

confidence: 84%

Mineralogical, petrological, and geochemical studies of drill core samples from the Manson impact structure, Iowa

Koeberl¹,

Reimold²,

Kracher³

et al. 1996

Special Paper 302 the Manson Impact Structure Iowa Anatomy of an Impact Crater

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The Manson crater is a 36-km-diameter, well-preserved, but buried, impact structure in the United States of America. In 1991 and 1992, 12 cores were drilled in a joint Iowa Geological Survey Bureau-USGS effort. We have sampled 11 of the 12 cores, as well as the two cores drilled in 1953. About 140 samples from these drill cores were studied for their petrographical and geochemical characteristics to accumulate a database for target rocks and impact lithologies present at the Manson crater. The results provide a complete petrographical and geochemical database for impactite and target lithologies at the Manson crater. A variety of impactite lithologies are present, consisting of impact melt rocks, suevites, and several different types of breccia, including an unusual impact melt breccia that contains melt in the matrix as well as some melt clasts. The composition of the impactites can be reproduced by mixtures of the different types of target rocks present. Our results from least-square mixing calculations show that the M1 impact melt breccia has been formed from a mixture of shale, Red Clastics, a mafic component ("amphibolite"), and granite, with minor contributions from carbonate and biotite granite. The results of the calculations indicate about 19% shale, 20% Red Clastics (sandstone, siltstone), 37% amphibolite gneiss, 3% biotite gneiss, and 19% granite for the M1 impact melt breccias. The calculations for the M1 suevite did not produce mixing proportions that were as well constrained as for the M1 impact melt breccias, but about 25% shale, 9% Red Clastics, 43% amphibolite gneiss, 4% biotite gneiss, and 17% granite are the best fit. The composition of the M11 melt breccias can be reproduced by about 19% shale, 25% Red Clastics, and 48% mafic gneiss components, with some contribution (7%) from the granitic target rocks. In addition, we have studied the composition of feldspars from the M1 drill core in comparison with feldspars from the Crow Creek Member in South Dakota, which had been proposed before to be a distal impact ejecta of the Manson crater. We find slight differences between the compositions of the two feldspar populations.

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“…Compositions of terrestrial impact-melt breccias can be successfully modeled as mixtures of rocks known to occur in the target area of the impact [e.g., Dence, 1971;Grieve, 1975;Grieve and Floran, 1978;Korotev et al, 1996b]. Attempts to model the Apollo mafic melt breccias have not been as successful, in part because there is less independent knowledge of the lithologies at the target site than in the typical terrestrial case.…”

Section: Mass-balance Modelmentioning

confidence: 99%

The great lunar hot spot and the composition and origin of the Apollo mafic (“LKFM”) impact‐melt breccias

Korotev¹

2000

J. Geophys. Res.

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Abstract. Thorium-rich, marie impact-melt breccias from the Apollo 14-17 missions, that is, those breccias identified with the composition known as "LKFM," are regarded largely as products of basin-forming impacts that penetrated the feldspathic crust and sampled underlying marie material and magma-ocean residuum carrying the compositional signature of KREEP (potassium, rare earth elements, phosphorous). Despite considerable compositional variation among such breccias, compositions of all of them correspond to mixtures of only four components: (1)

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Geochemical comparison of four cores from the Manson impact structure

Cited by 4 publications

References 11 publications

The case for an Imbrium origin of the Apollo thorium‐rich impact‐melt breccias

The case for an Imbrium origin of the Apollo thorium‐rich impact‐melt breccias

Mineralogical, petrological, and geochemical studies of drill core samples from the Manson impact structure, Iowa

The great lunar hot spot and the composition and origin of the Apollo mafic (“LKFM”) impact‐melt breccias

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