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Simonds, C. H.

Publications and source records attributed to Simonds, C. H..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

The role of volatiles and lithology in the impact cratering process

A survey of published descriptions of 32 of the largest, least eroded terrestrial impact structures shows that the amount of melt at craters in crystalline rocks is approximately two orders of magnitude greater than that at craters in sedimentary rocks. A model is proposed for the impact process, and it is examined whether the difference in melt abundance is due to differences in the amount of melt generated in various target materials or due to differences in the fate of the melt during late stages of the impact. The model accounts semiquantitatively for the effects of porosity and water and volatile content on the cratering process. Important features of the model are noted. Even if the recondensation of released volatiles is very efficient, the cumulative effect of repeated impacts on accreting planets would be to continually transfer volatiles toward the outer surface. By this process, volatiles might be enriched toward the outer layer of a growing planet.

Kieffer, S. W.↗
NASA NTRS1979

Introduction to the Apollo collections: Part 2: Lunar breccias

Basic petrographic, chemical and age data for a representative suite of lunar breccias are presented for students and potential lunar sample investigators. Emphasis is on sample description and data presentation. Samples are listed, together with a classification scheme based on matrix texture and mineralogy and the nature and abundance of glass present both in the matrix and as clasts. A calculus of the classification scheme, describes the characteristic features of each of the breccia groups. The cratering process which describes the sequence of events immediately following an impact event is discussed, especially the thermal and material transport processes affecting the two major components of lunar breccias (clastic debris and fused material).

Mcgee, P. E.↗
NASA NTRS1979

Petrology of impactites from Lake St. Martin structure, Manitoba

The 23-km Lake St. Martin crater was produced 200 to 250 million years ago in Archean granitic to amphibolic gneiss, overlain by 400 to 500 m of Ordovician to Devonian limestone and dolomite. In the present paper, a schematic model of the field geology, petrology, and geochemistry is presented. The scenario is built in part on the calculations of Kieffer and Simonds and observations made on the Lake St. Martin structure.

Simonds, C. H.↗
NASA NTRS1978

Manicouagan impact melt, Quebec. I - Stratigraphy, petrology, and chemistry

A sheet of clast-laden impact melt 230 m thick and 55 km in diameter forms an annular plateau surrounding an uplift of shocked anorthosite within the moderately eroded Manicouagan structure. Three gradational units of the melt sheet are characterized with respect to grain size, inclusions, texture, and mineralogy. The melt rocks as a group are chemically homogeneous with a bulk composition similar to that of latite and with no statistically significant regional chemical variations. The melt is not completely chemically homogeneous as a local mafic variant represented by two samples with poikilitic texture was found. These poikilitic rocks texturally resemble some Apollo 17 impact melt rocks and are inferred to have had a similar origin and thermal history.

Floran, R. J.↗
NASA NTRS1978

Petrogenesis of melt rocks, Manicouagan impact structure, Quebec

It is suggested, on the basis of previous theoretical studies of shock waves, that the Manicouagan melt formed in 1 or 2 s in a 5-km-radius hemisphere near the point of impact. The melt and the less shocked debris surrounding it flowed downward and outward for a few minutes until the melt formed a lining of a 5- to 8-km deep, 15- to 22-km-radius cavity. Extremely turbulent flow thoroughly homogenized the melt and promoted the incorporation and progressive digestion of debris that had been finely fragmented (but not melted) to grain sizes of less than one mm by the passage of the shock waves. The equilibration of clasts and melt, plagioclase nucleation, and readjustment of the crater floor are discussed.

Simonds, C. H.↗
NASA NTRS1978

The thermal history of the Manicouagan impact melt sheet, Quebec

Calculations for the heat transfer between superheated silicate melt and evenly dispersed 1-mm cold clasts indicate that most of the thermal gradients are smoothed out in 100 s and that the rate of equilibrium is sufficiently high so that clasts whose dissolution in the melt is slow may be preserved. The calculations also show the extent to which cold debris and clasts are melted. Calculations for cooling of the 200-m-thick melt sheet at Manicouagan suggest that complete crystallization takes 35 years at 10 m from the edge and 1600 years at the center.

Onorato, P. I. K.↗
NASA NTRS1978

Rb-Sr isochron age of the Manicouagan melt sheet, Quebec, Canada

Rb-Sr isotopic data for mineral separates from a rock of the Manicouagan impact melt sheet define an isochron of age T = 214 + or - 5 (2 sigma) m.y. which agrees with the K-Ar age of 210 + or - 8 (2 sigma) calculated by Wolfe (1971). The initial Sr-87/Sr-86 ratio I is found to be 0.70991 + or - 0.00007 (2 sigma); four whole rock samples yield age-corrected I values ranging from 0.70965 to 0.71006. These high I values support the hypothesis that the melt sheet was derived by total melting of Grenville basement rocks during the impact event 214 m.y. ago.

Jahn, B.↗
NASA NTRS1978

Luna 24 - Lateral heterogeneity in the lunar crust

Results of petrological investigations of Luna 24 soil samples are compared with data from Apollo and other Luna missions in order to determine the large scale composition of the lunar surface and crust. Modal analysis of the 90 to 150 micron soil fraction and electron microprobe analysis of glass spheres and fragments of the Luna 24 core sample are presented. High and low MgO mare basalt compositional clusters are found, suggesting the derivation of southern Mare Crisium basalts from two magmas. A model of Luna 24 soils as being composed of a mixture of glass-poor mare material and glass-rich highland material is found to be consistent with glass and agglutinate modal abundances. Comparisons show that potassium, and by inference all lithophile trace elements, are depleted on the eastern limb of the moon relative to the central nearside. The observed depletion is interpreted to be characteristic of the underlying crust and mantle as well as the surface.

Warner, J. L.↗
NASA NTRS1978

West Clearwater, Quebec impact structure. I - Field geology, structure and bulk chemistry. II - Petrology

A field study at the 30-km-diameter West Clearwater impact crater was carried out during the summer of 1977 to identify the nature of the flow of impact melt and less shocked debris during the excavation stage of the cratering process. The present paper investigates: (1) comparisons with other impact craters and lunar samples; (2) generation and emplacement mechanisms of impact melts and associated clastic debris; and (3) the geometry of the transient cavity and the pristine morphology of the crater.

Simonds, C. H.↗
NASA NTRS1977

Comparisons of Mercury and the moon; Proceedings of the Conference, Houston, Tex., November 15-17, 1976

Papers are presented outlining various comparisons of Mercury and the moon. Specific topics include the planetary magnetism and the interiors of the moon and Mercury, the relationship between crustal tectonics and internal evolution, global tectonics, the origin and relative age of lunar and Mercurian intercrater plains, and the relative preservation states of secondary craters. Comparisons are also discussed between lunar and Mercurian rayed craters, large impact structures, isostasy and average crustal viscosity. Attention is given to global seismic effects of basin-forming impacts, interpretations of optical observations of Mercury and the moon, and the production of simple molecules on the surface of Mercury.

Simonds, C. H.↗
NASA NTRS1977

Introduction to the Apollo collections. Part 1: Lunar igneous rocks

The basic petrographic, chemical, and age data is presented for a representative suite of igneous rocks gathered during the six Apollo missions. Tables are given for 69 samples: 32 igneous rocks and 37 impactites (breccias). A description is given of 26 basalts, four plutonic rocks, and two pyroclastic samples. The textural-mineralogic name assigned each sample is included.

Mcgee, P. E.↗
NASA NTRS1977

Lunar highland rock types: Their implications for impact-induced fractionation

Lunar rocks may be classified into three major groups: (1) coarse-grained igneous rocks, (2) fine-grained igneous rocks, and (3) breccias. Group 1 is interpreted as primitive lunar crustal rocks that display various degrees of crushing and/or annealing. Group 2 is interpreted as volcanic rocks. Group 3 is interpreted as resulting from impacts on the lunar surface and is subdivided on the basis of matrix textures into fragmental breccias, crystalline breccias that have been annealed, and crystalline breccias with igneous matrices. A synthesis of the data concerning lunar highlands polymict breccias compels the prediction that the breccias should have homogeneous matrices from rock to rock within regions of the highlands of limited size where impact mixing has been efficient and extensive. But the returned breccias, even from one landing site, display a wide range in composition. This incompatibility between prediction and observation is a paradox that may be resolved by a process that acts after impact mixing to cause a differentiation of the breccia compositions. Partial melting of the local average crustal composition (as modeled by the average soil composition for each site) and separation of melt and residue in ejecta and/or fall-back blankets are compatible with the reviewed data and may resolve the paradox.

Phinney, W. C.↗
NASA NTRS1977

Apollo 14 revisited, or breccias aren't so bad after all

A study of large Apollo 14 samples suggests that they were formed by the same processes which formed the impactites found at Apollo 16 and 17 and in terrestrial craters, especially those in crystalline targets. The abundant crystalline matrix breccias of the Apollo 14 samples generally show higher clast contents and less refractory clast populations than the clast-laden impact melts abundant at the other Apollo nonmare landing sites. The Apollo 14 characteristics are attributed to the mixing of a greater amount of cold clastic debris into the superheated melt formed during impacts. The other major lithology at Apollo 14, the vitric matrix breccias, are made in part from agglutinate-bearing soil and cannot be the protolith of crystalline matrix breccias, because of differences in structure and composition. Variations among the breccias indicate the occurrence of several impact events.

Simonds, C. H.↗
NASA NTRS1977

Feldspathic granulitic impactites and pre-final bombardment lunar evolution

It is suggested that feldspathic granulitic impactites, which are characterized by a high model plagioclase content of between 70 and 80%, all formed in the period after consolidation of the lunar crust and before the final bombardment. The granulitic impactites contain essentially no KREEP component, which suggests that KREEP appeared on the lunar surface mostly after the formation of the granulitic impactites, at about the start of the final bombardment. The granulite metamorphism indicated by the matrix textures of these samples requires 1000 C temperatures for prolonged periods of time. The apparent sequence of formation is granulitic impactites before the final bombardment, crystalline-matrix breccias during the final bombardment, and vitric-matrix breccias after the final bombardment. The sequence is consistent with a described thermal model of breccia lithification and with characteristics of the decay of the meteorite flux rate.

Warner, J. L.↗
NASA NTRS1977

Dynamical implications of the petrology and distribution of impact melt rocks

Petrographic and structural relations of rocks resulting from melting of target materials during impact indicate constraints that can be applied to theoretical models and experimental production of craters. Topics discussed in this context include the motion of shock melted material, the mixing of melts, the energies required for heating and melting the necessary volumes of target rocks, diameter to depth ratios, and the formation of structural modifications. The motion of shock melted material involves ejection of some of the lowermost parts of the target, incorporation of distant fragmental material, outward flow, settling into cracks after breccia formation, and completion in a short time span. Melts must be completed within tens of seconds to a couple of minutes after impact.

Phinney, W. C.↗
NASA NTRS1976

Thermal regimes in cratered terrain with emphasis on the role of impact melt

The distribution of bombardment energy in the moon's crust and the types of phase transformation resulting from this energy input are investigated. It is seen that the major significance of impact melts in the period of intense cratering is that they transfer most of the high-temperature heat following cratering and thus take part in many of the phase transformations on planetary surfaces. Energy partitioning studies suggest that of the projectiles' total kinetic energy, 23 to 35% is converted into heat by passage of the shock fronts, 43 to 53% transports ejecta and then is dissipated at modest temperature increases over a broad area, 8 to 24% is consumed comminuting country rock, and less than 1% becomes seismic and radiant energy. Subsequent to its formation, the melt is violently mixed with much colder debris to form the sheets of impact melt and the breccias.

Simonds, C. H.↗
NASA NTRS1976

Apollo 17, Station 6 boulder sample 76255 - Absolute petrology of breccia matrix and igneous clasts

The matrix of 76255 is the finest-grained, most clast-laden, impact-melt polymict breccia sampled from the Station 6 boulder. The paper speculates on how the matrix of 76255 fits into and enhances existing thermal models of breccia lithification. Emphasis is on the detailed petrology of five lithic clasts, two of which display mineralogical and textural affinities to mare basalts, while three, a gabbro, a norite, and a troctolite are considered primitive plutonic rocks.

Warner, J. L.↗