Pre-Orientale Southwest Peak-Ring Basin: Gravity Structure, Geologic Characteristics, and Influence on Orientale Basin Ring Formation and Ejecta Emplacement

The Orientale impact basin is the youngest and most well-preserved of the lunar multi-ring basins. The generally well-preserved ring structures and basin facies are distinctly anomalous in the southwestern quadrant; the outer Cordillera ring extends significantly outward, the Outer and Inner Rook mountain rings are more poorly developed and show anomalous characteristics, and the Montes Rook Formation varies widely from its characteristics elsewhere in the basin interior. Based on the gravity, image, and topography data, we confirmed that the southwest region of the Orientale basin represents the location of a pre-existing ~320 km rim–crest diameter peak–ring basin centered at 108.8°W, 28.4°S, and characterized by an ~170 km peak–ring diameter. We model the structure and morphology of this large pre-Orientale peak–ring basin (about one-third the diameter of Orientale) and show that its presence and negative relief had a distinctive influence on the development of the basin rings (disrupting the otherwise generally circular continuity and causing radial excursions in their locations) and the emplacement of ejecta (causing filling of the low region represented by the peak–ring basin, creating anomalous surface textures, and resulting in late stage ejecta movement in response to the pre-existing peak–ring basin topography. The location and preservation of the peak–ring basin Bouguer anomaly strongly suggest that the rim crest of the Orientale basin excavation cavity lies at or within the Outer Rook Mountain ring.

Download Full-text

Statistics of spiral patterns and comparison of our Galaxy with other galaxies

Symposium - International Astronomical Union ◽

10.1017/s0074180900000243 ◽

1970 ◽

Vol 38 ◽

pp. 18-25 ◽

Cited By ~ 2

Author(s):

G. De Vaucouleurs

Keyword(s):

Morphological Type ◽

Ring Structure ◽

Spiral Pattern ◽

Radio Structure ◽

Total Range ◽

Galactic System ◽

Ring Diameter ◽

Ring Structures

Apparent relative frequencies of various types of spirals are given for 900 spirals with the best revised Hubble classifications. Mean diameters of inner ring structures vary from 2.1 kpc in ordinary spirals (SA) to 4.4 kpc in barred spirals (SB) with a total range of 10 to 1 within each type. The probable morphological type of our galaxy is estimated from 6 criteria (multiplicity of spiral pattern, inner ring diameter, broken ring structure, radio structure of nucleus, Yerkes type, HI diagram); arguments advanced in 1963 for an SAB(rs) structure of the inner regions of the galactic system are strengthened by this analysis. Several examples of galaxies in this area of the classification plane are discussed.

Download Full-text

Lunar impact basins revealed by Gravity Recovery and Interior Laboratory measurements

Science Advances ◽

10.1126/sciadv.1500852 ◽

2015 ◽

Vol 1 (9) ◽

pp. e1500852 ◽

Cited By ~ 80

Author(s):

Gregory A. Neumann ◽

Maria T. Zuber ◽

Mark A. Wieczorek ◽

James W. Head ◽

David M. H. Baker ◽

...

Keyword(s):

Bouguer Anomaly ◽

Marked Change ◽

Laboratory Measurements ◽

Frequency Distributions ◽

Ring Diameter ◽

Lunar Impact ◽

Gravity Recovery ◽

Lunar Basins ◽

Identification And Characterization

Observations from the Gravity Recovery and Interior Laboratory (GRAIL) mission indicate a marked change in the gravitational signature of lunar impact structures at the morphological transition, with increasing diameter, from complex craters to peak-ring basins. At crater diameters larger than ~200 km, a central positive Bouguer anomaly is seen within the innermost peak ring, and an annular negative Bouguer anomaly extends outward from this ring to the outer topographic rim crest. These observations demonstrate that basin-forming impacts remove crustal materials from within the peak ring and thicken the crust between the peak ring and the outer rim crest. A correlation between the diameter of the central Bouguer gravity high and the outer topographic ring diameter for well-preserved basins enables the identification and characterization of basins for which topographic signatures have been obscured by superposed cratering and volcanism. The GRAIL inventory of lunar basins improves upon earlier lists that differed in their totals by more than a factor of 2. The size-frequency distributions of basins on the nearside and farside hemispheres of the Moon differ substantially; the nearside hosts more basins larger than 350 km in diameter, whereas the farside has more smaller basins. Hemispherical differences in target properties, including temperature and porosity, are likely to have contributed to these different distributions. Better understanding of the factors that control basin size will help to constrain models of the original impactor population.

Download Full-text

Variations in Surface Textures of Quartz Sand using Electron Microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100069466 ◽

1970 ◽

Vol 28 ◽

pp. 494-495

Author(s):

Eugene J. Amaral

Keyword(s):

Electron Microscopy ◽

Glass Industry ◽

Glass Slide ◽

Distilled Water ◽

Early Paleozoic ◽

Secondary Effects ◽

Surface Textures ◽

High Silica ◽

Sand Deposit ◽

The U.S

Examination of sand grain surfaces from early Paleozoic sandstones by electron microscopy reveals a variety of secondary effects caused by rock-forming processes after final deposition of the sand. Detailed studies were conducted on both coarse (≥0.71mm) and fine (=0.25mm) fractions of St. Peter Sandstone, a widespread sand deposit underlying much of the U.S. Central Interior and used in the glass industry because of its remarkably high silica purity.The very friable sandstone was disaggregated and sieved to obtain the two size fractions, and then cleaned by boiling in HCl to remove any iron impurities and rinsed in distilled water. The sand grains were then partially embedded by sprinkling them onto a glass slide coated with a thin tacky layer of latex. Direct platinum shadowed carbon replicas were made of the exposed sand grain surfaces, and were separated by dissolution of the silica in HF acid.

Download Full-text

TEM study of lanthanum aluminate

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100178434 ◽

1990 ◽

Vol 48 (4) ◽

pp. 1060-1061

Author(s):

C.Y. Yang ◽

Z.R. Huang ◽

Y.Q. Zhou ◽

C.Z. Li ◽

W.H. Yang ◽

...

Keyword(s):

Domain Boundary ◽

Point Group ◽

Optical Microscope ◽

Dark Field ◽

Zone Axis ◽

Superconducting Film ◽

Ion Milling ◽

Lanthanum Aluminate ◽

Ring Diameter ◽

Diffraction Patterns

Lanthanum aluminate(LaAlO3) single crystal as a substrate for high Tc superconducting film has attracted attention recently. We report here a transmission electron microscopy(TEM) study of the crystal structure and phase transformation of LaAlO3 by using Philips EM420 and EM430 microscopes. Single crystals of LaAlO3 were investigated first by optical microscope. Stripe-shaped domains of mm size are clearly seen(Fig.1a), and 90° domain boundary is also obvious. TEM specimens were prepared by mechanical grinding and polishing followed by ion-milling.Fig.lb shows μm size stripe domains of LaAlO3. Convergent beam electron diffraction patterns (CBED) from single domain were taken.Fig. 2a and Fig. 2c are [001] zone axis patterns which show a 4mm symmetry, and the (200) dark field of this zone axis gives 2mm symmetry(fig.2b). Therefore the point group of this crystal is either 4/mmm or m3m. The projection of the first order Laue zone(FOLZ) reflections on zero layer (fig. 2c) shows that the unit cell is face centered. A tetragonal unit ceil is chosen, with a=0.532nm and c=0.753nm, c being determined from the FOLZ ring diameter.

Download Full-text