Despinning plus global contraction and the orientation of lobate scarps on Mercury: Predictions for MESSENGER

Observations by the Mariner 10 spacecraft suggest that the lobate scarps on Mercury, which have been interpreted to record at most 1-2 km of radial contraction of the planet after the end of the Late Heavy Bombardment, possess a global, preferred N-S orientation but lack a strong latitudinal dependence on their surface expression. Here, we reexamine the idea that a decrease in the planetary rotation rate (despinning) coupled with global contraction of at least 3-5.5 km prior to the end of Late Heavy Bombardment resulted in global N-S oriented thrust faults. The surface expression of these faults is assumed to have been erased by the end of the Late Heavy Bombardment, and the faults were subsequently reactivated by later global contraction, producing generally N-S oriented thrust faults from an isotropic stress field. We use the estimate of >3-5.5 km contraction prior to ∼4 Ga as an additional constraint to thermomechanical simulations of the evolution of Mercury, finding that a wide range of models are consistent with this observation. The fact that a wide range of states are consistent with the contraction of Mercury prior to the end of Late Heavy Bombardment but only a restricted set of states are consistent with the at most 1-2 km of subsequent contraction bolsters the idea that there may be hidden strain on Mercury, features unseen by Mariner 10 but likely visible to the MESSENGER spacecraft.     

Lithospheric structure and tectonics at Isidis Planitia, Mars

We characterize the lithospheric structure of Isidis Planitia on Mars by analyzing Mars Global Surveyor and Mars Odyssey gravity and topography data using a flexural model of a thin elastic shell including bending and membrane stresses. Isidis Planitia is a circular, relatively flat plain formed near the end of the Early Noachian, at the edge of the highlands-lowlands boundary and the site of a large free-air gravity anomaly, features consistent with modification and filling of an impact basin. Our results suggest that the bulk density of the fill material inside Isidis must be more than 2600 kg m⁻³ and higher densities are probable. A comparison of the faulting observed at Nili Fossae to the predicted zone of extensional strain northwest of Isidis constrains the thickness of the elastic lithosphere to be 100-180 km thick beneath the basin at the time of loading. We also find that loads outside of the basin play a significant role in the interpretation of the tectonics; simplified models tend to overestimate the lithospheric thickness. We place relatively narrow bounds on the thermal gradient (3.4-6.5 K km⁻¹) and heat flux (13.6-26 mW m⁻²) at Isidis at the time of loading.     

The rheology of olivine and spinel magnesium germanate (Mg2GeO4): TEM study of the defect microstructures

Synthetic polycrystals of α-Mg₂GeO₄ (with the olivine structure) and γ-Mg₂GeO₄ (with the spinel structure) deformed at high temperature and pressure in their respective stability fields were investigated by analytical transmission electron microscopy. Specimens with a mean grain size of 20–30 µm deform by dislocation glide and/or climb. The predominance of glide versus climb depends on stress and grain orientation. The defect microstructures of both polymorphs are very similar to those observed in their respective silicate analogues, α- and γ-(Mg,Fe)₂SiO₄, and, in the case of the spinel phase, very similar to those observed in magnesium aluminate spinels. These observations suggest that Mg₂GeO₄ is a good rheological analogue for the Earth’s upper mantle. A spinel specimen deformed under the same conditions of temperature and strain rate as an olivine specimen was approximately three times stronger than olivine. In specimens of both phases deformed at or above 1400 K, a thin amorphous film composed of Mg, Ge, and O was detected along some grain boundaries. Grains ≤10 µm diameter surrounded by a film of amorphous phase (>10 nm thick) exhibited low dislocation densities, and deformation appeared to have occurred by grain boundary sliding.     

Organic geochemistry indicates Gebel El Zeit,Gulf of Suez,is a source of bitumen used in some Egyptian mummies

Molecular geochemical properties of crude oils and surface petroleum seeps from the southern part of the Gulf of Suez were evaluated. The characterizations of individual aliphatic, aromatic, and biomarker compounds were based on gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS) analyses. The results provided strong evidence for a close genetic association of these samples. The geochemical characteristics suggest an origin from Tertiary source rocks deposited in a normal marine environment that received continental runoff. The molecular signatures of the investigated samples were very similar to those of the Lower Miocene Rudeis Formation source rock in the southern Gulf of Suez. Further, biomarker fingerprints of the investigated oil seeps were compared with those of the Dead Sea asphalt, as well as the bitumen from some Egyptian mummies reported in the literature. The results demonstrate that oil seeps from the southern end of Gebel El Zeit were used by ancient Egyptians for embalming. © 2005 Wiley Periodicals, Inc.     

A critique of homeostatis: Season and metabolism

Summary Bioclimatologic investigation has shown that the fluid bathing the body cells—the internal environment—exhibits definite seasonal variations with regard to the concentration of substances in that fluid. Physiologic theory, on the other hand, maintains that the concentration of substances in the internal environment is kept relatively constant by means of a complex homeostatic (neuro-endocrine) mechanism. As a consequence physiology teaches that man is free and independent of the cosmic environment. This conflict is examined in the case of calcium and phosphorus metabolism. It is concluded that the internal environment isnot constant. It follows then that man is not free and independent of the changes in the cosmic environment.

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Zusammenfassung Die bioklimatologische Forschung hat festgestellt, daß die Flüssigkeit, die die Körperzellen umgibt—das innere Milieu—hinsichtlich der Konzentration der in ihr enthaltenen Substanzen bestimmte jahreszeitliche Schwankungen zeigt. Anderseits steht die physiologische Theorie auf dem Standpunkt, daß die Konzentration der Substanzen im Körperinnern durch einen komplexen homöostatischen (neuro-endokrinen) Mechanismus relativ konstant gehalten wird; infolgedessen lehrt die Physiologie, daß der Mensch frei und unabhängig von kosmischen Umwelteinflüssen sei. Dieser Widespruch wird in bezug auf den Calcium- und den Phosphor-Stoffwechsel geprüft und dabei festgestellt, daß das innere Milieunicht konstant ist. Der Mensch ist somit nicht frei und unabhängig von den Vorgängen des äußeren Milieus.

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Résumé Les recherches bioclimatologiques ont montré que le liquide entourant les cellules corporelles—le «milieu interne»—est soumis à certaines variations saisonnières quant à la concentration des substances qui'il renferme. Par contre la physiologie admet que la concentration de ces substances est maintenue relativement constante par un mécanisme homéstatique complexe (neuro-endocrinien); elle enseigne par conséquent que l'homme ne dépend pas des influences cosmiques. On examine cette contradiction à l'endroit du métabolisme du calcium et du phosphore et on constate que le milieu interne n'est pas constant. L'homme n'est doncpas indépendant des phénomènes du milieu extérieur.

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Based on a paper presented at the 30th Anniversary Meeting of the American Meteorological Society, St. Louis, Mo., January 3–6, 1950.     

Technical note: Estimating water shed S-graphs using a diffusion flow model

A simplification of the two-dimensional (2-D) continuity and momentum equations is the diffusion equation. This simpler dynamic model of two-dimensional hydraulics affords the hydrologist a means to quickly estimate floodflow effects for overland flow. To investigate its capability, a numerical model using the diffusion approach is applied to a set of hypothetical watersheds in order to develop unit hydrographs. The model is based on an explicit, integrated finite-difference scheme, and the floodplain is simulated by use of topographic elevation and geometric data. Synthetic unit hydrographs (S-graphs) developed from use of the simple 2-D model show interesting correlations to the well-known S.C.S. unit hydrograph (S-graph).     

Inverse gravity problems for models composed of bodies of Sretenskii’s class

An inverse gravity problem is solved for a geological model consisting of bodies of Sretenskii’s class. The position of the middle plane is fixed for each body. It is required to determine the upper and lower boundaries of a body, which are described by analytical functions and are parameterized. The solution of the problem is illustrated by an example.