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Golombek, M. P.

Publications and source records attributed to Golombek, M. P..

102 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

On the Absence of Strike-slip Faults from the Planets and Satellites

Lunar grabens are bounded by two downward converging 60 deg dipping normal faults. These faults intersect below the surface at a major mechanical discontinuity in the shallow crust between the megaregolith (total ejecta built up by repeated cratering) and the underlying in situ fractured rock. The ymmetry and simplicity of lunar grabens demands that the bounding faults initiate at this mechanical discontinuity and propagate up. Wrinkle ridges are though to result from thrust faulting or compressional folding of mare basalts. Identification and analysis of a number of terrestrial analogs that are morphologically similar to lunar and martian examples indicates that wrinkle ridges results from thrust faulting. The location of wrinkle ridges above suggested subsurface basin structures indicates that the trend and location of many wrinkle ridges are inherited from these pre-existing basin structures. This implies that the thrust faults responsible for wrinkle ridges initiate at the ase of the basalt-basin floor contact. This contact almost certainly represents a mechanical discontinuity in the shallow lunar crust because mare basalts are undoubtedly stronger than the underlying fall-back ejecta of the basin floor.

Golombek, M. P.↗
NASA NTRS1985

Lunar Mascon Loading: an Example of the Importance of Fault Initiation Depth on Fault Type Predictions from Stresses on Planetary Surfaces

Geophysical models that predict fault type from stresses calculated at the planetary surface (zero depth) can be misleading because faults generally initiate at depth under a different stress regime and propagate to the surface. The generally accepted and most commonly employed criteria for fault prediction from calculated stresses on planetary surfaces points out problems in neglecting the effects of non-isotropic overburden stresses and the use of realistic material constants and shows a well known example (mascon loading on the moon) where neglecting this effect predicts a different type of fault than is actually observed.

Golombek, M. P.↗
NASA NTRS1985

Fault type predictions from stress distributions on planetary surfaces - Importance of fault initiation depth

The prediction of fault type on planetary surfaces from model stresses calculated at depth is discussed. These fault-type predictions yield different faults than those predicted using the surface criteria commonly employed in geophysical models. For elastic-plate flexure models of mascon loading on the moon, stresses calculated at the surface predict the occurrence of strike-slip faulting at the radial distance where grabens are found. Normal faults bounding lunar grabens and thrust faults responsible for wrinkle ridges are analyzed. It is found that the former initiate at the mechanical discontinuity that separates the breccia of the megaregolith from in situ fractured rock and that the latter initiate at the mechanical discontinuity between basalt layers and the underlying basin floor. The difference between elastic constants for the outer few kilometers of brecciated megaregolith and the underlying lunar lithosphere are evaluated. Superposing nonisotropic stresses resulting from the weight of overburden to the depth of the relevant mechanical discontinuity yield stresses that predict wrinkle ridges in the basin centers and grabens outside the basin margin, and eliminate the predicted zone of strike-slip faults.

Golombek, M. P.↗
NASA NTRS1985

Tectonic rotations within the Rio Grande rift - Evidence from paleomagnetic studies

Paleomagnetic studies on Miocene Pliocene volcanic rocks from the Espanola basin of the Rio Grande rift, New Mexico, reveal directions discordant form the expected mean direction for North America. The Paliza Canyon Formation, Tschicoma Formation, and Lobato Basalt, all sampled in the Jemez Mountains west of the Pajarito fault zone, have mean declinations east of the expected mean. The Cerros del Rio volcanics, lying east of the Pajarito fault zone, have a westerly declination. Combined with published data on the Santa Fe Group sediments east of the fault zone, and the Valles Rhyolite, west of the fault zone, distinct rotations of the two areas are evident. The western block has rotated clockwise 12 deg, while the eastern block shows 16 deg of conter-clockwise motion. Differential rotations of 25-30 deg are calculated between the two blocks; 4 deg/m.y. is the minimum differential rotation for the past 5 m.y. Geologic explanations for these rotations include the opening of the Rio Grande rift in response to clockwise rotation of the Colorado Plateau and significant left slip along the Rio Grande rift.

Brown, L. L.↗
NASA NTRS1985

Rifting on Venus: Implications for lithospheric structure

Lithospheric strength envelopes on Venus are reviewed and their implications for large scale rifting are discussed. Their relationship to crustal thicnesses and thermal gradients are explored. Also considered are the implications of a theory for rift formation.

Banerdt, W. B.↗
NASA NTRS1985

Lithospheric strength of Ganymede: Clues to early thermal profiles from extensional tectonic features

While it is generally agreed that the strength of a planet's lithosphere is controlled by a combination of brittle sliding and ductile flow laws, predicting the geometry and initial characteristics of faults due to failure from stresses imposed on the lithospheric strength envelope has not been thoroughly explored. Researchers used lithospheric strength envelopes to analyze the extensional features found on Ganymede. This application provides a quantitative means of estimating early thermal profiles on Ganymede, thereby constraining its early thermal evolution.

Golombek, M. P.↗
NASA NTRS1983

Grabens, basin tectonics, and the maximum total expansion of the moon

Information from lunar grabens is used to address the question of whether the grabens and wrinkle ridges are tectonic or volcanic in origin. The geometry of simple grabens is discussed, and the kinematics and mechanics are addressed in terms of an elastic response model, a brittle response model, the mechanics of the megaregolith, and total extension for all lunar grabens. Constraints on the thermal evolution of the moon are considered, including thermal history calculations and grabens in space and time. Mare basin tectonics is discussed in terms of two kinematic models/ subsidence by increased radius of curvature and subsidence with no increase in radius of curvature. It is concluded that the observable geological history of the moon is inconsistent with any significant expansion of the moon since about 3.9 billion years ago. Both thermal and tectonic models of lunar evolution are critized.

Golombek, M. P.↗
NASA NTRS1982

Constraints on the expansion of Ganymede and the thickness of the lithosphere

Since grooved terrain has formed from extensional faulting of at least one half of the surface of Ganymede, grooves may be due to planetary expansion which can be constrained by determining the extension associated with groove formation. The geometry and kinematics of a fault or group of faults must be known in order to determine the extension. Although neither of these is known for grooves on Ganymede, geologically reasonable end members of the dip, displacement and extension of faults which bound the graben can be estimated in order to place valuable constraints on possible surface area and radius increases as well as on the thickness of the Ganymede lithosphere. Minimum lithosphere thickness is estimated to be 5 km in the Marius and 9 km in the Galileo regions, at the time of furrow formation, and 4 km at the time of groove formation.

Golombek, M. P.↗
NASA NTRS1979

Tharsis Province of Mars - Geologic sequence, geometry, and a deformation mechanism

Tharsis development apparently involved two stages: (1) an initial rapid topographic rise accompanied by the development of a vast radial fault system and (2) an extremely long-lived volcanic stage apparently continuing to the geological present. A deformation model is proposed in which a first-order mantle convection cell caused early subcrustal erosion and foundering of the low third of the planet. Underplating and deep intrusion by the eroded materials beneath Tharsis caused isostatic doming. Minor radial gravity motions of surficial layers off the dome produced the radial fault system. The hot underplate eventually affected the surface to cause the very long-lived volcanic second stage.

Wise, D. U.↗