EMPLACEMENT OF A RADIATING DIKE SWARM IN WESTERN VINMARA-PLANITIA, VENUS - INTERPRETATION OF THE REGIONAL STRESS-FIELD ORIENTATION AND SUBSURFACE MAGMATIC CONFIGURATION

Citation
Eb. Grosfils et Jw. Head, EMPLACEMENT OF A RADIATING DIKE SWARM IN WESTERN VINMARA-PLANITIA, VENUS - INTERPRETATION OF THE REGIONAL STRESS-FIELD ORIENTATION AND SUBSURFACE MAGMATIC CONFIGURATION, Earth, moon, and planets, 66(2), 1994, pp. 153-171
Citations number
41
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Astronomy & Astrophysics","Geosciences, Interdisciplinary
Journal title
ISSN journal
0167-9295
Volume
66
Issue
2
Year of publication
1994
Pages
153 - 171
Database
ISI
SICI code
0167-9295(1994)66:2<153:EOARDS>2.0.ZU;2-D
Abstract
Magellan radar data from western Vinmara Planitia on Venus reveal a sy stem of radiating lineaments extending 450 km from a small central ann ulus. Spatial variations in lineament density, orientation, and morpho logy, as well as structural and volcanic correlations, provide strong evidence that formation of the lineaments was related to subsurface di ke emplacement. We infer from the observed surface deformation that th e dikes were emplaced laterally, at shallow depth, from a large centra l magma reservoir. This configuration is analogous to that of radiatin g dike swarms found on Earth. Because dikes inject normal to the least compressive stress direction, swarm plan view geometry will reveal th e greatest horizontal compressive stress trajectories. We interpret st rongly radial orientations near the swarm center to represent radial s tresses linked to pressurization of the magma reservoir. Increasingly non-radial behavior dominating at greater distances is interpreted to reflect a N60E+/-20 degrees regional maximum horizontal compressive st ress. Contrary to previous inferences that a persistent E-W compressiv e stress dominated throughout, analysis of the arachnoid indicates tha t a N60E compressive stress must have existed across western Vinmara P lanitia during a portion of its deformation. This and the absence of d istributed shear within the adjacent deformation belts indicates that the regional maximum horizontal compression orientation has varied ove r time. Comparison between the regional stress orientations inferred f rom the arachnoid and several nearby ridge belts illustrates that stre ss orientations may potentially be useful for determining relative bel t ages in areas where the timing of ridge belt formation is difficult to assess by more direct means. This demonstrates one way that identif ication and analysis of giant radiating dike swarms can provide new in formation critical for regional stress interpretations on Venus.