Flexural Stresses and Reservoir Stability: Implications for Magma Propagation in the Lithosphere and the Formation of Giant Radial Dike Swarms on Venus

Details Flexural Stresses and Reservoir Stability: Implications for Magma Propagation in the Lithosphere and the Formation of Giant Radial Dike Swarms on Venus Flexural Stresses and Reservoir Stability: Implications for Magma Propagation in the Lithosphere and the Formation of Giant Radial Dike Swarms on Venus

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p11b1345g&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #P11B-1345

Physics

[5480] Planetary Sciences: Solid Surface Planets / Volcanism, [6295] Planetary Sciences: Solar System Objects / Venus, [8434] Volcanology / Magma Migration And Fragmentation, [8439] Volcanology / Physics And Chemistry Of Magma Bodies

Scientific paper

Giant radial fracture systems on Venus are prominent, widely distributed volcano-tectonic structures that record interactions between the lithosphere and subsurface magmatic processes, specifically the lateral transport of magma at shallow depths. Here we show that the interplay between flexural uplift and magma chamber pressurization can create stress conditions favoring the emplacement of radial dikes. We use elastic, gravitationally-loaded axisymmetric finite element models that incorporate depth-dependent lithostatic stresses and Winkler restoring forces at the base of the elastic lithosphere. To generate uplift, we apply buoyant (upward) loads at the base of a 20 km-thick lithosphere near the model center, with a maximum thickness of 5 km and 200 km in radius, using conical and disk load shapes. An overpressured spherical reservoir, emplaced in each model, is used to simulate magmatic inflation and determine reservoir failure patterns. Stress orientations predicted by our models are helping us understand how laterally spreading sub-lithosphere bodies flex the lithosphere, affect intrusion patterns (radial to circumferential faults/grabens), and influence both magma ascent and eruptive patterns. Loading due to a conical basal load produces a flexural stress state with high differential stresses in the extensional upper and compressional lower lithosphere, separated by a low-stress neutral plane. Principal stress alignments in the upper lithosphere favor the emplacement of laterally extensive radial intrusions. In contrast to this, sill formation is favored in the lower lithosphere. Magma reservoirs emplaced in the upper lithosphere or within the underlying zone of low differential stress fail at the crest, favoring the ascent of magma. Reservoirs emplaced in the lower lithosphere tend to fail near the midsection under conditions that will yield horizontal intrusions. In sharp contrast, disk-shaped or ellipsoidal uplift loads move the flexed part of the lithosphere outwards, creating stress states that favor sills and circumferential dikes in the upper lithosphere with radial dikes at the lower lithosphere. This outcome demonstrates the sensitivity of our results to uplift load geometry. With the exception of sill-producing, near-midsection rupture of magma chambers in the uppermost and lowermost lithosphere, failure generally occurs at the reservoir crest, and higher overpressures are required for failure, suggesting reservoir stability. These loads also produce surface radial and hoop strains conducive to the formation of circumferential grabens a distance (~50-180 km) from the model center. However, increasing the elastic lithosphere thickness (Te) to 40 km reduces the load shape differences, creating similar stress states for both conical and disk-shaped loads.

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