Astronomy and Astrophysics – Astrophysics
Scientific paper
May 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agusm.p33d..11r&link_type=abstract
American Geophysical Union, Spring Meeting 2004, abstract #P33D-11
Astronomy and Astrophysics
Astrophysics
5418 Heat Flow, 5430 Interiors (8147), 5475 Tectonics (8149), 6295 Venus, 8121 Dynamics, Convection Currents And Mantle Plumes
Scientific paper
The coexistence of dynamically supported highlands and coronae is difficult to reconcile with models of Venusian mantle convection. Coronae are well explained by transient discrete mantle upwellings (thermals), which are characteristic of weak cooling due to the stagnant lid style of convection expected in one-plate planets. In contrast, topographic highlands such as Atla, Beta and Themis Regio are better explained by persistent axisymmetric plumes more typical of the Earth's mantle, which is cooled strongly by subduction and plate tectonics (i.e. mobile lid convection). From the observed crater distribution, it is also inferred that the surface of Venus has a mean age of ~700 Ma. One explanation for this young surface age is that it is a result of a recent and catastrophic resurfacing event. We test a hypothesis that the occurrence of highlands and coronae are a consequence of the style of transient mantle convection driven by sudden overturn of the lithosphere. A series of stagnant lid and mobile lid convection control experiments at thermal equilibrium under conditions appropriate for Venus' mantle are first performed. The mobile lid regime is achieved using a conveyor belt at the cold boundary. Next, we investigate the thermal and temporal characteristics of transitions from steady-state stagnant lid to mobile lid, and from mobile lid to stagnant lid regimes. Using a combination of time-lapse video, shadowgraphs and analyses of time-series of temperature and heat flux data, we identify the qualitative changes in convective regime, the quantitative changes in the heat transfer characteristics of the flows, and the characteristic time scales over which transitions occur. Three regimes are observed: (i) steady-state stagnant lid mode characterized by time-dependent hot (rising) and cold (sinking) thermals; (ii) steady-state mobile-lid mode characterized by active stirring and long-lived plumes; and (iii) a transient mixed mode characterized by the coexistence of thermals and long-lived plumes as the overturning cold boundary impinges and spreads on the hot lower boundary. Applied to Venus, preliminary results support our proposal that coronae and highlands coexist as a consequence of the transient convective regime in the mantle following a global resurfacing event.
Jellinek Mark A.
Robin C. M.
Thayalan Vid
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