Bob Grimm - Venus

GEODYNAMICS OF VENUS

Research highlights. See Curriculum Vitae for citations.

Established that conduction was the dominant mode of planetary heat loss over the preserved surface age of Venus (0.5-1 b.y), not volcanism or plate tectonics (Grimm and Solomon, 1987)

Established limits to average crustal thickness <30 km (Grimm and Solomon, 1988; Grimm,1994a, Grimm and Hess, 1997) and average thermal gradient <20 K/km (Grimm and Solomon, 1988; Brown and Grimm, 1996a).
Determined that the mean rate of tectonic deformation of Venus over the last 0.5-1 b.y. is ~1e-17/s, logarithmically intermediate between plate-tectonic Earth (1e-15/s) and thermally contracting Mars (1e-19/s) (Grimm, 1994b).
With C. David Brown, inferred that Artemis Chasma is not a true subduction zone but a region of large-scale and coherent but limited underthrusting (Brown and Grimm, 1995; 1996b).
Also with Brown, used tectonic patterns to trace monotonic thickening of the lithosphere of Venus over the past several hundred million years (Brown and Grimm, 1999).

Evolution of tectonic style on Venus (Brown and Grimm, 1999). Each panel schematically shows tectonic wavelength over a yield strength envelope (YSE), and an image of the resulting tectonic style. Left: "Early" (>0.5-1 b.y.), hot Venus with small yield-strength envelope and ubiquitous, short-wavelength deformation (tessera). Middle: Transitional behavior with strong upper mantle and upper crust but weak lower crust, resulting in dual surface wavelengths as in ridge belts. Bottom: "Late" (<0.5-1 b.y.), cold Venus with strong crust and upper mantle, long-wavelength surface deformation (Artemis Chasma).
Reviewed the formation and evolution of the crust of Venus and calculated that the contemporary rate of crustal production on Venus is comparable to the intraplate crustal-formation rate of Earth. (Grimm and Hess, 1997)

Episodic resurfacing of Venus (at intervals of ~0.5-1 b.y.) is characterized by generation of new tholeiitic crustal plateaus and volcanic plains. During quiescent intervals, volcanism is dominated by alkali basaltic shields. From Grimm and Hess (1997).