GEOLOGICAL EVOLUTION OF THE TERRESTRIAL PLANETARY BODIES: CLUES TO THE ORIGIN OF PLATE TECTONICS (Invited Presentation)

Two parallel revolutions occurred in the last half-century: 1) development of the global plate tectonics paradigm and an understanding of Earth as a planet, and 2) intensive exploration of the Moon and terrestrial planets, and an appreciation of Earth as a member of a family of Solar System objects. Among results of these revolutions: 1) The Earth is the only terrestrial planetary body (TPB) known to have currently active plate tectonics; 2) The mode of origin and onset timing of Earth plate tectonics are currently unknown; 3) Smaller TPB (Moon, Mercury, Mars) have a high surface area/volume ratio and are thus efficient radiators of internally generated heat, conducting through the outer thermal boundary layer (the lithosphere), and being lost to space; 4) The efficient cooling of smaller terrestrial planetary bodies results in rapid lithospheric thickening and increasing difficulties in initiating subduction (the current lunar lithosphere is ~60% of the Moon’s radius); 5) For these reasons, the Moon, Mercury and Mars have globally continuous and unsegmented lithospheres and are known as “one-plate planets”; 6) One-plate planets preserve the record of early solar system history (e.g., primary crust formation, impact crater and basin formation and evolution, and significant volcanic resurfacing); 7) Vertical tectonics (e.g., mantle convective upwelling and lithospheric loading), and global stress state changes related to thermal evolution (global heating, then cooling) dominate one-plate-planet tectonic evolution; 8) Any “plate tectonics” on these bodies must have occurred as part of magma ocean cooling and solidification, or prior to the time of the large-cratering surface record, which is not tectonically disrupted; 9) These smaller bodies offer potential clues to forces that might have initiated plate tectonics on Earth (e.g., large impact basins, vertical crustal accretion and subsequent density instabilities, rapid global cooling and circumferential shrinkage); 10) Venus, the planet most Earth-like in size, density and position in the Solar System, currently has no active plate tectonics; 11) Could Venus have episodic plate tectonics, or have evolved from plate tectonics to a stagnant lid, one-plate planet?; 12) The Venus geological record is examined for clues to the answer to this question.