Abstract: Active Tectonics on Venus: Evidence from Coronae and Chasmata

Donna M. Jurdy

Venus, the twin planet of Earth, was radar mapped by Magellan in 1990-1992 with nearly complete coverage. Although earth-like plate tectonics are not evident and horizontal motions are limited, Venus exhibits tectonic activity. Chasmata, linear to arcuate troughs extending thousands of kilometers, show the greatest relief, as much as 7 km over a horizontal distance of 30 km, and may be sites of active rifting. Coronae, perhaps unique to Venus, are circular uplifts hundreds of kilometers across surrounded by ridges. The closest analog may be Earth's hot spots. The distribution of Venus' coronae and impact craters are related to chasmata. Coronae are almost twice as dense near the chasmata as a random set of the same size. Of the various morphological types of coronae, the adial-concentric (dominated by radial faults) and multiple (several linked features) are even more highly concentrated near chasmata, whereas the concentric-caldera (collapse) type are absent near the chasmata. Venus has nearly 1000 impact craters, mostly unmodified, nearly randomly distributed, and the density consistent with a mean planetary surface age of 500 Ma. When distributions are compared with random sets, there is a deficit of about 15-20 craters close to the chasmata. Craters modified by tectonism and volcanism tend to be near the rift zones, and their distribution closely resembles that of the coronae. The higher proportion of tectonized, and especially volcanically-embayed, craters within 5-10° of the chasmata, is about the fraction that would be expected from modificat on of the full set of craters within a band 100-200 km about the chasmata. Craters and coronae fill disjoint regions that are more connected than regions of randomly assigned points. This suggests that the volcano-tectonic process creating coronae may be the same one destroying craters.

AAPG Search and Discovery Article #90948©1996-1997 AAPG Distinguished Lecturers