Physics
Scientific paper
May 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999icar..139...32k&link_type=abstract
Icarus, Volume 139, Issue Icarus, pp. 32-39.
Physics
10
Scientific paper
From several indicators, Venus has had a low level of tectonism and volcanism, compared to Earth, since resurfacings 500-1000 My ago. This behavior is generally ascribed to Venus having a very dry upper mantle and crust. Most indicators constrain only the last ~20% of Venus's evolution. Consistent with the dryness-leading to a stiffer, more impenetrable lithosphere, thence smaller length scale convection and smaller percent partial melts-is the deficiency of ^40 Ar in the atmosphere: 24(+/-10)% of the generated ^40 Ar, based on an average K/U of 7220(+/-1220) and primordial mantle abundance 21(+/-3) ppb of U (contrasting to 52+/-9% for the Earth). This potassium/argon constraint applies to the entire history of Venus. Water must have been expelled from the upper mantle within the first few 100 My, since all argon would have been expelled at the same time. The condition that the upper mantle must have been dry throughout Venus history also favors episodic overturns, in which most of the argon now in the atmosphere would have been outgassed. U abundances at the lander sites indicate partial melts of about 4%. If we assume the frequency of episodes declined with the rate of heat generation, then there have been eight, the most recent at about 0.75 Ga. Each episode scavenged the K+Ar from 2-2.5% of the mantle and produced about 1-km average thickness of resurfacing. The 3.3 ppb of radiogenic argon in the atmosphere sets an upper limit on the potassium in the crust, and hence the crustal thickness: 22+/-10 km; assuming a 10-km decay depth, it also implies 1.0% average surface density of K_2O. The present heat delivery from the mantle of this model is 24 mW/m^2, about 20% higher than the upper limit for stagnant lid convection (C. C. Reese et al. 1998, J. Geophys. Res. 103, 13,643-13,657). Reductions of the mantle U and K/U and increase of the atmospheric argon by one standard deviation each would reduce the heat delivery to 16 mW/m^2.
No associations
LandOfFree
Constraints on Venus Evolution from Radiogenic Argon does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Constraints on Venus Evolution from Radiogenic Argon, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Constraints on Venus Evolution from Radiogenic Argon will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1377176