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Large Volcanic Rises on VenusLarge volcanic rises on Venus have been interpreted as hotspots, or the surface manifestation of mantle upwelling, on the basis of their broad topographic rises, abundant volcanism, and large positive gravity anomalies. Hotspots offer an important opportunity to study the behavior of the lithosphere in response to mantle forces. In addition to the four previously known hotspots, Atla, Bell, Beta, and western Eistla Regiones, five new probable hotspots, Dione, central Eistla, eastern Eistla, Imdr, and Themis, have been identified in the Magellan radar, gravity and topography data. These nine regions exhibit a wider range of volcano-tectonic characteristics than previously recognized for venusian hotspots, and have been classified as rift-dominated (Atla, Beta), coronae-dominated (central and eastern Eistla, Themis), or volcano-dominated (Bell, Dione, western Eistla, Imdr). The apparent depths of compensation for these regions ranges from 65 to 260 km. New estimates of the elastic thickness, using the 90 deg and order spherical harmonic field, are 15-40 km at Bell Regio, and 25 km at western Eistla Regio. Phillips et al. find a value of 30 km at Atla Regio. Numerous models of lithospheric and mantle behavior have been proposed to interpret the gravity and topography signature of the hotspots, with most studies focusing on Atla or Beta Regiones. Convective models with Earth-like parameters result in estimates of the thickness of the thermal lithosphere of approximately 100 km. Models of stagnant lid convection or thermal thinning infer the thickness of the thermal lithosphere to be 300 km or more. Without additional constraints, any of the model fits are equally valid. The thinner thermal lithosphere estimates are most consistent with the volcanic and tectonic characteristics of the hotspots. Estimates of the thermal gradient based on estimates of the elastic thickness also support a relatively thin lithosphere (Phillips et al.). The advantage of larger estimates of the thermal lithospheric thickness is that they provide an explanation for the apparently modest levels of geologic activity on Venus over the last half billion years.
Document ID
19970041182
Acquisition Source
Headquarters
Document Type
Contractor Report (CR)
Authors
Smrekar, Suzanne E. (Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA United States)
Kiefer, Walter S. (Lunar and Planetary Inst. Houston, TX United States)
Stofan, Ellen R. (Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA United States)
Date Acquired
September 6, 2013
Publication Date
January 1, 1997
Subject Category
Lunar And Planetary Exploration
Report/Patent Number
NAS 1.26:205865
NASA/CR-97-205865
Accession Number
97N32266
Funding Number(s)
CONTRACT_GRANT: NAS7-100
PROJECT: RTOP 889-62-02
CONTRACT_GRANT: NASw-4574
PROJECT: RTOP 151-01-70-59
CONTRACT_GRANT: NAGw-3814
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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