Stratigraphic and geographic distribution of steep-sided domes on Venus: Preliminary results from regional geological mapping and implications for their origin

Analysis of the stratigraphic position of 44 steep-sided domes in a global band of C1-MIDRs at 30 degrees N latitude shows that in a region representi ng over 11% of the surface of Venus, the vast majority of steep-sided domes are closely associated stratigraphically with shield plains (Psh), a unit characterized by a very high abundance of small shields of apparent basalti c extrusive origin. Previously reported heterogeneities in areal and altitu de distribution are now more plausibly interpreted in terms of formation in association with this unit and burial by subsequent regional plains units. Measurement of abundances of steep-sided domes presently exposed in shield plains and extrapolation to areas below younger units suggest that over a thousand of these features may have formed originally. Interpretation of th e mode of formation of the steep-sided domes in the context of these new da ta favors hypotheses for their origin which call on remelting of basaltic c rust to produce more silica-rich magmas. Occurrences of some steep-sided do mes in association with summits of large shields (e.g., Tepev Mons and Sapa s Mons) indicate that other mechanisms of dome formation (e.g., evolution o f magma reservoirs) have also operated at other times in the history of Ven us.