Venera 8 landing site geology revisited

Photogeologic mapping of the Magellan images of the Venera 8 site showed that practically all geologic units of this area correlate with the geologic units distinguished by Basilevsky and Head [1995a, b] in many other regions of Venus; however, areal abundance of the units in different areas may significantly differ. In particular, an anomalously high abundance of small volcanic shields was found in the landing site area and especially in the landing circle thus suggesting that the material sampled by the Venera 8 could represent these shields. The formation of shield fields, instead of vast basaltic floods more typical for Venus, is believed to be due to low magma replenishment rates [Crumpler et al., 1997]. These conditions might favor intra-chamber magma differentiation and/or contamination in the crustal material, thus being a cause of the enrichment of the material sampled by the Venera 8 in K, U, and Th. This conclusion is very tentative, and a possible petrologic link between the presence of shield fields in the landing site and the nontholeiitic character of the sampled material demands further studies. The observed correlation between the high abundance of small volcanic shields in the landing area and the nontholeiitic character of the sampled material implies that other small shield field localities on Venus could be possible sites of high-K nontholeiitic materials too. The Venera 8 landing site should be considered as one of the potential targets for future missions to Venus designed to study the surface geochemistry of different geologic units.