Magma Channelization on the Earth and Planets: Ongoing Reevaluation of Formation Mechanism

Abstract:

Ever since the discovery of the lunar sinuous rilles at the dawn of the Space Age, geologists have speculated about the processes that could form such long, channel-like volcanic conduits. The initial studies of the lunar sinuous rilles and martian lava channels in the 1960s and 1970s coincided with the discovery of terrestrial komatiites and recognition of komatiite-hosted magmatic ore deposits, which are located at the base of channels resulting from thermomechanical erosion of sulfide-rich footwall rocks by low-viscosity, turbulent komatiite lavas. Through the 1970s-1990s, most attention was focused on 1.5D analytical-numerical modeling of thermal erosion by lava to produce these channels in various planetary settings. Part of this focus on modeling thermal erosion was motivated by the inferred composition of these lavas, i.e., ultramafic and emplaced by low-viscosity, likely turbulent flows. This contrasts with active terrestrial basaltic volcanism, in which more viscous basalt lava channels appear to be dominated by constructional mechanisms (although thermal erosion by modern basalt lavas has been documented, but at much smaller scales than observed beneath komatiites or modeled for planetary channels). In recent years new studies have been initiated to more fully investigate the constructional and erosional mechanisms for lava channel formation, taking advantage of new investigative technologies and new planetary data. New 2.5D modeling approaches under development that utilize fully numerical methods should provide greater insights by allowing more realistic parameterizations.