Title: Experimental constraints on the rheology, eruption and emplacement dynamics of analog lavas comparable to Mercury's northern volcanic plains,
Abstract: We present new viscosity measurements of a synthetic silicate system
considered an analogue for the lava erupted on the surface of Mercury. In
particular, we focus on the northern volcanic plains (NVP), which correspond to
the largest lava flows on Mercury and possibly in the Solar System.
High-temperature viscosity measurements were performed at both superliquidus
(up to 1736 K) and subliquidus conditions (1569-1502 K) to constrain the
viscosity variations as a function of crystallinity (from 0 to 28\%) and shear
rate (from 0.1 to 5 s 1). Melt viscosity shows moderate variations (4-16 Pa s)
in the temperature range of 1736-1600 K. Experiments performed below the
liquidus temperature show an increase in viscosity as shear rate decreases from
5 to 0.1 s 1, resulting in a shear thinning behavior, with a decrease in
viscosity of 1 log unit. The low viscosity of the studied composition may
explain the ability of NVP lavas to cover long distances, on the order of
hundreds of kilometers in a turbulent flow regime. Using our experimental data
we estimate that lava flows with thickness of 1, 5, and 10 m are likely to have
velocities of 4.8, 6.5, and 7.2 m/s, respectively, on a 5 degree ground slope.
Numerical modeling incorporating both the heat loss of the lavas and its
possible crystallization during emplacement allows us to infer that high
effusion rates (>10,000 m3/s) are necessary to cover the large distances
indicated by satellite data from the MErcury Surface, Space ENvironment,
GEochemistry, and Ranging spacecraft.