Volcanism on Mercury Paper by Head et. al Presentation by Nicole Bonneau

Where the data came from  Mariner 10 flybys in the 1970s showed that there were smooth areas with very few craters  When MESSENGER went to Mercury in 2008 it determined that the plains were lava flows

MESSENGER findings  These flows are younger than the surrounding areas and craters.  There are buried craters called ghost craters  The smooth plains sit above the older rougher plains  The color of the smooth plains is homogenous and differs from the surroundings  They cover about 4.7 x 10 6 km 2 or about 6% of the planet

Figure 1

What the ghost craters tell us  That the flow happened after the Bombardment period  How thick the flow is  Average between 1-2 kilometers and in some places it is thicker

Features of the flow  The plains have wrinkle edges and arches that are younger than the top layer of the plains  These smooth plains flowed over each other at different time intervals  There is no evidence that this is ejecta or impact melt sheets from a large impact

Figure 2

Using MDIS to discover the sources  Looked for source vents, edifices, and other lava flow features.  Pits were found (figure 3A) that were interpreted to be the source vents  Also, tear-drop shaped ridges look to be shaped by lava flowing underneath the surface

Figure 3

What do the vents mean?  Combined with the tear-drop escarpments they are consistent with rapid deposition of a high- temperature but low-viscosity flood basalt.

Differences of the plains  Figure 2A shows what looks to be a basin that was later filled with basalt  Figure 3C shows the edge a flow that was flowing across the land

How old are the plains?  When compared to the Caloris basin we can see that the plains are very similar in age  Unlike the Caloris basin, the northern plains were created independently of large cratering events  The frequency of large craters (>8km) on the plains, and also the Caloris basin, tells us that they were both formed at the end of the late heavy bombardment about billion years ago

Figure 4

Conclusions  These flows show that at the end of the late heavy bombardment period Mercury underwent an extensive melting of it’s mantle  This melting resulted in the eruption of high- temperature, low-viscous lava flows that gushed onto the crust at a very high rate

References J. W. Head et al., Science (2011). J. W. Head et al., Earth Planet. Sci. Lett. 285, 227 (2009). B. W. Denevi et al., Science 324, 613 (2009). D. M. Hunten, D. E. Shemansky, T. H. Morgan, in Mercury, F. Vilas, C. R. Chapman, M. S. Matthews, Eds. (Univ. of Arizona Press, Tucson, AZ, 1988), pp. 562 –612.