The role of plains volcanism in the formation of Mercury's crust

Details The role of plains volcanism in the formation of Mercury's crust The role of plains volcanism in the formation of Mercury's crust

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p43e..09d&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #P43E-09

Mathematics

Logic

[5455] Planetary Sciences: Solid Surface Planets / Origin And Evolution, [5464] Planetary Sciences: Solid Surface Planets / Remote Sensing, [5480] Planetary Sciences: Solid Surface Planets / Volcanism, [6235] Planetary Sciences: Solar System Objects / Mercury

Scientific paper

Mercury has experienced widespread resurfacing. Plains cover much of the surface, and no terrain is as heavily cratered as the lunar highlands. Plains formation appears to have occurred throughout much of Mercury's history. Intercrater plains formation extended through the period of heavy bombardment, and smooth plains formation may have continued into the second half of solar system history, with a continuum of ages in between. However, the mode of formation of these plains is not clear in all cases. Strong evidence for a volcanic origin of many plains units indicates that volcanism played an important role in shaping Mercury's crust, but many plains units lack clear evidence for source regions, flooding or embayment relationships, or color boundaries, suggesting that alternate mechanisms of formation are possible (e.g., impact-produced melt or fluidized basin ejecta). We focus on the origin of these more ambiguous plains units, particularly the intercrater plains, to understand their role in crustal formation. Preliminary maps of plains covering ~55% of Mercury were produced from Mariner 10 and MESSENGER flyby data. We have extended these maps with global orbital image mosaics (monochrome at 250 m/pixel; color at 1 km/pixel) and targeted high-resolution images (up to ~10 m/pixel). We find many regions where morphologic boundaries between plains units are gradational and no difference in spectral properties is detected. The distinction between such units appears to be largely the enhanced population of secondary craters in some locations, which destroy evidence of an original morphologic boundary or mask the original character of the unit. Many of these units also lack a clear association with any large basin, suggesting that an origin as basin ejecta is unlikely. Thus, some portion of more heavily cratered plains units may simply be degraded versions of smooth plains and share a common volcanic origin. We also explore the origin of smooth plains units contained wholly within impact craters. Impact melt production is predicted to be 14 times higher on Mercury than on the Moon, consistent with initial observations of comparatively larger melt volumes. A quantitative comparison of observed melt volumes and model predictions will help to separate plains produced by the primary cratering events from later volcanic activity in cases where morphologic evidence is ambiguous. A better understanding of the various modes of plains formation throughout Mercury's history aids in understanding the nature of Mercury's crust. The geologic and spectral evidence is consistent with a crust shaped by volcanic eruptions through time, rather than a primitive crust such as that produced by a global magma ocean.

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