THERMAL EVOLUTION OF MERCURY: RECONCILING EARLY VOLCANISM, TECTONISM AND MAGNETISM (Invited Presentation)

Thermal evolution models for Mercury are challenged to reconcile three characteristics of the planet’s early geologic record. First, the planet is marked by widespread effusive volcanism to produce a crust ~20 – 60 km thick by ~4-3.5 Ga. Second, Mercury’s surface is characterized by extensive tectonic structures indicative of crustal shortening, resulting from 1-10 km of radial contraction during secular cooling of the planet. Cross-cutting relationships with craters suggest that these shortening structures began to form at ~3.9 Ga, at a rate that then monotonically declined to the present day. Third, crustal magnetic fields suggest a core dynamo was active at ~4-3.5 Ga. The driving mechanism for an ancient core dynamo has remained unexplained.

Here, we revisit the thermal history of Mercury, and incorporate an improved parameterization of the production and advection to the surface of buoyant partial melt to produce the planet’s thick basaltic crust. Incorporating mantle melting and crustal differentiation produces a strong mantle cooling effect that both favors an ancient core dynamo and explains the contractional evolution of the planet. Therefore, we develop a self-consistent model for Mercury’s early evolution and, more generally, propose an approach to assess the volcanic control over the evolution of any terrestrial body.