Viscosity of the Mercurian Magma Ocean: Implications of Sulfur-Free and Sulfur-Bearing Magma Oceans for Differentiation and Crustal Petrogenesis

Conference · Fri Mar 20 04:00:00 EDT 2020

OSTI ID:1768443

Mouser, M. D.; Dygert, N.; Hrubiak, R.; Kono, Y.; Shen, G.; Anzures, B. A.; Grambling, N. L.; Parman, S. W.

Mercury is believed to have had a magma ocean in its early evolution whose solidification dynamics contributed to the planet’s present day surface composition. The surface is characterized by two main geological provinces; the Northern Smooth Plains (NSP),and the Heavily Cratered Terrain (HCT) and Intercratered Terrian (IcT). These provinces are defined by the differences in morphology, composition, and age. The NSP are located in the northern hemisphere and have low Mg/Si, Ca/Si, and S/Si ratios and high Al/Si ratios, and are compositionally analogous to a magnesian alkali basalt. The HCT/IcT cover the majority of the planet and are older than the NSP, and are characterized by high Mg/Si, Ca/Si, and S/Si ratios and low Al/Si ratios. The dichotomy in surface composition motivates the study into the structure of the mantle as a product of magma ocean solidification. Two important and interrelated parameters that determine the efficiency of crystal fractionation during magma ocean solidification are convection vigor and viscosity of the magma ocean. Crystal suspension in a cooling magma ocean could be efficient or inefficient which suggests two end member possibilities for magma ocean solidification. The first is the formation of a compositionally stratified mantle reflecting a cumulate sequence produced along a fractional liquid line of descent. The second is the formation of a well-mixed, batch crystallized mantle by high viscosity and/or vigorously convecting magma ocean. Determining which of these end members, or where on the spectrum between them is most relevant to Mercury’s magma ocean can be experimentally constrained through high P-T falling-sphere viscometry experiments.

• Research Organization: Argonne National Laboratory (ANL)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA) - Office of Experimental Sciences (NA-113); USDOE Office of Science - Office of Basic Energy Sciences - Scientific User Facilities Division
• DOE Contract Number: AC02-06CH11357
• OSTI ID: 1768443
• Country of Publication: United States
• Language: English