Date: Monday 02-Nov-2020
Time: 11:15-12:15
Location: Online via Zoom (link sent out to the PALS distribution list prior to the talk)
Speaker: Dan Moriarty (GSFC)
Title: Evidence for a Stratified Upper Mantle Preserved within the Moon's South Pole - Aitken Basin
Like the Earth, the Moon is layered into a crust and mantle. The Moon's layering was shaped by an early global melting event known as the "Lunar Magma Ocean." As the magma ocean solidified, dense minerals sank to form the mantle, while less-dense minerals floated to form the crust. Elements such as thorium do not easily incorporate into mineral structures, and remain in the liquid. Because of this, a thorium-rich dreg layer was sandwiched between the crust and mantle. These dregs are very dense and are expected to sink into the lower mantle during or soon after crystallization. We have discovered that the Moon's largest and oldest impact basin excavated material from this dense, thorium-rich layer before it sank. The exposed material was then diluted and obscured by four billion years of impactcratering and volcanic eruptions. However, we have identified several pristine exposures created by recent craters. The impact basin also melted rocks from greater depths than the rocks it ejected. These melted rocks exhibit a much different composition. This indicates that the lunar upper mantle included two compositionally-distinct layers that were exposed in different ways by this large impact event. These results have important implications for understanding the formation and evolution of the Moon.
For further information contact PALS coordinator Dr. Lori Feaga at feaga@astro.umd.edu or (301)-405-1383.
SPECIAL ACCOMMODATIONS:Special accommodations for individuals with disabilities can be made by calling (301) 405-3001. It would be appreciated if we are notified at least one week in advance.
