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Excavation Depths as Indications of Magnesium Spinel Formation via Impact Melting

Author: 
Mikala Garnier
Topic: 
Education & Public Outreach
Delivered As: 
Poster
Abstract Text: 

Pink-spinel anorthosite, recently found on the moon by the Moon Mineralogy Mapper (M3), has a very unique composition which consists of anorthosite, 20-30% mg-spinel, and less than 5% of mafic materials. The mg-spinel (Mg(Al2O4)) in this anorthosite requires certain conditions to occur, such as high pressures and high temperatures. The spinel’s composition can only be achieved by an interaction of a basaltic mix with the anorthositic crust. Such interactions have been hypothesized in four theories; volcanism, impactor remnants, excavation, and impact melting. Our research consists of analyzing 36 craters, 30 of which contained spinel in their central peaks. We calculated the excavation depth of each crater, checked for patterns in location and diameters, and looked for any correlation with our data and the proposed hypotheses. After analyzing and comparing our data to other research we found inconsistencies in the volcanism, impactor remnants, and excavation theories concerning excavation depths and pressure(>.5kbar) and temperature (1300˚C) constraints. Our data conflicts with the excavation theory because the excavation depths do not protrude deep enough to excavate magnesium spinels from the specified depths. Addressing the volcanism theory, we observed that there are no signs of volcanic activity in proximity to the mg-spinel deposits. The impactor remnants theory is unlikely because the spinel would be randomly distributed throughout the crater and ejecta blanket. Impact melting presents the ideal conditions for spinel to form in all excavation depths as long as the craters are located over a mafic intrusion (i.e dike swarm). As an impactor hits the lunar surface it creates the required pressures and heat to melt the anorthositic crust and the basaltic dikes under the surface. As this melt mixture crystallizes, the spinel is formed and then brought up through the central peak during the modification stage of the impact.

Co-Authors: 
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SSERVI Identifier: 
NESF2016-052

About SSERVI
Recognizing that science and human exploration are mutually enabling, NASA created the Solar System Exploration Research Virtual Institute (SSERVI) to address basic and applied scientific questions fundamental to understanding the Moon, Near Earth Asteroids, the Martian moons Phobos and Deimos, and the near space environments of these target bodies. As a virtual institute, SSERVI funds investigators at a broad range of domestic institutions, bringing them together along with international partners via virtual technology to enable new scientific efforts."