On the potential for lunar highlands Mg-suite extrusive volcanism and implications concerning crustal evolution

Content Provider	Semantic Scholar
Author	Prissel, Tabb C. Whitten, Jennifer L. Parman, Stephen W. Head, James W.
Copyright Year	2016
Abstract	Abstract The lunar magnesian-suite (Mg-suite) was produced during the earliest periods of magmatic activity on the Moon. Based on the cumulate textures of the samples and a lack of evidence for Mg-suite extrusives in both the sample and remote sensing databases, several petrogenetic models deduce a predominantly intrusive magmatic history for Mg-suite lithologies. Considering that ∼18% of the lunar surface is covered by mare basalt flows, which are substantially higher in density than estimated Mg-suite magmas (∼2900 versus ∼2700 kg/m3), the apparent absence of low-density Mg-suite volcanics is surprising. Were Mg-suite magmas predominantly intrusive, or have their extrusive equivalents been covered by subsequent impact ejecta and/or later stage volcanism? If Mg-suite magmas were predominantly intrusive, what prevented these melts from erupting? Or, if they are present as extrusives, what regions of the Moon are most likely to contain Mg-suite volcanic deposits? This study investigates buoyancy-driven ascent of Mg-suite parental melts and is motivated by recent measurements of crustal density from GRAIL. Mg-suite dunite, troctolite, and spinel anorthosite parental melts (2742, 2699, and 2648 kg/m3, respectively) are considered, all of which have much lower melt densities relative to mare basalts and picritic glasses. Mg-suite parental melts are more dense than most of the crust and would not be expected to buoyantly erupt. However, about 10% of the lunar crust is greater in density than Mg-suite melts. These areas are primarily within the nearside southern highlands and South Pole-Aitken (SP-A) basin. Mg-suite extrusions and/or shallow intrusions were possible within these regions, assuming crustal density structure at >4.1 Ga was similar to the present day crust. We review evidence for Mg-suite activity within both the southern highlands and SP-A and discuss the implications concerning crustal evolution as well as Mg-suite petrogenesis. Lower crustal densities measured by GRAIL are consistent with the lack of observed Mg-suite extrusives. If Mg-suite extrusive volcanism was prevented by the low density of the crust, it would suggest the lunar crust was fractured shortly after solidification (>4.3 Ga). The thermal- and stress-state of the lunar crust may have also inhibited Mg-suite extrusion.
Starting Page	319
Ending Page	329
Page Count	11
File Format	PDF HTM / HTML
DOI	10.1016/j.icarus.2016.05.018
Volume Number	277
Alternate Webpage(s)	http://www.planetary.brown.edu/pdfs/4978.pdf
Language	English
Access Restriction	Open
Content Type	Text
Resource Type	Article