A reappraisal of the petrogenesis of Apollo 17 lunar dunites 72415-72417: Relics of the deep lunar mantle?OPEN ACCESS 

· by · in , ,

K. K. Bhanot, H. Downes, B. G. Rider-Stokes, E. S. Jennings, M. Anand, J. F. Snape, M. J. Whitehouse

MAPS, Version of Record online: 13 November 2024

LINK (OPEN ACCESS)
PDF (OPEN ACCESS)

“Lunar dunite samples 72415–72417, collected by Apollo 17 astronauts from a South Massif boulder in the Taurus–Littrow valley, are crushed breccias composed of several types of olivine- and clinopyroxene-rich clasts, some of which are (or contain) intergrowths of Cr-spinel and pyroxenes or plagioclase. Among the clasts are ellipsoidal symplectites of Cr-spinel and pyroxene, up to 300 μm in diameter, which have bulk compositions consistent with those of olivine + garnet. These symplectites are inferred to originally have been olivine + Mg-Cr-rich garnet (pyrope–uvarovite) that formed deep in the lunar mantle and were subsequently transported closer to the lunar surface (spinel- or plagioclase-peridotite stability fields), perhaps during gravitationally driven overturn. Abundant microsymplectite (30 μm diameter) intergrowths of Cr-spinel and pyroxene inside olivine grains, many associated with inclusions of plagioclase and augite, formed during a later decompression event (perhaps excavation to the lunar surface). These inclusions have not previously been recorded in these samples and could be responsible for earlier reports of igneous zoning in olivine. Electron backscatter diffraction data show evidence of high shock pressures (>50 GPa), which are inferred to have occurred during the impact which excavated the dunites from the shallow anorthite-bearing lunar mantle. Apatite veinlets post-date the shock metamorphism and have been dated to 3983 ± 72 Ma and 3913 ± 118 Ma by the U–Pb method. This age is consistent with that inferred for the Imbrium impact basin, suggesting that the dunite was finally excavated from the mantle during formation of the Imbrium basin.”

Related posts (automatically generated):

  1. Nano- and micro-structures in lunar zircon from Apollo 15 and 16 impactites: implications for age interpretationsOPEN ACCESS 
  2. Calcium Isotopic Composition of the Lunar Crust, Mantle, and Bulk Silicate Moon:A Preliminary Study
  3. Spinel assemblages in lunar meteorites Graves Nunataks 06157 and Dhofar 1528: Implications for impact melting and equilibration in the Moon’s upper mantle
  4. An analysis of Apollo lunar soil samples 12070,889, 12030,187, and 12070,891: Basaltic diversity at the Apollo 12 landing site and implications for classification of small-sized lunar samples.
  5. A New Lunar High-Ti Basalt Type Defined from Clasts in Apollo 16 Breccia 60639
  6. Apollo 12 breccia 12013: Impact-induced partial Pb loss in zircon and its implications for lunar geochronology
  7. Petrographic and geochemical analysis of lunar meteorite NWA 11788: Parallels with Luna 20 and the Apollo magnesian granulitesOPEN ACCESS 
  8. Mineralogy and petrogenesis of lunar magnesian granulitic meteorite Northwest Africa 5744OPEN ACCESS 
  9. Cosmic ray effects on the isotope composition of hydrogen and noble gases in lunar samples: Insights from Apollo 12018OPEN ACCESS 
  10. Assessing the shock state of the lunar highlands: Implications for the petrogenesis and chronology of crustal anorthositesOPEN ACCESS 
Tags: , , , , ,