Cordierite-Spinel Troctolite, a New Magnesium-Rich Lithology from the Lunar Highlands
Abstract
A clast of spinel troctolite containing 8 percent cordierite (Mg2Al4Si5O18) has been identified among the constituents of Apollo 15 regolith breccia 15295. The cordierite and associated anorthite, forsteritic olivine, and pleonaste spinel represent a new, Mgrich lunar highlands lithology that formed by metamorphism of an igneous spinel cumulate. The cordierite-forsterite pair in the assemblage is stable at a maximum pressure of 2.5 kilobars, equivalent to a depth of 50 kilometers, or 10 kilometers above the lunar crust-mantle boundary. The occurrence of the clast indicates that spinel cumulates are a more important constituent of the lower lunar crust than has been recognized. The rarity of cordierite-spinel troctolite among lunar rock samples suggests that it is excavated only by large impact events, such as the one that formed the adjacent Imbrium Basin.
- Publication:
-
Science
- Pub Date:
- February 1989
- DOI:
- 10.1126/science.243.4893.925
- Bibcode:
- 1989Sci...243..925M
- Keywords:
-
- Cordierite;
- Lithology;
- Lunar Geology;
- Lunar Surface;
- Magnesium;
- Spinel;
- Apollo 15 Flight;
- Breccia;
- Highlands;
- Lunar Crust;
- Recrystallization;
- Regolith;
- Lunar and Planetary Exploration; Moon;
- MOON;
- HIGHLANDS;
- TROCTOLITE;
- MAGNESIUM;
- LITHOLOGY;
- SAMPLES;
- LUNAR;
- SPINEL;
- CORDIERITE;
- BRECCIAS;
- APOLLO 15;
- 15295;
- MINERALOGY;
- ORIGIN;
- COMPOSITION;
- FORMATION;
- METAMORPHISM;
- CLASTS;
- CRUST;
- DEPTH;
- ABUNDANCE;
- PHOTOMICROGRAPHS;
- LABORATORY STUDIES;
- CRYSTALLIZATION;
- CUMLATES