Gravitational Separation of Quenching Crystals: A Cause of Chemical Differentiation in Lunar Basalts
Abstract
The low viscosity of lunar lavas allowed skeletal quenching crystals, which formed during post-eruption cooling of the flows, to sink and accumulate despite the low gravitational acceleration. The crystals which sank were not in chemical equilibrium with the liquid. Hand specimen bulk compositions are related to each other by differential movement of the materials composing the cores and rims of the skeletal 'phenocrysts', and not by any equilibrium chemical process. Crystal sinking must have occurred, and cumulates must have formed. Mafic hand specimens, consisting of skeletal phenocrysts in a more feldspathic groundmass, represent the cumulus enriched material and not the original liquids. The lava compositions were much more feldspathic, and were controlled by fractional crystallization at low pressures. The effects of such fractionation must be considered and, in most cases, restored before valid petrogenetic inferences about the mineralogy and chemistry of the lunar interior can be drawn.
- Publication:
-
Philosophical Transactions of the Royal Society of London Series A
- Pub Date:
- March 1977
- DOI:
- 10.1098/rsta.1977.0054
- Bibcode:
- 1977RSPTA.285..177O
- Keywords:
-
- Basalt;
- Crystal Growth;
- Lunar Crust;
- Lunar Evolution;
- Lunar Gravitational Effects;
- Lunar Rocks;
- Chemical Composition;
- Lava;
- Petrography;
- Selenology;
- Lunar and Planetary Exploration;
- BASALT;
- CRYSTAL GROWTH;
- LUNAR CRUST;
- LUNAR EVOLUTION;
- LUNAR GRAVITATIONAL EFFECTS;
- LUNAR ROCKS;
- CHEMICAL COMPOSITION;
- LAVA;
- PETROGRAPHY;
- SELENOLOGY