Adcumulus growth of anorthosite at the base of the lunar crust
Abstract
Unzoned plagioclase crystals imply isothermal adcumulus solidification and cannot result from reactive equilibrium crystallization in dry magma. Extraction of latent heat upward through lunar crust results only in chilled or cotectic mesocumulate rocks, not anorthosite or adcumulates. Adcumulus growth of anorthosite requires exchange of refractory for incompatible components between the site of crystal growth and nearby fresh magma, and the extraction of calories from growing crystals to the flowing, supercooled magma. Supercooling can be acquired at remote sites like upwellings and then be carried by convective flow beneath crust which is accreting plagioclase by flotation or in situ nucleation and growth. If transport distances are larger than the scale of rockbergs, cotectic norites and troctolites may result. Impact-induced upwellings tend to promote growth of buoyant rather than mafic crust, hence impacts are not solely destructive.
- Publication:
-
Lunar and Planetary Science Conference Proceedings
- Pub Date:
- 1982
- DOI:
- 10.1029/JB087iS01p00A10
- Bibcode:
- 1982LPSC...13...10M
- Keywords:
-
- Anorthosite;
- Lunar Crust;
- Lunar Geology;
- Lunar Soil;
- Basalt;
- Cooling;
- Crystallization;
- Latent Heat;
- Magma;
- Olivine;
- Pressure Effects;
- Pyroxenes;
- Solidification;
- Lunar and Planetary Exploration;
- Moon Crust:Formation;
- ADCUMULATES;
- ANORTHOSITES;
- CRUST;
- MOON;
- HIGHLANDS;
- PLAGIOCLASE;
- THERMAL PROPERTIES;
- ANALYSIS;
- FORMATION;
- DIAGRAMS;
- ANT;
- COMPOSITION;
- MODAL ANALYSIS;
- MINERALOGY;
- MAGMAS;
- PHOTOMICROGRAPHS;
- COOLING;
- DIFFUSION;
- GRADIENTS;
- Moon;
- Mineralogy;
- Petrology;
- and Crystal Chemistry: Paragenesis;
- petrography;
- and petrogenesis;
- Planetology: Interior of moon (tectonics;
- force fields;
- composition;
- etc.)