Growth of Planetary Crusts
Abstract
The planets and satellites of the Solar System show much diversity, but most have formed crusts which differ substantially from their bulk compositions. Three principal types of crust may be broadly distinguished: primary, formed after accretional heating (e.g., lunar highlands); secondary, formed following partial melting in planetary mantles (e.g., lunar maria, terrestrial oceanic crust); and tertiary, formed by processing of secondary crusts, of which the continental crust of the Earth is the only identifiable example. Crustal growth before 3800 m.y. was complicated by the heavy planetesimal bombardment: active erosion on the Earth is likely to have destroyed the brecciated rubble resulting from over 200 Mare Orientale-scale events in this period. The Mercurian crust is probably primary, perhaps analogous to the lunar highlands. In contrast, the observable Martian and Venusian crusts are secondary, dominated by basaltic volcanism. The icy crusts of the satellites of the outer planets are mixtures of both primary and secondary crusts, with complex histories. Ganymede is of special interest in displaying a secondary (grooved terrain) water ice crust which has split an older more heavily cratered, possibly primary crust. Slight expansion has resulted probably from polymorphic transitions from high density ice VIII to low density ice I. The primary lunar crust, 12% of lunar volume, grew in 10 8 years; secondary crusts derived by partial melting of mantles grow at a much slower rate—total production of terrestrial oceanic crust over 4000 m.y. is only 2% of planetary volume, whereas terrestrial continental crustal growth is even slower, producing over the same period a volume only about 0.33% that of the Earth. Crustal growth on the other planets appears to be an irreversible process, without evidence of recycling. No evidence for massive planetary expansion, as required by expanding earth hypotheses, is apparent on the other planets or satellites of the Solar System.
- Publication:
-
Tectonophysics
- Pub Date:
- 1989
- DOI:
- 10.1016/0040-1951(89)90151-0
- Bibcode:
- 1989Tectp.161..147T
- Keywords:
-
- PLANETS;
- CRUST;
- BOMBARDMENT;
- EROSION;
- VOLCANISM;
- SATELLITES;
- ORIGIN;
- ICE;
- FORMATION;
- CRATERING;
- MOON;
- MERCURY (PLANET);
- MARS;
- VENUS;
- JUPITER;
- GANYMEDE;
- COMPARISONS;
- EARTH;
- EVOLUTION;
- TIMESCALE;
- MARIA;
- VOLUME;
- MODELS;
- RECYCLING;
- PRODUCTION RATE