Planetary basalts: Chemistry and petrology

Abstract

Basaltic rocks have continued to receive considerable attention in the period 1975‐1978. This is largely due to the recognition of their effectiveness as probes of planetary interiors. Basalts that have formed by partial melting in planetary interiors and have been delivered to the planetary surface without gain or loss of material carry clues to: (1) the formation and earliest differentiation history of the terrestrial planetary bodies, (2) residual mineralogy and phase chemistry of the source region, (3) temporal evolution of the source region, (4) depth of the source region, (5) the thermal history of the planetary body, and (6) the intensive thermodynamic values that obtained during basalt petrogenesis. Because basalts are key indicators of planetary evolution, an experimental project, entitled “Basaltic Volcanism on the Terrestrial Planets Studies Project,” was organized by the Lunar and Planetary Institute, Houston, Texas. The project, funded in part by NASA, is a pilot project in comparative planetology involving approximately 80 scientists representing a variety of disciplines including observational astronomy, cosmochemistry, geochemistry, geology, geophysics, mineralogy, petrology and volcanology. The project was initiated in 1977 and will culminate in 1980 with a book entitled “Basaltic Volcanism on the Terrestrial Planets,” which will summarize the results of the project. The major advances in our understanding of terrestrial basalt petrogenesis that have occurred in the past four years are to a large extent a consequence of the Deep Sea Drilling Project's crustal drilling program. Deeper penetration and improved recovery on Legs 34, 37, 45‐46, 49, 51‐53, and 55 have provided spatial and temporal controls on sampling of the oceanic crust with a much greater areal coverage than can be achieved by submersibles.

Radiogenic isotopes: the case for crustal recycling on a near-steady-state no-continental-growth Earth

“…they demand inhibition of crustal differentiation processes for the first, and presumably hottest, 1 Ga of Earth history. The formation and differentiation of the meteorite parent bodies and the moon nearly 4.6 Ga ago is an undisputed fact to cosmochemists (see, for example, Papike & Bence 1979). Rapid accretion of the Earth (Wetherill 1971(Wetherill , 1972 and presence of short-lived nuclear species like 26A1 at the time of planet accretion (Lee et al 1977) provide an in hot-Earth evolutionary models.…”