No abstract

Major and trace element compositions of basalts from the lower part of Hole 504B indicate their cogenetic nature. The cored sequence of interlayered pillow lavas and massive lava flows was produced by eruption of lavas, slightly variable in composition. Plagioclase and olivine crystallization in a shallow magma chamber, followed by small-scale fractionation at higher levels, is responsible for these variations. Except in highly fractured zones within the basement, there are systematic variations in the style and degree of rock alteration with depth. Trace element characteristics of altered rocks and secondary minerals indicate that progressive changes in sea water composition occurred as it reacted with basaltic crust.

A study made on the geochemistry of gaseous products for the Tolbachik basaltic eruption in Kamchatka (1975–1976) has shown that magmatic gases, submicron ash, and aerosols are enriched in chalcophile elements. Active volcanism represents one of the main sources. The annual input of chalcophile elements from the volcanoes of the world to the atmosphere is found to be in agreement with the amounts brought into the oceans by the water‐soluble component of the river runoff.