TRACE ELEMENTS IN PELITIC ROCKS

Abstract

The range in composition of pelitic shales, schists, and gneisses has been investigated for a number of trace elements and has been compared with previous work on similar materials. An interesting distribution law has appeared (logarithmic), namely that the range in composition extends from zero to about twice the mean value for almost every element. The probability that a rock will fall outside this range is low. Fairly good positive correlation has been found between chromium, vanadium, and nickel, with cobalt participating to some extent. All these elements tend to be high or low together, but the most regular correlation is between nickel and chromium. In general, the content of the trace elements studied is what would be expected from erosion and transfer from the average igneous rock, with no loss or gain on the way. Copper is an exception with a clear loss, whereas lithium and strontium show an increase. Comparison with suites of silicic and basic igneous rocks emphasizes some differences between these and pelitic rocks, but also shows that in many cases the composition fields overlap extensively. Certain revisions in crustal abundance (average igneous rock) figures are suggested.