Geochemistry of the Igneous Rocks

Major and trace element analysis of 223 samples and 61 additional repeat analyses were made using a Philips 1220 X-ray fluorescence spectrometer.For the major elements, including sodium, 1.5 g of sample was fused into a glass disc with 3 g of lithium tetraborate and ground and polished to an optically flat surface.Trace element analyses were made on 3 g samples in pressed pellet form with a polyvinyl alcohol cement.Trace element analysis has so far been completed only for Rb, Sr, Ba, and Ni.An iterative matrix correction and data reduction were made either by a central CYBER computer or by an on-line PDP-11.Diagrams were plotted using a VERSATEK plotter.A measure of the precision is given by a comparison of 61 pairs of replicate analyses (Table 1).The samples were analyzed against USGS standard rock W-l using the 1972 major element values (Flanagan, 1973) and trace element values of Abbey (1973).As an accuracy check further samples of standard rocks W-l and AGV were run as unknowns and the results are shown in Table 2. Interlaboratory analytical variation is discussed by Wright (this volume).The XRF analyses consistently show lower AI2O3 and slightly higher FföOj than those analyzed by the classical wet chemical methods.We interpret these differences as resulting from the problems of separating the "R2O3" group by wet methods.Several samples have been taken from single 1.5meter-long sections of core, and some of these samples were analyzed in duplicate.The high level of precision indicated by the replicate analyses 1 emphasizes the variations between samples from single core sections and the reader is referred to the listings of analyses, in particular: Hole 322A, Core 8, Section 1; Hole 332B, Core 19, Section 1; Hole 332B, Core 20, Section 3; Hole 332B, Core 21, Section 1; Hole 332B, Core 22, Section 4; Site 335, Core 9, Section 5.The apparent variation of up to ±0.5% MgO within single core sections suggests that the samples taken B. M. GUNN, M. J.