ENDMEMBER ANALYSIS OF METALLIFEROUS SEDIMENTS FROM THE GALAPAGOS RIFTAND EAST PACIFIC RISE BETWEEN 2-DEGREES-N AND 42-DEGREES-S

594 sediment samples from the Galapagos Rift System (GRS) and the cres t of the East Pacific Rise (EPR) were chemically analyzed for 12 eleme nts. Carbonate-free compositional datasets associated with each of 3 r egions, the GRS, the EPR 2 degrees N-4 degrees S and the EPR 10 degree s S-42 degrees S, were separately subjected to endmember analysis. The compositions of endmember estimates were constructed for each dataset . These compositions largely confirmed the identities of endmembers th at had previously been inferred from the varimax rotated loadings of a conventional factor analysis (of the correlation matrices) of the sam e 3 datasets. In view of the widely-reported unreliability of the corr elation structure of compositional data, the confirmation by endmember analysis of the results of a factor analysis is itself quite remarkab le. However, the particular advantage of endmember analysis is that th e chemical compositions of extreme sources are estimated, and may read ily be interpreted. The samples in the dataset can then be expressed a s mixtures of these extreme sources. By contrast, the varimax rotated loadings of a factor analysis indicate only those elements that are as sociated together on a single factor which may or may not be an endmem ber, the composition of which nevertheless remains unknown. (C) 1997 E lsevier Science Ltd.