INTERELEMENT RELATIONSHIPS IN FERROMANGANESE CRUSTS FROM THE CENTRAL PACIFIC-OCEAN - THEIR IMPLICATIONS FOR CRUST GENESIS

The fine-scale chemical variations in ferromanganese (Fe-Mn) crusts fr om the central Pacific Ocean were investigated using a variety of tech niques in order to elucidate their genesis. Thirty-seven major, minor and trace elements were determined by ICP-OES and ICP-MS in sub-sample s collected at approximately 2 mm intervals throughout the crust seque nces. An inverse relationship is observed between the logarithm of the elemental distribution coefficients [log (C-Mn/C-SW)] and the mean re sidence time (t(T)) of elements in seawater. These associations provid e evidence supporting the strong link between seawater and Fe-Mn crust chemistry. Results of factor analysis reveal that elements in crusts can generally be partitioned into four major groups with selected elem ents displaying associations with several groups. These statistical as sociations are interpreted to represent hydrogenetic (Mn, Ni, Co, Cu, Ce, Zn), biogenic (Ba, Zn, Cu, Pt, Fe), detrital (Al, Si, Fe) and carb onate fluorapatite (Ca, P, REE) groups. A comparison between elemental associations in fine-scale data from individual crust sequences and b ulk compositional data from samples collected in separate locations re veals very similar elemental associations. The similar elemental assoc iations in bulk samples and in fine-scale subsamples from individual c rusts are consistent with the notions that hydrogenetic crusts exhibit no significant post-depositional remobilization of elements, and that elemental distributions within crusts reflect the chemistry of oceani c water during the period in which they accreted. Chemical paleotracks are proposed based on factor scores derived from chemical variations as a function of depth in individual crusts. Our results show that the re is internal consistency between the chemical evolution, previously proposed seamount paleotracks, and nanofossil biostratigraphy dating r esults.